Today, Ronic and I optimized the locking at the amplifier current of 2 A and obtained ~ 21 kW inside the cavity.
- When all the iris open, the injected power is 10 W and the coupling is ~ 40%, corresponding to an effective gain of 2,100 and a full gain of 5,250. But the coupling may not be the true value because there is a large spot around the output beam.
- We have optimized the CEP, alignment, D-shaped mirrors and locking state. We optimized alignment after leaving the iris open and the inside power went from 14kW to 21kW.
- The transmission and reflection signals both have some same fluctuations, and they seem to come from the cavity. It's possible that the over-angled mirror mount could be the cause, but not sure. We will check in different power and see the stability of the signal.
- In addition, we found that the design values of the mirror incidence angles for the SBOX (3.359°, 5.900°) are different from the mirror ratings (1.146°). This may result in parameters such as reflection and transmission being different from the datasheet. It will also change the estimated maximum finesse, gain, and power inside the cavity. It might be better if the mirror parameters could be recalculated based on the actual angle of incidence.
| Xinyi Lu wrote: |
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- Today, Ronic and I locked at the amplifier current of 2 A and obtained ~60% coupling after optimizing the CEP (see Figure 1).
- The injected power is 10 W at 2 A. We measured only 14 kW inside the cavity, which corresponds to an effective gain of 1,400 and a full gain of 2,300. The cavity finesse is 23,000 and the normal gain should be around 6,200.
- We found fluctuations in transmission, possibly because of mode degradation. Tomorrow we will use D-shape mirrors to suppress high-order modes and optimize alignment and locking.
| Xinyi Lu wrote: |
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Today, Ronic and I installed the new telescope and locked the cavity.
- We locked at the amplifier current of 1 A and obtained 32% of coupling. (see Figure 1)
- The telescope was designed for a current of 2 A (output power ~10 W). To inject this power, we need to add some filters to devices.
- For CEP tuning, when we changed the AOM frequency while cavity locking, sometimes it caused unlock and power drops. It will be dangerous in high-power cases. So it's better to optimize the AOM frequency in low power and just tune the laser current in high power. Now the current variation range of the menhir laser is 750mA to 950mA.
| Xinyi Lu wrote: |
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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 um, w_y=873.90 um.
- The next step is to design the telescope and improve the coupling efficiency.
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