From: Joseph Webster (J.Webster@centenary.usyd.edu.AU)
Date: Mon Nov 16 1998 - 18:37:42 EST
At 22:35 13/11/98 PST, Derek Schulze wrote: > Hello everyone! > > We are having a problem with a our Spectra Physics laser (6W argon > Stabilite 2016 running at 100mW)). Essentially the current creeps up on it > over time when it is in power mode. You didn't say how much the current changes or over what time-frame, so it's hard to advise if you should worry or not. Several things come to mind: Do you let the laser temperature stabilise sufficiently before aligning the laser mirrors? I suggest a 30 minute warmup before touching anything; some lasers take longer. One of our lasers I warm up for 2 hours, but that is a special case. !-) What about the water temperature? That must be stable for the laser alignment to hold. (after initial warmup of course) Laser types vary in temperature tolerance so I can't comment on your particular model; a few degrees should not matter, but I would worry about large fluctuations. > This is easily corrected by adjusting > the mirrors until the current level drops sufficiently. The trouble is > that my alignment seems to change or laser output is not the same after I > adjust the mirrors ?? My light scatter changes and my FL means shift?? When you adjust the laser mirrors you move the beam direction, and that will affect the scatter and fluorescence results. That's why the laser is adjusted before the cytometer optics. > If I ignore the current drift my light scatter and FL means stay consistent. That's good! :-) That indicates that both the laser beam direction and power are staying constant. > In my ignorance I assume that a laser will continue to lase in the same > path that the tube is aiming regardless of how the mirrors are adjusted. > The mirrors should just affect the efficiency of light production. (??) In fact it's the other way around. The tube is simply a hole filled with some very excited gas molecules, and so long as it doesn't touch the sides, the tube won't affect the beam. The mirrors define the beam path through the hole. !-) > Is tube age an issue here? Unlikely; an old tube *usually* gives lower power rather than changing power for a given current. ;-) > My fear is that the power mode circuit is not > operating properly (it indicates 100mW consistently). If the power control was not holding constant, the scatter and fluorescence intensities would change along with the current. I have not answered your question directly, but I hope I have at least given you some pointers for further investigation. Good Luck, Joseph. -- Joseph Webster Flow Cytometry Facility Centenary Institute
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