Generally speaking, the peak power density of a pulse from OPA is huge high (the OPA work with a pulse repetition rate of 1KHz ,time duration ~100fs, pulse energy ~1mJ), it may damage the objective or the sample in the focus plane.
Thank u for that ,i guess your fs pulse laser come from an Ti-sapphire oscillator ,it works all right.but for me ,my pulse laser come from OPA with pulse energy ~mJ ,more than 10,000 times of yours,so it may damage the optics in the microscope (like Objective )or the sample in the focus plane still,i',m interested in your laser model ,what's the wavelength tuning range ?
OK,we are almost there .As you know ,an femtosecond pulse oscillator usually output the laser wavelength around/centralized at 800nm ,may be better ,tuning wavelength within the range 690-1040nm,when i need laser wavelength longer than that,i had to turn to the OPA available ,which can extent the laser wavelength to several micrometers.
There comes the problem :i can not directly guide it to the microscope to study the nonlinear optical response of my micro/nano sized samples with this longer wavelength because of the high energy pulse, and i don't think i can afford the potential damage of tentative experiments with reduced power .
There are standard reflective microscope objectives:
http://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=6933&gclid=CjwKEAjw0ueeBRCmhozc-_DRrlUSJABihBEEwGGlRTS0qFltKbN4OBz2jtglFnkK0J_Och7Env1BNxoC80zw_wcB
Presumably they can be coated for high power.
Basically, to reiterate/summarize the key points from the preceding responses, it would be best to use reflective and not transmissive optics for your microscope. This will avoid issues of accessing nonlinearities in transmissive optics and damaging such optics due to high peak power densities (i.e. high fields).
This is a separate issue from the type of damage inflicted by high average power described by Oskar, which is essentially burning or ablation. However, for 1mJ, focusing may also lead to large average power densities that could damage reflective optics. So it would be best to get high power coating and/or attenuate before the microscope. The second may not be practical if you intend to excite nonlinear processes in single micro/nano-structure samples, which I assume must be under study in order to require the microscope.
There is another approach, although it is more complicated, and that is to use pulse stretching and recompression. That way the peak power is reduced.In principle you could pre-chirp the pulse such that the rest of the delivery optics re-compresses the pulse.
Just out of curiosity.... is this a home-built system?
From commercial 1kHz Ti:sapph CPA amp you can get few mJ at ~800 nm. Are you really getting few mili J then from OPA?
It would be also interesting to hear answer on Oskar's question regarding what is the sample you are hitting with all this energy? They are cutting glass and machining metal already with microJ....
The first question that comes to my mind is: If the peak intensity damages MO then it should damage any other material used for microscopy. To invoke NLO coefficients in any materials few micro joules are sufficient (assuming you are using some bio-mateiral or organic) since the focal diameters are typically few microns.
For OPA based optics one needs to use special microscope objectives!!! which can transmit in the near IR region. Normal MO's do not work beyond 1.5 microns.
Still very curious on how to get to mJ/pulse with OPA....
and why a simple variable attenuator would not work just fine...
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