FP cavity alignment, posted by Ronic Chiche at ThomX igloo about lasers and optics
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as the iris used to locate the FP-cavity axis have been removed before moving the table inside the Igloo, we have to find again this FP-cavity axis.
this morning with Viktor, we started to make the alignment of the FP-cavity with a red laser using only the "input window" iris mount
built by Yann. |
FP cavity alignment, posted by Ronic Chiche at ThomX igloo about lasers and optics
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This afternoon, we continued the alignment of the red laser.
we did it using the 2 final injection mirrors.
we still see a clear transmission after M2, a weak transmission after M3, and almost nothing after M4 due to the power loss going through the dielectric |
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FP cavity alignment, posted by Ronic Chiche at ThomX igloo about lasers and optics
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A continuation of the alignment process was done, there was change in it due to variation in temperature,
it was done using the semiconducting laser, and we were able to obtain an output at M2.
2 references were placed before the alignment mirrors Ma and Mb , to fix the line when changing from semiconducting laser to CW "koheras" |
FP cavity alignment , posted by Manar Amer at ThomX igloo about lasers and optics 
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Note the direction of injection is M1 - M2 - M3 - M4
P1 - S2 - S3 - P4 |
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FP cavity alignment , posted by Manar Amer at ThomX igloo about lasers and optics
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The alignment is on hold until next week 17th - 18th Jan
an Alignment attempt will be done when the ring part close to the FP cavity is opened.
Manar |
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Documentation about mechanics on Atrium, posted by Ronic Chiche at ThomX igloo about mechanics
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https://atrium.in2p3.fr/0dded51a-1cb0-43e6-ae0d-626cd5db7078
a lot of schematics regarding the FP cavity are stored by the mechanic group on the Atrium repository. |
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FP cavity alignment , posted by Manar Amer at ThomX igloo about lasers and optics
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***** Continuation of the alignment ---- FP Cavity Open --- ****
The cavity was put under outer pressure and was opened for the alignment
The alignment was done using CW koheras infrared laser and the inside mirrors irises |
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FP cavity alignment , posted by Manar Amer at ThomX igloo about lasers and optics
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Yesterday, we did the alignment again using Iris and beam profilers to obtain a more precise result.
at the end of the alignment procedure, we successfully obtained the beating modes.
the geometrical alignment seems good (weak odd modes) but we could need to put a telescope on the Koheras line as the beam size seems quite different |
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FP cavity alignment , posted by Manar Amer at ThomX igloo about lasers and optics | detectors and electronics
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Installed and inputs:
CW laser ; power = 101 mW
PDH ;
at output
Low pass filter 50 ohm DC-1.9 MHz
at
input
freq = 8.4 MHz , Ampl = 1.2 V , phase = 160 /
voltage = ~ 6 V
EOM |
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FP cavity alignment , posted by Manar Amer at ThomX igloo about lasers and optics | detectors and electronics
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This afternoon, I did some alignment of the injection mirrors with a fast scan on the LaseLock to get a regular transmission photodiode signal.
the coupling increased to 10-15%
I got a first lock of the cavity only with the PZT. |
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FP cavity alignment , posted by Manar Amer at ThomX igloo about lasers and optics | detectors and electronics
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This morning with Manar, we installed the AOM+RF amplifier and the associated fast feedback loop.
Now the locking with the Koheras is good with a coupling of 20%.
Tomorrow is dedicated to the measurement of the Finesse.... we will have to add the 2nd EOM. |
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FP cavity alignment , posted by Manar Amer at ThomX igloo about lasers and optics | detectors and electronics
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Adding Oscilloscope images
delocked + locked intervals showing the 20% coupling
lock when the housing panels are closed + airflow on .
lock
when the housing panels are closed + air flow at lowest setting
an additional factor to the PZT voltage sensitivity |
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FP cavity alignment , posted by Manar Amer at ThomX igloo about lasers and optics | detectors and electronics
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Ending alignment series !!
Manar
Amer wrote:
Adding Oscilloscope images |
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FP cavity alignment , posted by Manar Amer at ThomX igloo about lasers and optics | detectors and electronics
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As it can be seen on the first plot, even with a good locking (good reduction of "high" frequencies noise: we had better locking than on the
picture) we still have very low frequency (~ 1Hz) fluctuations
these fluctuations prevent having a good measurement of the Finesse and they need to be understood. |
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Cavity Lock and Finess measurment , posted by Manar Amer at ThomX igloo about lasers and optics | detectors and electronics 6x
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This morning, me and Ronic managed to obtain the FSR and image of the finesse which is to be analyzed.
Adding:
Beam Image at P4 propagation, no lens is added.
Image of the Finesse on Oscilloscope
more information to |
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FP cavity alignment , posted by Manar Amer at ThomX igloo about lasers and optics | detectors and electronics
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The fluctuation problem has been solved.
It was simply the new scheme to inject 2 RF frequencies in a single EOM.
It maybe produces some standing waves in the EOM RF input and creates some phase noise. |
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Cavity Lock and Finess measurment , posted by Manar Amer at ThomX igloo about lasers and optics | detectors and electronics
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to measure the Finesse, instead of having 2x EOM for the PDH and for the modulation sweep, I simply used 2x generators coupled with DC-blocks
to a T connector (SMA) screwed directly on the EOM input. |
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Cavity Lock and Finess measurment , posted by Manar Amer at ThomX igloo about lasers and optics | detectors and electronics
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After changing the way of injecting modulation for PDH and modulation for FSR scanning (we split the modulations to 2 different EOMs), the locking
is very stable and we can measure the Finesse. |
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Cavity Lock and Finess measurment , posted by Manar Amer at ThomX igloo about lasers and optics | detectors and electronics
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one thing which could reduce the Finesse is the L-shape metal piece if it is slightly inserted in the FP-cavity mode path.
understanding where this L-shape effectively is is not easy... some pictures are attached.
Manar |
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FP cavity mode axis change and Finesse measurement, posted by Ronic Chiche at ThomX igloo about lasers and optics
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this morning with Manar, we did a cavity mode axis change.
we checked the cavity mode centroid position on the beam profiler (placed behind P4) and changed it by roughly 1mm on the X-axis and by 500µm
on the Y-axis. |