new cavity, posted by Alice Renaux at Optical room about lasers and optics
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Yesterday, we changed the M1 mirror to a 161185 Gamma Factory mirror of transmission 460ppm, the cavity
finesse is now 13360.
We managed to lock it today. |
new cavity, posted by Alice Renaux at Optical room about lasers and optics 
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The 2-mirrors cavity has 460ppm of transmission for M1 and 10ppm for M2 which should exhibit a Finesse around 13400.
Today, we managed to lock the NKT laser (with an AOM for fast feedback) onto the cavity, and we made 5 Finesse measurements with the modulation
technic : 14151, 13847, 13968, 14604, 13892 with an average around 14000 => LW = 216MHz/F ~ 16kHz. |
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Finesse measurement, posted by Alice Renaux at Optical room about lasers and optics
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Today, with Ronic, we measured the finesse of the 2-mirror cavity witht the NKT CW laser.
We were able to perfrom the measurement only once, and the results of the measurement are attached to this note. We added sidebands to the laser
spectrum peak thanks to an EOM, and we sweeped the modulation frequency on a 1MHz span around an estimated FSR of 216.63MHz in 10s. We found a 82kHz linewidth, |
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Finesse measurement, posted by Alice Renaux at Optical room about lasers and optics
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(Finesse 2651 is consistent with that obtained from the mirrors' transmission coefficients, which is about 3100.)
Alice
Renaux wrote:
Today, with Ronic, we measured the finesse of the 2-mirror cavity |
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Installation of the avalanche photodiode, posted by Ronic Chiche at Optical room about lasers and optics | detectors and electronics
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After installing the 2nd EOM, we had some trouble to be able to lock again.
One possible reason was the very low signal level in transmission, which is important to trigger the locking system (and stop it).
See the Alice post for details, but we were able to measure only once the Finesse of the cavity at around 2600. |
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Successful lock (finally !), posted by Alice Renaux at Optical room about lasers and optics
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Today, with Ronic, we managed to get a successful lock with the NKT laser by setting up a new PDH box from scratch (photodiode + amplifer + mixer).
Me measured the injected power (5.4mW) and the transmitted power (33µW) after a wedge (92% transmission) and a 7ppm transmission mirror,
so the intracavity power was 5.1W. We have a 950 enhancement factor for a 3100 finesse cavity, so a nominal enhancement factor of 2500. The lock was very |
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2-mirror cavity locking, posted by Alice Renaux at Optical room about lasers and optics
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In June, we encountered some problems regarding the transmission and error signals (see images here),
looking as if the laser was switched off before the cavity was filled.
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first attempt to lock, posted by Ronic Chiche at Optical room about mechanics | lasers and optics | detectors and electronics
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With Alice, we installed the EOWaves oscillator to be locked on the FP-cavity (T1 ~ 2500ppm, T2 ~ 10ppm => F ~ 2500)
FSR = 216MHz => LW = 86kHz.
We installed the PDH box, and we got some error signal, but the shape of the transmission signal and error signal is a bit strange... |
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Damaged mirrors test, posted by Alice Renaux at Optical room about lasers and optics
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Today with Dorian we tested three mirrors with which we previously haven't been able to obtain any resonance or optical beating :
- C16111/11 : The mirror looks normal under a microscope, apart from a few inclusions and maybe a small scratch towards the edge. We tested it
with a 161186 M1 mirror and we weren't able to obtain any optical beating on the cavity's mirrors or resonance. |
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2-mirror cavity full setup, posted by Alice Renaux at Optical room about lasers and optics
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Today with Ronic, we changed the FP cavity's mirrors to Layertek (Gamma Factory) mirrors :
- M1 : n°161186 --> fused silica, unknown absorption, unknown diffusion, T1=2500ppm transmission planar mirror ;
- M2 : n°161182 --> fused silica, unknown absorption, unknown diffusion, T2=10ppm transmission, 5m ROC mirror. |
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2-mirror cavity alignment, posted by Alice Renaux at Optical room about lasers and optics
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Yesterday and today, I replaced the OEWaves CW laser with the NKT CW laser. Its screen does not display anything, so it has to be operated through the
GraphiK software.
I then re-aligned the cavity with a new adjustment adaptation tool between the mirror mounts and the irises. |
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2-mirror cavity alignment, posted by Alice Renaux at Optical room about lasers and optics
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The NKT laser PZT sensitivity is ~0.09pm/V of wavelength variation, which is equivalent to ~ 25MHz/V
So, the full range of the scan is roughly 250MHz (more than a FSR) for 10V.
It seems impossible to get such large resonances unless the Finesse is very low => let's try to change M1 by a spare GammaFactory plan |
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2-mirror cavity alignment, posted by Alice Renaux at Optical room about mechanics | lasers and optics
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At the beginning of the week, I installed a half-wave plate, a beamsplitter cube and a quarter-wave plate, as well as the end-of-cavity mirror, which
I unsuccessfully tried to align.
I removed the end-of-cavity mirror and started the laser injection over again with the two motorized mirrors placed in front of the vacuum chamber |
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Alignment of a 2-mirror FP cavity, posted by Ronic Chiche at Optical room about mechanics | lasers and optics
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today with Alice,
- we measured the height of the SBOX windows center : 140mm from the optical table.
- we set the laser fiber colimator exactly at this height. |
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optical table cleaning, posted by Ronic Chiche at Optical room about utilities
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this morning with Alice and Daniele, we removed all the optics elements and equipments from the SBOX optical table and started to clean it.
the dust meter count 0 on all particle sizes after the cleaning.
we observed a small part of the SBOX which seems to be oxydised (see picture). |
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optical table cleaning, posted by Ronic Chiche at Optical room about utilities
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this afternoon, we checked the dust meter which is at 0 for 1 and 5µm dust particles but ~ 2000-3000 for 0.3µm particles.
we opened the two top panels to let the air flow clean the inside of the vessel.
we observed some other minor oxydised regions (than the one taken in picture) on the external parts of the inox panels but at first sight, nothing |
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optical table cleaning, posted by Ronic Chiche at Optical room about utilities
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now, it seems the table is clean enough (dust meter counts 0 particles) to install a 2 mirrors FP-cavity.
Ronic
Chiche wrote:
this afternoon, we checked the dust meter which is at 0 for 1 and |
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CELIA 100W laser amplifier repair , posted by Ronic Chiche at Optical room about lasers and optics
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this morning with Alice, we sent the Menhir 160MHz injected in a fiber (with 6mW at the end of a long fiber) into the laser amplifier, to look for leakage
or damage in the first stages of the amplifier (the amplifier is totally off).
first of all, we checked for light scattering around the laser crate with a sensitive optical card => nothing |
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CELIA 100W laser amplifier repair , posted by Ronic Chiche at Optical room about lasers and optics
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this afternoon, we saw some electric cables badly connected to their power supply.
we fixed it by soldering them together and screwing the result to the power supply.
(see 1st image) |
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CELIA 100W laser amplifier repair , posted by Ronic Chiche at Optical room about lasers and optics
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friday morning, we add a zoom call with Jerome Lhermite about the amplifier repair.
he approximately confirmed the amplifier scheme from the Loic thesis.
he suggested to: |
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Menhir 216MHz laser, posted by Alice Renaux at Optical room about lasers and optics
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The Menhir 216MHz laser has been put back in place on the cavity table. Its output power is measured to be 160mW with an attenuator. Its spectrum is
available in "spectre.xlsx" and "spectre.png". The main wavelength is a bit shorter (1028.75nm) and the spectrum a bit narrower (4.73nm)
than expected. |
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Menhir 160MHz laser, posted by Alice Renaux at Optical room about lasers and optics
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The Menhir 160MHz has been put back in place on the CELIA amplifier setup. Its output power is measured to be 150-160mW with an attenuator as expected.
Its spectrum is available in "spectre_avant_cvbg.xlsx" and "spectre_avant_cvbg.png".
The pulses are stretched by means of a CVBG. Their spectrum is available in "spectre_apres_cvbg.xlsx" and "spectre_apres_cvbg.png". |
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D-shape mirrors positionning status, posted by Ronic Chiche at Optical room about mechanics | lasers and optics | detectors and electronics
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This afternoon we opened the cavity and put the D-shape mirrors at their correct place, close to the beam.
we checked the relative position of the mirrors to the beam using the 2nd stage of the amplifier (<1W) and with the sensitive (and cleaned) orange
optical card. |
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D-shape mirrors positionning status, posted by Ronic Chiche at Optical room about mechanics | lasers and optics | detectors and electronics
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The cavity box is vacuum pumped at 6*10^-2 mbar.
Ronic
Chiche wrote:
This afternoon we opened the cavity and put the D-shape mirrors at |
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D-shape mirrors positionning status, posted by Ronic Chiche at Optical room about mechanics | lasers and optics | detectors and electronics
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summary:
- the motors used to move the D-shape are the Newport Picomotors 8303-V
the sensitivity is roughly 30nm/step |
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2 mirror cavity high power experiments, posted by Xinyi Lu at Optical room about lasers and optics
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Today, Ronic and I recorded some intracavity power and cavity mode size as shown in Fig. 1.
Coupling was calculated using the locking curve of this overcoupled cavity. Pr/Pi = 1-Cgeo*Cimp, Cimp = 1-|1-2T1/RTL|^2
We can see that the effective gain, coupling, and mode size decrease with increasing power. And the beam is constantly moving. |
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high-power experiments of 2-mirror cavity, posted by Xinyi Lu at Optical room about lasers and optics
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Today, Ronic, Daniele and I redo the high-power 2-mirror cavity experiments, and the results are shown in the table (Figure 1 and Excel 2 ).
- The intracavity power ~500kW can be obtained at 47W injection, but we then have no increase or even a decrease in intracavity power when
increasing the injection power, and the coupling is decreasing. It looks like the saturation power of the current device. |
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high-power experiments of 2-mirror cavity, posted by Xinyi Lu at Optical room about lasers and optics
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here is a Matlab code to try to optimize the telescope for a hot cavity,
taking into account the thermal lens in the coupling mirror.
from that code, one can deduce using the "Gaussian Beam" software (using the attached xml file) an optimized telescope with 100% geometrical |
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high-power experiments of 2-mirror cavity, posted by Xinyi Lu at Optical room about lasers and optics 6x
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Here's a summary of our experiment last week:
The initial telescope position: 920 mm (f=+250mm) and 1148 mm (f=-150mm) from the amplifier output.
Mon May 6: We moved the concave lens 0.5mm closer to the cavity. |
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Fiber injection, spectrum and connection of 2nd stage amplifier, posted by Xinyi Lu at Optical room about lasers and optics
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Today, Daniele and I injected the laser into the fiber, installed the telescope, connected the second stage of the amplifier, and obtained resonances.
- The output power of the menhir laser @ 216MHz is 150mW, after CVBG is 28mW , 9.6mW injected into the fiber, and 1.6mW via AOM and EOM. This
is not far from the minimum 1mW seed power required by the amplifier. |
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Install 2-mirror cavity, posted by Xinyi Lu at Optical room about lasers and optics
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Today, Viktor and I started installing the two-mirror cavity.
- Firstly, we cleaned the environment and the dust counter showed good cleanliness
- After opening the cavity we tried to determine the source of the strange spot with a laser detection card and found that the beam was |
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Install 2-mirror cavity, posted by Xinyi Lu at Optical room about lasers and optics
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Today Viktor and I completed the installation of the two-mirror cavity and managed to lock and measure the finesse.
- The finesse is 36k now (see figure 1). For the designed value of the mirror, the expected finesse is ~50k.
- The diameter of M2 transmission is 1.67 mm,1.65 mm (see figure 2). |
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Finesse measurement of 2-mirror cavity, posted by Xinyi Lu at Optical room about lasers and optics
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- Today Daniele and I cleaned the spherical mirror by wiping it with alcohol, and the finesse increased to 47k in air.
- After vacuuming, the final finesse is about 45k. The enhancement factor is expected to be 23k.
- Then we tuned the cavity length, FSR = 216.666 MHz. Aurélien helped us to install the menhir laser of 216 MHz. |
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Finesse measurement (35k), posted by Xinyi Lu at Optical room about lasers and optics
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These days, Ronic, Aurélien and I use OEwaves CW laser to measure the finesse of SBOX. We made 5 measurements at 100kHz / 4s sweeps.
The finesse is around 35k (see Figure 1), corresponding to an enhancement factor of 14k.
In our experiments, we only saw up to 9k gain with 70% coupling, corresponding to an enhancement factor of 12.8k. |