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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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. |
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 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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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 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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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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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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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. |
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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. |