I need to bring a fibre containing laser pulses into a cryostat via a vacuum feedthrough.
I will be using a laser with pulse energy 0.3 mJ, wavelength 905 nm, pulse length 3 ns and repetition rate 500 Hz. Coupled to a 200 um core this gives a instantaneous power density of around 0.4 GW/cm2.
The fibre feedthroughs from Thorlabs, LewVac etc only quote a CW maximum power of 1 W which I am well below, but have no details of instantaneous power thresholds. The type of product I am interested in is a Thorlabs VC2H2S.
As these feedthroughs are essentially core to core with a small air interface is it safe to assume the limiting factor would be the theoretical silica/air breakdown of around 5 GW/cm2 (1 GW/cm2 safe limit)?
If not does anyone have experience of coupling nanosecond pulsed through a CF/KF feedthrough?
Yes, it obviously depends what commercial fibre feedthrough you are using. They should state a damage threshold, and if not you should look up the specs of the fibre type they are using.
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