Re: PERMANENT THREAD: Ebay& other internet FINDS of interest- read all the OP please
why bid at all???
I win lots by NOT bidding--
(PM me if you want my 'secret')
awesome that this thread is now 112 pages long..
last search found >20 listings for gas lasers--so how does one weed out the dead ones??
Not easily -- Sam has something to share on this
Compare info from multiple sources if possible - the more agreement there is, the higher the probability that the information is correct.
Also see the section:
Buyer Beware for Laser Purchases.
Buyer Beware for Laser Purchases
In perusing the various laser offerings from time-to-time at the
eBay Auction Site as well as the on-line or print catalogs of various surplus outfits, it very often seems that given the model or size of the laser, the claimed power output ratings are considerably higher than what may be realistic while still achieving a reasonable system lifetime, or are not possible at all. The most common error (intentional or not) is to use the CDRH safety sticker value rather than the manufacturer's or measured power output in the description of the laser.
This is an upper bound - the actual capability can be
anything lower! And, even if the seller states that they measured the actual output power, there's no guarantee that their laser power meter was calibrated within the last century or that they knew how to use it properly!
Here are some comments on laser power and other claims that you should be aware of before purchasing a used laser:
Helium-Neon (HeNe) lasers: The power discrepancy is particularly evident with HeNe lasers where the model number and/or dimensions are provided. The tendency seems to be - possibly due to lack of knowledge, possibly for other reasons - to use the CDRH safety sticker rating (which is an upper bound for the laser safety classification) rather than the actual measured or specified optical power. Sometimes they do say 'max' (possibly in the fine print).
This doesn't mean it is (or ever was) possible to run the laser at that power, and the actual output may be less than half of the maximum value listed (assuming the laser is functioning near its new product ratings). HeNe tubes are essentially constant optical output power devices - there is no way to get more power either with greater tube current (beam power actually goes down) or by using pulsed drive. For example, a HeNe laser with a CDRH Class IIIa 5 mW sticker may produce as little as 1 mW when new and even less after thousands of hours of use! A true 5 mW HeNe laser head will be at least 15 inches long and have a Class IIIb safety sticker.
A classic defense of using the 'max' rating is to say that "the laser was spec'd as (say) 5 mW and thus calibrated at the factory for this power level but could go much higher".
Balderdash!
The only way to trim power of an HeNe laser (without an external attenuator) is to (1) run it with reverse polarity to sputter overcoat the anode-end mirror (which is irreversible) or (2) to slightly misalign one or both mirrors (which would compromise beam quality and stability and isn't likely to be done on purpose). Having said that, it
is true that slight misalignment of the mirrors is common (either from use, thermal cycling, shock, or less than perfect quality control at the factory) and boosting power by some (usually modest) amount may be possible, even likely, by tweaking the mirrors - just don't count on it - or on a huge increase. But, first see the sections starting with:
Problems with Mirror Alignment because it is very easy to totally mess up the alignment (or even break the tube) and never see any coherent light from your buy of a lifetime HeNe laser forever-after!
Note that there are some multi-mode (non-TEM00) HeNe tubes with wider bores and a different mirror curvature that produce up to perhaps twice the power output for a given tube length. However, with multiple axial modes, these are not suitable for many applications like interferometry and holography. They are also not very common compared to single-mode TEM00 HeNe tubes.
Also, the power output of non-red HeNe lasers - green (543.5 nm), yellow (593.9 nm), and orange (611.8 nm) - will be only about 1/10th to 1/4th that of an equivalent red (632.8 nm) one.
Thus, a 20 inch green laser head is good for about 2 mW (compared to 8 to 15 mW for red) and a 10 inch head, perhaps only .2 mW (1 to 2 mW for red). As with normal red HeNe lasers, there is no way to boost power and the CDRH sticker rating is normally much greater than what is actually possible. However, the beam WILL look a lot brighter mW/mW compared to red due to the response curve of the eye, which can be misleading to sellers and buyers alike.
Note: Since the gain of these wavelengths is so low, they also have a shorter life and the chance of finding working surplus green or yellow HeNe lasers is much lower than for red. I would not recommend bidding on an eBay auction for one of these unless guaranteed to be working. The likelihood of the problem for an "unknown condition" green or yellow HeNe laser being just mirror alignment is small to none!
And, just because the male
Alden connector of the laser head fits into the mating female socket of a randomly selected power supply doesn't mean they will work together! HeNe lasers of all sizes usually use the identical connectors! (Many people have been known to throw out perfectly good HeNe tubes and heads if they failed to start or operated erratically when in fact, power supply compatibility was the real problem!) On the other hand, don't assume compatibility just because the laser tube or head and power supply were
supposed to work together - many of these same people have no idea what this means and make the assumption that because the laser worked once (if that), it would be fine forever. The life of the HeNe tube and/or power supply may be shortened and/or power output may suffer.
Large-frame HeNe lasers like the Siemens LGK-7676/L/S and functionally similar Spectra-Physics 107/907 which show up on eBay and from surplus dealers either untested or without measured output power are probably high mileage tubes which may run but will not meet new power specs. However, they are very well built, really nice to play with, and probably have a lot of life left. Just don't expect good as new performance from them. Around 50 percent of rated power is typical.
Finally, HeNe laser heads in like-new condition that show up as surplus or on eBay without end-caps (output aperture and Alden connectors) were probably manufacturing rejects pulled from the line before being completed since they didn't meet spec in any of a number of areas including: output power value, stability with warmup, mode cycling percentage, polarization ratio, or other aspects of beam quality. Thus, what you end up with may have undisclosed problems.
This is also likely true of bare HeNe tubes (often without any identifying labels) - especially 'other color' (than red) types in pristine condition but where the locking collars or mirror adjusters are loose and the seller suggests that "alignment is all that is needed to make them lase and then you will have gotten a great deal". Note that it is likely that some of these have found their way to resale via less than legitimate channels - especially if the serial numbers have been removed! Even if they do work or can be made to work, items like this have trouble written all over them. And, don't believe claims that tubes were "purchased new and used very little" if they don't have any labels. A tube sold as a tube (not part of a laser head) will almost certainly be labeled with model and serial numbers at the very least, usually with a sticker on the side. Similarly, a laser head should also have a similar label. It's the law in both cases. And, even the manufacturer can't tell specs by inspection!
Having said all this, a used or off-spec HeNe laser
may still be just fine for many purposes as long as you understand exactly what you are getting. For more information on HeNe laser sizes and power output, see the sections starting with:
Internal Mirror HeNe Tubes up to 35 mW - Red and Other Colors. And some have very interesting and unusual behavior.
Argon and/or krypton (Ar/Kr) ion lasers: It is much more difficult to determine actual ratings of small air-cooled Ar/Kr ion lasers based on size alone because the output from the same size laser head can span a range of 100:1 or more depending on specific model, age, operating current, or condition. The advertisement may specify the output when running at a current level that would result in a tube life of only a few hours or one not even obtainable with a typical power supply.
Also see the section:
Expected Output Power and Used Ion Lasers.
^^^^^^^^^^^^
this is also good to know.
............
(this bit is also worth reading Sam's has specs for almost every gas laser every made-
this helps match head to PS.- just because the alden plug fits does NOT mean that's the right one
Locating Laser Specifications
It is often difficult to determine the capabilities of a particular model laser in terms of wavelength and power output based on a single catalog listing or description alone. (For testing of an laser you have, see the chapter(s) for that specific laser type.)
Obviously, for a model that is still being sold, the manufacturer's literature or Web site will often provide enough info. User and service manuals may also be available as well as for older lasers that they still support. In addition, there may be many variations on a given model depending on the type of optics installed and possible tube replacement or upgrade.
Unfortunately, few manufacturers maintain detailed specifications or other information readily accessible (e.g., on-line) for older models. After all, why should they help you fix the laser that you've been happy with for the last 5 years for only $500 when they can sell you a shiny new and improved one for $20,000!
There are a variety of other places to look for specifications but their accuracy can vary based on the objectives of the provider (e.g., honesty, vested interests, optimism, technical knowledge).
Vintage Lasers and Accessories Brochures has scans of older catalogs, specifications sheets, and price lists, from several popular manufacturers (mostly HeNe lasers at present).
Companies that sell used or surplus laser equipment - If the model in question is in their catalog, the information you seek may be there. For example,
Laser Resale, Inc has extensive listings for virtually all types of laser systems. Many others can be found in the sections:
Mail Order - Lasers, Laser Parts, Optics, Accessories and
Laser Sales and Service Companies.
Just keep in mind that these are items for sale so power output ratings must be taken with a sliver of optical glass (at least for lasers like ion and ruby/YAG where output power is adjustable).
