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Am adjustment on the lenses position to have a smaller waist.
+ 250 mm @ 88 cm from amplifier
-150 mm @ 111 cm from amplifier
the overlap with this placement is ~ 91%
the measured beam FWHM at the injection point M1 estimated to be ~ 0.94 mm
waist = 0.85*0.94 = 0.79 mm , it is still much larger than the needed 0.58 mm radius waist.
There is an improvement in reducing higher order modes, but the fundamental is still too weak to see, we observe higher order even modes 11 , 44 , ...
| Manar Amer wrote: |
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Note the correct beam divergence is approximately ~ 2.3 mrad
M2 = 1.1 in this fit, but it is not yet optimized !!!!! could be reason for not accurate telescope reading.
Have tInstalled a new telescope with lenses
250 mm @ 86.8 cm from amplifier ,
-150 mm @109 cm (~ 22 cm between lenses)
the beam waist measured at a point on the reflection which is relatively the same distance to the injection mirror and the beam was much smaller than before
@ ~ 2 meters from amplifier + telescope , FWHM = 1.2 mm , waist = 0.85 * FWHM = 1.02 mm
| Manar Amer wrote: |
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Here is a view of beam propagation in the optical software : GaussianBeam
the red filled shape is the model of the CELIA amplifier beam propagation with a divergence of 4.46 mrad
(the 2 black dots is the measurement of the beam size without any lens to change the beam propagation).
the 2 black lines have been put at the input and output cavity mirrors position relative to the CELIA amplifier position, respectively 2m and 2.7m roughly.
the cavity mode radius should be 0.55mm and 0.7mm respectively.
the cavity mode shape is represented by the 2 red lines (very close to the red filled shape which is the beam).
the most simple working telescope could be a +250 lens at 280mm from the CELIA amplifier.
it gives a beam radius of 0.53mm at the input mirror and 0.64mm at the output mirror.
the overlapping is more than 99%
the 2nd file is the GaussianBeam file.
| Manar Amer wrote: |
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I placed a periscope to adjust the high of the beam from the amplifier output from ~ 10 cm from the table to ~ 15 cm
a dichroic mirror placed after it to reject the pump laser, all the mirrors on the path to the cavity were replaced with dielectric mirrors BB01-E03
the length of the path from the amplifier output to the cavity coupling mirror ~ 2 meters
setup defines the different optics placed in the path
Note: the beam goes all the way to the cavity, put it is not yet optimized to the irises.
| Manar Amer wrote: |
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Beam divergence was measured using a method called "Focal Length Divergence Measurement Method"
Where a lens of a known focal length is placed on the beam path and the beam waist is measured at the focal distance using a beam profiler.
We ramped the power up to 10 W
for a focal length = 400 mm,
we measured a FWHM = 2.1 mm,
corresponding to a divergence = 4.45 mrad (edit : wrong software use)
for comparison, we measured the FWHM 8.1 mm @ 1.55 m and extracted the divergence directly 4.46 mrad (edit : this measurement is wrong - wrong use of the software)
Note: better to use a lens of a focal lens higher than 100 mm (to reduce the error in the distance measured)
| Manar Amer wrote: |
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The previous Sbox telescope was dismantled and the mechanical components cleaned.
its lenses are still in the mounts, it looks that two of them are spherical and two are cylindrical
2 are -100 mm and 2 are +150 mm, there is also a box containing fused silica lenses that could be used.
Note: at high power use only fused silica lenses not BK7 type
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