what diagnostics to use

Posted by Guy Cox on
URL: http://confocal-microscopy-list.275.s1.nabble.com/Re-pre-chirping-what-diagnostics-to-use-tp590162p590163.html

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Shalin wrote;

 

 What diagnostics do you use for tuning of two photon laser or OPO? Is laser spectrum analyzer enough?

The laser spectrum analyser should get you back exactly to your

wavelength, and give a pretty good idea of the pulse length.

Lastek in Australia make a software system which works with a

spectrum analyser to give you pulse length and it seems pretty

good provided it is carefully calibrated.  (It's probably sold under

some other name in the States).

 

But if you have users who want to know the pulse length precisely

it's really worthwhile buying an autocorrelator. 

 

We have a shared two photon (MIRA 900F Femtosecond configuration) and OPO from Coherent. One of the main user is very afraid of tuning it - so he always has a service engineer tune it to 830nm and longest possible pulse (since he does spectroscopy). There are two more of us who will benefit by tuning it for two-photon and SHG (different wavelengths and shortest possible pulse).

 

830 is quite OK for SHG (brings the harmonic to 415 which is within

the range of conventional interference filters (they start to absorb a lot

at anythong shorter).  But it's a bit limiting for 2P.

How is the 'reproducibility' of laser beam profile when working with these lasers? One of the main concern that other user has is that - if you cannot come back to exactly 830 nm after tuning to say 740 nm, the custom optical setup will go out of alignment.

In the early days one make of Ti-S laser was notorious for beam

wander as you tuned it but even so it should go back when you

returned it to the original wavelength.  Nowadays they seem really

stable, and I don't think your Mira should be a problem there.  The

only thing I find with a Mira is that it's  best to let it warm up for

half an hour before doing any tweaking of the alignments (and often

that way you find you didn't really need to do any tweaking anyway).

 

                                                                                            Guy