fiber coupling of nanosecond laser pulses

[heko]

I want to couple nanosecond laser pulses of a q-switched Nd:YAG Laser into a usefull fiber. (pulse duration = 5ns, pulse energy = 20mJ)
To avoid fiber damage I have to use silica fibers of 600um core diameter. Can someone tell me what kind of coupling optics I have to use for this specification? The Problem is that because of the hughe core diameter the numerical aperture of the incomming beam has to be very low (assuming gaussian beam optics,which leads to long focal length. I have also heard that the input beam divergence angle must be higher than 30 percent of the fiber NA.
Thank you for help.

 

[Jerre]

Hi.......Index matching and coupling between the optical coponents become very important in achiving near zero interfacing losses and damage.

The NA into the Fiber should match or be greater than the NA of the Gausian beam input.
The NA(fiber)=sqrt[N(cladding)-N(core)]. Index matching is the big thing.

For high power lasers. the index matching cement, fluids, greases and optics, must be able to withstand the heat associated with the optical losses at each interface no matter how small it may be. I have used NA matching Microscope Objective lense for coupling into fibers.

A very clean environment is required, because dust on optics cause laser optical damage.