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Beam size at the amplifier output:
to make this measurement, I switched ON only 1st and 2nd stage.
the dichroïc mirror seems to work the best in reflection at normal AOI !!!
it's strange as most dichroïc mirrors seem to be specified at AOI = 45° ! => to be checked ! => the dichroïc mirror was set on its wrong face !!! => problem solved
the 2 images correspond to the beam measured at 24cm from the amplifier output.
we cannot use the gaussian fit due to the pump beam shape which perturbate the measurement.
I used the FWHM measurement => DX = 2.6 mm, DY = 1.8mm
Pulse shape model:
dP(x,y,t) = DP * exp( - ln(2) * ( (x/DX_fwhm)² + (y/DY_fwhm)² ) * sech²( t / tp )
=> can we use safely the Newport 20Z40DM.10 mirrors to transport the amplifier beam ?
they are specified for 500 W/cm2 CW and 4 J/cm2 for 10 nsec pulses @ 1064 nm.
- if I am correct, for the previous shape model, the average power is :
Pmoy (W) = 2pi / ln(2) * tp * DP * DX_fwhm * DY_fwhm * Frep
with DP=500W/cm2, DX_fwhm=2.6mm DY_fwhm=1.8mm, tp=77ps, Frep=216MHz => Pmoy = 3.5 W !!!
this means that we should not exceed this average power with these mirrors !?!
- if I am correct, for the previous shape model, the maximal energy density (in the pulse center) is :
DE (J/cm2) = tp * DP => Pmoy = 2pi / ln(2) * DE * DX_fwhm * DY_fwhm * Frep
with DE= 4J/cm2, DX_fwhm=2.6mm DY_fwhm=1.8mm, Frep=216MHz => Pmoy = 366 MW !!!
if one applies a safety factor due to the pulse duration ratio (77ps / 10ns) => Pmoy = 2.8 MW !
this specification seems much less restrictive !
=> can we use safely the Thorlabs BB1-E03 mirrors to transport the amplifier beam ?
they are specified for 10 kW/cm CW (linear power density) and 0.5 J/cm2 for 10 nsec pulses @ 1064 nm.
- the linear power density (LPD) is defined as the average power divided by the beam diameter (1/e²)
LPD = Pmoy / DXY = Pmoy / (1.7 DXY_fwhm) => Pmoy = LPD * 1.7 DXY_fwhm
with LPD=10kW/cm and DY_fwhm=1.8mm => Pmoy = 3 kW
- for maximal energy density:
with DE= 0.5J/cm2, DX_fwhm=2.6mm DY_fwhm=1.8mm, Frep=216MHz => Pmoy = 45 MW !!!
if one applies a safety factor due to the pulse duration ratio (77ps / 10ns) => Pmoy = 350 kW !
| Ronic Chiche wrote: |
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The "ThomX" CELIA amplifier is installed on the optical table.
I added all the rubber pieces available between the 2 racks to isolate as best as possible the top rack, which embeds some fans, from the bottom rack from which the laser beam is going out to the FP cavity.
1ST STAGE
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if I put 1mW (minimum input power) on the input fiber of the amplifier and I switch ON the first stage, one can measure 7mW on the 5% output tap on the front panel.
then it is mandatory to check this power before swtiching ON the other stage.
this 5% output tap on the front panel MUST BE ABOVE 7mW
input power : 1mW => 5% output tap : 7mW => amplifier output : 260µW
with the present setup, I can reach 6.8mW of input power, but the 5% output tap seems to saturate at ~ 8mW.
in this condition, the amplifier output is around 800µW
the SMA connector on the rear panel does not output any signal with the 1st stage ON.
2ND STAGE
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then, one can switch ON the 2nd stage : amplifier output is around 1.4 W (without any iris or dichroïc mirror).
the SMA connector on the rear panel does not output any signal with the 2nd stage ON.
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