Etalon for SP 165 - Question September 4 2003 at 7:23 AM
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I recently purchased another Spectra Physics 165 head and 265 power supply. I got the head lasing. It came with an Etalon that has an electric cord with 6 large round pins on the end of the connector. It is air spaced intra cavity. The etalon I have in my original 165 does not have this electric cord and they look pretty similar. The question I have is, does anyone know what this cord does? When I put the Etalon in I cannot get the laser to output a beam. Is it some type of shutter. Does it need to be connected or shorted (close circut)? I did not try too long on walking in the etalon as I figured I should find out what this extra accessory does first. Thank you in advance, John.
OK, I found out the etalon is heat contolled not air spaced I believe. So my next question is there anyone out there that has a controller for this etalon? Thanks again.
I found it was a temperature controlled Etalon, thank you. BTW, I did not know of that news group. I assume it is the one I found on Google alt.lasers? Looks great, thanks!
I assume this should be similar to the coherent etalon I was using
so far, ie, there should be a temp dependent resistor (NTC or PTC)
in the case plus a few power resistors for heating. For this case
it is easy to set up a small circuit for temp stabilization,
an operational amplifier and some power transistor or mosfet should
do it. I have cooked up such a circuit and it is described here:
You may need to adjust it a little bit if the heating resistor is
different from the 220Ohms in my case, and the NTC is different
from the 100KOhms. The temp I was aiming for was about 35C and it
seems to be OK like that. The only difficulty is that it takes
quite some time until it stabilizes, and this can easily take 1/2h
or more. Before that one can observe lots of mode hops.
If it doesn't lase at first, no surprise. The tuning of the whole
thing is extremely critical, the etalon introduces a large loss
into the cavity and this means it does lase only if everything is
perfectly aligned. So try to tune the laser optimally wihtout
etalon, and then insert the etalon and then turn the current up
very high (so that you have a lot of gain), and try to get it
lasing by first setting it parallel to the other mirrors. It
can take a long time until it works, perhaps using a HeNe may help
here (set it up when the argon lases without etalon and then don't
touch the HeNe anymore). When everything is optimal, you need to
very slighly tilt the etalon "to the next smaller peak" to achieve
single mode operation.
The whole process is quite a hell and can take some while. Ideally
you have the whole thing in a thermally stable environment, then
you have the chance that the laser comes into its optimal working
mode just by itself after heating up - otherwise you may have to
repeat the procedure from time to time.
Excellent, thank you. You seem to have experience witht the temp controlled etalon. Let me ask you a question. What are the advantages to using a temp controlled etalon vs. an air spaced etalon? Is it worth doing the conversion? In the past I have made some pretty lengthy exposures with the air spaced etalon with any problems. TIA,
Well so far I have experiences only with solid etalons, and not
air spaced ones. The solid ones have a strong temperatur dependence,
hence the stabilization. But they have higher losses than the air
spaced ones, I guess that's why the air spaced ones are used with
large argons with lots of gain. In general, the solid etalons give
you more output power. Then there is the issue of tunability;
actually the Lexel site is up again and there is some nice info on
these issues: http://www.lexellaser.com/techinfo_features_single-freq.htm http://www.lexellaser.com/techinfo_features_single-freq_503-etalon.htm
In fact just a few days ago I happened to receive a genuine Lexel
etalon for my laser (exactly as described in the above link), which
works much better than the cumbersome Coherent one I used so far.
There has been a PCB board coming along with it, which is supposed
to keep the temp constant to 0.01C. I am about tracing the (simple)
circuit in order to figure out how to hook it up.
