Amplifier power and mirror transmission, posted by Xinyi Lu at Optical room about lasers and optics 
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Today, Ronic, Daniele, Aurélien and I measured the amplifier power and mirror transmission.
Current (A)
0 (2rd stage)
1
2
3
4
5
6
7
7.5
8
Power
(W)
1
1.8
11.8
23.5
35.5
47
57.5
66.9
70.7
74.9
For |
100W CELIA laser amplifier "Power vs Pump current" curve, posted by Ronic Chiche at Optical room about lasers and optics | detectors and electronics
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We measured again the 100W CELIA laser amplifier with a pump current until 8A.
as the first current pump of the amplifier has a Peltier issue, we don't exceeded 6A on this stage and we compensated with the 3 other stages.
7A average current is obtained with 6A / 7.3A / 7.3A / 7.4A |
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High power experiments (500kW), posted by Xinyi Lu at Optical room about lasers and optics
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Last week, we achieved a stable intracavity average power of 500kW, limited by amplifier power. The experimental data are shown in Figure 1.
- We measured the transmitted laser with a power meter in the windows behind M2 and M4 respectively, and the results were consistent, so the
measurements were credible. |
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High power experiments (520kW), posted by Xinyi Lu at Optical room about lasers and optics
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Yesterday, Ronic, Xing, Qili and I achieved a more stable 520kW power at 7.5A (71W injection) by optimizing the alignment and locking parameters. (Figure
1)
- The cavity can be stable locked when airflow is on. At 7.5A, the pump temperature is about 28℃. The chiller temperature didn't |
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High power experiments (550kW), posted by Xinyi Lu at Optical room about lasers and optics
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- Today we moved the position of the D-shaped mirror at 6A. When motor1 (vertical) is 0.2mm away from the spot, the power in the cavity rises from 457kW
to 483kW. Gain=8407 is similar to that at low power (Gain=8511). So the D-shaped mirror lost some of the gain in the previous experiments. At 4A and 5A
we did not move the D-shaped mirror. (Figure 1) |
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Larger beam size & Spectrum, posted by Xinyi Lu at Optical room about lasers and optics
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- We re-measured the gain before moving the mirror. Gain ~9000 was achieved at 3A, but as the power increased, the gain dropped and was difficult to
optimize. In fact, we found that each day the gain was a little higher than the previous day.
Amp current (A)
Injection power (W)
Circulating |
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Different cavity modes & Pulse width, posted by Xinyi Lu at Optical room about lasers and optics
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- Last week, we obtained three curves of the variation of different cavity modes with power (Fig. 1). By comparing the gain for similar cavity mode sizes,
we found that the gain always drops with increasing power.
- We measured the pulse width. The pulse width of the seed laser, after CVBG, amplified at 2A was measured by UPD (rise time < 70ps). Code |
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Different cavity modes & Pulse width, posted by Xinyi Lu at Optical room about lasers and optics
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Additional information:
The pulse duration has been performed in RF on a UPD-70-IR2-P photodiode from Alphalas GmbH by carefully deconvoluting the response function
of the photodiode measured directly with the sub-picosecond laser beam. |
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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. |
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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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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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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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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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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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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). |