lgs for sam optical design
DESCRIPTION
LGS for SAM Design Review September 2007, La Serena. LGS for SAM Optical Design. R.Tighe, A.Tokovinin. Laser Box on one of the serrurier trusses at bent-cass port #2 at 45Deg from IR Nasmyth. Working solution: - PowerPoint PPT PresentationTRANSCRIPT
September 28, 2007 LGS for SAM – PDR – Optics 1
LGS for SAMLGS for SAMOptical DesignOptical Design
R.Tighe, A.Tokovinin.
LGS for SAM Design Review September 2007, La Serena
September 28, 2007 LGS for SAM – PDR – Optics 2
IR Nasmyth Optical
Nasmyth
Laser Box on one of the serrurier trusses at bent-cass port #2 at 45Deg from IR Nasmyth.
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).
Working solution:Laser control
and cooler position (on the ledge at the IR Nasmyth pillow-
block level).Beam Transfer
Laser Launch Telescope
The LGS System on SOAR
September 28, 2007 LGS for SAM – PDR – Optics 3
The Laser umbilical cable handling on SOAR
The Laser control & Cooler Rack.
Cable length = 7m.
Laser cable layout fit-test (yellow line).
September 28, 2007 LGS for SAM – PDR – Optics 4
truss
IR Nasmyth
Focus
Cable-wrap; mobile
Cable-wrap;static
Yellow line is the 7m Laser
Umbilical Cable Layout
Rack for laser control, power and Cooler at pillow-block level
Laser Cable and Rack at IR-Nasmyth
September 28, 2007 LGS for SAM – PDR – Optics 5
LLT
IR
m4
m3
Laser Box
SOAR Elevation Ring
The LGS system (GB propagation)
Requirements:
LLTm1: R=1000mm, =300mm (pupil).
GB 1/e² diameter footprint on LLTm1=260mm.
Decided:
LLTm2: R=30mm, =15mm.
September 28, 2007 LGS for SAM – PDR – Optics 6
Laser-Box
UV
VIS
Soleil-BabinetCompensator
8x Beam Expander
Beam Profiler CCD
355nm Tripled Nd:Yag Laser
355nm laser-line Dump switch-Mirror
Alignment Mirrors Am1&Am2 (coating450-700nm )
UV Laser Beam Dump
Blue Alignment Laser( 473nm)(or better400-420nm?)
8mm Gaussian Beam Exit Window
Intra-cavity Shutter
LLT
Laser Launch Telescope Beam Transfer
The LGS system
September 28, 2007 LGS for SAM – PDR – Optics 7
The optimized LLT:
LLTm1:
Diameter(mm) Radius(mm) Conic
300 1000 -0.99979
LLTm2:
Diameter(mm) Radius(mm) Conic
15 15 -1.00001
485mm
LLT
30Arcsec Field (on sky)
13 to 24mm1/e² diameter GB Image at 7 to 14km from SOAR M1, respectively.
The Laser Launch Telescope
September 28, 2007 LGS for SAM – PDR – Optics 8
485mm
LLT
30Arcsec Field (on sky)
13 to 24mm1/e² diameter GB Image at 7 to 14km from SOAR M1, respectively.
OPDComa=57nmOPD rms = 59nmOPD p-v =115nmStrehl Ratio= 0.88
Comatic PSF
The working LLT:
LLTm1 (pivots around center of curvature of LLTm2):
Diameter(mm) Radius(mm) Conic
300 1000 -0.9702
LLTm2:
Diameter(mm) Radius(mm) Conic
15 15 -0.0
The Laser Launch Telescope
September 28, 2007 LGS for SAM – PDR – Optics 9
The Laser-Box
The S-B compensator (UV):
8-500-UV-25 (10) from Special Optics
CA=25 (or10)mm, Max. Retardation=400nm,
Resolution=0.5nm
Space needed(Lxwxh)≈110x229.4x165.4mm UV
VIS
Soleil-Babinet Compensator
8x Beam Expander
Beam Profiler CCD
355nm Tripled Nd:Yag Laser
355nm laser-line Dump switch-Mirror
Alignment Mirrors Am1&Am2 (coating450-700nm )
UV Laser Beam Dump
Blue Alignment Laser (473nm)(or better400-420nm?)
~8mm Gaussian Beam Exit Window
Intra-cavity Shutter
~1.5m The Beam Expander (355nm):
Galilean, 2-8x magnification.
Focusing on sliding rails.
The Laser (Tripled Nd:Yag, 355nm):
M²<1.2 => spot roundness better than 85%.
Waist (single mode radius) = 0.13mm (420mm behind laser output).
Waist (mixed modes radius) = 0.1424mm.
Divergence 1.8mRad.
September 28, 2007 LGS for SAM – PDR – Optics 10
The Beam-Transfer
LLT
IR
m4
m3
Laser Box
SOAR Elevation Ring
m4: slow active x, y. Centers the beam on m3.
LLTm1: slow (~1Hz) active x, y. Pointing correction loop.
Laser box: x, y as a whole.
Centers the beam on m4.
m3: one-time x, y adjustments. Aligns LLT optical axis to Beam Transfer.
September 28, 2007 LGS for SAM – PDR – Optics 11
Polarization Issues
~/4
Goal:
>90% LGS return flux reaches the S-H CCD. UV
VIS
S-B
B-E
Laser Linear pol. horizontal
8mm GB circularly polarized
WFS Field Stop
/4
Retarder
SAM LGS WFS
The Goal:
>90% LGS
return flux
reaches the
S-H CCD.
September 28, 2007 LGS for SAM – PDR – Optics 12
The Polarization Strategy
polarization
-1
-0.5
0
0.5
1
-1 -0.5 0 0.5 1
phase=p
phase=2p-p/10
p=/2The Laser pol. is Linear Horizontal.
The S-B is ~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.
This phase retardation is constant and will be measured. If the de-phase error ≥ /14 flux loss ≥ ~10%), it can be compensated in the WFS path.
September 28, 2007 LGS for SAM – PDR – Optics 13
The Optical Tolerances
LGS System Tolerances
Surface Shape Tolerance Decenter Dec. Tilt Tilt
Component Conic Radius Tolerance r Resol. Tolerance 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: Z range=36um (7km to ∞); Z 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.
Table 6. Summary of tolerancing considerations for the LGS optical components.
Merit function:
GB waist 1/e² diam.=8mm on LLTm2.
GB waist at 10km from SOAR M1.
Image Strehl =0.8.
Image off-axis = 30”.
September 28, 2007 LGS for SAM – PDR – Optics 14
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 15
The Coatings for LGS Optics
Component Component Coating Component/Coating Code Plot
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 16
The Coatings for LGS Optics
Plot2 (BBDS) Plot1 (Y3)
Plot3 (BBD1) CVI_AR_355nm
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
250 300 350 400 450
Wavelength, nm
%R
Plot4
September 28, 2007 LGS for SAM – PDR – Optics 17
The Coatings for LGS Optics
Plot5
September 28, 2007 LGS for SAM – PDR – Optics 18
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 Max
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
lens 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
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 19
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.