Lasers wet or dry

Eric Van Buren aa9080 at
Thu Sep 28 15:06:00 EST 2000

>Hi Folks
>Has anyone compared directly air cooled and water cooled lasers for 488
>excitation. I
>am thinking of replacing my aging 100mW ILT with a larger water cooled unit.
>Simon Monard

We just did a quick check of _our_ aging "100mW" ILT (hasn't output 100mW for
quite some time now) versus our 1986 Coherent Innova 90 5W water-cooled argon
ion laser (plasma tube last refurbished 1996). Using BD's DNA QC Kit
(PI-labeld CEN and CTN, and 2 micron beads), we looked at %CV of the singlets
(CENs and beads) or G0/G1 peak (CTNs) as a measure of laser performance, since
air-cooled lasers reportedly are "noisier" than water-cooled lasers.

The ILT actually outperformed the I90 when both were set to output 40 mW of
488 nm light. But, if I remember correctly, that is because our vintage I90
laser does not regulate well below 100 mW output (but newer Coherent models
may). Adjusting the I90 to 100 mW produced a CEN %CV less than the ILT (at
40 mW), but the CTN and bead %CVs were still higher. At 200 mW, the I90 had
better CEN and CTN %CVs. At 300 mW, the bead %CV was finally better. At 500 mW,
all 3 samples' %CVs continued to improve. The FACS Vantage was adjusted for
sample (PMT HV) to place the peak of interest at channel 200 (on a 1024 linear
scale). This avoided the bias of using different channels (see previous
discussion on Purdue list), but the I90 data did enjoy diminished noise
generated by the PMT as a result of lower HV settings. Here are the CTN %CVs
(from ModFit):

4.27 (ILT), 6.01 (40mW), 4.48 (100mW), 4.04 (200mW), 4.11 (300mW), 3.88 (500mW)

(The I90 may be noisier than normal since I had to switch to 488 nm after 4
years of almost exclusive UV usage.) In fact, previously, the same I90 laser
set for 100 mW UV output produced lower %CVs (less than 2.5) using CTNs (from
an expired lot, no less) stained with either DAPI or Hoechst 33342... and the
I90 was the second laser in a dual-laser setup!

Now, what I'd _really_ like to see is a comparison to Coherent's not-yet-
released-but-recently-announced-at-ISAC solid-state 488 nm laser. Any word
on this laser?


/\/\/\_ Eric Van Buren, aa9080 at
\ \ \   Karmanos Cancer Institute and Immunology & Microbiology
 \_^_/  Wayne State University, Detroit, Michigan, USA

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