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Argon laser

   Argon lasers are gas ion lasers, where Ar+ ions are the active medium. Ions excitation is obtained by collisions with free electrons - electric current flowing through the laser cavity. In these lasers current flowing through the gas is pretty high (in my laser it's 10 amps), therefore the cavity construction is quite sophisticated. It's made of metal, glass and beryllia (beryllium oxide). A thin bore along the laser tube, through which the electric current flows and where the laser action occurs, is made of beryllia because the temperature there is so high that glass would melt. Beryllia (actually it's powder) is highly toxic when inhaled so never smell broken argon laser tube ;) A nice picture showing how the laser tube is made is HERE. As said before, current flowing through this laser is quite high. Voltage drop across the tube is typically about 100V, so power consumption of such laser is 1kW! Optical power of the emitted light is about 100mW at these conditions, so practically all consumed power turns into heat. That's why proper cooling is needed, in a laser like mine a large fan is a MUST. Running such laser without cooling even for a moment can end with permanent damage!

   Argon laser often works at several spectral line, from UV to green color. The most powerful lines are 488 and 514nm. Although there are also single line argon lasers, where special optics in the laser cavity is used so that all lines besides the desired one are attenuated. There are also Argon-Krypton mixture (Ar-Kr) lasers. Krypton adds some red spectral lines so the laser emits white light beam. The argon lasers can give even a few dozen watts of light so they are used in large laser shows. These lasers have also many other applications, in medicine or e.g. as energy pumps in dye lasers. More info about how ion laser works and how it's made can be found here:

  • http://www.lexellaser.com/techinfo_gas-ion.htm

       As far as I found out, my argon laser works at one spectral line with probably 488nm wavelength. Maybe it's a single line laser or maybe it's simply burnt-out because it's pretty old. I bought it on eBay for relatively low price. It was cheap because the condition was unknown :) Here are some pictures of this laser.

       It's pretty small toy as for an argon laser, but still it's 33x14x11cm (not including the fan) and 5kg weight. It's from National Laser Company, I have no idea what was it's application. The safety sticker on it says 160mW max., measured power at 10 amps is about 80mW (I can't push it higher because my PSU gives 10A max). In the last picture you can see a built-in running time counter which shows 45 thousand hours. However, there's also a sticker saying that the laser has been remanufactured after 31 thousand hours of work. Durring the remanufacture they're refilling the laser with new gas or even changing the whole tube for a new one. That gives 14 thousand hours running time after that remanufacture, which still is pretty long. In this situation I'm glad that the laser gives that 80mW of power :)

       Below pictures of the laser gust.

       In the first pic you can see a massive heatsink mounted in the middle of the tube. Inside the tube, on the left end, there's a heated cathode. It's the rear end of the laser so there's also a HR mirror. The other end (right on the pictures) is the output of the laser.
       In the second picture you can see a tube label and in front of it a thermal fuse mounted to the heatsink. That thick black wires provides filament current and also tube current (the cathode is directly heated).
       The third picture shows the other end of the laser tube, there's a beam splitter and photocell mounted on it for measuring laser power. It's needed in power stabilization mode of operation (you can see the photocell itself in the fourth picture). The black box with a 'danger' sticker is an ignition circuit. When anode voltage appears this circuit generates a high voltage pulse that ionizes the gas and causes ignition of an electric arc. This circuit is powered from anode voltage and is fully independent.
       The last picture shows the power connector. I haven't found any pinout description for it, but with help of the priceless Sam's Laser FAQ and conductivity tester I managed to figure out which pin is what. Below a pinout description of this connector.

    	1, 6	Cathode (A) 
    	2, 7	Cathode (B)
    	3	Fan, counter (A) (110V AC)
    	4, 8	Anode
    	5	not connected
    	9	Fan connector control (A)
    	10	Power sensor (+)
    	11	Ground/Case
    	12	Fan, counter (B)
    	13	Thermal fuse
    	14	Fan connector control (B)
    	15	Power sensor (-)

       I think it's clear and doesn't need any comments. As you can see the running time counter is connected in parallel with cooling fan. Normally, there's a short between 9 and 14 pins. A break of this connection means that a fan connector inside the laser casing fell off. It's a protection against running laser when the fan is stopped, which would damage the laser after several seconds.

       That's all about the laser, now I will write something about the power supply which is pretty interesting too. I used really cool JDS Uniphase argon laser PSU, model 2114. I bought this PSU before the laser, because it was cheap :) Actually, it was the fact of possession of this PSU what pushed me to look for an argon laser.

       This model is quite popular and can be find on eBay pretty often. Here are some pictures of this power supply:

       It gives 105V on the output and the current is regulated in range of 4-10 amps. The current value is set by an analog input at one pin of the DB25 connector (0-10V signal). There are two modes of operation available: current or output power stabilization. To use the second mode a calibrated power sensor is needed of course. I used this PSU for powering unknown laser made by a manufacturer other than the PSU, so I could use only the current stabilization mode. The PSU has also outputs providing voltage signals representing the laser current (100mV/A) and output power (100mV/mW). Obviously I can't use the output power signal in my case. There's also filament power provided and 110V AC for powering the cooling fan, so everything what is needed to run the laser.

       I found the DB25 connector pinout description in Sam's Laser FAQ, in the following PDF file:

  • kccucp1.pdf

       I made a simple control panel based on that schematic - a piece of universal PCB with one switch and one potentiometer for current adjustment.

       The laser socket pinout description comes from Sam's Laser FAQ too. Here's that description:

    JDS Uniphase 2114 argon laser PSU connectors
    Power connector (view from front of the connector on the end of laser head cable): 6 .-------. 3 |D O O| 9 2 |O O C| 8 1 |D O O| 7 +-------' 4 Pin Number Signal Description Cable Wire Color ----------------------------------------------------------- 1 DC+ Black 2 Case/Earth Ground Green/Yellow Stripe 3 Cathode/Filament (F1) Yellow 4 NC or Hour Meter 5 Case/Earth Ground Green/Yellow Stripe 6 Cathode/Filament (F1) Yellow 7 NC or Hour Meter 8 Cathode/Filament (F2) Blue 9 Cathode/Filament (F2) Blue Control/Light Feedback Connector (view from the front of connector on the end of laser head cable): 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Pin Number Signal Description Cable Wire Color -------------------------------------------------------- 1 +15 VDC White 2 Start+ (See text) Fat Purple 3 Signal Ground Dark Green 4 Interlock 1 Orange 5 -15 VDC Black 6 Start- Fat Dark Green 7 Signal Ground Blue 8 No Connect 9 No Connect 10 No Connect 11 Light Feedback Red 12 Interlock 2 Orange 13 No Connect 14 Signal Ground Dark Green
    This data came from Sam's Laser FAQ

       When running my laser I didn't use the round socket of the PSU. I only had to short two pins responsible for interlock. Pins 4 and 7 from the rectangular socket provides 110V for powering the running time counter and, what is more important, the cooling fan. Firstly I didn't know that it concerns also the fan, hence there's a small variac in some of the photos - I used it for making 110V out of 230V for powering the fan :P

       Running the power supply wasn't easy at all (although it should have been easy). I wasn't sure if it's in totally working condition, so I decided to connect a ballasting resistor in series with the laser anode to limit the current in case of failure. I used an electric kettle as the resistor. It's shown on the pictures below.

       The first thing I've noticed was ... that the laser works!!! So the money I spent on it was worth it. But unfortunately, there was no reaction to current regulation signal in the PSU. As you can see on the second picture the anode current was 3,5A (the kettle was 1800W@230V so the numbers fits: I=105V/(230V^2/1800W)=3,57A), so it was less than the lowest current available in current regulation mode which is 4A. So instead of the kettle I put there heaters that I took out from broken microwave oven. You can see it in the next three pictures and in the video.

       This time the current was almost 7A, but there was still no reaction for current regulation. 7A is in the middle of the regulation range so that was strange. After a long reflection and trying to figure out what's wrong with the PSU I had a thought, that maybe the PSU gives the laser a shot of max current (to make the ignition easier?) and then limits the current to the set value. When there was a ballast resistor the PSU tried to achieve the max current for that shot but it couldn't. Then I connected the laser without any ballast in hope that it won't blow up, and it turned out that everything works fine!
       After that I made better connections between the laser plug and PSU socket (till that moment that currents, including filament current, were flowing through small crocodile clips :P). It turned out that pins from MOLEX sockets fits perfectly to the PSU connector - I have a lot of them from DVD writers.
       The finished, working set of laser with PSU is shown on the pictures below.

       The multimeter from the first picture that is connected to the controller board if for measuring signal from current measure output of the PSU. In two pictures on the right the power measure is shown. When powering at full current, that is 10 amps, the laser emits about 80mW of light.

       Five photos below shows a comparison of the argon laser working at full power with a 100mW green DPSS laser module and also the beam splitted by diffraction grating and a CD disc.

       The next step to do was running this laser with my galvo scanners. The galvos has already been shown in violet BluRay laser article, but I haven't write much about them there. These galvos are G100PD from General Scanning, I have also a dedicated GSI amplifiers with them. Each scanner has a capacitive position sensor inside. The position signal goes back to the amplifier as a feedback - it's called closed loop control. That improves the galvos' speed and precision. The amplifiers itself are pretty sophisticated analog circuits, which I didn't have to build by myself fortunately :) The X-Y analog signals that goes into the amplifiers comes from DACs connected to LPT port of the computer. All that stuff is controlled by Popelscn 3.1 software. A schematic of the DAC interface is available in my RGB laser article. There's also my program for converting BMP files to Popelscan's MOT files available for download.

       Below a few pictures of the laser working with these galvo scanners. I think I don't have to say that the effects are much much better when you watch it in real than in photos :) The last picture (with Creamfields logo) is a comparison of the argon laser with a 10mW green pointer.

       You can see some additional thin lines in projection with letters, that shouldn't be there. The laser should have been blanked in that moments, but blanking is not so as easy with gas lasers as it is with diode lasers. Acousto-optic modulators (AOMs) are used to do this, and I don't have one yet :P Also, a third galvo can be used as a shutter blocking the light beam, but I don't have a third one either :P

       At the end a short video with the described laser and below it some useful links.

  • http://www.repairfaq.org/sam/laserarg.htm
  • http://insulatorz.home.att.net/argon.htm
  • http://user.web-gear.com/andreas-kilchenmann/argonlaser.html

    [ ADDED ON 30.01.2011 ]

       Sometime in March 2010 I found a nice argon laser power supply on the Polish internet auction service allegro.pl. The most interesting thing for me was that the power supply had a rectangular socket on the front panel, that seems to be compatible (at least mechanically) with my NLC laser's head cable. The power supply is a model 9600 by Laser Drive. It's a nice switch mode PSU with output current regulated in 3.5 to 12A range. Laser output power stabilization is also available. Additional controller is not needed because the power supply has some switches, a regulation pot and even a power/current meter placed on the front panel. After some research on the internet I found out that the rectangular socket most likely is electrically compatible with the NLS laser head. Quick way to make sure - conenct the laser and see what happens :D To do so, I had to provide 115VAC to the PSU - that's what a spec sticker said. I used a variac to lower the mains voltage down to 115V, you can see the variac in the first of the pictures presented below. I run the PSU with the NLC head hooked up to it and the laser was working fine emitting 75mW of light! After that, I found out that the input voltage of the PSU can actually be changed by switching a jumper inside. You can see the jumper on the third picture. The white wire has to be plugged into 230V NEUTRAL connector, instead of 115V NEUTRAL. The fourth picture shows the laser successfully running off 230V after changing the jumper position.

       Suprisingly, not long after I bought the Laser Drive power supply, a nice argon laser head popped up on the allegro.pl service (argon lasers are not common on this auction service). The laser head was selled as-is, without a cooling fan and in unknown condition. It was very cheap though, so I decided to buy it anyway.
       After I received the laser it turned out to be a Spectra-Physics SP163 head - well known and popular among laser hobbyists. The safety sticker says that the max output is 0.16W. You can see the head in the following pictures.

       There was a lot of dust inside, but mechanical condition seemed to be fine. In fact, when I connected the laser to a power supply, it started working after a few ignition shots. When I was sure that the laser works, I spent some time on cleaning it. I also found an hour meter inside (mercury type, shown in the first of the following pictures). The reading was 3000 hours.

       Clean laser head, put back together with a cooling fan attached to it is ready to run. I connected it to the JDSU 2114 power supply that I've had before. The last two pictures show both laser sets: NLC head with Lased Drive PSU and SP163 with JDSU 2114 PSU, running at the same time. In the last picture there's also some other lasers and a description with power measurements for comparison.

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