How can I ensure the output laser beam that comes out from Non-collinear optical parametric amplifier be collimated? and What things that I need to consider to create such condition, i.e. the output beam of the laser from NOPA is collimated?
Thank you
I have not much experience with NOPAs but I think it’s important to consider the acceptance angle of the crystal which still satisfies the phase matching of the different beams.
I would expect that the beam waist is in the crystal and together with the converted beam quality it will determine the divergence. If the divergence is too high, you can recollimate it to a different beam diameter using an air spaced doublet or PCX lens.
Okay thank you very much!
Hi @Ilyas_Maulana_Yahya , my response is rather late, but I’d like to share some thoughts here too. Usually, the basic “geometric” idea with collimation is that the beam’s “size” (e.g., its diameter or its transverse surface area) remains the roughly the same near the output of the laser and at a desired distance from that output. However, as @Daniel_Csati suggested, the beam’s waist may not necessarily be at the output, but rather, inside the crystal. Therefore, I guess that one “general” way to collimate this output is to first bring the beam to a focus with a first lens, followed by collimating that focus with a second lens. However, if the beam is Gaussian (i.e., its transverse profile is Gaussian or TEMoo), then collimation actually requires to bring the beam to a “distant focus” such that the beam’s transverse size reaches roughly SQRT(2) times its waist size at focus. Anyway, by now, you probably have solved your problem! 
No problem at all. Thank you very much for you suggestions as well.