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    Argon/Krypton Ion Lasers

    Sub-Table of Contents

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  • Back to Argon/Krypton Ion Lasers Sub-Table of Contents.

    Introduction, Acknowledgement, Ar/Kr Ion Laser Safety

    Introduction to Ion Lasers

    Argon and krypton (rare gas) ion lasers find applications in many diverse fields including (1) very high performance printing, copying, typesetting, photoplotting, and image generation; (2) forensic medicine, general and ophthalmic surgery; (3) entertainment; (4) holography; (5) electrooptics research; and (6) as an optical 'pumping' source for other lasers. From the hobbyist's point of view, items (3) and (4) are generally the most important (aside from the pure project value of such higher power lasers). However, common sources for these lasers when they show up on the surplus market are from (1).

    Also see the following:

    Note: For the purposes of this discussion, argon ion and krypton ion lasers are very similar - they are both rare gas ion lasers, their basic principles of operation are similar, and the same basic hardware configuration and power supplies can usually be used. Differences are primarily in gas fill of the plasma tube and the mirrors/prisms for selecting the output wavelength. Keep this in mind since where we describe something for an argon ion laser, most likely it applies to a krypton ion (or mixed gas 'white light') laser as well. However, this doesn't mean you can just replace one type with another. For more information, see the section: Comparison of Argon and Krypton Ion Tube Characteristics and the chapter: Ar/Kr Ion Laser Power Supplies.

    These are the types of lasers generally used for large scale light shows as well as in some types of high performance phototypesetters or other digital imagers, and for use in holography and other optics research. Unlike diode and HeNe types, a serious interest in these also represents a very serious investment of time, money, and caution.

    The types of small argon ion (krypton ion types would be rare) lasers that are turning up on the surplus market are often from various high performance scanners, duplicators (not your ordinary office copier), printers, and phototypesetters.

    The Xerox 9700 (and possibly the 8400 as well) has an ALC-60X argon ion laser. The common ALC-60X laser was made to the Xerox "X" standard for a high speed duplicator/printer, hence the X in the part number. The NEC-3030 is also a printer laser. Many of these older but expensive systems are still being maintained and are now being retrofitted with newer technology such as high power IR diode lasers or Diode Pumped Solid State (DPSS) lasers. Therefore, more small air-cooled argon (mostly) ion laser heads and power supplies should be showing up on the surplus market at attractive prices.

    However, many older laser printers and related equipment were based on HeNe lasers so don't assume there is an argon ion laser in that dusty thing at the salvage yard (even if quite large) just because it has a laser warning label! (Newer consumer/office type laser printers use relatively low power IR diode lasers.)

    On-line Introduction to Argon Ion Lasers

    There are a number of Web sites with laser information and tutorials.

    Acknowledgement for Ar/Kr Ion Laser Information

    Much of the material on argon and krypton ion lasers has been provided in one form or another by Steve Roberts (osteven@akrobiz.com) via direct contribution of text and photos and via email discussions. Many thanks to Steve for making this material available. I have edited the material and rounded it out but do not have one of these toys to play with. (I would be very interested if someone would be willing to make a loan of such a laser for the sole purpose of enhancing this document.)

    Argon/Krypton Ion Laser Safety

    It is not possible to over-emphasize the hazards involved in working with argon ion lasers. Having said that, argon ion lasers represent the Holy Grail for laser enthusiasts who will likely turn up their collective noses at HeNe lasers once they have become hooked.

    Additional Comments on Argon/Krypton Ion Laser Safety

    Safety is a major concern, as these are HV high current devices. The major hazard is instant eye damage, and although you can slightly burn certain materials such as black thermoplastic, these are not burning and cutting lasers even when focused, and walls don't burst into flame when the beam hits them. The tubes are usually made of beryllium oxide, kovar and copper (though there are a few quartz ones out there as well). There is a hazard if the BeO ceramic is ground or powdered and inhaled, and most people who buy one don't know about that. (But then, if you are grinding the tube, you don't have a working laser anymore. However, keep this in mind should you come across a certifiably dead argon/krypton tube and become overly curious.)

    I'm sure you've seen the posts on the sci.optics or alt.lasers newsgroups that go something like: "I just got a big laser. What type is it? What can I do with it? Etc." One of these guys is going to look down the bore and get blinded or worse. So I'd also like to see a site up for that reason. Well it turns out there is such a site. There is a excellent laser safety site at: Rockwell Laser Industries.

  • Back to Argon/Krypton Ion Lasers Sub-Table of Contents.

    Basic Characteristics, Other Information Sources

    Basic Characteristics of 'Small' Argon Ion Lasers

    WARNING: These are in a whole different league (compared to common diode and helium-neon lasers) with respect to safety hazards as the optical power levels involved are generally much higher (20 mW to many WATTS - Class IIIb and Class IV) and the power supplies are more dangerous as well. There is no margin for error in dealing with either the operating laser or its power supply.

    Note: Since comparisons are made throughout this discussion between argon (and krypton) ion lasers and helium-neon (HeNe) lasers, it is worthwhile to first read the Chapter: Helium-Neon Lasers if you are not familiar with those devices.

    The basic design of the argon/krypton laser is conceptually similar to that of the HeNe (or other gas) laser - plasma tube containing the active medium (argon and/or krypton gas) mirrors forming a Fabry-Perot resonator. However, unlike HeNe lasers, the energy level transitions that contribute to laser action come from ions of argon or krypton - atoms that have had 1 or 2 electrons stripped from their outer shells. Spectral lines at wavelengths less than 400 nm come from atoms that have had 2 electrons removed. Longer wavelengths come from singly ionized atoms. There are many possible transitions in the UV, visible, and IR portions of the spectrum. With suitable optics coherent light from a single spectral line or many lines may be produced simultaneously. An adjustable intra-cavity prism can even be included to permit the desired wavelength to be selected via a thumb-screw adjustment.

    Beam characteristics in terms of diameter and divergence are similar to those of HeNe lasers but the spectral line width is wider and therefore the coherence length (without additional optics) tends to be shorter.

    To excite the ionic transitions and achieve a population inversion, much more current is needed than for a HeNe laser. A 'small' argon laser may use 10 AMPs of current (rather than the 3 to 8 mA typical of a HeNe laser tube). Even at a tube voltage of 100 VDC, this represents about 1000 W of power dissipation. (Think of a typical space heater inside a small box!) High flow rate forced air cooling is absolutely essential - the tube would melt down in short order without it. Larger ion laser tubes may pass more than 100 AMPs of current at up to 400 VDC or more - and require three-phase power and water cooling - figure on utility substation just for your laser!

    Thus, while Ar/Kr ion lasers and HeNe lasers are conceptually similar, the approximately 3 orders of magnitude greater tube current and two orders of magnitude greater power dissipation compared to a HeNe laser mean that the construction details are vastly different. You won't find one of these in a laser pointer!

    Ar/Kr Ion Laser Tube Electrical Characteristics

    Both HeNe and Ar/Kr ion tubes use a gas discharge in a narrow capillary bore to excite the laser medium to upper energy states, they both need a starting pulse to overcome the initially non-conducting gas, and a current controlled power supply to regulate the discharge. However, the similarities pretty much end there.

    The following assumes a small air-cooled Ar/Kr ion tube like that used in the American Laser Corporation 60X/Omnichrome 532 or the Cyonics tube described in the section: Cyonics Argon Ion Tube.

    Large frame Ar/Kr lasers may require 35 A at 400 V running on three-phase 240 VAC, 30 KV or more to start, and gallons-per-minute of tap water cooling!

    More Information on Argon/Krypton Ion Lasers

    General information on argon ion laser tube construction and power supplies can be found at the IBM Patent Server Site.

    The following patents are particularly relevant with respect to small io lasers:

    The complete patent documents including diagrams are available for download. Each of these patents references others that may be useful as well. You can easily spend centuries surfing the IBM patent site!

    While patents do not provide all the details needed to construct your own system, they are valuable nonetheless as a starting point for understanding basic principles of operation and system design. Some of the electronics are described in substantial detail.

    However, some of these appear to match actual hardware very closely. Of particular interest are the two ALC patents. These outline the principles of operation and provide fairly complete schematics of the power supply for the ALC 60X/Omnichrome 532 laser.

    Some information may also be available from the major manufacturers of ion lasers. See the chapter: Laser and Parts Sources for addresses and links.

  • Back to Argon/Krypton Ion Lasers Sub-Table of Contents.

    Wavelengths, Spectra, Efficiency, White Light Lasers

    Argon Ion and Krypton Ion Laser Wavelengths

    While HeNe lasers invariable output a single wavelength, argon and krypton ion lasers can be designed and/or set up to output many wavelengths at the same time. Not all lines will lase simultaneously in a given laser, some of these are only available in larger lasers with more current density. Others will compete with each other for gain. Therefore special mirror coatings or an intracavity prism (etalon) may be required to obtain output on a few of these lines. Consult factory for details about which optics set is needed for your application. Large output powers at UV and IR will require special tube processing and/or crystalline quartz Brewster windows to avoid losses, solarization, and color center formation in the optics.

    Single-Line and Multi-Line Output

    Since the argon and krypton lasing mediums have substantial gain at several spectral lines (see the section: Argon Ion and Krypton Ion Laser Wavelengths), a given laser can be set up to output on a single line or more than one at the same time depending on how the optics are designed and adjusted. The tube current also affects this to some extent as increasing the current will bring in progressively more lower gain lines.

    A laser set up for multi-line operation will usually result in highest total output power but there are many applications where a monochromatic beam is required.

    Multi-line operation requires a set of mirrors with reflectivities designed to achieve laser operation for all the desired spectral lines. Any intracavity prisms are removed.

    Single line operation can be implemented in a couple of different ways:

    More Comments on Argon/Krypton Spectral Lines

    The 457.9 nm, 488 nm, and 514 nm lines are common as single lines for air-cooled tubes due to their strength. The majority of power will be in those lines

    An air-cooled argon tube will only lase at:

    Krypton lines are sensitive to pressure and magnetic field strength. All water-cooled ion lasers have axial electromagnets around the bore to concentrate the arc. A krypton laser will have a high/low field switch as well.

    The tables below list the relative strengths of all the important lines for a typical 30 watt argon/7 watt krypton laser with:

    Normally, optics are selected to support the mission of the laser - i.e., surgery wants only the blue lines; ophthalmology needs green, red, and yellow; Raman Spectroscopy needs 647 and 676 nm; laser shows use argon for blue, green, and violet, and krypton for red and yellow. Mixed gas lasers use optics selected for 55% red, 20% green, and 25% blue and violet. To kill a line, one of the optics is made more then 15% transmissive at that line.

    The 488 and 514 nm lines are lower then normal on this list - other manufacturers claim more power for these 2 lines.

    Argon lines:

         Wavelength    Relative Power    Absolute Power
          454.6 nm          .03               .8  W
          457.9 nm          .06              1.5  W
          465.8 nm          .03               .8  W
          472.7 nm          .05              1.3  W
          476.5 nm          .12              3.0  W
          488.0 nm          .32              8.0  W
          496.5 nm          .12              3.0  W
          501.7 nm          .07              1.8  W
          514.5 nm          .40             10.0  W
          528.7 nm          .07              1.8  W
    Krypton lines (magnetic field optimal for majority of lines, but not all).
         Wavelength    Relative Power    Absolute Power
          406.7 nm          .036              .9  W
          413.1 nm          .07              1.8  W
          415.4 nm          .02               .28 W
          468.0 nm          .02               .5  W
          476.2 nm          .016              .4  W
          482.5 nm          .016              .4  W
          520.8 nm          .028              .7  W
          530.9 nm          .06              1.5  W
          568.2 nm          .044             1.1  W
          647.1 nm          .14              3.5  W
          676.4 nm          .048             1.2  W
    Depending on gas fill, current, optics, and luck, there may be other weak lines present including: 437 nm (argon), and 457.7 nm, 461.9 nm, 657.0 nm, 687.0 nm, and 799.3 nm (krypton).

    As a side note, the color saturation with an ion laser is unbelievable, it's possible to get 16.8 million distinct shades with off the shelf hardware. I know the eye can't resolve that but the results you can see are beautiful.

    Efficiency of Argon Ion Lasers

    The output couplers on argons are 5 to 7% transmissive, (much greater than the helium-neon output side mirror). So an argon has more gain and it scales as a semi-log function of current density. The upper limit is the tube material melting - about 100 watts output at present in experimental tubes. (A HeNe tube peaks in output power and then declines as current is increased.) However, 100 mW beam power out for 1680 W in is still only about .006 percent efficient - not quite as 'efficient' as a HeNe laser!

    White Light Lasers

    The term 'white light laser' typically refers to one that is capable of producing a set of wavelengths which if mixed in the proper proportion can 'simulate' the effect of a white light source in full color displays and laser shows, for some spectroscopy or other applications. However, they generally don't produce a broad spectrum like an incandescent light bulb.

    The most common white light lasers are large frame ion types with a mixture argon and krypton for the gas fill.

    White light lasers are now even available in air cooled format. All use a mix of argon and krypton. Many are made for a roughly 60:20:20 ratio of red, green, and blue lines for proper white balance. Their reliability is increasing with cost staying a little above normal Ion laser prices. Spectra Physics, Coherent and Lexel all manufacture tubes for this, and LaserPhysics Inc sells the air-cooled version that runs off single phase 220 VAC and does 400+ milliwatts. Most of these lasers are modified for reduced operator skills with sealed mirrors and simplified power supplies. So yes they are out there, and laser company reps tell me the demand is going up as people start to use them for lab and industrial applications as well as display. CREOL in Florida and quite a few other labs have demonstrated RGB as well in diode pumped frequency doubled YAG lasers so smaller and more practical is just around the corner as soon as ways are found around the materials and QC problems with solid state laser components, right now they have to test 4 or 5 crystals for every good one they get.

    Note that other technologies can be used for white light lasers. For example:

    (From: Colin Evans (c.j.evans@goose.ac.uk)).

    A white light laser was developed in this department several years ago. It was based on a helium-cadmium mixture which could lase simultaneously at red, green and blue wavelengths. There was no automatic balance between the three colours and had to be carefully adjusted using the pressure and temperature. Also, I don't know whether the three colours could be regarded as "coherent" in any sense. Advantages are very strict polarization, and narrow parallel beams, neither of which are much use in a projector.

    (From: Marco Lauschmann (lauschm@hrz.uni-kassel.de).

    The only real white laser I know of used a Bucky-ball (carbon) compound which was optical pumped by the 488 nm line of a argon ion Laser. The emission was a real white light continuum - not like the 488 nm, 514, nm and 647 nm lines of an Ar/Kr ion laser system which looks like white light to the human eye. Researchers at the University of Manchester Institute of Science and Technology have demonstrated that confined buckyballs emit strong white light when excited by blue light from an argon-ion laser. Although work is at an early stage, the group has already identified some possible applications for this new material. They suggest that it may form the basis of a new laser material or new types of optical displays.

    Another source for a white light continuum is a Ti:Sapphire regenerative amplifier with a frequency doubler. So, a white light continuum could be produced with 800 nm output of 150 Fs, 500 uJ pulses at 1 KHz from a Ti:Sapphire regenerative amplifier, which extends from 400 to 1500 nm. A 5 cm long piece of fused silica is the non-linear element and was used to generate the continuum. This is only an example - there are systems which deliver a white light spectrum with average power of more than 1 W with repetition rates of 250 KHz or more.

  • Back to Argon/Krypton Ion Lasers Sub-Table of Contents.

    A Typical Small Argon Ion Laser - the ALC-60X/Omni-532

    Description of a Typical Air-Cooled Argon Ion Laser

    Unlike HeNe lasers, there are not that many models of argon ion lasers out there and even fewer available to the hobbyist-scrounger type. Therefore, the description below, while generally applicable to most low to medium power argon ion lasers, is written from the point of view of the American Laser Corporation Model 60X which was second sourced by Omnichrome, Inc. as the Model 532. (However, there are physical differences between the two. For example, Omni-532 heads have a cast aluminum alloy L shaped resonator while ALC-60Xs have the traditional rod and end plate resonators floating on a baseplate.) Other air-cooled argon/krypton ion lasers are similar but not identical. Keep this in mind where specific component values or designs are described - variations are likely where a different laser is concerned.

    An air-cooled tube is a neat little thing about four times the diameter of an average glass HeNe tube. Most have external mirrors and Brewster windows, but many are of the sealed mirror variety. What they all have in common is a heated cathode (like a vacuum tube such as a magnetron) requiring 3.2 volts at 10 to 25 amps. They operate from a range of 4 to 10 AMPs through the arc (Yes, that is AMPs) at around 100 VDC. The tube current is fed to the cathode via a center tap on the filament winding of the transformer to balance the arc on the center of the cathode to avoid plasma etching of the cathode supports. Hence the need for a beefy transformer with #14 or #10 wire on the secondary. Rewound microwave oven transformers work well for this purpose.

    The tube is designed for a 100 to 105 V voltage drop, and is ran directly off the rectified and filtered AC line. This makes regulating the tube current a very interesting problem in design because we also have a series injection igniter (similar in function to a HeNe starter) which is a 3" toroid with 80 turns on the secondary and one turn on the primary. A 10 uF cap is charged to 110 or 400 V depending one the model of laser and is dumped directly into the 1 turn primary through an SCR which has a reverse connected fast switching (10 ns) diode across it. You end up with a 500 Khz 30 KV ringing wave pulse applied to the tube, which can blow the arc out as well as ignite it. The winding on the igniter transformer is also #14 wire as it also carries the entire tube current. There is no ballast resistor (as would be found in a HeNe laser power supply) as it would have to dissipate up to 1,000 watts at times. There is a .2 ohm resistor in the anode lead inside the head to sense the current for feedback to the supply, and a beam-splitter sampler that drives a solar cell for the fine loop, which keeps the light level constant to .05% and is used to cancel out noise and oscillations in the beam.

    An air cooled tube's current is usually regulated by either a series pass-bank of 4 high power NPN power transistors in linear mode, with two 700 V, 20 A PNP transistors ahead of them in switch mode. Alternatively, two 400 V, 25 amp FETs are used in a buck mode converter at 80 Khz. Larger water cooled lasers which run off three-phase and need 20 to 35 amps of tube current use about 100 large NPNs in series/parallel strings for fine adjust and SCR's on the incoming phases for course adjustment.

    The fun part starts when you buy the laser, the power supplies are scarce and run about $900 to $1,250 used. When the laser tubes are pulled for a rebuild every 5,000 hours the PSU stays in the photocopier/printer/medical instrument/typesetter or whatever until the whole unit is discarded. So the laser heads show up, but supplies keep their initial value.

    A tube is good for 2 to 3 rebuilds, and after 5,000 hours they usually have 1,000 to 2,000 or more hours left for they hobbyist to enjoy. Most of the lasers are built as 150 milliwatt units and ran at 20 milliwatts to enhance lifetime, so even an old laser still has a lot of potential.

    There is no book on how to maintain these things either and since it is the Holy Grail of laser hobbyists to own one, maybe its time they learned how to maintain them, clean the optics, align the mirrors, peak the performance and find out how to avoid paying $3,800 for a used one when you can get one for less then $1.000. I (Steve Roberts) paid $125 for my head, and built my own power supply.

    Photos of the Major Components of the ALC Model 60X

    This laser was also second sourced as the Omnichrome Model 532. In addition, see Photos of Various Laser Systems, Power Supplies, and Components for many more detailed views of ALC laser heads and power supplies.

    The Intracavity Prism

    On the opposite end of the output aperture, there may be something that looks like an angled mirror or prism covered with a metal cap. This is called an intracavity prism and is used to select which line lases. It operates by deflecting each of the lines by a slightly different amount - as any ordinary self-respecting prism would to create a spectrum. :-) Only photons of the selected wavelength make it through the prism-mirror combination in such a way that they bounce back down the bore of the cavity and contribute to the lasing process. (The intracavity prism can be replaced with a broadband mirror for all the lines to lase.) Turning the vertical adjust nut/screw/knob on the rear mirror will select the line. Set the current at around 8 to 9 A when you adjust it. Beware of touching adjustments on the prism itself.

    Also see the section: Typical Behavior of Wavelength Tuning Assembly.

    Typical Behavior of Wavelength Tuning Assembly

    This is from the ALC-60X/Omni-532 user/service manual and lists the typical optical power levels on each spectral line as a function of the thumb-screw position. It is altering the precise angle of the intra-cavity prism.
          Spectral       Plasma Tube Current         Thumb-Screw Rotation
            Line        6 A      8 A     10 A      Clockwise from 514 nm Line
            514 nm     6.8 mW  24.0 mW  48.0 mW                0 Turn
            501 nm     0.0 mW   1.2 mW   5.0 mW              1/4 Turn
            496 nm      .9 mW   4.5 mW  10.8 mW              3/8 Turn
            488 nm    17.6 mW  37.0 mW  60.0 mW              1/2 Turn
            476 nm     2.4 mW   7.3 mW  14.3 mW              3/4 Turn
            472 nm     1.0 mW   3.5 mW   7.5 mW              7/8 Turn
            465 nm     1.5 mW   2.3 mW  11.5 mW            1     Turn
            457 nm     1.3 mW   4.6 mW  10.0 mW            1-1/4 Turn
            454 nm     0.1 mW   1.1 mW   2.5 mW            1-1/4 Turn

    Comparison of Argon and Krypton Ion Tube Characteristics

    A fresh 60X argon ion tube should drop about 106 to 109 Volts at 10 amps doing 95 to 107 mW, all lines, with TEM00 optics. This would typically mean a 60 or 200 cm radius output coupler (OC) and a flat high reflector (HR). It outputs about 200 mW with a 60 cm radius OC and a 60 cm radius HR. Of course the diameter and divergence suffer!

    When filled with krypton, the same tube with a 45 cm radius OC and a 45 cm radius HR outputs 647 nm and 676 nm red at about 35 mW while dropping ONLY 85 volts at 10 A. These were the only optics we could find, and were less then optimal.

    Krypton runs at a lower voltage, but unlike argon which is a semi-log curve in output versus current, krypton has a knee curve for gain. There is a certain threshold above which all hell breaks loose. I doubt we were at that threshold and we didn't have time to experiment with the pressure of the fill. Below the curve you get mostly 676 nm. A 60X emitting a cherry red beam is a rare sight indeed and we did it just to see if it could be done as many people told us it could not be! We even took it to a conference to ensure witnesses!

    There are a couple of tricks to making a small air-cooled tube like the 60X operate with a krypton fill including a large gas ballest and special cathode processing. It will only last a few minutes if you just chop and pump the tube with krypton. NEXT UP, a 60X white light laser, I (Steve) have the optics on order!!

    Steve's Favorite Questions About the ALC-60C/Omni-532

  • Back to Argon/Krypton Ion Lasers Sub-Table of Contents.

    When You Really Want an Ion Laser, Great Deals, and Other Tid-Bits

    Ross's Quest for an Argon Ion Laser

    (From: Ross McEwan (G.R.McEwan@hw.ac.uk)).

    It was a real bit of luck. I study physics at Heriot-Watt University and was walking by the physics department skip (dumpster?) and saw this dirty great metal box with Coherent Radiation Model CR-5 Ion Laser printed down the side.

    How could I resist. At this point I knew zero about argons and assumed it was capable of maybe tens to low hundreds of milliwatts and would make a nice contrast to the red HeNes and diodes that everyone thinks are so cool (they are but blue is better :) ). So I dragged it out of the skip and loaded it into the back of my car, drove it back to the flat (apartment) and opened it up.

    Oh dear :-(. The cathode end of the tube has shattered and someone has been raiding the electronics for parts. I asked the department about the head and this is the story. It worked. Perfectly. As did four other argon and krypton head they threw out later despite my attempts to get hold of them first. The tubes break when the heads drop four feet onto metal and concrete. Apparently the lasers are "too old to use" and "we use solid state now" so they throw them out . Sorry about the mild rant but it kind of annoys me to see several perfectly good lasers destroyed just because they bought new ones and they don't want curious undergrads messing with the old ones. Grrrrr...

    (It would drive me nuts to think that perfectly good lasers were trashed when I can think of so many good homes for them! Probably too many lawyers or whatever you call them over there! --- sam)

    They're called solicitors - yet soliciting is a crime. Go figure :). I think the judge is called "My Lord" too. And they wear funny wigs. I don't pretend to understand the legal system......

    Well that is sort of the reason. For a while (10 years or so) now there has been all sorts of crud flying about worker safety and dangers at work. Now as you know a 5W argon and PSU presents a fair few ways to injure yourself and the uni is VERY strict about safe working with them in the labs. NO-ONE is allowed in a lab with an operable laser unless they have had an eye test, read the rules about laser safety and have appropriate eye wear. If you want to chat to your mate in the laser labs they have to shutter off the beam, leave the lab, close the door. If there is no-one left in the lab the laser must be turned off etc.

    So you can imagine their mild horror when I go round asking for help to get their old lasers running in my flat. They do have a valid point and I agree that they would get a good roasting if they GAVE me a laser and I fryed myself but I promised any lasers they were chucking would get anonymised (labels peeled, ID numbers ground off, etc) and I'd deny everything as it were but they still insisted on breaking them. Still, I have rescued one and should get it working so I am happy.

    In defense of the university who are (perhaps rightly) getting a mild roasting here, when Nigel (mate and laser enthusiast) and I asked the optoelectronics boss about the chucking out policy he did give us a dead 1W Nd:YAG with parts missing and said as long as we didn't take it off campus we could fix it up and tinker with it. As it is missing Q switch, cavity, PSU and most of the head electronics it is unlikely to work any time soon. We may end up converting it to pulsed operation. More likely we will let it rot in Nigel's lab. He also offered us a tour of one of the laser labs which has argons, kryptons, excimers and I believe a TEA. I get the impression personally he'd have liked to help.

    Anyway, I phoned Coherent UK. They said "you are not a company so we can't deal with you". They wouldn't even send me schematics on a laser that is 30 years old and hasn't been supported for the past 10? 15? years. So I looked around the Web and emailed a few companies asking for schematics and/or parts. Laser Innovations said they had a tube I could have (for free! if I pay shipping so I don't mind if it isn't up to commercial rebuild standards) so I am very close to having a complete head.

    I already have a design for the PSU. It was initially going to be a line powered switcher with a small linear pass-bank but it turned out it was easier and cheaper to build a BIG pass-bank (40 - IRF740 power MOSFETs) and water cool the heatsink. It's loosely based on the original Coherent design but missing a few of the more exotic bits (due to price and parts availability). The Lexel 88 schematics are pretty much identical to those in the Coherent manual. I guess there's only so much you can do with a linear design.

    I doubt my design is as good as Lexel's or Coherent's and I doubt it meets CE standards but it will (slowly) charge the caps, fire the starter and regulate the current all without melting. :) Ferrites, chokes and other moderately exotic parts are very hard to get hold of in UK unless you are a business or university or lab.

    I will buy PSU parts soon, a major capacitor manufacturer have generously donated a big filter capacitor so I estimate 200GBP for the rest of the bits and pieces.

    Side note: I like the magnetic oscillator in the Lexel 88 starter, very clever.

    Deal of the Week?

    Well, we all know about the efficiency of ion lasers! I hope he has a power substation nearby :).

    (From: Richard and Debora Everett" (everett@oz.net)).

    I just bought two argon medical lasers from a local auction. One of them is a Coherent model 900. It has a manufacture date of 1981, and the little meter inside says 79 hours. It is water cooled and rated for 9 watts output. The funny thing is, it takes three-phase 208 V at 35 amps! This thing must really be inefficient!

    The second laser is much newer with a manufacture date of 1988. When I got it home, I was pleasantly surprised to find it has TWO tubes in it, a 10 watt argon and a 3 watt krypton. Both of these tubes are water cooled and made by Spectra-Physics. The laser itself was made by Cooper Vision and Hewlett Packard.

    Now I have little (okay, zero) experience with ion lasers, although I have worked with HeNe and CO2 lasers before. I am a little concerned about the integrity of the Cooper Vision/Hewlett Packard laser tubes, because the &#$# loading dock guy dropped the whole cabinet assembly about 4 to 6 inches from his pallet jack. I have looked at the tubes (very cool looking) and see no visible cracks, although most of the tube seems to be in a metal jacket. I am not sure how to tell if either tube survived all of this.

    Anyway, I only paid $200 for all of this, so I guess I will not be out that much if they don't work.

    A Strange Small Argon Ion Tube

    (Quoted text from: Axel Kanne (axel.k@swipnet.se)).

    "When I was visiting a local laser company (Latronix AB) to acquire my first HeNe tube, a Russian made 1.2 mW tube manufactured only a year ago and probably never used, price ~$12 :), I saw something pretty interesting on display in a locker. Stupidly, I didn't ask about it, but maybe someone here knows anything about it.

    Here's an ASCII illustration:

             |        \
             |         \          ____________________
          +--+          \---------+--------------------------------------+
          |                                                              |
          |                                                              |
          +--+          /------------------------------------------------+
             |         /
             |        /
    The base of the tube was wide, and the rest was maybe 1 inch or so. A thin glass tube was spiraled around the long tube (the strange looking thing on the illustration :). The total length was about 16 inches.

    3 wires stuck out from the base. The only thing readable on the label (from my viewing angle) was "made in Russia" and some obscure model number. I don't remember anything about the electrodes. I think it had mirrors on the ends, but it might have had Brewster windows. Any ideas about what this laser might be?

    Label on My Tube:

                                        HeNe Gas Laser
                                   <Number (S/N??)>    04-97
                                        Made in Russia
    Label on Strange Tube:
                                        ????      ????
                                        Made in Russia
    The only things readable from my angle was a bit of the logo and "Russia".

    Hmmm.. I will pay the company another visit in a month or so to get a larger HeNe tube and maybe a diode laser and then I'll take another look at it. I wonder if they would sell the strange tube to me. At least it would look good as a hi-tech glass display :)."

    (From Sam):

    Since there aren't that many types of low power gas lasers, it might be a HeNe but the spiral tube thing is really strange. Any chance of getting another look? Conceivably, it could be a high quality tube designed to have ring magnets on the outside to focus and stabilize the beam or something.

    Of course, it could be a lot of other things!

    "Maybe.. But the spiral tube would be in the way.. And 3 connection wires? And, it had the same type of label as my HeNe."
    (From:Chris Livingston chrisliv@aol.com)).

    I may be wrong here, but it sounds like a NEC Type Argon tube, The wide part, sounds typical of the NEC tubes, and the cathode is normally suspended inside this "Wide Part" which on my nec is about 4-5" and the "spiral" sounds to me like it may be the gas return like used on the NEC tubes, which is from the wide part back toward the anode region. The mirrors are connected on both ends.

    (From: Sam).

    But glass? Argon ion tubes are usually made of materials like beryllium oxide and tungsten to withstand the intense heat of the discharge.

    "Today, I paid the local laser company a visit again. Result: One REALLY small Siemens HeNe tube (total length 11.6 cm, diameter 2.3 cm, power 0.7 mW, makes a nice laser pointer) and a large ~10 mW Uniphase tube which I'm going to use for a laser show.

    Most important result (for this letter's purpose at least):

    The strange unidentified beast is indeed an argon ion tube (I asked them). I thought argons had large cooling fins and a lot of metal structure, but this one is mostly glass. Now, I just wonder what power it might be. Can't be too high since there seems to be no means of cooling (though the spiral tube might also be a water jacket). The tube also has a strange vent port in the wide section, In all, really strange. :-)"

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