Publication number WO A2 Publication type Application Application number PCT/US2006/046704 Publication date Aug 2, 2007 Filing date Dec 7, 2006 Priority date Jan 13, 2006 Also published as,, Publication number PCT/2006/46704, PCT/US/2006/046704, PCT/US/2006/46704, PCT/US/6/046704, PCT/US/6/46704, PCT/US2006/046704, PCT/US2006/46704, PCT/US, PCT/US200646704, PCT/US6/046704, PCT/US6/46704, PCT/US6046704, PCT/US646704, WO 2007/087017 A2, WO A2, WO A2, WO-A2-, WO2007/087017A2, WO A2, WOA2 Inventors, Applicant Export Citation,, (4), (5), (3) External Links. USE OF STEAM CRACKED TAR FIELD OF THE INVENTION [0001] The invention relates to a method for improving the solubility of steam cracked tar in useful compositions. In an embodiment, the upgraded steam cracked tar is added to fuel oil.

BACKGROUND OF THE INVENTION [0002] Steam cracking, also referred to as pyrolysis, has long been used to crack various hydrocarbon feedstocks into olefins, preferably light olefins such as ethylene, propylene, and butenes. Conventional steam cracking utilizes a pyrolysis furnace that has two main sections: a convection section and a radiant section. In the conventional pyrolysis furnace, the hydrocarbon feedstock enters the convection section of the furnace as a liquid (except for light feedstocks which enter as a vapor) wherein it is heated and vaporized by indirect contact with hot flue gas from the radiant section and optionally by direct contact with steam. The vaporized feedstock and steam mixture (if present) is then introduced through crossover piping into the radiant section where the cracking takes place. The resulting products comprising olefins leave the pyrolysis furnace for further downstream processing. [0003] Pyrolysis involves heating the feedstock sufficiently to cause thermal decomposition of the larger molecules. Among the valuable and desirable products include light olefins such as ethylene, propylene, and butylenes.

My take on it is that in the beginning, before SCT, b and g or someone cracked open one of these pcms, desoldered the flash chip and dumped it, if they were lucky they would find it wasnt encoded and there was no crc check, if not they would have to reverse the software. After that they would have to. Download aaa logo 3.10 full cracked batzal roof designer 2013 crack emicsoft flv converter crack code for kaspersky winzip 8.1 free download full version ezdrummer 2.0 keygen mac torrent ikea malm slats fall through crack du speed booster pro apk full version sct advantage iii crack cocaine crack red orchestra 2 cheats.

The pyrolysis process, however, also produces molecules that tend to combine to form high molecular weight materials known as steam cracked tar or steam cracker tar, hereinafter referred to as 'SCT'. These are among the least valuable products obtained from the effluent of a pyrolysis furnace. In general, feedstocks containing higher boiling materials ('heavy feeds') tend to produce greater quantities of SCT. [0004] SCT is among the least desirable of the products of pyrolysis since it finds few uses. SCT tends to be incompatible with other 'virgin' (meaning it has not undergone any hydrocarbon conversion process such as FCC or steam cracking) products of the refinery pipestill upstream from the steam cracker. At least one reason for such incompatibility is the presence of asphaltenes.

Asphaltenes are very high in molecular weight and precipitate out when blended in even insignificant amounts into other materials, such as fuel oil streams. [0005] One way to avoid production of SCT is to limit conversion of the pyrolysis feed, but this also reduces the amount of valuable products such as light olefins. Another solution is to 'flux' or dilute SCT with stocks that do not contain asphaltenes, but this also requires the use of products that find higher economic value in other uses. [0006] In US 4,446,002, the precipitation of sediment in unconverted residuum obtained from a virgin residuum conversion process is taught to be suppressed by blending the unconverted residuum with an effective amount of a virgin residuum having an asphaltene content of at least about 8 wt% of the virgin residuum at a temperature sufficient to maintain both residuum components at a viscosity of no greater than about 100 cSt (centistokes) during blending.

Virgin residuum is the bottoms product of the atmospheric distillation of petroleum crude oil at temperatures of about 357 to 385°C. [0007] In US 5,443,715, steam cracked tar is upgraded by mixing with a 'hydrogen donor', preferably hydrotreated steam cracked tar, at or downstream of quenching of the effluent of a gas oil steam cracker furnace. In this regard, see also US 5,215,649; and US 3,707,459; and WO 9117230. [0008] Other references of interest include US 3,622,502; US 3,691,058; US 4,207,168; US 4,264,334; WO 91/13951; DE 4308507; and JP 58-149991. [0009] There has recently been described a process wherein a pyrolysis furnace feedstock is provided to the convection section of the pyrolysis furnace, whereby at least a portion of the feedstock is vaporized, followed subsequently by passing the at least partially vaporized feedstock, optionally with steam, to a flash drum, wherein a vapor phase and liquid phase are separated. Smith And Wesson Model 915 Manual Lymphatic Drainage.

The vapor phase is fed to the radiant section of a pyrolysis furnace, and products, including desirable light olefins, are obtained as effluent of the furnace. The liquid phase or bottoms product of the flash drum contains substantially all of the asphaltenes (if present) in the feedstock. Such processes and apparatus therefore are described in US Applications 20; 7; 20; 20; 20; 20; 20; 20; 20; 20; 20; 20; and 20. [0010] The present inventors have surprisingly discovered that SCT is highly compatible with the flash drum bottoms product in the aforementioned processes, and the two materials may be blended to produce a composition having higher solubility in various petroleum products, particularly fuel oils, e.g., heavy fuel oils or Bunker fuels. SUMMARY OF THE INVENTION [0011] The invention is direct to a process wherein the liquid or bottoms product of a flash drum downstream from the convection section inlet of a pyrolysis furnace and upstream of the crossover piping to the radiant section of said pyrolysis furnace is obtained and mixed with steam cracked tar (SCT).

[0012] In preferred embodiments, the mixture of said bottoms product and said SCT is subsequently mixed with fuel oils and/or Bunker fuels (and optionally flux). [0013] The invention is also directed to a composition comprising steam cracked tar (SCT) and the liquid or bottoms product of a flash drum integrated with a pyrolysis furnace. [0014] In any of the aforementioned embodiments, SCT is optionally fluxed.

[0015] In any of the aforementioned embodiments, the SCT is optionally mixed with steam cracked gas oil (SCGO) and/or atmospheric gas oil (AGO). [0016] In preferred embodiments of any of the aforementioned embodiments, the composition of the invention further comprises fuel oils, such as heavy fuel oils and/or Bunker fuels. [0017] It is an object of the invention to compatibilize SCT for economically useful purposes, such as for use in fuels for diesel engines in large machinery.

[0018] These and other objects, features, and advantages will become apparent as reference is made to the following detailed description, preferred embodiments, examples, and appended claims. DETAILED DESCRIPTION [0019] The invention is direct to a process wherein the liquid or bottoms product of a flash drum downstream from the convection section inlet of a pyrolysis furnace and upstream of the crossover piping to the radiant section of said pyrolysis furnace is obtained and mixed with SCT.

Liquid product and bottoms products are synonymous with regard to the flash drum components. As used herein, the phrase 'bottoms product of a flash drum integrated with a (or 'said') pyrolysis furnace' will mean 'liquid or bottoms product of a flash drum downstream from the convection section inlet of a pyrolysis furnace and upstream of the crossover piping to the radiant section of said pyrolysis furnace' for the sake of brevity. [0020] The term 'pyrolysis furnace' is used herein to be synonymous with the term 'steam cracker'. It is also known in the art as a 'thermal pyrolysis furnace'.

Steam, although optional, is typically added inter alia to reduce hydrocarbon partial pressure, to control residence time, and to minimize coke formation. In preferred embodiments of the present invention, the steam may be superheated, such as in the convection section of the pyrolysis unit, and/or the steam may be sour or treated process steam. [0021] According to the present invention, a feedstream is provided to the inlet of a convection section of a pyrolysis unit, wherein it is heated so that at least a portion of the feedstream is in the vapor phase. Steam is optionally but preferably added in this section and mixed with the feedstream. The heated feedstream with optional steam and comprising a vapor phase and a liquid phase is then flashed in a flash drum to drop out the heaviest fraction (e.g., asphaltenes), and further processing the overheads from the flash drum, through crossover piping into the radiant section of a pyrolysis unit. [0022] One of the advantages of having a flash drum downstream of the convection section inlet and upstream of the crossover piping to the radiant section is that it increases the feedstreams available to be used directly, without pretreatment, as feed to a pyrolysis furnace. Thus, crude oil, even high naphthenic acid containing crude oil and fractions thereof, may be used directly as feed.

[0023] The terms 'flash drum', 'flash pot', 'knock-out drum' and knock-out pot' are used interchangeably herein; they are per se well-known in the art. In a preferred embodiment, the composition of the vapor phase leaving the flash drum is substantially the same as the composition of the vapor phase entering the flash drum, and likewise the composition of the liquid phase leaving the flash drum is substantially the same as the composition of the liquid phase entering the flash drum, i.e., the separation in the flash drum consists essentially of a physical separation of the two phases entering the drum. [0024] The preferred flash drum and the of the flash drum with pyrolysis units have previously been described in U.S.

Patent Application Publication Nos. 20; 7; 20; 20; 20; 20; 20; 20; 20; 20; 20; 20; and 20. [0025] Another preferred apparatus effective as a flash drum for purposes of the present invention is described in U.S. 6,632,351 as a 'vapor/liquid separator'.

[0026] In the process of the present invention, the flash drum preferably operates at a temperature of from 800 0F (425°C) to 850 0F (455°C). [0027] Surprisingly, it has also been discovered by the present invention that 1000°F+ (538°C and greater) vacuum tower resid fractions from the petroleum refining pipestill is an equivalent of the liquid or bottoms product of the aforementioned flash drum. Thus, this material may also be used alone or mixed with said liquid or bottoms product, provided it is derived from crudes or fractions there of having a low pour point as described in more detail below. [0028] In the present invention, feedstreams may comprise any crude oil or fraction thereof, however it has been found that crudes having Pour Points greater than 15°C do not provide integrated flash drum bottoms product that make good solvents for tar asphaltenes and therefore must be used in very high proportions or require too much fluxing to be beneficially useful. Preferred feeds are low sulfur (e.g, maximum sulfur content of less than 2.0 wt% or 1.5 wt% or 1.0 wt% or less than 1.0 wt% S), low Pour Point, even more preferably medium weight crudes that are non-waxy. In anohter embodiment, the preferred crudes or fractions thereof having a Pour Point of or 55 wt%, of the liquid or bottoms product of the aforementioned flash drum, with ranges from any of the aforementioned lower values to any of the aforementioned higher values also contemplated. The remainder of the composition is SCT (based on the composition consisting of liquid or bottoms product of the aforementioned flash drum and SCT).

Thus, preferred proportions of SCT may also be given as from 20 wt%, or 25 wt%, or 30 wt%, or 40 wt%, or 45 wt%, to 70 wt%, or 60 wt%, or 55 wt%, of SCT, with ranges from any of the aforementioned lower values to any of the aforementioned higher values also contemplated. These proportions do not include fluxant and/or SCGO or AGO, but are based solely on SCT and bottoms of the integrated flash drum. [0034] SCT thus compatibilized with the liquid or bottoms product of the aforementioned flash drum may be mixed in any proportions with additional materials, advantageously so that no asphaltenes precipitate. [0035] In preferred embodiments, the aforementioned mixture is blended with heavy fuel oils and/or Bunker fuels.

Typical specifications are provided below for an RSFO blend meeting the 3S0 centistoke (cSt) requirements for Fuel Oil is given below. For a composition according to the present invention, the most important specifications (with regard to meeting the various specifications for published fuel oil requirements) are Kinematic Viscosity (KV), Specific Gravity (SG) and compatibility (e.g., one or both of the sediment criteria listed below). It is an important and surprising discovery of the present inventors that such specifications can be met for a mixture containing steam cracked tar.

[0036] One typical specification for a fuel oil is listed in Table 1. Table 1 RFSO Standard Fuel Oil S ecifications in Sin a ore Platt's.

[0037] Yet another surprising discovery of the present inventors is that the blend according to the invention may be advantageously fluxed with stream cracked gas oil (SCGO). This is a great advantage of the present invention not the least of which because SCGO is another of the products of the pyrolysis furnace that is generally considered undesirable because of lack of end uses. In embodiments, if SCGO or AGO is unavailable, HAGO or HDDO may be used as fluxant. Patent Citations Cited Patent Filing date Publication date Applicant Title * Jan 16, 1928 Sep 15, 1931 Standard Oil Co Fuel oil * Apr 15, 1970 Sep 12, 1972 Exxon Research Engineering Co Production of single-ring aromatic hydrocarbons from gas oils containing condensed ring aromatics and integrating this with the visbreaking of residua * Apr 17, 1970 Dec 26, 1972 Exxon Research Engineering Co Cracking hydrocarbon residua * Jul 3, 2002 Jan 8, 2004 Stell Richard C. Process for steam cracking heavy hydrocarbon feedstocks.

Sam's Laser FAQ - Diode Lasers Sam's Laser FAQ, • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • Back to. Basic Characteristics, Structure, Safety, Common Types Note: Throughout this document, we will use the terms 'laser diode' and 'diode laser' somewhat interchangeably although we will tend to use the term 'diode laser' when referring to a complete system or module. When a device is called a 'laser diode', this generally refers to the combination of the semiconductor chip that does the actual lasing along with a monitor photodiode chip (for used for feedback control of power output) housed in a package (usually with 3 leads) that looks like a metal can transistor with a window in the top. These are then mounted and may be combined with driver circuitry and optics in a 'diode laser module' or the common (red) laser pointer. Shows some examples.

Diode lasers use nearly microscopic chips of Gallium-Arsenide or other exotic semiconductors to generate coherent light in a very small package. The energy level differences between the conduction and valence band electrons in these semiconductors are what provide the mechanism for laser action. This is not the sort of laser you can build from scratch in your basement as the required fabrication technology costs megabucks or more to set up. You will have to be content with powering a commercial laser diode from a home-made driver circuit or using a pre-packaged module like a laser pointer. Fortunately, laser diodes are now quite inexpensive (with prices dropping as you read this) and widely available.

The active element is a solid state device not all that different from an LED. The first of these were developed quite early in the history of lasers but it wasn't until the early 1980s that they became widely available - and their price dropped accordingly. Now, there are a wide variety - some emitting many *watts* of optical power. The most common types found in popular devices like CD players and laser pointers have a maximum output in the 3 to 5 mW range.

A typical configuration for a common low power edge emitting laser diode is shown below: + + o o ______________ ______________ _______ _______ Laser P type semiconductor Laser P type beam beam ooooooooooooooo Junction---^ End ->N type semiconductor This configuration above is called a 'homojunction' since there is only one P-N junction. It turns out there are benefits to using several closely spaced junctions formed by the use of layers of P and N type materials. These are called 'heterojunction' laser diodes. There are many many more advanced structures in use today and new ones are being developed as you read this! For example, see the section: for a description of one type that has the potential to have a dramatic impact in many areas of technology. The 'end facets' are the mirrors that form the diode laser's resonant cavity.

These may just be the cleaved surfaces of the semiconductor crystal or may be optically ground, polished, and coated. For these types of integrated laser diodes, everything takes place inside the chip.

Therefore, the output wavelength is fixed and determined by the properties of the semiconductor material and the device's physical structure. Or, at least that's the way it is supposed to work though with some, reflection of the laser light back into the chip can cause stability problems or even be used to advantage to frequency stabilize the output. There are also tunable diode lasers using external cavity optics to provide a continuous and in some cases, quite wide range of wavelengths without mode hopping. There are also pulsed laser diodes requiring many amps to to reach threshold and providing watts of output power but only for a short time - microseconds or less. Average power is perhaps a few mW. These are gallium arsenide (GaAs) heterojunction laser diodes. They are not that common today but some surplus places are selling diodes like these as part of the Chieftain tank rangefinder assembly.

They mention the high peak power output but not the low average power.:( Modern devices with similar specifications are also available from manufacturers like. Go to 'Products', 'High Power Laser Diodes', 'Product Catalog.' , 'Pulsed Laser Diodes in Plastic Packages'.

Electrical input to the laser diode may be provided by a special current controlled DC power supply or from a driver which may modulate or pulse it at potentially very high data rates for use in fiber optic or free-space communications. Multi-GHz transmission bandwidth is possible using readily available integrated driver chips. However, unlike LEDs, laser diodes require much greater care in their drive electronics or else they *will* die - instantly.

There is a maximum current which must not be exceeded for even a microsecond - and this depends on the particular device as well as junction temperature. In other words, it is not sufficient in most cases to look up the specifications in a databook and just use a constant current power supply. This sensitivity to overcurrent is due to the very large amount of positive feedback which is present when the laser diode is lasing.

Damage to the end facets (mirrors) can occur very nearly instantaneously from the concentrated E/M fields in the laser beam. Closed loop regulation using optical feedback to stabilize beam power is usually implemented to compensate for device and temperature variations. See the sections on CD and visible laser diodes later in this document before attempting to power or even handle them. Not all devices appear to be equally sensitive to minor abuse but it pays to err on the side of caution (from the points of view of both your pocketbook and ego!). In their favor, laser diodes are very compact - the active element is about the size of a grain of sand, low power (and low voltage), relatively efficient (especially compared to the gas lasers they replaced), rugged, and long lived if treated properly.

In fact, high power laser diodes - those outputting WATTs of optical power - are without a doubt the most efficient light emitter - not just lasers - in existence. Some have electrical to optical efficiencies (DC W in to light W out) of greater than 50 percent! In other words, put 2 watts of DC power in and get out 1 W of light. And, research is in progress to improve this to 80 percent or beyond. The common incandescent lamp is only 5 percent, fluorescent lamps are 15 or 20 percent efficient, high intensity discharge lamps are somewhat better, but even the best can't match the laser diodes in existence now. Just think: If those super high efficiency high power laser diodes could be mass produced in visible wavelengths and were used to replace all light bulbs, the World's electicity usage would be cut way down, not to mention hobbyist access to high power lasers!

(Which is of much more significance!) OK, back to reality.:) Laser diodes do have some disadvantages in addition to the critical drive requirements. Optical performance is usually not equal to that of other laser types. In particular, the coherence length and monochromicity of some types are likely to be inferior. This is not surprising considering that the laser cavity is a fraction of a mm in length formed by the junction of the III-V semiconductor between cleaved faces. Compare this to even the smallest common HeNe laser tubes with about a 10 cm cavity.

Thus, these laser diodes would not be suitable light sources for high quality holography or long baseline interferometry. But, apparently, even a $8.95 laser pointer may work well enough to experiment in these areas and some results can be surprisingly good despite the general opinion of laser diode performance. Even if not as good as a helium-neon laser in the areas of coherence and stability, for many applications, laser diodes are perfectly adequate and their advantages - especially small size, low power, and low cost - far outweigh any faults. In fact, these 'faults' can prove to be advantageous where the laser diode is being used simply as an illumination source as unwanted speckle and interference effects are greatly reduced. As noted, not all laser diodes have the same performance.

See the section: for comments that suggest some common types may indeed have beam characteristics comparable to typical HeNe lasers. And, for short range applications, see:. Also see the section:. The following sites provide some relatively easy to follow discussions of the principles of operation, construction, characteristics, and other aspects of laser diode technology: • Go to 'Resource Library'. Diode laser characteristics, artifacts, corrections. Go to 'Technical Articles', 'Lasers'.

Includes laser diode modules, beam expanders, spatial filters, more. Includes info on GaN blue/viodlet/UV LEDs and laser didoes. Free info may be requested on a variety of topics related to laser diode characteristics, profiling, and correction.

Go to 'Tehcn Notes'. Articles on a variety of topics including laser diode construction. A summary article on laser diode types, applications, drivers, etc. Here's a link to a historical look at the early days of laser diodes: • shows those typically found in CD players, CDROM drives, laser printers, and bar code scanners. These were scanned at 150 dpi. Descargar La Biblia Latinoamericana Gratis En Español Para Pc.

The laser diodes on the left are from CD players, CDROM drives, and laser printers. The one in the middle is also from a laser printer. The components of the diode laser module on the right are from a bar code scanner. The actual laser diode is mounted at the rear end of the aluminum block and the single element plastic lens is all that is needed to provide a reasonably well focused beam. The closeups below were scanned at 600 dpi - laser diodes (at least the small ones we are dealing with) are really not this HUGE! These two laser diodes can also be found in the group photo, above. The from the shows a type that is found in many CD players and CDROM drives manufactured by Sony.

The actual laser diode is inside the brass barrel shown in the photo of the optical pickup. The front of the package is angled so that the exit window (anti-reflection coated) is also mounted at angle to prevent any remaining reflections from the window's surfaces - as small as the are - from feeding back into the laser diode's cavity or interfering with the detected signal. The output of these edge emitting laser diodes is polarized. See the section:.) The shows one that is from a laser printer.

It was mounted in a massive module (relative to the size of this laser diode, at least) which included the objective lens and provided the very important heat sink. In some high performance laser printers, a solid state Peltier cooler is used to stabilize the temperature of the laser diode. The low power laser diodes in CD and LD players, and CDROM and other optical drives (at least read-only types) get away with at most, the heat sink provided by the casting of the optical block - and many don't even need this being of all plastic construction. (From: Don Stauffer (stauffer@htc.honeywell.com).) One can think of an LED as a laser without a feedback cavity. The LED emits photons from recombining electrons.

It has a very broad spectrum. When we add a high Q cavity to it, the feedback can be high enough to trigger true laser action. Most laser diodes have the cavity built right into the device but there are such things as external cavity diode lasers. The addition of the high Q cavity cuts down drastically the number of modes operating (in fact, it is almost improper to speak of mode structure with an LED.

The result is that the emission line narrows drastically (more monochromatic) and the beam narrows somewhat spatially. One can still not easily get true single mode lasing with normal diode lasers, however, so the line will not be as sharp as a gas laser, nor the beam as narrow. For more info, see the section:. While a laser diode is a true laser and not just a glorified (and expensive) LED, there are major difference compared to a gas or solid state laser - not all of them bad.

(From: Don Stauffer (stauffer@htc.honeywell.com).) Yes indeed, a diode laser is a true laser. That being said, looking at matters quantitatively, it is harder to make a diode laser with a very narrow line emission than a gas laser or large crystal laser. Adding cavity length to a laser in general acts to narrow the line (in spectral space, though a higher Q cavity does tend to narrow beam in space also).

It is possible to use a larger, high Q external cavity with a laser diode to increase its coherence. (From: David Schaafsma (drdave@jnpcs.com) and Rajiv Agarwal (agarca@giascl01.vsnl.net.in).) A couple of minor points: High Q cavities narrow the spatial profile only if they are confocal - planar high Q cavities (as in diode lasers, and especially vertical-cavity diode lasers) are prone to problems with walk-off and the mode must be confined physically. In a gas laser, you also start with a much narrower fluorescence line and thus the gain spectrum is limited spectrally.

Diode lasers (being band-to-band or excitonic semiconductor transitions) have much broader fluorescence spectra. The typical edge-emitting diode laser actually lases in quite a few fundamental modes (especially when operated using its own facets as the cavity) and though each lasing mode is 'monochromatic', the overall spectrum really isn't. External cavities are really the only way to obtain approximately single mode operation from an edge-emitting diode laser. VCSELs are usually true single mode devices. The reason you can get away with lengthening the cavity in a gas laser is that you don't need to worry about lowering the free spectral range because the gain bandwidth is small.

DFB or DBR lasers achieve very similar results and have Side mode suppression ratios better than 30 db. These lasers have been the mainstay of Optical fiber base telecom for a while now.

DFB Lasers are use for long haul telecommunications network - the kind used by say Sprint (>1GB for up to 25 miles) for their phone networks between cities. These have been for Trans-Atlantic cables (TAT) between US and Europe. LEDs are used more for FDDI type application between computers (~100Mb and less than 1 mile).

(From: Vishwa Narayan (vishwa.narayan@ericsson.com).) While LEDs are quite popular in Datacom applications (read short distances), Telecom applications typically use DFBs, either directly modulated for low speeds (e.g., OC-3 155 Mb/sec) or externally modulated for high speeds (e.g., OC-48 2.5 Gb/sec). Distances can typically range over tens of kilometers, to hundreds of kilometers with optical amplification, sans repeaters.

Despite their small size and low input power, diode lasers may still represent a significant hazard to vision. This is especially true where the output is collimated and/or invisible (near IR), and/or higher power than the typical 3 to 5 mW. At least you don't have to worry about getting zapped by any high voltage (as in a HeNe or argon laser).

One should never look into the beam of any laser - especially if it is collimated. Use an indirect means of determining proper operation such as projecting the beam onto a white card, using an IR detector card or tester (where needed), or laser power meter.

• Laser diodes in CD players operate at 780 nm (near IR, virtually invisible). While safely tucked away inside the optical pickup, risks are quite minimal because the output is usually less than 1 mW and the emerging beam is highly divergent. However, if modifications are made to the pickup (such as by removing the objective lens), a 5 mW collimated beam may be produced which can burn holes in the retina of your eye without you even being aware there is a problem. • Common visible red laser diodes, diode laser modules, and laser pointers produce 1 to 5 mW at various wavelengths between 670 and 635 nm. When collimated (as in the case of a module with internal optics or a laser pointer) the entire beam can enter the eye and burn holes in the retina. Note that light at 635 nm appears more than 5 times as intense as light at 670 nm.

Therefore, the apparent brightness of a source is not a reliable indication of its actual optical power output. Currently, green laser pointers are not simple diode lasers but are Diode Pumped Solid State Frequency Doubled (DPSSFD) lasers (this may change in the future, however). For a given power, green appears substantially brighter than red wavelengths but are also limited a maximum power of 5 mW. However, since there is a high power IR laser diode inside a green pointer and not all include an adequate IR-blocking filter, there could be other dangers lurking even if the green output is weak or dead. (From: Gregory Makhov (lsdi@gate.net).) According to a recent report by Dr. David Sliney, who is one of the leading 'gurus' of laser safety, there are no confirmed accidents or injuries caused by laser pointer of 5 milliwatts radiant power or less.

There is an awful lot of nonsense and false claims about this. Pointers are extremely bright, can cause visual distraction, afterimages, and other effects, such as headaches, but under most any typical usage condition, DO NOT cause eye injury. Sliney works for US Army, and has published papers and books on laser safety for over 20 years. With both of these, the beam from the bare laser diode is highly divergent and therefore less of a hazard since the lens of the eye cannot focus it to a small spot. However, there is still no reason to look into the beam.

• Writeable optical drives (WORM, CD-R) may use IR laser diodes producing 10s of mW. A typical CD-R drive sets the laser power at 3 to 5 mW for read and 25 to 30 mW for write. Various types of laser cameras and laser typesetters may use laser diodes of 100s of mW. These are extremely dangerous even if not that well collimated. Furthermore, since they also use near-IR wavelengths so that there is essentially no warning that a beam is present. In fact, since the response of the human eye to near-IR radiation results in an weak indication of red light, one may be led to the false conclusion that the output is a weak visible beam when the actual optical power is 10,000 times higher and the damage has already been done.

• Much higher power visible and IR diode lasers are available and becoming much more common and affordable with the popularity of diode pumped solid state lasers (including green laser pointers which contain a high power IR laser diode). These represent even greater danger to vision and potentially even risk of heat damage or fire from a focused beam. With these high power laser diodes, even the divergent beam from the bare device is a definite hazard at close range.

Where there are collimating optics (even an almost invisible microlens), the result is a mostly or totally invisible beam that can be dangerous to vision from direct exposure and specular reflection at distances of several feet. These are particularly scary especially for people who have become complacent about diode laser safety due to their expectation of a widely diverging beam. For IR laser diodes in particular, especially if you are considering selling a product: (Portions from: Steve Roberts (osteven@akrobiz.com).) You need to take a close look at the CDRH rules, because there is no blink reflex in the IR. IR diode lasers are considered much more dangerous and therefore are in a higher class. CDRH has a curve of power versus wavelength that is used for determining safety classes. The only way a IR laser gets less then a IIIb rating (read: dangerous) is if the beam is totally enclosed or of very low power. Go to, call them and request a manufacturers' packet by mail.

It's huge and confusing, but covers the requirements for products using IR laser diodes such as 3-D scanners, perimeter sensors, and so forth. The most common laser diodes on the planet by far are those used in CD players and CDROM drives. These produce a (mostly) invisible beam in the near infrared part of the spectrum at a wavelength of 780 nm. The optical power output from the raw laser diodes may be up to 5 mW but once it passes through the optics, what hits the CD is typically in the.3 to 1 mW range. Somewhat higher power IR laser diodes (up to about 30 mW) may turn up in surplus WORM (Write Once Read Mostly) or other optical drives. Visible laser diodes have replaced helium-neon lasers in supermarket checkout UPC scanners and other bar code scanners, laser pointers, patient positioning devices in medicine (i.e., CT and MRI scanners, radiation treatment planning systems), and many other applications. The first visible laser diodes emitted at a wavelength of around 670 nm in the deep red part of the spectrum.

More recently, 650 nm and 635 nm red laser diodes have dropped in price. Due to the nonuniformity of the human eye's response, light at 635 nm appears more than 4 times brighter than the same power at 670 nm. Thus, the newest laser pointers and other devices benefitting from visibility are using these newer technology devices. Currently, they are substantially more expensive than those emitting at 670 nm but that will change as DVDs become popular: Laser diodes in the 635 to 650 nm range will be used in the much hyped DVD (Digital Video - or Versatile - Disc) technology, destined to replace CDs and CDROMs in the next few years. The shorter wavelength compared to 780 nm is one of several improvements that enable DVDs to store about 8 times (or more - 4 to 5 GB per layer, the specifications allow up to 2 layers on each side of a CD-size disc!) the amount of information or video/audio as CDs (650 MB). A side benefit is that dead DVD players and DVDROM drives (I cannot wait) will yield very nice visible laser diodes for the experimenter.:-) Like their IR cousins, the typical maximum power from these devices is around 3 to 5 mW.

Cost is in the $10 to $50 for the basic laser diode device - more with optics and drive electronics. Higher power types (10s of mW) are also available but expect to spend several hundred dollars for something like a 20 mW module. Very high power diode lasers using arrays of laser diodes or laser diode bars with power output of WATTs or greater may cost 10s of thousands of dollars! A rough diagram of a laser diode of the type found in a laser pointer or CD player is shown below. This is in no way to scale.

The size of the overall package will typically be 5 to 10 mm overall but the actual laser diode chip will be less than 1 mm in length. ___ Metal case _______________________________ _____________________________ LD -------:===:------------------+ __ __ ___ ______ ______:: :: PD -------:===:----+ Main beam ___ ____ _____________ _:: (divergent) Photodiode Laser diode :__: __________________________ Protective window Com -------+ Heat sink _____________________________ _______________________________/ ___ The main beam as it emerges from the laser diode is wedge shaped and highly divergent (unlike a helium-neon laser) with a typical spread of 10 by 30 degrees.

External optics are required to produce anything approaching a parallel (collimated) beam. A simple (spherical) short focal length convex lens will work reasonably well for this purpose but diode laser modules and laser pointers might use a lens where at least one surface is aspheric (not ground to a spherical shape as are with most common lenses). In the case of a sample I removed from a dead diode laser module, the surface facing the laser diode was slightly curved and aspheric while the other surface was highly curved and spherical. The effective focal length of the lens was about 5 mm.

It appeared similar to the objective lens of a CD player - which was perhaps its original intended application and thus a low cost source for such optics. Due to the nature of the emitting junction which results in a wedge shaped beam and unequal divergence (10 x 30 degrees typical), a laser diode is somewhat astigmatic. In effect, the focal length required to collimate the beam in X and Y differs very slightly. Thus, an additional cylindrical lens or a single lens with an astigmatic curvature is required to fully compensate for this characteristic. However, the amount of astigmatism is usually small and can often be ignored. The general beam shape is elliptical or rectangular but this can be circularized by a pair of prisms.

The light from these edge emitting laser diodes is generally linearly polarized. You can easily confirm this even with a simple laser pointer by reflecting at about a 45 degree angle from a piece of glass (not a metal coated mirror). Rotate the pointer and watch the reflection - there will be a very distinct minimum and maximum with the elongated shape of the beam at close range being aligned with the glass and perpendicular, respectively.

For the advanced course, determine the Brewster angle.:) For addition information, see the section:. The beam from the back end of the laser diode chip hits a built-in photodiode which is normally used in an opto-lectronic feedback loop to regulate current and thus beam power.

Note that the photodiode is likely mounted at an angle (not possible to show in ASCII) so that the reflection does not interfere with the operation of the laser diode. CAUTION: Some complete modules may use the reflection from external optics along with an external photodiode for power stabilization as it is more accurate since the actual output beam is sampled. For these, one should never attempt to clean or even focus the lens when operating near full power as this may disturb the feedback loop and damage the laser diode. Here are the major parameters that are listed in manufacturer datasheets for small (i.e., 5 mW) laser diodes. This is for the Sony SLD1135VS visible laser diode, typical of those found in newer laser pointers and small diode laser modules. Most of the same parameters are used for high power laser diodes but those types generally don't include the internal monitor photodiode. And, of course, actual values will be quite different.

Note: Some of the symbols below are not exactly what is found in the datasheet so they can be represented in ASCII. However, the meaning should be obvious. Parameter Symbol Conditions Min Typ. Max Unit ------------------------------------------------------------------------------ Threshold current Ith 30 40 mA Operating current Iop Po = 5mW 35 45 mA Operating voltage Vop Po = 5mW 2.2 2.4 V Wavelength lambdap Po = 5mW 650 660 nm Radiation angle Perpendicular theta_ _ Po = 5mW 22 30 40 Deg.

Parallel theta Po = 5mW 5 7 12 Deg. Positional accuracy dx,dy,dz Po = 5mW +/-150 um Angular accuracy Perpendicular phi_ _ Po = 5mW +/-3 Deg. Parallel phi Po = 5mW +/-3 Deg. Differential eff. ND Po = 5mW 0.3 0.6 0.9 mW/mA Astigmatism As Po = 5mW 7 15 um Monitor PD current Imon Po = 5mW, Vr = 5V 0.05 0.1 0.25 mA Descriptions of the parameters are provided below: • Threshold current - The lowest current at which lasing action takes place. Note that no minimum is specified - some units may start lasing at currents lower than specified.

• Operating current - The current resulting in a power output of 5 mW (for this example). Note the wide range - 10 mA. This is the reason that it isn't possible to just set a current using a resistor or or fixed regulator.

The entire range of output powers from 0 mW to destructive levels is covered by this range of current - actual behavior depends on the particular sample and its actual temperature. • Operating voltage - The voltage across the laser diode at the specified operating current. Probably the only real need to know this is to be able to accommodate the maximum operating voltage in your driver design. It is NOT possible to design a regulator based on laser diode operating voltage alone. • Wavelength - The output wavelength can vary from sample-to-sample and due to temperature. These laser diodes cannot be used as wavelength references!

• Radiation angle - The beam divergence parallel (horizontal) and perpendicular (vertical) relative to the gain region of the laser diode. Note the wide variation. • Positional and angular accuracy - The tolerance in mounting of the laser diode chip. • Differential efficiency - Once the current threshold has been exceeded, the incremental increase in output power with current is fairly linear, measured in mW/mA. However, it can vary widely from sample-to-sample and with changes in temperature.

• Astigmatism - The difference in virtual point source of the parallel and perpendicular beams. • Monitor current - Sensitivity of the monitor photodiode with respect to laser diode output power. The datasheet will also of course include pinout and package info which I have omitted here. It is possible to buy visible laser diodes capable of a half watt or more: 'I was just browsing site, and noticed that they have 635 nm diodes rated at 500 mW. Has anyone ever dealt with these things? Looking around on the site, it appears I could put together a half watt red diode laser for under $600, or a 250 mW one for under $400.

Is there some catch to using these? The whole setup would be cheaper than a 25 mW HeNe laser'. Aside from the ease with which one of those pricey diodes can be blown out due to improper drive, the beam quality is no where near that of even a cheap HeNe laser. It is multimode and very non-circular and astigmatic. The latter can probably be dealt with using some (expensive) optics. However, multimode operation means that these are unsuitable for applications like holograpy or interferometry.

(From: Frank DeFreitas (director@holoworld.com).) I have a 500 mW laser diode from Polaroid. 660nm I believe. It needs the heftier driver that Meredith offers - the one that can put out 1000 mA or so.

The laser diode is gain guided/multi-mode, rather than index guided/single (mono) mode -- so you can pretty much forget any application that would call for any type of coherency or high contrast fringes. The output beam profile is basically a line. It is very similar to taking a standard HeNe beam and sending it through a cylindrical lens. (However, on the other hand, I'm wondering if a cylindrical lens would actually help it when used in the other dimension. Or at least bring it to a spot which could be collimated utilizing secondary optics in the path.) I'd also like to point out that it's not a diode to play around with. The optical output at 500 mW is not going to knock any missles out of the sky, but will certainly warrant caution when working with the beam.

The beam is much more powerful than it appears at 660 nm due to the eye's reduced sensitivity at that wavelength compared to HeNe 632.8 nm. You may have read about truly high power laser diodes - those putting out WATTs, 10s of WATTs, or even 100s of WATTs from a one diode or an array (bar) of diodes in a single package, or multiple laser diode bars. These are usually near-IR emitters, often at 808 nm. Solid State Diode Pumped (DPSS) lasers are driven by these light sources with some providing upwards of 1,000 WATTs (and the upper limit is climbing as you read this). Also see the section:. About those laser diode bars: (From: Walter Skrlac (Walter.Skrlac@t-online.de).) 'Bars are a 10 mm wide chip with typically 16 to 24 emitters, each emitter being about 150 microns wide and emitting up to 2 watts of power per emitter. The highest power for solid state laser pumping is 40 watts from a 19 emitter bar.

Almost all bars are a single chip, multiple emitter device. I do know that in the beginning days of bars, Siemens produced a 5 watt device consisting of 5 separate 1 watt laser diodes mounted in a row 10 mm long. The individual laser diodes are connected in parallel so you can't switch them individually.'

The good news is that this technology is developing very rapidly. The bad news from our perspective is that there are no really low cost sources, new or surplus, for these diode lasers as far as I know at the present time.

However, prices have been dropping rapidly since this was first written. The cost of 1 W 808 nm laser diodes has dropped below $100 new, and with luck, much cheaper from surplus sources and on eBay. Actually, it isn't necessarily the diode itself that is so expensive. A 1.5 W 800 nm diode chip goes for about $10 when they are purchased in reasonably large quantities.

However, these are only about 0.5 mm on a side and maybe 0.1 mm thick. Mounting means using low temperature solder and flux to bond the chip to a large heat sink and copper strip (for the two connections - no monitor photodiode, that function must be performed externally).

The soldering is best done on a hot plate (to raise the temperature of the heat sink and chip to almost the melting point of the solder), with a fine tip iron for the last few degrees. They have an HR and OC side, and a top and bottom, and thus orientation matters.

So, if you have access to a surface mount rework station with a stereo microscope, a steady hand, infinite patience, and don't sneeze much (which will blow your chips away to never be found again), you could try your hand at the mounting. I have a couple of these diode chips so once I get up the nerve to try this, I will report on success or failure.

The better way to deal with these laser diodes is to have them already mounted on a heat sink. But now we're talking about $100s for a single unit. But, for a number of reasons, the best type of high power laser diode to get is probably a fiber-coupled module. Then you don't have to mess with beam shape issues, the diode is safely tucked away out of harm, and the fiber output can easily be adapted to your favorite crystal shape. Some power is lost in the coupling but it appears as though the specs I've seen are similar for the bare diode assembly and fiber-coupled module. Of course, the cost for such a module now appoaches that of a nicely equipped PC.:) For more info, see the section:.

Laser diode bars/assemblies of much higher power are available - up to the kW range and beyond. Of course, the prices go up as well. Check out as one possible supplier.

They have a wide variety of really interesting items but unfortunately without any prices. Bars can be connected in series to ease the power supply requirements enabling them to be driven with lower current at higher voltage (e.g., a 4 bar configuration would use 8 V at 50 A instead of 2 V at 200 A). With individual chips on a common heat sink, this really isn't an option. Note that most high power diode lasers are near IR - often around 800 nm for pumping DPSS lasers or 830 to 870 nm for thermal platesetters. High power visible laser diodes are much less common and usually limited to less than a watt at 670 nm. Not that this is terrible.:) If you have your heart set on one of these for your birthday, all I can suggest at the present time is to keep track of what is available surplus and to check with the manufacturers listed in the chapter:. They do show up on eBay but accuracy of the description and operating conditoin may be unknown.

If this is for some sort of academic project with a legitimate research objective, you may be able to obtain a cosmetic reject or one that doesn't quite meet specs by persistent pleading with one of the laser diode manufacturers. Or, if you can deal with the bare chips, it may be possible to beg a few from one of the companies that produces DPSS laser systems since they use them by the carload, and when purchased by the carload, the cost goes way down.

Keep in mind that obtaining the diode is only a small part of the problem. To drive them reliably, particularly near their maximum power rating, will require a suitable constant current laser diode driver and proper cooling. However, if reasonable precautions are taken and they aren't run near their maximum ratings, actually blowing them out totally isn't nearly as easy as with their low power counterparts. And, needless to say, at these power levels, your eyes (and flammable objects) don't get a second chance - laser safety must be at the top of your list of priorities. You may have seen offers of IR laser diodes with 9 W or 14 W or much higher too-good-to-be-true power ratings from various surplus companies. These are pulsed ratings and the power rating is peak. Such laser diodes have been available surplus as part of the laser rangefinder from the Chieftain tank.

Since they are actually not that expensive to buy new as these things go (maybe $20 to $100). Unfortunately, while they have nice peak power ratings, the average power ratings are typically only a few mW as they must be run at a very low duty cycle - typically 0.1 percent (1 part in 1,000) or less.

Furthermore, the most common wavelengths are between 850 and 910 nm and these aren't much use for most laser projects (though wavelengths from 780 to 980 nm are available). There isn't any realistic possibility of efficiently frequency doubling these to visible (though a few blue photons might be possible if focused into a KTP crystal at a funny angle) and the wavelength isn't useful for pumping common solid state laser crystals. However, they would be suitable for rangefinder or similar applications. These laser diodes come in plastic packages that look much like LEDs and thus there is no real possibility of decent cooling. Therefore, power dissipation is one of the major limiting factors. It may be possible to use a lower peak current with a longer pulse width than what's specified in the datasheet as long as the average power dissipation rating isn't exceeded. However, with the high threshold current, this probably doesn't provide much benefit.

And, no guarantees of any kind with laser diodes! There is some info on driver circuits for pulsed laser diodes in the section:. The following assumes a device rated at 16 W peak power, 100 ns max pulse width, 0.1% max duty cycle: (From: Roithner Lasertechnik' (office@roithner-laser.com).) The absolute limit is the heat stress of the LD chip inside. Under normal conditions, the laser will emit a pulse of the rated 16 W, 100 ns at 10 kHz (200 ns at 5 kHz is the absolute limit) - which is highly recommended for an expected long lifetime of several khours with usual chip degradation. Take this integrated V x I (voltage x current) thermal heat stress as a final constant. If you run with a higher frequency than the rated, but with a shorter pulse width, still never go higher than this constant.

If you go higher, the laser pulse power will go down rapidly due to overheating of the LD chip (still reversible, LD is not yet blown) but overall lifetime is shortened. Keep in mind, that the rise and fall time of this LD is typically 1 ns, so you will get the next limit soon. Most laser diodes up till now (as well as most of those discussed in this document) are edge emitters - the beam exists from the cleaved edge of the processed laser diode chip. These are also called Fabry-Perot (FP) diode lasers since the cavity is essentially similar to that of a conventional gas or solid state laser but formed inside the semiconductor laser diode chip itself.

The mirrors are either formed by the cleaved edges of the chip or (for high performance types like those that are very stable or tunable) one or both of these are anti-reflection (AR) coated and external mirrors are added. VCSELs, on the other hand, emit their beam from their top surface (and potentially bottom surface as well). The cavity is formed of a hundred or more layers consisting of mirrors and active laser semiconductor all formed epitaxially on a bulk (inactive) substrate. This approach provides several very significant technical advantages: • Beam characteristics - Much of the behavior of the VCSEL can be controlled or at least affected by selecting the number and thickness of mirror layers and other process parameters.

The potential capabilities of this technology to finely tune behavior is hard to imagine. VCSELs operate in a single longitundinal mode but possibly multiple transverse modes. • Beam shape and profile - Whereas the typical conventional low power FP laser diode has an emitting area of 1x3 um (they are all long and narrow because the junction where laser action takes place is almost zero thickness), the shape of the emitting region of a VCSEL can be made whatever is desired for the application - even in the form of a doughnut or ring for optimal coupling to the outer part of a multi-mode optical fiber. The beam from a typical VCSEL exits from a circular region 5 to 25 um in diameter. Since this is much larger than for the FP laser diode, the divergence of the resulting beam is much lower.

And, because it is also circular, no corrections for asymmetry and astigmatism are required - a simple lens should be able to provide excellent collimation. • Lower lasing threshold and drive current - A typical telecom or CD laser diode may have a threshold current of around 30 mA while a VCSEL with similar output power may require only 1 or 2 mA! This results in lower electrical power requirements, potentially faster modulation, simpler drive circuitry, and reduced RFI emissions.

VCSELs are also more robust in terms of power supply drive. Current control is generally sufficient and there is no need for optical feedback using a monitor photodiode to prevent destruction as with most low power edge emitting laser diodes where COD (Catastrophic Optical Damage) can occur in a ns as a result of the peak optical power at the 1x3 um output facet. With VSCELs, the emitting area is much larger so COD isn't nearly as significant a problem. • Implementation of VCSEL arrays becomes trivial. All that is required is to dice up the wafer into blocks of adjacent good VCSELs and package these as a single unit. The packing density of such devices can be an order of magnitude higher than for FP laser diodes (see below). This is a significant advantage for constructing high speed optical busses and interconnects.

There are also numerous manufacturing and cost advantages: • Smaller size - Unlike the FP cavity of an edge emitting laser diode which is 250 to 500 um in length, the entire size of a VCSEL is limited by the dimensions of the emitting region and space for electrical contacts. Thus, the die for a complete VCSEL can potentially be only slightly larger than the beam size! Currently available devices with a 25 um circular beam are about 100 um on a side but this can certainly be reduced to 50 um or less. Smaller size can translate into a larger yield per wafer and lower costs as well a higher packing densities for laser array applications. • Simplified manufacturing - FP laser diodes must be diced up (and possibly even mounted) just to determine which are good and which are bad.

They cannot be tested at all when part of the original wafer since the edges haven't been cleaved yet. This is an expensive time consuming process and results in a lot of wasted effort and materials.

On the other hand, an entire wafer of VCSELs can be tested as a unit with each device evaluated for lasing threshold and power, and beam shape, quality, and stability, It is possible to form millions of VCSELs on a single wafer as a batch process and then test and evaluate the performance of each one automatically. The entire wafer can be burned in to eliminate infant mortalities and assure higher reliability of the final product. Each device can then be packaged or thrown away based on these findings. • Simplified mounting and packaging. Virtually the same equipment that is used for final assembly of devices like other ICs can be used for VCSELs since they are attached flat on the package substrate and shine through an window like that of an EPROM (but of higher optical quality) or merged with an optical fiber assembly as required. Since the active lasing semiconductor and mirrors are buried under the top surface layers, a hermetic seal is unnecessary.

VCSELS can use inexpensive plastic packaging and/or be easily combined with other optical components as a hybrid or chip-on-board assembly. All this further contributes to reduced cost.

VCSEL technology is in its infancy and its potential is just beginning to be exploited. Quite possibly, VCSELs will become the dominant type of laser diode in the future with capabilities so fantastic and costs so low as to be unimaginable today. There is some technical information at the following sites: • (part of ).

• • (Includes links to VCSEL datasheets) For a general review article, see: 'The Ideal Light source for Datanets', K.S. Giboney, L.B. Aronson, B.E. Lemoff, IEEE Spectrum V.35 (2) p. 43, Feb 1998. If you want to play with VCSELs, bare chips, packaged chips, and even VCSEL arrays are available from various laser suppliers and prices aren't totally rediculous.

For example, see. Available wavelengths are currently 780, 850, 980 nm, but wavelengths beyond 1,300 nm are available from other suppliers and the range is being extended in both directions. If you suspect that one of your laser diodes might be a VCSEL without admitting it, just check the raw beam pattern. The output of a VCSEL will be fairly symmetric while that of an edge emitting laser will typically have a 4:1 angular spread as discussed above. There is also something called a 'Resonant Cavity LED', which in essence places an LED junction between mirrors.

Some of these efforts result in stimulated emission with the appearance of a longitudinal mode structure, but not enough gain to reach lasing threshold. However, I'm not sure if these structures differ from VCSELs in any fundamental way. See, for example:. Nearly all semiconductor lasers are powered by electrical current through the gain medium. However, for certain materials, it's also possible to use another laser to optically pump it.

This has some significant advantages in terms of controlling transverse and longitudinal modes and beam shape. The first commercial OPSL was the Coherent, Inc. 'Sapphire', a replacement for low power argon ion lasers at 488 nm. (I think the use of Sapphire is unfortunate as this has absolutely nothing to do with the Ti:Sapphire laser with which it may be confused.) The Sapphire is a Vertical External Cavity Surface Emitting Laser (VECSEL), but one that is optically pumped. (Also see the next section.) The resonator is in many ways similar to that of a frequency doubled Diode Pumped Solid State (DPSS) laser but with an InGaAs quantum-well semiconductor instead of a laser crystal as the gain medium. It is pumped by a high power 808 nm laser diode and lasing at the fundamental IR wavelength of 976 nm.

This is intracavity doubled to 488 nm. Go toe, then 'Lasers and Systems', 'OPSL' for more information. One beauty of the OPSL approach is that with an appropriate choice of material and doping, the basic gain medium - the semiconductor disk - can be designed to lase at most or all of the range from 635 nm to 1,500 nm and beyond. (The UV/blue area is probably not viable yet). Thus, this entire range of wavelengths as well as one half the wavelength (frequency doubled or SHG), and possibly higher harmonics are available with the beam characteristics of a solid state laser.

This technology may also be called a 'Semiconductor Disk Laser'. Several other companies are developing lasers using a similar approach and systems at many wavelengths - including those in the yellow/orange 'no laser land zone' - are now available or will be in the near future. And, apparently, some companies call their OPS lasers 'DPSS' even though strictly speaking, they aren't solid state in the traditional sense. There are a couple of ways of telling if a DPSS laser is really solid state: • If the wavelength of the laser isn't a fundamental or doubled vanadate, YAG, YLF or other popular solid state laser crystal line, or one of the common sum-frequency mixing wavelengths (e.g., 593.5 nm), then it's a frequency doubled semiconductor-based laser. • If the wavelength and/or linewidth is specified as more than a tiny fraction of a nm.

Since the lasing wavelength of semiconductors is determined to a much greater extent by the material composition and temperature, a '488 nm' laser is probably not going to be exactly 488 nm but can vary over a range of a nm or so. The first is the extended cavity semiconductor laser like the optically pumped Coherent Sapphire, but they may also be electrically driven like a normal laser diode (so only one laser instead - no pump diodes), and mentioned in the next section.

However, many companies are now using a directly doubled diode approach - a laser diode feeding a doubler crystal outside the laser cavity, possibly periodically poled lithium niobate (PPLN) or KTP (PPKTP). This is probably not efficient enough to be practical for high power lasers, but for a 10s of mW, it's much simpler. This is very similar to the OPSL, above, but uses electrical pumping similar to a conventional edge-emitting laser diode or VCSEL. However, the extended cavity allows frequency doubling to be performed much like in the OPSL with an external OC mirror and intracavity non-linear crystal. These lasers are direct competition to the OPSL and not surprisingly, have been introduced with similar wavelengths and output powers. One company that was a leader in this area was Novalux Two relevant patents (listed on a Novalux laser) are: • U.S. Patent #6,243,407: High Power Laser Device • U.S.

Patent #6,404,797: Efficiany High Power Laser Device But Novalux seems to have ceased production of these lasers as end-user products and are concentrating on OEM applications like light sources for large screen TVs and portable projectors. The Novalux Web site is gone. However, there is an overly fluffy Web site for with information on the technology and applications.

It's not clear how much of it is real though. But imagine buying replacement multi-watt RGB laser modules at consumer electronics prices or salvaging them from broken TVs!:) And other manufacturers are developing similar technology, so there will be competition.

This is a 5 mW (rated), 488 nm laser system. One configuration is shown in consisting of the laser head, a lab-style controller, and a 5 VDC power pack. In addition to the laser head connector, there is also a socket for an interlock (just a shorted 1/8' mono phone plug), and a 'DATA' connector. There are also 5 LEDS: Power, Temperature Lock, Laser On, Laser Lock, and Error.

I could not find anything like RS232 levels on the DATA connector, even though it only has pins 2 and 3 wired to the main PCB, and pin 5 to Ground. This suggests that it is intended for RS232, though these controllers have it receive-only, dead, or never enabled. I would have expected a negative voltage on pins 2 or 3 but they both read 0 V, though they are connected to something (from ohmmeter checks). Except for the Laser Head connector, everything else is on a mezzanine PCB that attaches to the main PCB via power and signal cables. Other configurations include at least two different types of OEM controllers.

One is a shorter silver box with no LEDs or switches, but with a Molex connector labeled DATA. The main PCB inside is identical (except possibly the revision) for the two controllers. For the lab controller, the Power and Data connectors are replaced by the inter-PCB cables.