first data with 3A on the 3rd stage, posted by Ronic Chiche at Optical room about lasers and optics 
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2 pictures :
typical beam with HOM
typical beam after moving the D-shape motor : no more HOM |
Optical amplifier polarization state, posted by Ronic Chiche at Optical room about lasers and optics
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We placed a PBS + 2 photodiodes (PhD1, PhD2) at the output of the amplifier to check how the polarization of the amplifier changes with power.
example with 2nd stage @ 6A :
PhD1 = 24.7 mV |
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Optical amplifier polarization state, posted by Ronic Chiche at Optical room about lasers and optics
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The polarimeter was giving a strange 50% of DOP of the light coming from the cavity.
we had to calibrate (LONG calibration process with care) the polarimeter to get a proper 100% of DOP !
the polarimeter needs also a good alignment with 2 mirrors, a colimated beam and a max power on photodiode between 0.7 and 0.8 (use electronic gain |
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Beam size behind M2, posted by Ronic Chiche at Optical room about lasers and optics
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the telescope matchs the cold cavity beam, so it is normal to have a power decrease on the transmission photodiode when the cavity is heating at high
power.
we can try to adjust the telescope by moving lens, one by one, to increase the cavity power. |
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Optical amplifier polarization state, posted by Ronic Chiche at Optical room about lasers and optics
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polarization state of the cavity at higher power : 20kW, 30kW and 33kW (slight CEP and alignment optimization) :
the polarization state changes only a little to ~ 87° and is almost linear.
Ronic |
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Beam size behind M2, posted by Ronic Chiche at Optical room about lasers and optics
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Yesterday, we tried to better adapt positions of the telescope lenses, dynamically, during the lock, to improve the matching between input beam and cavity
mode.
it is a difficult task because it is quite sensitive to the alignment. we need to realign very often... and it is a long process. |
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Cavity beam axis moving with power, posted by Ronic Chiche at Optical room about lasers and optics 9x
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how the cavity beam axis is moving during a lock when the cavity is hot ?
could it explain a part of the Transmission / Coupling signal decay ?
we placed 2 Basler camera, one at (30+Z) cm and the other at (85+Z) cm (Z is about 15cm) from the M3 mirror, we recorded the video during a lock |
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Microscope and cleaning of SBOX mirrors, posted by Loïc Amoudry at Optical room about lasers and optics
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The mirrors went in the cavity the 28th of november (We did several power up to 30kW stored and only one to 40kW then the power went down to 2kW
during the run).
Microscope study shows that mirrors get some dust during the handling [travel from microscope to SBOX --> installation --> |
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analysis of stored and reflected power, posted by Ronic Chiche at Optical room about lasers and optics 6x
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the 10th of January, we increased the power of the amplifier to study the cavity transmitted and reflected power signals.
analyzing the noise transfer functions of transmitted and reflected power one could deduce the Finesse of the cavity.
the power of this technic (if it is confirmed) does not depend on the decay time of one signal which depends on the speed of the cut off but on |
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analysis of stored and reflected power, posted by Ronic Chiche at Optical room about lasers and optics
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A chart which summarizes the data we have or we can estimate.
in orange, the case 1, where we suppose the initial cold Finesse is the one measured by modulation technique in December 2019 (F=20.8k). |
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AFM analysis of M1, posted by Loïc Amoudry at Optical room about lasers and optics
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AFM has been proceeded on M1 and M2.
The pdf shows the first images taken with the PLIC room Leica microscope (zoom x10 and x80).
Then the hole has been studied with a handmade microscope. It brought a better resolution. We can now see the hole has an edge, a center structure |
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AFM analysis of M2, posted by Loïc Amoudry at Optical room about lasers and optics
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We had enough time to proceed a quick scan of M2 which has also a hole but not centered on the mirror.
The hole is larger and higher than the one on M1. But the vertical range was to high for the AFM. Then we cannot see if there are sparkles or
not on this image. Further study with microscope would be welcome. |
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CFBG removed from ThomX CELIA amplifier, posted by Loïc Amoudry at Optical room about lasers and optics
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The CFBG has been removed successfully and the amplifier is closed now.
The soldering machine had a calibration trouble and was sent to the company for review during holidays.
The output power has been checked and is the same as before (tested until 30W ouput power). |
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Glow discharge cleaner on SBOX mirrors, posted by Loïc Amoudry at Optical room about lasers and optics
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The glow discharge cleaner has been tested on the SBOX mirrors.
I've put them 1 by 1. Each run was 15min long at 15mA. The mirrors HR face was always away from the electrode and ~35° angle
with the support. These values have been choosen thanks to the reference: |
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SBOX mirrors cleaned, posted by Loïc Amoudry at Optical room about lasers and optics
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Today, SBOX mirrors have been cleaned with spin coater on HR face and isoprop on back face. They show similar spots as before.
They also have been installed in the SBOX. The M1 mount has been displaced so the beam doesn't go in its center (spot). |
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SBOX mirrors cleaned, posted by Loïc Amoudry at Optical room about lasers and optics
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Yesterday, after installation and alignment of mirrors and cavity, the Finesse has been measured with cavity at air pressure, with Koheras and modulation
technique.
the measurement has been done 7 times with quite different fits for the Finesse : 21.5k, 21.5k, 23.7k, 21.3k, 22.3k, 22k, 21.5k |
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SBOX mirrors cleaned, posted by Loïc Amoudry at Optical room about lasers and optics
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Today we put the cavity to vacuum (~ 0.1 mBar) and we measured again the Finesse with Koheras and modulation technique.
the measurement has been done 3 times with Finesse of 23.2k, 23.8k, 23k
Loïc |
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analysis of stored and reflected power, posted by Ronic Chiche at Optical room about lasers and optics
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with this Finesse around 22-23k, the technique comparing TRANSMISSION and REFLECTION signals doesn't work, even in taking into account individual
photodiode time responses.
It seems that the cavity is not completely stationnary and the shapes are not comparable easily with just a Low Pass Filter related to the Finesse. |
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Power up to 48kW crater effect again, posted by Loïc Amoudry at Optical room about lasers and optics
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As we said, after glow discharge and spin coater we recovered a low power finesse ~23000 (aligning away from the M1 crater).
Today, we have made some power up to 48kW (3A on 3rd stage). At this power, there was no important effect on the transmission which can be compared
with the coupling (see image "3A_136mWtrans"). We waited ~20min without aligning and the power dropped slowly (misalignment) to 39kW. |
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Mirror's cleaning and microscope imaging, posted by Loïc Amoudry at Optical room about lasers and optics 14x
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On 10th of december 2020 we cleaned the SBOX mirrors and took microscope images (the name of the images indicates what they are).
There are 7 mirror, the initial M1 (spot in the center), M2 (spot on the edge), M3 and M4 which made the 200-400kW and the M2, M3 and M4 SPARE.
The difference we make between M3 and M4 SPARE is the number on the box (11 or 13). |