Claude Cantin writes: >Just out of curiousity: we do Ca++ mobilisation with an Enterprise >laser set at 20mW UV, but in visible light regulation mode. It is a >fairly new model / laser, with about 6 months use... and of course, well >warmed up. However, it varies quite a bit in UV output over time: say, >after setting at 20mW it can vary around 23mW +/- 5mW. (In UV >regulation, the 488 output varies enough that populations may be shifted >outside the gate; of course, 488 output is very stable in visible light >regulation mode, as is UV output in UV regulation mode.) This is ok for >indo ratio-ing, but probably not so hot for DNA and other more critical >applications. I was hoping you might give me a range of what you have >found for stability of UV output in visible light regulation mode... >I'm wondering if our Enterprise wanders more than most, or if this is >typical of the Enterprise. The UV lines of an argon laser are low gain lines, and very sensitive to slight changes in optical alignment caused by just about anything; the 488 nm line is a high gain line and relatively insensitive to changes of the same or greater magnitude. You could probably spit on the dual wavelength mirrors and get 488 nm output; unless they're pristine and precisely aligned, you can forget about UV output. This means that the power output of whichever line (UV or visible) you choose not to regulate will fluctuate appreciably. The behavior is typical of any argon laser capable of simultaneous UV and 488 nm emission, not just the Enterprise. And yes, fluctuating UV output will probably give you unacceptable CV's for DNA measurement. Unfortunately, commercial flow cytometers do not feature source noise compensation, which would be a relatively inexpensive way (no more than a few hundred dollars) of getting around the problem. After you have split the UV and 488 nm beams, you could conceivably put the unregulated one through an electro-optic modulator (several thousand dollars) and control its output - if there's room in the instrument. Not an easy or a cheap solution (although probably cheaper than adding another 488 nm laser), but a solution. -Howard
This archive was generated by hypermail 2b29 : Sat Mar 10 2001 - 19:31:11 EST