Download Laser Adaptive Optics for Advanced LIGO Mode

Laser Adaptive Optics
for Advanced LIGO
Liang Zhang
with Malik Rakhmanov, Joe Gleason
David Tanner, David Reitze, Guido Mueller
University of Florida LIGO Group
Optics Session
3/17/2004
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Acknowledgement
NSF
Lonnie Houck
Derek Kennedy
Jinho Lee
Christina Leidel
Rachel Parks
Luke Williams
Wan Wu
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Outline
Introduction
 Theory
 Experiment
 Future Work
 Conclusion

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Optical configuration of Advanced LIGO
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Input Optics subsystem
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Schematic layout of adaptive-lens mode
matching telescope
Nd:YAG
Laser beam
Adaptive lens
HBS1
(OG515) HBS2
Mirror 1
Heating Beam
Mirror 2
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Transmittance of SCHOTT glass OG515
1.0
514nm
(Argon)
0.5
0.0
200
1064nm
(Nd:YAG)
500
1000
(nm)
Thickness: 3 mm (sample)
Thickness: 15mm (experiment)
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Thermal lensing in OG515
Argon laser beam
YAG laser beam
OG515
An Argon laser is used as heating beam; a YAG laser is used to
‘read’ the thermal lensing effect of OG515.
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Optical path length (OPL) change due to
thermal effects

Temperature-dependent refractive index
dn
OPL (r ) 
LT (r )
dT

Thermal Expansion
OPL (r )   (n  1) LT (r )
: coefficient of thermal expansion .

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Photo-elastic Effect
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Theoretical calculation of temperature profile
(from J. Lee and R. Parks (UF))
r
Boundary Conditions: T
T
z
R
z
4P
T (r , z )  
2 2
n 1 KR w

L

R
0
2
e
r R
0
z 0, L
0
r 2
w2
 r 
J 0  k n r dr 
 r
 R
J
 f n ( z)
0  kn
( J1 (k n )) 2
R


P: power of the incident light
: absorption coefficient
K: thermal conductivity
w: beam radius
R:radius of OG515
k

 ( n  ) L
 ( kRn  ) L
kn
k 
R  e
1
1 R z e R
 1  Rn z  z 
f n ( z) 
e 
e
e 
k L

k n 2  k n  2 kn L
2 n
2

 ( )
e R 1
 e R  1


R
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Theoretical temperature profile
P (Argon laser): 6W
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T(room temperature): 293K.
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Theoretical OPL
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Experimental Setup
R4
Argon Laser
Polarizer
Single-Mode Fiber
R3
R2
M2
Nd:YAG Laser
F1
M3
M4
R1
F2
M1
Faraday
Isolator
M5
Beam Scan
R5
Beamsplitter
OG515
M1, M2, M3, M4, M5 are lenses; R1, R2, R3, R4, R5 are mirrors; F1 and F2 are fiber-optic couplers
The diameter of collimated Argon laser beam is 16 mm; the diameter
of YAG laser on OG515 is 2mm.
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Experimental results
P( Ar  )
Thermal Lensing
Beam Diameter of
YAG (um)
2450
0W
2350
4W
2250
6W
2150
8W
2050
1950
1850
-30
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-20
-10
0
10
20
Distance from OG515 (inch)
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Focal length of adaptive lens
Power of Heating beam (W)
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Beam Profile
Without thermal lensing
With thermal lensing
The thermal lens doesn’t introduce large amplitude
higher order Gaussian modes.
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Future work

OG515 in a vacuum chamber will be tested.
 Fabry-Perot cavity will be used to measure
higher order modes mode matching.
 Bullseye wavefront sensor will be used to
measure and correct mode-matching.
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Conclusion
A variable thermal lens is formed using
different powers of a pumping beam. It is
possible to control this variable lens to
compensate the thermal lensing effects of the
optical elements in advanced LIGO.
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