Locking of the cavity and setup changing, posted by Blanc at Optical room about lasers and optics | detectors and electronics 
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We change the setup a bit to have the same polarization on the photodiode and the PDH (in reflexion of the cavity). CF: schematics (futur).
Thanks to that, the symetry between reflexion and transmission is better now (as you can see on the plot).
We also put more power on PHD to have a better SNR by changing splitters. (We had 100 µW and now we have more than 1 mW, at the expense |
Polarisation Results of the NKT, posted by Blanc at Optical room about lasers and optics
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To have the polarisation, we must have 1 value because the laser in entry of the system has 1 polar. Due to that, the graphe of the ellipticity is not
true, it is the mean value on the following table which shows the ellipticity and the polarization.
Blanc |
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Ring light in the cavity, posted by Blanc at Optical room about lasers and optics
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We put a diaphragm in the input beam but it doesn't work to suppress the ring light only but it attenuates the whole transmitted beam (cavity mode
and ring light) viewed on the camera. |
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Polarization Results in transmission, posted by Blanc at Optical room about lasers and optics
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After data processing, I finally find the polarization in transmissin of the FPC. As you can see below, the polarisation is not linear but elliptical.
The four ellipsies are here due to having not enougth parameters to extract with certainty one ellipse. |
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Reflection Line Polarization Measuremet, posted by Manar Amer at Optical room about lasers and optics
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With the help of Ronic the cavity was locked in preparation to measure the polarization of the reflection line when the cavity is locked (measurement
when it is not locked was done before)
the purpose is to compare the two measurements (locked vs not locked) |
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1GHz oscillator Frep measurement, posted by Blanc at Optical room about mechanics | lasers and optics | detectors and electronics
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a previous cavity FSR measurement was giving a center frequency around 867.5MHz.
the present 1GHz oscillator Frep measurement is about 879.888MHz.
the
present shift is about 12.4MHz which is equivalent to move one cavity lenght by 4.3mm which is HUGE !!!
as the 1GHz oscillator does not have any motor,
one has to move the FP cavity mirrors instead.
the PZT inside the 1GHz oscillator (Thorlabs PC4QR) has a dynamic range of (20µm for 150V... we will |
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ip adress of smaract driver, posted by Aurélien Martens at Optical room about detectors and electronics | software
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the ip adress of the smaract driver is now 10.0.53.10:5000
please think about putting such kind of changes in the logbook |
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new position of smaract motors, posted by Aurélien Martens at Optical room about mechanics | detectors and electronics | software
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following the measuremetn at 879.9 MHZ of the laser theoptical cavity length has been adjusted to that value from 876MHz setting of the 5th of may 21.
new motor positions:
M3/M4 : -2.9mm |
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piezo actuation range, posted by Aurélien Martens at Optical room about lasers and optics | detectors and electronics
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A 10V applied on the laser piezo was found to induce a frequecny change of about 5kHz, compatible with expectations from the piezo sensitivity. this
was measured by a freqeuncy analysis of the signal produced by the laser itself on a photodiode det10a
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phone is noise, posted by Aurélien Martens at Optical room about detectors and electronics
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doing the sensitivty measurement of the piezo we observed satellite peaks around 800 to 900 Mhz. Removing the phones from the experience room(in the
cupboard in the sas) removed that effect immediately. |
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new position of smaract motors, posted by Aurélien Martens at Optical room about detectors and electronics | software
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| a cavity length measurement gave 880.9Mhz. The m1/M2 have been put to +5.1000mm both M3/M4 srill at -2.9mm |
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new position of smaract motors, posted by Aurélien Martens at Optical room about detectors and electronics | software
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to find the fundamental mode we moved the cavity mirrors to new positions:
+5.104mm for both planar mirrors in closed loop
spherical unchanged (-2.9mm) |
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new position of smaract motors, posted by Aurélien Martens at Optical room about detectors and electronics | software
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the M1 is not at 5.1045mm to put the fundamental on the scanning range of the laser piezo
M2 still at 5.104mm
M3/M4 at -2.9mm still |
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new position of smaract motors, posted by Aurélien Martens at Optical room about detectors and electronics | software
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after 3hours (1pm --> 4pm) the cavity moved by 12um in total
new positions: +5.1065mm on M1 and M2 (5.1050 before)
the drift is 4um/hour which amounts to about 10kHz drift / hour+the temperature of the optics room also changed unfortunaltey (linked to extinction |
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Locking with fast analog loop on AOM, posted by Ronic Chiche at Optical room about lasers and optics
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in addition to the standard locking scheme with the GHz laser PZT,
we added an AOM after the PDH modulation EOM and we drove it with an FM modulated signal generator (FMDev = 2.4MHz) seeded by the error signal.
(we didn't put a 50ohm plug to adapt the error signal coming from the PDH box, otherwise, it is too much smaller) |
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Finess and coupling measurement, posted by Blanc at Optical room about lasers and optics | detectors and electronics
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We did the measurement of the Finess and coupling with the NKT, with 2 EOM, without AOM (so the lock signal is noisy), on the burst line.
For the coupling, we have the same value as with the GHz locked on the burst line too, which is around 20 percent.
it seems this low coupling comes from the geometrical coupling as we observed an incoming beam bigger than the cavity mode on the cameras. |
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Setup and measurements, posted by Blanc at Optical room about lasers and optics | detectors and electronics
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To summerize the results of this week :
We made the setup in attachement 5 and align it to have the good mode in the cavity (TEM00).
With the good alignment, we found the lock of the GHz, in attachement 1. We used the motors in the cavity to position very precisely the mirrors |
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PZT resonant frequencies, posted by Ronic Chiche at Optical room about mechanics | lasers and optics | detectors and electronics
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we have excited the PZT with a swept sinus wave from 1kHz to 10kHz and from 10kHz to 100kHz.
here are the 2 different spectrums:
- the 1kHz-10kHz is a standard spectrum where we see the impedance behavior of the PZT: Zpzt ~ 1/jCw |
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Amplitude GHz oscillator phase noise with PZT effect, posted by Ronic Chiche at Optical room about lasers and optics
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3 phase noise measurements made on the Amplitude GHz oscillator with different PZT configurations :
- black curve: PZT connector is open
- green curve: PZT connector is shorted by 50 ohms |
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Phase noise measurement of the Amplitude MIKAN, posted by Ronic Chiche at Optical room about lasers and optics | detectors and electronics
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MIKAN phase noise and RIN measurements:
Ronic
Chiche wrote:
Coupling into a 50-50% fiber coupler using the Thorlabs XYZ table |