Distances between mirrors , posted by Manar Amer at Other about mechanics | software 
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At the reference zero the distance between the mirrors is (taken from a reference presentation "status9nov2020" attached):
M1-M2 = 88.029 mm
M3-M4 = 84.6895 mm |
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Alignment using Koheras , posted by Manar Amer at Other about lasers and optics 6x
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Following the Helium Neon Alignment + change in the distance between the mirrors to be; M3-M4 = 90.5 mm , M1-M2 = 80.2 mm -→ The alignment
using the Koheras CW laser is done.
Additional components used:
for monitoring beam : Photodiode (power of beam), Beam Profiler (shape, position, power |
Mode observed and cavity Lock , posted by Manar Amer at Other about lasers and optics
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** Following up from yesterday an observation about the TM00 mode : it has been seen with similar dimensions and its position is the same, this was before
restarting the temperature regulator.
--> after restarting the temp. regulator |
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Lock, cavity length and finesse estimate, posted by Aurélien Martens at Optical room about lasers and optics | detectors and electronics
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Ronic just suceeded in obtaining a reasonably good lock on the cavity. Air flow is switched off.
We stopped all movements (closed loop, click STOP in the PTC interface) and saw immediately a fair but not excellent lock.
We then switched off the smaract motors and the obtained lock was good. Switching on again the smaract means tthat the references are lost. |
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Distances between mirrors , posted by Manar Amer at Other about mechanics | lasers and optics | software
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New update on the position of the Motors for the cavity
***** we moved the motors to set the cavity at 876MHz, and checked it right after with the RF modulation at FSR.
So compared to the expected setting we had to move inwards the two planar mirrors by 0.9 mm each. |
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Theoretical Finesse, Gain and Coupling, posted by Ronic Chiche at Optical room about lasers and optics
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For spherical mirrors M3 and M4 (batch C117I054) the reflectance (R) is around 99.9987% (if T+R=1 => T=13ppm)
For plan mirror M2 (batch C217G054) the reflectance (R) is around 99.9977% (if T+R=1 => T=23ppm)
(1) => For plan mirror M1 (batch C217H023) the reflectance (R) is around 98.96% and transmittance (T) is around 1.14% (T=11400 ppm) |
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Mode observed and cavity Lock , posted by Manar Amer at Other about lasers and optics
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New configuration is made. The new mode observed in NF_Trans is the following :
Manar
Amer wrote:
** Following up from yesterday an observation about the TM00 mode : |
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Lock, cavity length and finesse estimate, posted by Aurélien Martens at Optical room about lasers and optics | detectors and electronics
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we observed that the transmitted light coming from the cavity is made of the cavity mode light and the scattered light on the borders of the mirrors.
the scattered light on the borders of the mirrors is triggered by the cavity mode itself when the cavity is locked.
we didn't put an iris to cut this scattered light coming from the cavity. |
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Polarisation Results of the NKT, posted by Blanc at Optical room about lasers and optics
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I made many tests about polarization and we can see some points thanks to the following figures :
1- The ellipsicity of the NKT is near to 0 (between -0,2 and 0,2) which means the polarization is rectilinear horizontale (attachement 1).
2- The power of the NKT has no influence on the polarization, verticale or horizontale (attachement 2 and 3). |
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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 |
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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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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) |