Download SAM LGS optical design

LGS for SAM Design Review
September 2007, La Serena
LGS for SAM
Optical Design
R.Tighe,
A.Tokovinin.
September 28, 2007
LGS for SAM – PDR – Optics
1
The LGS System on SOAR
Laser Box on one of the serrurier trusses at
bent-cass port #2 at 45Deg from IR Nasmyth.
Working solution:
Laser control
and cooler
position (on the
ledge at the IR
Nasmyth pillowblock level).
Beam Transfer
IR
Nasmyth
Optical
Nasmyth
Laser Launch Telescope
Note: a 7m long Laser umbilical cable has been tested. It can be laid out from
the base of the truss directly onto the IR-Nasmyth cable-wrap mobile section
passing over the elevation bearing and reaching the pillow-block (next picture).
September 28, 2007
LGS for SAM – PDR – Optics
2
The Laser umbilical cable handling on SOAR
Laser cable layout fit-test (yellow line).
The Laser control & Cooler Rack.
Cable length = 7m.
September 28, 2007
LGS for SAM – PDR – Optics
3
Laser Cable and Rack at IR-Nasmyth
Cable-wrap; mobile
truss
Cable-wrap;static
Yellow line is
the 7m Laser
Umbilical
Cable Layout
IR
Nasmyth
Focus
Rack for laser control, power and Cooler at pillow-block level
September 28, 2007
LGS for SAM – PDR – Optics
4
The LGS system (GB propagation)
LLT
m3
Requirements:
LLTm1: R=1000mm,
F=300mm (pupil).
m4
GB 1/e² diameter
footprint on
LLTm1=260mm.
Decided:
LLTm2: R=30mm,
F=15mm.
Laser Box
SOAR Elevation Ring
September 28, 2007
IR
LGS for SAM – PDR – Optics
5
The LGS system
8mm Gaussian Beam
Exit Window
Soleil-Babinet
Compensator
8x Beam
Expander
Alignment Mirrors
Am1&Am2
(coating450-700nm )
Beam Profiler CCD
355nm laser-line
Dump switch-Mirror
UV Laser
Beam Dump
Intra-cavity
Shutter
Blue Alignment
Laser( 473nm)
(or better400420nm?)
355nm Tripled
Nd:Yag Laser
VIS
UV
LLT
Laser Launch Telescope
September 28, 2007
Laser-Box
LGS for SAM – PDR – Optics
Beam Transfer
6
The Laser Launch Telescope
The optimized LLT:
LLTm1:
Diameter(mm)
300
485mm
Radius(mm)
1000
Conic
-0.99979
Radius(mm)
15
Conic
-1.00001
LLTm2:
Diameter(mm)
15
13 to 24mm1/e² diameter
GB Image at 7 to 14km from
SOAR M1, respectively.
30Arcsec Field (on sky)
LLT
September 28, 2007
LGS for SAM – PDR – Optics
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The Laser Launch Telescope
The working LLT:
LLTm1 (pivots around center of curvature of LLTm2):
Diameter(mm)
300
485mm
Radius(mm)
1000
Conic
-0.9702
Radius(mm)
15
Conic
-0.0
LLTm2:
Diameter(mm)
15
Comatic PSF
OPDComa=57nm
OPD rms = 59nm
OPD p-v =115nm
Strehl Ratio= 0.88
13 to 24mm1/e² diameter
GB Image at 7 to 14km from
SOAR M1, respectively.
30Arcsec Field (on sky)
LLT
September 28, 2007
LGS for SAM – PDR – Optics
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The Laser-Box
~8mm Gaussian Beam
Exit Window
The Laser (Tripled Nd:Yag, 355nm):
Soleil-Babinet
Compensator
M²<1.2 => spot roundness better than 85%.
8x Beam
Expander
Alignment Mirrors
Am1&Am2
(coating450-700nm )
Beam Profiler CCD
355nm laser-line
Dump switch-Mirror
UV Laser Beam
Dump
~1.5m
Waist (single mode radius) = 0.13mm
(420mm behind laser output).
Waist (mixed modes radius) = 0.1424mm.
Divergence 1.8mRad.
The Beam Expander (355nm):
Intra-cavity Shutter
Blue Alignment Laser
(473nm)
(or better400-420nm?)
355nm Tripled Nd:Yag
Laser
VIS
Galilean, 2-8x magnification.
Focusing on sliding rails.
The S-B compensator (UV):
8-500-UV-25 (10) from Special Optics
CA=25 (or10)mm, Max. Retardation=400nm,
UV
Resolution=0.5nm
Space needed(Lxwxh)≈110x229.4x165.4mm
September 28, 2007
LGS for SAM – PDR – Optics
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The Beam-Transfer
LLTm1: slow (~1Hz) active Qx, Qy.
Pointing correction loop.
m4: slow active Qx, Qy.
LLT
m3
m3: one-time Qx, Qy adjustments.
Aligns LLT optical axis to Beam Transfer.
m4
Centers the beam on m3.
Laser box: Qx, Qy as a whole.
Centers the beam on m4.
Laser Box
SOAR Elevation Ring
September 28, 2007
IR
LGS for SAM – PDR – Optics
10
Polarization Issues
8mm GB
circularly
polarized
SAM LGS WFS
~l/4
S-B
B-E
l/4
Retarder
WFS
Field
Stop
The Goal:
Goal:
VIS
Laser
Linear pol.
horizontal
UV
September 28, 2007
>90% LGS
return flux
reaches the
S-H CCD.
LGS for SAM – PDR – Optics
>90% LGS
return flux
reaches the
S-H CCD.
11
The Polarization Strategy
polarization
The Laser pol. is Linear Horizontal.
p=p/2
The S-B is ~l/4 (adjusted in lab).
The S-B is adjusted so that the
back-scatter from LGS collected by
the SOAR telescope is Circularly
Polarized at Nasmyth.
The SAM common path and the
WFS Optics may introduce some
s-p de-phase.
phase=p
1
phase=2p-p/10
0.5
0
-1
-0.5
This phase retardation is constant
and will be measured.
If the de-phase error ≥ l/14 flux
loss ≥ ~10%), it can be
compensated in the WFS path.
0
0.5
1
-0.5
-1
September 28, 2007
LGS for SAM – PDR – Optics
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The Optical Tolerances
Merit function:
GB waist 1/e² diam.=8mm on LLTm2.
GB waist at 10km from SOAR M1.
Table 6. Summary of tolerancing considerations for the LGS optical components.
Image off-axis = 30”.
LGS System Tolerances
Surface Shape Tolerance
Component
Conic
Image Strehl =0.8.
Decenter
Dec.
Tilt
Tilt
Radius
Tolerance Dr
Resol.
Tolerance DQ
Resol.
(mm)
(mm)
(um)
(Deg)
(Arcsec)
B-E
---
---
0.057
---
0.0032
---
Laser Box
---
---
(0.1) 0.304
---
0.0027
---
m4
---
---
(0.1) 19.958
---
0.0032
---
m3
---
---
(0.1) 6.845
---
0.0360
3.5
LLTm2
0.0390
0.1
0.073
---
(0.06) 0.1407
---
LLTm1
0.0012
0.1
0.073
< 0.5
0.0045
(< 0.2)
LLT
---
---
(0.1) 0.301
---
0.0086
---
LLTm1-LLTm2 distance: DZ range=36um (7km to ∞); DZ resolution=2.5um (depth of focus ~1000m).
Note1: The tolerance on Radius is driven by the mechanism’s designed focusing range ~0.5mm.
Note2: 0.1mm is the ”standard” position accuracy and 1mrad the angular, to be expected in fabrication.
September 28, 2007
LGS for SAM – PDR – Optics
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The Opto-mechanical Specs
Table 11. The complete LGS components positional, angular and adjustment specs for mechanical engineering.
______________________________________________________________________________________
Component
Pos.Tol.(mm) Pos.Range (mm) Pos.Res(mm) Angular Tol.(º) Tilt Range(º) Tilt Res.(º)
______________________________________________________________________________________
Laser Head
0.1
N/A
N/A
N/A
N/A
N/A
Dump-Switch Mirror
0.1
N/A
N/A
0.06 In-Out (~30º) (Repeat.~0.06º)
Blue Laser
0.1
N/A
N/A
0.06
N/A
N/A
Am1
0.1
N/A
N/A
0.06
±2
N/A
Am2
0.1
In-Out (30mm) (Repeat.~10um) 0.06
±2
N/A
B-E
0.057
±2
0.050
0.06
±1
0.0032
S-B comp.
0.1
N/A
N/A
N/A
N/A
N/A
Window
0.1
N/A
N/A
0.06
N/A
N/A
Laser-Box (as a unit)
0.1
N/A
N/A
0.06
±0.5
0.0027
m4
0.1
N/A
N/A
0.06
±2
0.0032
m3
0.1
N/A
N/A
0.06
±2
0.0035
LLTm2
0.073 (Z±0.2,washer/spacers) (Z=0.1washers) 0.06
N/A
N/A
LLTm1
0.073
±0.5
0.0005
0.0045
±0.057
0.00005
LLT (as a unit)
N/A
N/A
N/A
0.0086
±0.167
0.0014
LLTm1-LLTm2 (z-axis) 0.1
±0.1
0.0025
N/A
N/A
N/A
_____________________________________________________________________________________
September 28, 2007
LGS for SAM – PDR – Optics
14
The Coatings for LGS Optics
Component
Component
Coating
Manufacturer
Provider
Dump-switch mirror
CVI
CVI
Y3-1025-45-UNP
1
Am1
CVI
CVI
BBDS-PM-1037-C
2
Am2
CVI
CVI
BBD1-PM-1037-C
3
Beam expander (8 surf.)
Special Optics
Special Optics
AR-355 (T>97%)
4
S-B compensator (4 surf.)
Special Optics
Special Optics
AR-355 (T>97%)
4
Laser box window (2 surf.)
CVI
CVI
W2-PW1-1025-UV-355-0
4
m4
CVI
CVI
BBDS-PM-2037-C
2
m3
CVI
CVI
Y3-1025-45-UNP
1
LLTm2
CVI
CVI
Y3 on Al
5
LLTm1
Axsys Tech.
CVI ?
Y3 on Al
5
September 28, 2007
LGS for SAM – PDR – Optics
Component/Coating Code
Plot
#
15
The Coatings for LGS Optics
Plot1 (Y3)
Plot2 (BBDS)
CVI_AR_355nm
Plot3 (BBD1)
5
Plot4
4.5
4
3.5
%R
3
2.5
2
1.5
1
0.5
0
250
300
350
400
450
Wavelength, nm
September 28, 2007
LGS for SAM – PDR – Optics
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The Coatings for LGS Optics
Plot5
September 28, 2007
LGS for SAM – PDR – Optics
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Damage Thresholds for LGS Optical Surfaces
Opt.
laserGB
Laser GB
Laser GB
Dmg.Thrs.
Dmg.Thrs
CW
Pulsed
Dust
Factor
Dusty
Optics
Diam.
Pulsed
CW
CW
Pulsed
Safety
Safety
(absorp.
fraction)
Safety
Factor
El.
(mm)
(MW/cm2)
(kW/cm2)
(kW/cm2)
(MW/cm2)
Factor
Factor
Min
Max
Min
Mirr
1
3.74
1.27
2
15
2
4
0.007
0.025
0.3
1
4
0.23
0.08
2
15
25
64
0.007
0.025
4
11
8
0.06
0.02
2
15
101
256
0.007
0.025
17
42
1
3.74
N/A
N/A
300
N/A
80
0.007
0.025
13
33
2
0.94
"
"
300
"
320
0.007
0.025
54
134
4
0.23
"
"
300
"
1282
0.007
0.025
215
536
8
0.06
"
"
300
"
5127
0.007
0.025
858
2143
lens
Max
If Absorption fraction of the optical element is a:
(Where a= (1-R) for mirrors and (1-T) for lenses).
And df: is the T(orR) loss due to absorption by dust.
Safety Factor: (sfclean)= a(Dam.Thres.power)/a(GBpower)
Safety Factor: (sfdusty)= Damage Threshold/((1-df)(GB)+df/a(GB))
Conclusion: Only element with some risk (in ~6month period) is the laser beam-dump switching mirror.
September 28, 2007
LGS for SAM – PDR – Optics
18
Issues for Discussion and To Do List
Discussion:
LLTm1 tip-Tilt actuators.
LLTm2 focusing.
LLTm1 to m2 spacing control ?
To Do:
LLTm2: last search for a paraboloidal mirror.
Do the Optics Procurement.
Do the Lab experiments for laser beam and polarization
control.
September 28, 2007
LGS for SAM – PDR – Optics
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