First Lock with 2nd satge of amplifier : Finesse issue ?, posted by Ronic Chiche at Optical room about lasers and optics | detectors and electronics
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1st lock today with the second stage of the amplifier.
~ 300mW of injected power (but which proportion of the pump and of the signal ? => One must use a spectrometer to determine this proportion)
MAYBE the real injected power of the signal is lower => maybe the Finesse is higher ! |
First Lock with 2nd satge of amplifier : Motor issue ? , posted by Ronic Chiche at Optical room about mechanics 
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Global locking almost clean : tranmission and reflection are quite noiseless except the peaks at every 500ms.
During the amplifier 2nd stage lock, we experienced 2 strange behaviors :
- short "unlocks" every 500ms exactly all the time, during the whole lock process |
First Lock with 2nd satge of amplifier : Finesse issue ?, posted by Ronic Chiche at Optical room about lasers and optics | detectors and electronics
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First of all, we used and optical spectrometer to determine which proportion of pump and signal is in the injected beam.
the wavelength is THE SAME for the 2nd stage for the beam coming from the core or coming from the clad !
thus, it is impossible to use a spectrometer to obtain this proportion. |
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New locking scheme, posted by Ronic Chiche at Optical room about detectors and electronics
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Before, the locking scheme was to produce an error signal with the PDH box, send its output to the electronic amplifier box and then to the laser EOM
for the fast loop and to the Laselock input. The drawback was changing one loop gain, changes also the other loop gain.
Now, the locking scheme is the error signal coming from the PDH box is directly sent to the Laselock input and in a same time to the electronic |
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30Hz noise issue, posted by Ronic Chiche at Optical room about lasers and optics | detectors and electronics
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since some days, we observe the cavity is difficult to lock and a strange 30Hz noise has appeared on the PZT signal which normally compensate the phase
noise difference between the cavity and the laser.
to test if the problem could come from the laser, we changed the OneFive laser for the Koheras but we have exactly the same problem, thus we concluded |
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First Lock with 2nd satge of amplifier : Motor issue ? , posted by Ronic Chiche at Optical room about mechanics
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The 500 ms noise disapeared. We had to disable the "power save" mode of the smaract translation stage. AND turn OFF and ON the controler box.
Ronic
Chiche wrote:
Global locking almost clean : tranmission and reflection are quite |
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30Hz noise issue, posted by Ronic Chiche at Optical room about lasers and optics | detectors and electronics
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The 30 Hz noise issue has been solved !
It came from translation stage of P1 and/or P4.
Fabian remembered that close to the mirror's mount translation stage end coarse, there is a mechanical instability. The mount kind of "lift |
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Beam pulse duration, posted by Ronic Chiche at Optical room about lasers and optics
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We installed the 2 CVBG for compression after the amplifier.
We used an interferometric technique with a delay line and combining the two paths in a CCD to measure interferences... see interferences.avi video
file |
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Beam pulse duration, posted by Ronic Chiche at Optical room about lasers and optics
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Yesterday, Loic installed a telescope before CVBG's to reduce the spot size on CVBG's and reduced the incident angle 0.5-1° on them (on the
datasheet the specified incident angle is 2.8°).
We used an interferometric technique with a delay line and combining the two paths in a CCD to measure interferences. |
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Beam pulse duration, posted by Ronic Chiche at Optical room about lasers and optics
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Yesterday, Loïc put the CVBG's back to their specified angles.
We used an interferometric technique with a delay line and combining the two paths in a CCD to measure interferences.
After supressing the global shape of the superposed pulses, one measures the amplitude of the remaining fringes (standard deviation) each 50µm |
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Beam pulse duration, posted by Ronic Chiche at Optical room about lasers and optics
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Last Thursday (20th of February), Loïc and Titouan realigned the stretcher CVBG to its nominal angle and they used an interferometric technique
with a delay line and combining the two paths in a CCD to measure interferences.
After supressing the global shape of the superposed pulses, one measures the amplitude of the remaining fringes (standard deviation) each 50µm |
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Optical spectrum analyzer resolution, posted by Ronic Chiche at Optical room about lasers and optics
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The Koheras @0.5mW is directly connected with fibers FC/APC -> FC/PC to the Avantes optical spectrum analyzer.
The FWHM wavelength, measured with the Avantes software, is 0.126nm |
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Optical spectrum analyzer resolution, posted by Ronic Chiche at Optical room about lasers and optics
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Same measurement with Koheras @100mW and using fiber coupling lenses between Koheras and Avantes OSA.
The FWHM wavelength, measured with the Avantes software, is 0.116nm
Ronic |
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Optical spectrum before and after CVBG, posted by Ronic Chiche at Optical room about lasers and optics
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Measurement of the optical spectrum with Avantes OSA before (1st picture) and after CVBG (2nd picture) with 2nd stage on the laser amplifier.
The 1st CVBG stretches the beam horizontally due to the default incident angle and the fact that different wavelength are reflected in the CVBG
with different depth. |
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Amplifier laser diodes issue, posted by Ronic Chiche at Optical room about lasers and optics
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This is a long time issue for the ThomX amplifier : on the 4 pumping diodes available, the 1st diode has a higher temperature than the others around
40°C (see the picture).
the problem comes from the TEC which is not activated (see diodes parameter files in execel format). the related software windows are shaded. |
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Pointing stability with CVBG, posted by Ronic Chiche at Optical room about lasers and optics
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Yesterday, with Titouan, we made some measurements on pointing stability of the laser beam after amplifier and CVBG.
the amplifier beam go through a first telescope to be small enough and colimated before going to CVBG's, then go to CVBG's and then is sent
through the FP-cavity telescope to the FP-cavity itself. |
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Finesse measurement after the Edge installation, posted by Ronic Chiche at Optical room about lasers and optics
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After the Edge installation inside the cavity, the Finesse has been measured several times by modulation technique with an average around 16000:
(the scan speed is 50kHz in 10 seconds.)
So, it hasn't changed since the last measurement in June, just before the Edge installation. |
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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. |
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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" |