Ring frequency / Laser "day by day" locking, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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| today, the equivalent Smaract position corresponding to the 500.25MHz ring frequency is +156µm on MCS-1/ch0 (closed loop mode) |
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Laser / FP-cavity "day by day" locking, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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today, we locked the FP cavity at ~50kW with 30% laser amplifier ratio (16W) during almost all the day (from 10am to 4pm)
CEP optimized for MCS-1/Ch2 = -244µm at the end of the day.
once one finds the proper CEP value to reach to correct loops gain, the cavity lock and power are very stable: |
Ring frequency / Laser "day by day" locking, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics 
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temperature stable around 20.8°C
today, the equivalent Smaract position corresponding to the 500.25MHz ring frequency is +158.4µm on MCS-1/ch0 (closed loop mode)
it is very difficult to maintain both loops in the same time as soon as it is needed to move one motor (CFP or Laser) because of the one element |
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Laser / FP-cavity "day by day" locking, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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as the temperature is back to a normal value ~ 20.8°C, the injected power to the amplifier (PD_IN in the Alphanov software) is back to 3.15mW without
doing any alignment.
this morning the lock was around 48.5kW with 30% laser amplifier ratio (16W) after CEP/alignment tuning. |
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Laser / FP-cavity "day by day" locking, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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temperature since we moved to temperature probe (jump at the beginning of the plot) below the ring on a metallic base.
Ronic
Chiche wrote:
as the temperature is back to a normal value ~ 20.8°C, the injected |
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Ring frequency / Laser "day by day" locking, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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temperature stable around 21.7°C
today, the equivalent Smaract position corresponding to the 500.25MHz ring frequency is +147µm on MCS-1/ch0 (closed loop mode)
Ronic |
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Laser / FP-cavity "day by day" locking, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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temperature @ 22.3°C
today, all the PC applications were closed except the web browser.
I had to restart all of them, then try to relock. |
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Laser / FP-cavity "day by day" locking, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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temperature @ 21.9°C
48.5kW inside CFP for 30% amplifier ratio
Frep Laser motor = 123.4µm |
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Temperature control of the FP-cavity length, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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as the CFP motors displacements induce a cavity unlock, we try to change the cavity length by changing the temperature of elment of the cavity.
yesterday, we tried to put a "heating cable" borrowed to the vacuum group to change the temperature of one bellows between the FP-cavity
and the electron ring. |
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Temperature control of the FP-cavity length, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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several days ago, we installed a heating cable around the output flange (close to the X-hutch) of the FP-cavity vessel.
we are able to heat this cable by applying a DC voltage coming from 2 DC voltage supplies in serie (2 devices with 2x 0-30V / 3A => 0-120V /
3A). |
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Long term lock of Laser-FP cavity-RF reference, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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today for the first time, we were able to make a long term lock of all the elements (Laser on FP cavity and FP-cavity on RF reference) during 20
minutes @50kW without any single loss of lock.
the success of this long term lock was coming from the possibility to drive the Smaract motor in piezo-scan mode and to apply a heating on one |
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Temperature control of the FP-cavity length, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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today, I removed one of the DC voltage supply (as with 30V, we are already able to 30°C on the heating cable).
the remaining DC voltage supply is configured in series (2x30V = 60V max) and is at the IP address : 192.168.1.101
Ronic |
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Long term lock of Laser-FP cavity-RF reference, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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today, I did a 20 minutes "double lock" run w/o any single lock loss.
the attached file shows the recorded RMS beating voltage between 500MHz signals (laser harmonic and RF reference).
the end of the plot after iteration ~1.8k shows the lock loss to the RF reference. |
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Long term lock of Laser-FP cavity-RF reference, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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this afternoon, we did a new long-term "double lock" run w/o any single lock loss during 1/2h.
we did 2 acquisitions :
fig 1 : phase measurement between the 33MHz signal coming from the laser and the 500MHz RF. |
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Temperature control of the FP-cavity length, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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this afternoon, I started the heating cable after the warm-up of the FP-cavity :
14h20 : start to fill 50kW in the cavity
15h : start of the heating cable @10V (2x 5V) (iteration 2300) |
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Temperature control of the FP-cavity length, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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last friday, I locked the cavity and then, switched ON the heating cable after waiting the cavity reaches a steady state in frequency drift : see the
figure.
blue : temperature of the probe on the heating cable |
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Temperature control of the FP-cavity length, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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on last tuesday, I did a long-term measurement of the frequency drift when the heating cable is powered ON at 20V (2x 10V) @ t=0mn.
the freqeuncy drift (between the laser, locked in open loop on the FP-cavity, and the RF reference oscillator) acquisition was made by the National
Instrument software. |
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Temperature control of the FP-cavity length, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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today with Fatematuj, we did a long-term frequency drift measurement between the FP-cavity loaded with 50kW and the RF reference frequency... and without
any other thermal source (no heating cable !)
we had a small lock loss at t ~ 120mn. |
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20Hz oscillation in the locking between Laser and FP-cavity, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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yesterday I did 2 tests to try to understand the origin of the 20Hz oscillation which is dominant in the remaining 10-20ps rms jitter between the transmitted
pulses and the RF reference generator.
10ps rms jitter is equivalent to phase jitter dphi = 2*pi*f0*dt = 2mrad rms @ 33MHz or 30mrad rms @ 500MHz. |
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20Hz oscillation in the locking between Laser and FP-cavity, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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what does this 10ps phase jitter mean in term of cavity length variations ?
L = L0 + dL sin(2pi fm t) = L0 (1 + dL/L0 sin(2pi fm t))
F = c / L ~ F0 - F0² dL / c sin(2pi fm t) with F0 = c / L0 |