correlations between accelerometer and lock losses @ 20Hz, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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for this 20Hz oscillation, could it be a natural resonance of the optical table placed on its feet ?
typical mass of the table m ~ 8T
feets : |
correct parameters for locking the FP-cavity, posted by Ronic Chiche at ThomX igloo about software 
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Today, we restarted the FP-cavity locking, after 3 weeks without using it.
those 3 weeks have been used to set the machine ring at the new (better) frequency : 500.067MHz (corresponding to a change of -183kHz)
or 33.3378MHz in fondamental frequency (corresponding to a change of -12.2kHz) |
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correct parameters for locking the FP-cavity, posted by Ronic Chiche at ThomX igloo about software
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this morning I solved the problem of the 33MHz frequency beating which should be ~12kHz between the generator (at the new frequency 33.3378MHz) and the
laser cavity frequency (still at the old frequency which is 33.35MHz)...
the generator providing the 33MHz frequency has 2 channels, and only one was set at the proper frequency ! |
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correct parameters for locking the FP-cavity, posted by Ronic Chiche at ThomX igloo about software
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this morning, I finished the FP-cavity alignment with the new ring RF frequency.
I get back 50kW @ 33% amplifier ratio.
I'm also able to lock very smoothly on the 500MHz ring RF frequency. |
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controller M1 & M4 (plan mirrors) with IcePap controllers, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | cabling
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previously, we have connected motor M4 with an IcePap controller.
see this post : https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/278
due to the backlash behavior of the FP-cavity motors, it is impossible to work in both directions on one motor when the FP-cavity is locked. |
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controller M1 & M4 (plan mirrors) with IcePap controllers, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | cabling
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this double motors scheme works good.
if motor P4 is used by increasing value, the FP-cavityPZT signal (pink signal on scope) goes HIGHER
if motor P1 is used by increasing value, the FP-cavityPZT signal (pink signal on scope) goes LOWER |
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controller M1 & M4 (plan mirrors) with IcePap controllers, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | cabling
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at the begining of each session, it will be mandatory to avoid any backlash for the motors :
- for the P4 motor : one can go 2k steps DOWN, then 2k steps UP to go back to -360 000 and use the
steps UP without any backlash |
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bunker temperature curve, posted by Ronic Chiche at ThomX igloo about detectors and electronics
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air conditionning in ThomX Bunker, posted by Ronic Chiche at ThomX igloo about lasers and optics
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The temperature slitly increase in thomx Bunker from 23° to 24° during the last day.
The thermalisation of the CFP is very long...
In any case the operation of the CFP is so easy, it seems to be correlated to the weather... tody it's very nice as of hte rest of the week. |
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air conditionning in ThomX Bunker, posted by Ronic Chiche at ThomX igloo about lasers and optics
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after the new temperature setting for the bunker air cooling (winter to summer transition), the temperature drop from 24° to 20°C which induced
a slight misalignment between the onefive oscillator and the fiber injection.
the amplifier photodiode PD_IN which checks the amplifier power injection drop also from 3mW to 2.885mW... hopefully, it is enough to start the |
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air conditionning in ThomX Bunker, posted by Ronic Chiche at ThomX igloo about lasers and optics
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I finally got 93-94kW for 33% amp ratio.
I had to move the FP-cavity length to compensate the temperature change in the bunker.
doing that, I had the message "Low Limit SW pressed" when I tried to move P4z under -98 000 steps !!! |
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Xrays experiment with prostate, posted by Ronic Chiche at ThomX igloo about lasers and optics
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Today we do XRays for experiment.
The laser start to 33% at 93 KW but Pgain = 0.033
The laser is locked so stable for the moment. We have Xrays and the system is stable. |
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Wires in laser path, posted by Loïc Amoudry at Optical room about mechanics | lasers and optics | cabling
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| There was some ceramic wires close to the beem path right before P4. We moved them away (we can imagine they could move again with vibration). |
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Vessels vacuum at ambiant pressure, posted by Ronic Chiche at ThomX igloo about vacuum
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Last Friday and this morning, with Bruno, we close the ring/cavity valves and put some dry air in the two vessels through a filter to avoid turbulences.
Now, the two vessels are at ambient pressure and ready for opening (to remove the mirrors).
One can let the ambient pressure in the vessels as long as we want, the ring/cavity valves have been chosen to be compatible with the high vacuum |
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Vessel cleanliness, posted by Ronic Chiche at Optical room about mechanics | lasers and optics | vacuum
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looking in the vessel of the FP cavity using a UV lamp shows a lot of dust... more dust than outside the cavity !!!
here is picture where one can see a cleaned zone using a finger (with gloves).
question : where does come from this dust ? |
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Variable focal lens validation, posted by Ronic Chiche at ThomX igloo about lasers and optics
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we plan to use Electrically Tunable Lenses EL-10-30-C NIR to build the ThomX telescope but they need to be compatible with the powerful laser beam.
for CW regime, on the datasheet (see attached file), the optical damage threshold is 10 kW/cm².
with 70W laser power and 1mm² beam surface (which is much smaller than the real beam size), we are at 7kW/cm². |
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Tuning of the slow feeback loop analog BW + fast feedback loop gain + PID, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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Today with Daniele, we tuned the potentiometer after the Laselock which drives the analog BW of the PID on the laser PZT,
and we tuned also the fast loop gain (with the rotary potentiometer dedicated to it) => the PID parameters have changed.
so, the recipies has changed => to be updated |
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Transmission of the mirrors, posted by Loïc Amoudry at Optical room about lasers and optics
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We openned the cavity, removed S2 and measured trans of P1 and same for S2.
Pin ~= 3.91 mW
PS2 ~= 20 nW --> ~~ 5 ppm !!! |
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Transmission of the mirrors, posted by Loïc Amoudry at Optical room about lasers and optics
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After verification, transmission of P1 correspond to ~150ppm.
The 1337ppm come from a beam leakage. Reflection from P1 goes to the input window which reflects again a part of the beam directly into the cavity
between P1 and S3 then between P4 and S2. |
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Transmission of the mirrors, posted by Loïc Amoudry at Optical room about lasers and optics
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P1 transmission out of the mount (means angle of the mirror is not the real angle):
Pin = 3.2 mW
Pout = 545 nW |