May 2024
A potential Run 23 user requested an updated contrast measurement, as our last one looks like it was taking in 2019. A raised breadboard was setup over the optics pointing the beam into the compressor. The breadboard was wiped down but foil was still placed underneath the raised breadboard to prevent any dust/debris from falling on the optics.
The pulse was taken out of the compressor, after compression, by placing a 2" polarization changing periscope. A 3rd mirror was placed on the TPA auto-correlator table. The second periscope mirror, and mirror above the TPA were used to align into the Tundra.
Alignment
- Initial course tilt alignment of the Tundra was down placing a silver mirror at the entrance to look at the retro pointing. The Tundra manual describes what 2 irises to use for aligning using the external mirrors.
- Once signal was found on the PMT, the irises were ignored and alignment was done strictly by maximizing signal.
- After maxing signal with external mirrors, internal tweaks to the 2w and 3w rotation stage angle were made to maximize signal. These stages were not initially locked down and were never locked.
- Very minor tweaks of the curved mirror that points the 1w and 2w into the crystal. A very course scan from -100ps to 100ps in ~100fs showed that we had 8 orders of magnitude, which was deemed sufficient.
Scan
- A ~25 hour scan was setup. Range -500ps to 100ps, 10fs step-size, 10 points/location, median (not average)
- Here's the whole scan plotted against the scan from 2019 (full beam in the chamber)
- Here's a zoomed in version of the same plot
- At 5ps the contrast is 6 orders down and at 10ps it's about 7 orders down. That's pretty good!
It would be my suggestion that we do this measurement more than every 5 years...