Arunima Gokul ,

>What must be the laser energy I choose so that I could have enough energy to run my experiment?

Answer on your question depends on what delivering way (mirrors vs fiber) and from laser wavelength you will choose.

For the case of free-space propagation you have to be aware on building/ground vibrations. With 15-20 m distance amplitude of laser beam vibration on your target focusing lens can be very significant. So it will produce movement of the focused beam along your target. To avoid it, you should place your laser on some vibro protecting table, support.

To deliver beam by fiber amount of losses will depends on fiber input/output and inner fiber losses, all of which depends on laser wavelength for given fiber.

Hi Valeriy Sterligov,

Thanks a lot for your detailed and informative answer. We plan to have an Optical parametric oscillator as the pump laser. This means that we would like to use the pump wavelength between ~300 nm to ~1000 nm to excite various biomolecules of interest.

You are welcome, if you like, you can recommend my answer. But you are pointing 3 mJ/mm^2, which is energy density, not laser power... Or do you mean energy of single laser pulse?

@Valeriy,

You are right. I mentioned the energy density only. This is the minimum we require at the sample position. The rep.rate we wish to have ideally 1kHz. But lower rep.rate can also be considered. So the question is how much the laser energy should be needed so that we can have the required energy density (i.e. 3mJ/mm2) at the sample, considering the losses in the laser guiding.

Arunima Gokul , if you solved beam vibration issue I have mentioned above, you can calculate input laser power as (target power)/Rn, where R is mirror reflectivity and n is number of mirrors.

For the case of fiber delivering, it is difficult to give you definite answer because it depends on many unknown factors, which determine input/output and fiber propagation losses.

@Valeriy,

Thanks a lot for your answer. It's really helpful :)

One important factor to take into account is pulse duration. Fibre delivery in particular can be very difficult with ns-fs pulses, for fs pulses, dispersion in the fibre will stretch the pulse considerably, Ns to ps pulses can damage the fibre tip, making light coupling into the fibre near to impossible. Free space propagation seems to be the best option, but as mentioned by others, turbulence will affect beam pointing. Using tubing to contain the beam can avoid or diminish the effect of turbulence, although it may not be practical for such a long distance,

Raul Rangel-Rojo Thank you for your answer :)