Daniel noted that the new NPRO is almost certainly at a different frequency than the previous one. Also, since the PSL has been the most 'fussy' lately, we don't want to change it away from it's manufacturer-recommended settings (if we can help it), and instead want to change the other 3 lasers to match the new PSL frequency.
In the attachment, the top row is SQZ laser, the middle row is ALSX, and the bottom row is ALSY. The leftmost column is the beatnote frequency between the given laser and the PSL, the middle column is the CrystalFrequency offset that we can provide, and the right column is the amplitude of the RF beatnote.
To figure out "where to go", Daniel put in a set of steps (eg, using ezcastep) to the CrystalFrequency channels. You can see that he started with the SQZ laser, but wasn't finding it by using a positive frequency offset. He then found (using ALSY) that putting in a negative frequency offset of a little over 4 GHz (the CrystalFrequency numerical value is in units of MHz) brought the RFMON up, and the PLL loop was able to engage and bring the beat frequency to the right spot. Once the RF mon started increasing, he Ctrl-C'd to stop the stepping of values. Knowing that all 3 of these aux lasers at one point were matched to the PSL, he then set the SQZ laser and the ALSX laser to search around that -4 GHz value. In order to have the PLL loops engage and not complain, Daniel set the H1:ALS-X_FIBR_LOCK_TEMPERATURECONTROLS_HIGH and _LOW settings for all 3 lasers to be a wide acceptable window (eg, +/- 6000 MHz, rather than a normal +/- 600 MHz).
Once all 3 lasers had their PLLs locked, Daniel and Vicky went out to each laser to adjust the nominal temp such that the CrystalFreq offset can be closer to zero. My understanding of the procedure is that they will (with the PLL locked using the big offset) take a look at the current temp of the laser, according to the little LCD display on the front panel of the laser controller. They will unlock the PLL and set the CrystalFrequency offset to 0, and then adjust the analog knob on the laser controller such that the temperature is back at the temp it was with the PLL locked with big offset. They'll then allow the PLL to relock, hopefully not needing a very big CrystalFrequency offset. While at each laser, they will also check that the laser is not in a mode hopping region with this new temperature.
After this is done, and once the PSL tune-ups are done for the day, we'll be able to start locking!
Daniel, Vicky - adjusted temperatures on the ALS and SQZ lasers: 1) Noted the laser temp when TTFSS was running (> 4GHz off). This is the "nominal" new temperature. 2) Turned off TTFSS and set crystal frequency to 0 MHz. 3) Moved laser temperature knob to bring it to the "nominal" temperature. 4) Check TTFSS locks well. If needed, further adjust laser temperature knob to bring the crystal frequency is 0 MHz when TTFSS is running. 5) Check for mode-hopping.
To check for mode-hopping with laser temperature on the controller set at the new nominal, we turned off TTFSS and stepped the laser frequency +/- 200 (SQZ) or +/- 100 (ALS X/Y) MHz, then checked the beat note strength and frequencies made sense. All looked good at the new nominal laser temps. To make up the ~4 GHz laser frequency difference, we expected to change temperatures by like (-4.4 GHz / -3000 MHz/V) ~1.47 C, which is similar to what we did.
Laser temps changed as follows:
- SQZ: 24.83 C --> 26.30 C
- ALS X: 24.8 C --> 26.62 C
- ALS Y: 28.59 C --> 30.05 C
After the SQZ laser temperature was changed by ~4.4 GHz to meet the new PSL laser frequency, we had to change the OPO TEC temperature setpoint from 31.207 C --> 31.477 C. This is a bigger change than usual, but we had to adjust the temp to find and lock the OPO in dual-resonance (at first, there was almost no CLF6 beatnote, started out with RFMON around -40 when it should be around -11. By contrast the OPO locked fine yesterday).
At 31.477 C, we used the temperature to maximize NLG with seed light: amplified=0.133, de-amplified=0.0027, un-amplified=0.0087. NLG = amplified /unamplified ~ 15.25. Then H1:SQZ-CLF_REFL_RF6_DEMOD_RFMON = -10.9.