Q-Optics - Telescope Lunaire Moon
Introduction to Ion Lasers
Argon and krypton (rare gas) ion lasers find applications in many diverse fields including very high performance printing, copying, scanning, typesetting, photoplotting, and image generation; forensic medicine, general and ophthalmic surgery; entertainment; holography; electrooptics research; and as an optical 'pumping' source for other lasers. From the hobbyist's point of view, items and 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 mostly from.
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.
Argon ion lasers are not of the 'set it and forget it' variety. At least, not those even a financially independent hobbyist can afford. They require a certain amount of maintenance and fiddling to achieve optimal output power and maximize tube life (though
this is much less of an issue with internal mirror tubes).
The basic tubes are costly - even reconditioned ones with many hours already on them. Expect to spend several hundred dollars for one that is not even anywhere near to new or in tip-top condition. A new tube may go for $5,000 or more - just for the tube!
The power supply will be even more costly (possibly $1,000 or more used) unless you build it yourself since while refurb tubes are available, power supplies don't really wear out so they are in much shorter supply.
Argon/Krypton Ion Lasers
The Argon laser was invented in 1964 by William Bridges at Hughes Aircraft and is one of a family of Ion lasers that use a noble gas as the active medium. This laser is used in many applications such as:
- Forensic Medicine
- Telescope Lune technologie
- General Surgery
- Ophthalmic Surgery
- Optical "pumping" source
Equipment Using Argon Ion Lasers
As noted, argon and krypton ion lasers are used for many applications. Large water-cooled units (like the various Lexel models) with up to several WATTs of output power were often medical or surgical lasers. While locating one of these in working or even repairable condition at a good price might be your fantasy (it is mine), consider that such a beast will require at least 220 VAC (some use 440 VAC!) and possibly three-phase power, a tap water connection, and likely a fair amount of tinkering (and possibly cost as well) to get it going and keep it going. While your local electric company will probably be willing and eager to sell you all those kWHs, you may need a large phase converter to convert your residential single-phase power to three-phase or an upgrade your power feed (which may or may not be costly). Here are a couple of links to possible designs:
Single to Three Phase Convertor Info
LaserFX Hobby Archives - Phase Converter
At least the added plumbing shouldn't be much of a problem unless portability is an important consideration! This is not to say it cannot be done, just that you will have to be pretty determined to get that large laser going in an one-bedroom apartment! In any case, you can't just go and plug one of these beasts into the nearest AC outlet.
A small air-cooled ion laser is probably a more reasonable toy especially if you have to share the single 3-prong outlet in your place with the family microwave! And, some of these lasers still have outputs that can approach 500 mW (though most are much lower).
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, recorders, duplicators (not your ordinary office copier), printers, and phototypesetters.
The Xerox 9700 series and older 8700 series (and possibly the 8400 as well) utilized an American Laser Corporation (ALC) 60X argon ion laser. This 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 and OEM Spectra-Physics (SP) 161 lasers were used in a Times Graphics, Inc. printer. Other companies that manufacture or have manufactured equipment containing ion lasers include Dainippon Screens, Hell, and Ricoh.
Many of these older but expensive graphic arts 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 are showing up on the surplus market at attractive prices.
For reference, here are the typical wavelengths and expected power output from argon ion laser heads pulled from graphics arts equipment:
ALC-60X (external mirrors): 488 nm or 514 nm (20 to 40 mW), or multiline (retunable to much higher power).
NEC-3030 (internal mirrors): 488 nm (20 to 30 mW). There are a few multiline NEC-3030s but check with a grating to be sure. Some of these heads were rebuilt with 3050 tubes.
SP-161 (internal or external mirrors): 488 nm or 514 nm (15 to 20 mW), or multiline (up to 40 mW).
Other argon ion lasers that may turn up as pulls from graphic arts equipment include the Uniphase 2202-5BLT, 2202-30BLT, and Spectra-Physics 163, as well as several others.
Note that some lasers that at first appear to have excellent specs may be designed for pulsed operation. One example is the HGM Spectrum Compac A Argon Laser. This uses a American Laser 68B tube which would be good for 2.5 W with a proper power supply and adequate cooling but in this case is only designed for relatively low duty cycle pulsed operation. Pulse, cool, pulse, cool, etc. If the price is low enough, it may be worth buying just for the tube (assuming it is still good) but non-trivial modifications will likely be needed for it to run CW.
Mix and Match Ion Laser Components
When you obtain a laser that spent its former life as part of a fancy graphics arts machine (or from other sources as well for that matter), it may turn out to be composed of pieces from several manufacturers as parts were replaced or upgraded. Don't
panic! For better or for worse, this implies a high level of interchangeability among similar size lasers and the availability of replacements and substitute components, ideal for moon observation.
In fact, such a hybrid or may be better than the original because at least some of its parts will likely be newer than the original as they were replaced to provide an improvement in performance or life expectancy. The downside is finding
documentation on a half dozen different pieces from several manufacturers!
However, a word of caution: Just because the connectors look the same or the specs look like the power supply and laser head should be compatible doesn't make it so. Just plugging something together may result in smoke or shortened lifetime. It is a safe bet that if the components actually came from a working system, they will play happily together. On the other hand, if someone just connected a power supply to a laser head that it wasn't designed to drive, tested the combination for a couple of minutes, and sold it as a working system, there could be problems down the road.
Regardless of whether your laser is built like Frankenstein's monster, it WILL likely be missing the cooling fan and in some cases, even the head cover. The typical Patriot style fans are available surplus typically for between $15 and $30. Other type fans or blowers with similar ratings (220 cfm and up) will also work if the airflow direction is correct (i.e., for the ALC-60X, it must be sucking out of the head). In cases where the fan diameter is much larger than the opening in the head above the tube as with the Patriot and ALC-60X, a 1 inch collar will also be needed between them to act as an adapter plenum.
For laser heads like the SP-161 where the cover may be missing, replacements (including the fan) may be available from the original manufacturer or companies though the cost may be a good fraction of what you paid for the entire laser! (In the case of
the SP-161, the cover is really only needed for safety - the fan doesn't use the cover for mounting.) But, if you are just a bit handy, they can usually be fabricated relatively easily. Any interlocks that are missing will also need to
Also, don't be upset if the running time meter says something like 64,500 hours! This is typical of a graphic arts pull and doesn't reflect on how much time is on the tube itself - which is the only thing that really matters. You can be sure the tube has been replaced more than once but there is probably no way to actually determine how many hours are on the one that is installed.
Where the umbilical cable has been cut (this happens as well since whoever removed the unit may not have realized that the cable could be extracated non-destructively), a proper connector will need to be reattached. If they are the same type at both ends, the wiring is likely 1:1 so an ohmmeter can be used to determine the connections. However, if they are not the same type (e.g., a Jones type at one end and an AMP type at the other), you will need to find the wiring for each one. Ditto if either end is hard-wired. However, in the worst case, a lot of the wiring at the head-end at least can be determined by tracing connections inside the head. WARNING: A cut umbiliacal could also mean there could be compatibility problems as mentioned above if the head and power supply were not from the same piece of equipment and were never tested together. Even if they use the same AMP connector, there could still be problems. For example, an ALC or Omni power supply may melt down attempting to drive an NEC head or vice-versa without some rewiring and other changes (if it is even possible) even though the connectors mate.
The Argon Gas Laser System
Figure 1 shows all the wavelengths of light emitted by the Argon laser operating in multi-mode. Every wavelength is a monochromatic light source of itself and each wavelength has a very narrow bandwidth. The two dominant wavelengths, of 514nm "Green"
and 488nm "Blue" make up about 67% of the total beam output power. Single line operation is also possible by inserting prisms, diffraction gratings and other optical devices to "filter out" the unwanted wavelengths. Of course, when single
line operation is required, the total output power decreases dramatically as well.
The laser resonator is made up of two mirrors. One is highly reflective (HR) and other is a partially reflective mirror (OC). From this optic (the Output Coupler) the beam emerges as laser light. The Brewster's Angle optic mounted at both ends of the tube, minimizes reflection loses while creating a polarized beam. When the laser is first turned on, a delay allows for temperature stabilization.
Then a pulse of high voltage (8 kilovolts DC) ionizes the argon gas. Upon ionization, high DC current (45 Amps) and about 600 volts DC across the tube maintains a sufficient discharge to keep the gas ionized. The typical Argon laser tube has a tungsten bore which has a high melting point and allows the laser to operate at higher power levels with longer tube life.
Argon lasers with average powers of over three watts require tap water cooling and separate three phase 220 AC volt @ 50 Amps per phase electrical line feeds.
Argon laser emissions are hazardous to view. Both diffuse and direct exposures beyond the applicable MPE (Maximum Permissible Exposure) limit can cause permanent damage to the retina.
Argon Ion and Krypton Ion Laser Wavelengths
While most HeNe lasers output a single wavelength, argon and krypton ion lasers are often 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.
Argon ion visible lines (8 UV lines and 2 IR lines ignored):
454.6 nm, 457.9 nm, 465.8 nm, 476.5 nm, 488.0 nm, 496.5 nm, 501.7 nm, 514.5 nm, 528.7 nm.
Krypton ion visible lines (4 UV and 8 IR lines ignored)
406.7 nm, 413.1 nm, 415.4 nm, 468.0 nm, 476.2 nm, 482.5 nm, 520.8 nm, 530.9 nm, 568.2 nm, 647.1 nm, 676.4 nm. Which lines actually lase are sensitive to both tube current and gas pressure and thus the color balance (relative intensity of the various wavelengths) will shift as the tube heats up and with age.
Different types of optics may be used on a laser to optimize or select a particular performance characteristic. Where one or both mirrors are external, optics sets can be swapped to change behavior.
Single-line or multiline: This refers to the output spectral lines in the beam. For ion lasers, several wavelengths can be generated simultaneously. The reflectivity curve of the Output Coupler (OC) mirror and tube current determine which subset of the possible lasing lines are active.
Single-line - One and only one of the possible wavelengths is generated. no matter what the tube current (within its specifications). Example: 488 nm argon ion laser.
multiline - Some subset of the possible wavelengths are generated. Which of these is actually present in the beam will also depend on the tube current. As the tube current is increased, high gain lines appear first and the output beam power of each line increases with increasing tube current.
All-line optics are broadband coated to permit all the common wavelengths to be generated (e.g., up to 8 lines for argon ion.) For a mixed gas (argon/krypton) ion laser, white light output (red, green, and blue) may be obtained.
Line suppression optics may eliminate one or more lines selectively. (e.g., all lines except 514.5 nm.)
multiline optics may be used in conjunction with a line selecting prism (usually at the HR end of the resonator) to generate any of the possible wavelengths by turning a knob.
Single-mode or multimode: This refers to the axial mode structure of the output beam.
Single-mode optics produce a TEM00 beam with a Gaussian profile. This is highly desirable for many applications and essential in particular for interferometry and holography. Most helium-neon and argon/krypton ion lasers are set up to produce a TEM00 beam.
Multimode optics results in a beam with more than one 'hot spot'. For example, a TEM11 beam has a four quadrant appearance which will be very apparent if the beam is expanded (though it probably can be focused to a fairly decent spot). The individual sub-beams are not mutually coherent so it is somewhat like having several separate lasers whose beams have been combined side-by-side. The advantage of multimode optics is that much more output power can be obtained for a given size tube and operating current. These lasers are suitable for light shows and other applications that just want a large number of photons.
The total power output for all lines using multiline optics is greater than the sum of the single-line outputs at the same tube current. This is probably due to the contribution of the additional wavelengths (the other 5 of the 8 common argon ion lines) not shown in the table.
With multiline optics, the relative output power of each wavelength will be roughly the same as those indicated for single-line optics.
With multimode optics, 50 to 100 percent higher power output can be obtained for the same tube current (and tube life).
Ion Laser Power Output and Efficiency
So an advertisement for a 100 mW Cyonics-2201 or 300 mW ALC-60X. Should these be believed? Probably not, at least not if they are pulls from graphic arts equipment or some other similar source. There may be versions of these lasers that will do higher
output power (possibly with identical model numbers or ones that are close) but they usually don't show up at bargain prices - e.g., the ALC-60A, a current model, will do over 100 mW on all lines, but this isn't the same laser as the ALC-60X!).
Lasers from reputable dealers will have their *minimum* guaranteed output power clearly listed and may actually produce much more when new. That Cyonics *may* do only 10 mW and that ALC *may* do only 20 mW - or even less.
150 mW yes, 175 yes, 225 to 250, yes on a factory select tube. 300, hum... Rarely and not for long unless it was designed that way. Note where the PSU current limit is set when they claim this. Note that newer high-tech tubes can do this running on 115 VAC. One manufacturer does make a 300 mW sealed mirror retrofit for the 60X. Laser Physics' Reliant series certainly does.
What happened is when large quantities of these units were in use, a few companies made money rebuilding them in quantity. They bought large quantities of pulls for rebuilding. They didn't care which tube they installed in a unit, as long as it met spec and lasted out the warranty.
So therefore once in a while you can hit the jackpot on a used laser and get a hot tube. Once in a while you can also pick up a head that was designed for high power.
It's with special multimode optics and a high divergence doughnut mode or worse beam shape on a selected tube. Notice how vendors have power graded pricing, this lines up with the factory catalog of tubes. Note that lasers almost always are shipped doing well above the factory rating when new. Yes this gets you 275 mW or so on a fresh new high power tube at 10 A with brand new optics and a sweet new cathode. To sustain it for any length of time it takes 11 A.
The idea is buy a hot laser and run it lower then its rated power, and thus enjoy longer life. Thats why you could retune that tube to 110 mW or so, it was derated for longer service and the optics were tuned to run at a fairly constant power over its life. Run it at 60 to 70 mW and enjoy it for a long time.
And, as with any laser, the CDRH safety sticker or catalog listing may not be an accurate indication of useful or possible output power. Actual performance may be a small fraction of what you expected! This is a significant issue with ion lasers since they have many variables affecting output power (compared to internal mirror HeNe lasers, for example, where the output power is pretty much fixed - it isn't affected in a significant way by tube current or often not even much by age and use). The output power of an ion laser is a strong function of tube current and life expectancy is inversely proportional to tube current! So, the rating on the CDRH safety sticker is likely to be much much higher than what could be used with expectations of a reasonable tube life. And, unscrupulous or unknowledgeable people can list the power based on a ridiculously high tube current where life might only be a few hours! Ion tubes that are physically the same size and interchangeable in a laser chassis also can vary by a large factor in power ratings even if they are new depending on manufacturer and model. For tubes with external mirrors, the type of resonator (single-line fixed, single-line with line selecting prism, multiline) as well as alignment and cleanliness, strongly influence output power. At least you can remedy problems with some of these with some basic maintenance or parts replacement. However, age, total operating hours, and possible prior abuse, are also significant factors affecting ion laser performance and there is little you can do to revive a weak tube.
Most of these lasers came from xerox machines which were set up for single line 488 nm TEM00 running at about 6 to 7 amps when installed. New they would do about 15 to 20 mW in that configuration. There were also slightly different tubes (bore diameter) which would preclude higher current densities as the cross sectional area of the active region was smaller. You can and many do install broadband mirrors which would more than double the output. And, you can increase the current as much as 100% (double) as installed, which would give you the higher power limits advertized (and, of course, much shorter tube life). Additionally if the optics were not carefully aligned it was real easy to catch the rubber between the photocell and the front tilt plate when beam walking the laser which would smoke the rubber onto the front optic and beam splitter.
A used laser is just that - and priced accordingly unless the tube meets specifications as originally installed. And some units due to the smaller bore diameter will never attain the higher power levels.
So, you obtained a surplus argon ion laser from one of those printer things and would like to have an idea of whether it is performing anywhere close to what was claimed by the seller. Or, you are just curious.
The output couplers on argon lasers 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 (very large) tubes. (A HeNe tube peaks in output power and then declines as current is increased.)
However, for a typical small air-cooled argon ion laser, 100 mW beam power out for 1,000 W electrical power in is only about .01 percent efficient which is not quite as 'efficient' as a HeNe laser (e.g., 6 mA at 2,450 V for a typical 10 mW HeNe laser - about .07 percent).
For a mid-size water-cooled argon ion laser - say 4 W out 7,000 W in, the efficiency is somewhat better - about .057 percent.
Power outputs (and efficiency) for krypton ion lasers is must lower - perhaps 1/10th to 1/5th of the numbers listed above at the same power input.
So, from this very comprehensive listing, the larger the laser, the more efficient it is likely to be when operated at full power. Note that this doesn't take into consideration the losses in the power supply - figure another 10 to 30 percent reduction in efficiency for that!