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Yesterday, Loïc put the CVBG's back to their specified angles.
We used an interferometric technique with a delay line and combining the two paths in a CCD to measure interferences.
After supressing the global shape of the superposed pulses, one measures the amplitude of the remaining fringes (standard deviation) each 50µm of the delay line (100µm of round-trip). one gets the interferences pulse shape with a FWHM of 2.5 ps... (see curve)
from Fabian calculation, at 100kW, with w=2mm, the fluence on mirror should be around 0.05J/cm^2.
from this article (https://www.sciencedirect.com/science/article/pii/S0030402618313275), the damage threshold for SiO2/Ta2O5 multilayers should be around 4.8J/cm^2 @ 1030nm
| Ronic Chiche wrote: |
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Yesterday, Loic installed a telescope before CVBG's to reduce the spot size on CVBG's and reduced the incident angle 0.5-1° on them (on the datasheet the specified incident angle is 2.8°).
We used an interferometric technique with a delay line and combining the two paths in a CCD to measure interferences.
After supressing the global shape of the superposed pulses, one measures the amplitude of the remaining fringes (standard deviation) each 50µm of the delay line (100µm of round-trip). one gets the interferences pulse shape with a FWHM of 2 ps... (see curve)
we still see an 'after pulse'.
if the pulse is 1ps long and 100kW is stored in the cavity, it means 3GW peak for the whole beam... it is comparable with the damage threshold of the mirror !!!
| Ronic Chiche wrote: |
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We installed the 2 CVBG for compression after the amplifier.
We used an interferometric technique with a delay line and combining the two paths in a CCD to measure interferences... see interferences.avi video file
One can notice some misalignement at the end of the video.
After supressing the global shape of the superposed pulses, one measures the amplitude of the remaining fringes (peak-peak or standard deviation) each 250µm of the delay line (500µm of round-trip). one gets the interferences pulse shape with a FWHM of 6ps...
It seems that an 'after pulse' is visible in the interferences.
An other meausurement using a 2 photons photodiode will be used to confirm this measurement.
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