This morning, with Ronic and Daniele, we locked the cavity again (The lock was relatively easy and stable during the reading of the finesse)
We took 2 reading of finesse
1st : @ 33.2808 MHz (what the cavity length was at) : Finesse = 27 024
2nd : @ 33.3382 MHz (adjusted to match the pulsed laser) : Finesse = 30 433
The difference between the 2 is the FSR, during the change we also did some alignment to counter the reduced transmitted power.
We took an image of the beam profile before and after changing FSR and there was ~ 70 um change in the beam position on the Horizontal axis of the beam.
| Manar Amer wrote: |
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This morning with Daniele and Viktor,
- we confirmed the "potato" mode was well centered on the injected beam and was not due to some misalignment of the injected beam compared to the cavity axis.
we look at the reflected beam during a lock. we can see the direct reflected beam superposed with the cavity mode (cf attached image).
- then we assumed the "potato" mode problem could come from the too short distance between spherical mirrors which introduces ellipticity and finally can lead to some instability.
we manage to move further spherical mirrors S2 and S3 by moving them from 1 350 000 to 800 000 steps.
=> we increased the distance by 2x 550 000 steps (with 6µm for 1000 steps) => we increased the distance between spherical mirrors by 6.6 mm
the new mode shrinked a lot and at the end was spherical at 73%.
the mode size is now about 4400 x 6000 µm but with the major and minor axis still at 45° !
| Manar Amer wrote: |
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Yesterday morning we locked the cavity on a strange mode in the cavity (we call it mode, but not sure what it is ??)
we also managed to lock on a higher order mode 02
we get an estimated 30% coupling (expected value), and note that we have not installed a telescope yet.
| Manar Amer wrote: |
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Today, we prepared lenses for a telescope for the CW laser injection into the cavity, yet to be installed
Image of the transmission at P4 attached, an estimation of the beam size of the mode see is ~ 5.5 mm
The vacuum in the 2 optical cavities is decreasing but slowly. today it is 2.6 - 2.4 * 10^-7 mbar
| Manar Amer wrote: |
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Last week, with Ronic and Victor we aligned the cavity using CW laser (Koheras)
- we have also installed 4 mirrors in the cavity with the best theoretical qualities (serial number and images included)
- The Plan ULE mirror P4 thickness was not compatible with the piezoelectric mount. We had to install a metal spacer behind the mirror to be able to fix it. the metal spacers in from ThorLabs made from INOX, It is 1 inch diameter (25.4 mm), we drilled a hole in the middle of 15 mm in the Workshop in bat 200. Then cleaned it using an ultrasound bath in pure water, using a small Ultrasound bath machine in Maverics platform Vide and Surfaces next to ThomX eglo.
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- This gives some difficulties in imaging the transmission at P4. To help with the imaging, we used the plastic #D printed irises that Yann made long time ago
- we took images of the mode inside the cavity at P4 transmission.
- We also observed some oxidization on the metal bars of the controllers, more on the side of S2 and P4. we are yet to test the motion of the motors in the z-axis.
- Friday evening we closed the windows using a new copper rings (last one we have, Ronic placed a new order).
- The pump was turned on by Bruno and Eric yesterday afternoon. The current vacuum level is 6-7*10^-6 mbar
the pre and the turbo pimps are on so still too noisy to work, we have access all day tomorrow.
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