Mounts installation and cavity alignment, posted by Xinyi Lu at Optical room about lasers and optics
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Over the last two days, Viktor, Ronic and I have started to install the mirror mounts and try to align the cavity.
- We used the Menhir laser @ 160MHz for alignment.
- To make it easier to operate, we removed some lenses and waveplates, and kept only a few necessary reflective mirrors. |
Mounts installation and cavity alignment, posted by Xinyi Lu at Optical room about lasers and optics 
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Over the past few days, Viktor, Ronic and I have continued to align the cavity. We installed 4 mirrors and monitored the transmitted laser with
a CCD and photodiode. By adjusting the motors of the cavity mirror stages and the injector mirrors, we obtained resonances and less symmetric TEM20-like
patterns. Possible reasons for this are a mismatch between the beam sizes of the laser and the cavity mode, and the mounts are installed in rough |
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Mounts installation and cavity alignment, posted by Xinyi Lu at Optical room about lasers and optics
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- Over the last few days, Viktor, Ronic and I have reinstalled the mounts and realigned the cavity with CW laser and old mirrors. By optimizing the injector
mirrors, we got the fundamental mode at the transmission. We measured the beam size in the M2 window with a diameter of 2.5 mm.
- The current coupling efficiency is low. There is a need to increase the coupling in order to lock the cavity and measure FSR and finesse. |
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Coupling efficiency improvement, posted by Xinyi Lu at Optical room about lasers and optics
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- Recently we have focused on improving the coupling efficiency. Without the telescope, the original coupling efficiency was less than 3%.
- I measured the parameters of the incident CW laser using both a HASO wavefront sensor and a CCD. I designed and installed the telescope, but the
coupling efficiency still did not improve. |
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Coupling efficiency improvement, posted by Xinyi Lu at Optical room about lasers and optics
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- We got 30% coupling efficiency by installing a set of telescopes, adjusting the polarization and optimizing the alignment. The diameter of the cavity
mode is about 2.1mm.
- Ronic and I successfully locked the optical cavity. Tomorrow we will test the FSR and finesse. |
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FSR and Finesse measurement, posted by Xinyi Lu at Optical room about lasers and optics
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- Today, Ronic and I measured the finesse and FSR after optimizing the locking. FSR was adjusted to 160.27 MHz to match the pulsed laser repetition rate.
The finesse was 3029.
Note: It's now CW laser injected, SBOX's old mirrors. There are lots of dust on the old mirrors without cleaning. |
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Install new mirrors, posted by Xinyi Lu at Optical room about lasers and optics
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Today, Ronic and I installed the new mirrors and got resonance. We can see the oscillations in this high-finesse case. We haven't carefully
optimized the alignment. Coupling efficiency is about 15% and the cavity can be locked.
Tomorrow we will optimize the alignment and locking, and measure the finesse. |
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Install new mirrors, posted by Xinyi Lu at Optical room about lasers and optics
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- In the last two days, Ronic and I installed new mirrors after cleaning the environment, and locked the cavity.
- We added an AOM to feedback on the high-frequency noise, but the locking condition was still not good enough. We found out that the signal generator
available for this AOM has a long delay time (3 us), which may lead to low feedback bandwidth. So tomorrow we will use another AOM and signal generator |
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Install new mirrors, posted by Xinyi Lu at Optical room about lasers and optics
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- Today, Ronic and I changed the signal generator to a low-noise one (with a delay time of only 0.5 us). Then we moved the D-shaped mirrors, optimized
the alignment and locking. We re-measured the finesse and it is 16,760. It improves but not much.
- Tomorrow, we will clean the environment, open the cavity, and use UV light to see if there is any dust on the surface of the mirrors. |
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Install new mirrors, posted by Xinyi Lu at Optical room about lasers and optics
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Yesterday we checked the mirrors with UV light and there was some dust on the mirrors, especially M2.
Today, Daniele, Ronic and I removed M2 and observed it with a microscope. It was indeed dirty, despite we were careful in installing it before.
After that we cleaned it with alcohol and mirror paper, then with a spin coater and pure water. After cleaning, we observed it again and it was much better |
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Cleaning of Mirrors, posted by Xinyi Lu at Optical room about lasers and optics
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Today Daniele, Ronic and I cleaned the mirrors and locked the cavity. However, the finesse was only 13,000 because of the not clean enough environment
and not pure enough alcohol and water.
We will carefully clean the environment, clean the mirrors again with pure alcohol and water and measure the finesse when I return. If it doesn't |
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Cleaning of Mirrors, posted by Xinyi Lu at Optical room about lasers and optics
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- Today we cleaned the environment and put the spin coater and microscope inside the airflow.
- Tomorrow, Daniele and I will clean the mirrors one by one using pure alcohol and water, and measure the finesse each time. If it does not improve,
we will clean them with plasma. |
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Cleaning of Mirrors, posted by Xinyi Lu at Optical room about lasers and optics
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Today, Daniele and I cleaned mirrors one by one using pure water, alcohol, and the spin coater. Here are the measurements of finesse each time:
1. Initial value: 14,076
2. Clean Mirror 2: 20,606 |
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Cleaning of Mirrors, posted by Xinyi Lu at Optical room about lasers and optics
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- Today, Daniele and I cleaned the cavity inside, recleaned the M2 and M4 and their mounts, optimized the locking, and the finesse is now about
25,000.
- Although it's lower than the expected 30,000-40,000, we decided to move on to the next step. In addition, the mount of M4 is |
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Menhir pulsed laser locking, posted by Xinyi Lu at Optical room about lasers and optics
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These days, Ronic, Daniele and I achieved stable cavity locking with the menhir pulsed laser.
- After vacuuming, the current cavity finesse is now about 23,000. The diameter of the cavity mode is w_x=2.2mm, w_y=2.7mm.
- We had to compensate for frequency drift by manually adjusting the cavity length to keep locking. |
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Menhir pulsed laser locking, posted by Xinyi Lu at Optical room about lasers and optics
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Here is a simulation of the relative FP-cavity gain vs the CEP for a Finesse of 23000 and taking into account the Menhir laser optical spectrum and several
CVBG parameters.
I added the commented Matlab code to produce this plot. |
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Menhir pulsed laser locking, posted by Xinyi Lu at Optical room about lasers and optics
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Last week, Ronic and I focused on CEP measurements of the menhir laser.
Measurements without Cavity Locking:
Direct measurement of repetition rate (Frep) with a spectrum analyzer.
Altering the laser pump current from 950mA to 850mA, Frep changed by +28Hz.
Measurement of the variation of carrier-envelope frequency |
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Menhir pulsed laser locking, posted by Xinyi Lu at Optical room about lasers and optics
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here is the code to get this last curve
Xinyi
Lu wrote:
Last week, Ronic and I focused on CEP measurements of |
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Amplified laser injection, posted by Xinyi Lu at Optical room about lasers and optics
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In the last two days, Ronic and I connected the amplifier and locked the cavity.
- We installed an iris on the output to remove a part of the pump.
- We turned on the second stage of the amplifier. When locking, the injected power is 220 mW and the transmitted power after M2 is 26 uW. |
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Coupling efficiency improvement, posted by Xinyi Lu at Optical room about lasers and optics
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- These days, Ronic, Fatematuj and I measured the beam parameters of the output of the third-stage amplifier.
- We used 2 wedges and reflection filters to reduce the intensity on the CCD.
- We measured multiple points at pump current of 2 A (output power ~10 W). The waist diameter of the output is w_x = 792.26 |