Best sources for lasers

Dale Wood · Post by **Dale Wood** » Sat Jul 06, 2002 3:31 pm

Thanks, Colin. Encouraging.
The whip plug-in works quite nicely with your drawings.

wler · Post by **wler** » Mon Jul 08, 2002 9:13 am

Well I am using an argon for hobby holography (not since long, though). Air cooled ones are pretty bad and make lots of noise/air currents/temperature gradients (you dissipate one or more KW in the room), so I guess unless it is in another room you can't use it. Water cooled ones are much better for holography, but more expensive and also you need water lines, etc.

First of all, you need single line operation, while
many argons are sold with multiline mirrors. So you'd need single line optics to start with, or a prism which allows to tune through the various wavelentgs.

Apart from that, the coherence length tends to be bad, typically worse than a He Ne (due to the hotter plasma, more longitudinal modes will be excited). This can be corrected with an etalon in the cavity, which ensures single mode operation and coherence lengths up to 40m or so.

Obviously, this can be implemented only for argons with external mirrors - and most air cooled ones have internal mirrors; those you can safely forget for holography. And even the external mirror ones like ALC 60 have usually not enough space in the resonator for an etalon, so you would need to rebuild the resonator quite substantially.

On the other hand, for larger water cooled argons
an etalon is typically a standard extra, as well a prism for wavalength selection.

In summary, I think small air cooled argons are pretty difficult to use and while the power is typically less then 50-100mW single line, this may not be worthwhile.

I was just last weekend fitting an etalon into an OEM Lexel 88 head, and the coherence length jumped immediately from a few cm to several meters (more than I could measure). Still I need to improve on mode hopping and adjustments (eg by heating the etalon).
It does ca 500mW single line and perhaps 300mW with etalon, but other water cooled ones would have more than that.

Colin Kaminski · Post by **Colin Kaminski** » Fri Jul 12, 2002 11:14 pm

Do you mount the laser to the table? Do you have any problems with turbulence (in the water cooling) induced frequency drift?

I have often wondered how hard it would be to isolate a water cooled laser. Can you recommend a laser that has the features you describe?

wler · Post by **wler** » Sat Jul 13, 2002 2:19 pm

Well I do not have any comparison yet with other water cooled argons, but so far I am happy with an OEM Lexel 88 head - those are probably the cheapest and easiest to get. I modified it for single longitudinal mode and am about (literally.. doing my first holograms with large coherence length.

The resonator seems to be not very stable - it dejusts itself after a few days so that I have to retune it before using it for holography - no big thing, though.

I too was concerned with water induced vibrations but doing extensive interferometer tests it turned out that this is negligible. The head is mounted on a heavy steel plate anyway (perhaps 10kg) and I have placed it on another ca 20kg steel plate - that's so heavy that the water can't mechanically excite it, I guess. And the exposure time for a 4x5 is only 3-5sec anyway (or less if using more power).

I am setting up some explanatory web pages, the Lexel-holography part in particular isn't yet finished, but have a preliminary look at http://perso.wanadoo.fr/redlum.xohp/argonlaser.html

Colin Kaminski · Post by **Colin Kaminski** » Sat Jul 13, 2002 3:27 pm

Thank you! The pictures are great. Make sure you have some goggles!

Colin Kaminski · Post by **Colin Kaminski** » Sun Jul 14, 2002 3:06 pm

I read through your site yesterday and re-read the section at LEOT on argon lasers (thank you for reminding me of that resource) and I was wondering what etalon you used? Was there enough gain in the cavity to use an air-apaced etalon?

wler · Post by **wler** » Sun Jul 14, 2002 3:59 pm

Hi, no it is a quartz one, a surplus from Coherent. It
comes in a heatable temperature stabilized case, but I took it out because it fits so well in the mirror holder just as it is (it just looks like an ordinary argon mirror, a cylinder of perhaps 1cm diameter and 1cm high).
If I need to improve fringe drift then I may put it back into the heatable enclosure. I guess that's then similar to what you guys do with the diodes...

It really has a dramatic effect - putting it in makes interference fringes visible where before none could be seen. I am pretty sure similar things can be done eg for a DPSS if the resonator is large enough to fit this in - maybe even a glas plate would do. But it reduces power by 50% or so.

In fact yest eve I was doing some holograms and I could accidentally see on them some parts of the optical setup ca 80cm away, towards the collimating mirror (the holos didnt come out nice for other reaons).

Jeffrey · Post by **Jeffrey** » Tue Sep 24, 2002 2:55 am

Don't do it.
There is no etalon, and no space to stick one in. These are not precision light sources, just green beams.

Jeffrey · Post by **Jeffrey** » Tue Sep 24, 2002 3:02 am

There's a problem with goggles - you can't see what you're doing. In most laser apps using high power, goggles are of course recommended, but in holography, considering it's just you the expert, and not the public, and your system is under control (the beams all go to the FILM, right, not flying around the room!) and your whole art process is seeing what's going on, not just counting photons in a vacuum chamber or some abstract process, I have to say it's impossible to work w/ goggles. I have also gotten some vicious burns by not seeing where the beam was when adjusting a mirror. Just BE CAREFUL, and THINK.