Dear All,
We’re having unanticipated difficulty getting a Spectra Physics
375B dye laser to lase, using R6G and pumping with 2.5 W of 80 MHz 5 ps mode
locked 355 nm pulses (Spectra Physics Vanguard). I’m wondering if anyone
has any suggestions. More particulars follow.
Originally, the 375B, a cw flowing dye jet dye laser, was in an extended
cavity configuration with a cavity dumper at the far end. The overall
cavity length was adjusted so that the laser could be synchronously pumped
with ~100 ps, 80 MHz pulses from a 514.5 nm mode locked Ar+ laser (cw power
~ .7 W). This overall configuration was employed to produce tunable ps
pulses to use in time-correlated-single photon counting. From past
recollection, it was quite easy to get the dye laser lasing in the old
configuration. Our intention has been to use the Vanguard 2.5 W, 80 MHz,
355 nm pulse train in place of the Ar+ laser sync pump. We have not
obtained lasing with the extended cavity configuration. We then placed a
reflective mirror in front of the dye laser output face, essentially the
standard cw cavity configuration, but could not obtain lasing here either
(focus of output spots as specified in dye laser manual). Any suggestions
would be appreciated. What might be especially useful is a concentration
recipe known to be good for pumping any visible dye in a cw dye jet laser
with 355 nm.
Here are some factors that might be affecting us:
1. The beam diameter coming out of the Vanguard is ~ 1 mm, as opposed to
perhaps ~2-3 mm for the 514.5 nm output. This pump beam output is focused
on the dye jet with a concave mirror, but ultimate spot size on the laminar
flow surface probably differs slightly in the two cases.
2. We did not initially obtain lasing using the R6G recipe for dye
concentration originally given in the 375B manual for 514.5 nm pumping.
Looking at the dye absorbance, the OD at 355 nm is about 0.20 the value at
514.5 nm. On that basis, we increased the dye concentration by a factor of
5, but still did not get lasing. It is possible that the higher dye
concentration is causing luminescence reabsorbance problems.
3. The Ar+ 514.5 nm 80 MHz pulses were ~100 ps whereas the 355 nm pulses
are now ~5 ps. According to my understanding, the luminescence duration in
R6G is long enough that the shorter pump pulses in the 80 MHz (1.25 ns pulse
spacing) train should still be effective in producing lasing. Is this true?
Can anyone state if any common visible laser dyes might produce problems in
this respect?
All comments appreciated!
Thanks
Mark Sulkes
Tulane University
New Orleans, LA USA
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