Description of Measurement
The pulse duration in the tunnel is measured after the DSHM with an SSA. The beam exits the compressor through the window in the guillotine valve, goes through the PB and the bypass line and exits through the window on the 8in cube. It is then de-magnified by a factor of 5 with a permanently installed telescope. The beam is clipped by the bypass line down to 34.8mm, the telescope then reduces it to 7mm. The SSA accepts beams from 2-8mm in diameter. The SSA is calibrated before every measurement.
Measurement 11/8/2023
http://physics-elog.slac.stanford.edu/facetelog/show.jsp?dir=/2023/45/08.11&pos=2023-11-08T17:43:51
SSA calibration:
7.505mm to 7.380mm or 125um stage travel, 250um delay. 1.89ms delay.
New calibration: 250um on stage corresponds to 1.89ms. 250um path difference is 833fs so calibration
is 833 fs / 1.89ms= 440.7 fs/ms.
At brightest plasma grating setting, separation at 26.5
Pulse length on scope = 172 us FWHM
Pulse length (real) = 0.172 ms X 440.7 fs/ms / 1.5 = 50.5 fs FWHM
If moved to GDD compensation setting, gratings separation at 26.3,
Pulse length on scope = 168 us FWHM
Pulse length (real) = 0.168 ms X 440.7 fs/ms / 1.5 = 49.4 fs FWHM