Also is it possible to use the same expander (designed for 2mm input beam diameter) for focussed beam from a laser having large beam diameter?
I dont think so, because each expander was produced to support certain wavelength ranges and power. You may damage the lenses, safe margins should be described by specs. Aslo I suggest to design your own telescopic system based on your requirements.
I dont think so, because each expander was produced to support certain wavelength ranges and power. You may damage the lenses, safe margins should be described by specs. Aslo I suggest to design your own telescopic system based on your requirements.
the glue/oil between the lenses (if any) or the anti-reflecting coating (if any) will be the first thing to get damaged if you go beyond the manufacturer max power spec.
Even the lenses themselves can be damaged by high power density pulsed lasers.
It really depends on how "high" power above the threshold of low power beam expender you go. You can usually go a bit higher than the manufacturer suggestion but not too much above. You can contact them and ask for their safety factor. This will give you a good idea of how much above specs you can go without significant damages.
If you use a beam expander designed for small input beam diameters, to expand larger diameter input beams, the output may not be properly collimated due to aberrations.
Another difference between "low" and "high" power is the use of a diverging (negative) input lens to avoid focusing the beam.
"High" and "low" are relative .. It is better to look at numbers. Typical "standard" AR coatings have the damage threshold below 10J/cm^2, typical laser-grade coatings have bigger ratings. If you are safely within the critical energy density and power density, this is fine.
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