Thermal Headaches in Advanced LIGO Input Optics

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• Thermal Headaches in Advanced LIGO Input Optics
• Guido Mueller, Rupal Amin, David Guagliardo,
  David Tanner, and David Reitze
• Physics Department
• University of Florida
• Gainesville, FL

LIGO-G010130-00-Z
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Input Optics Functions

• RF Modulation
• Mode Cleaning
• Mode Matching
• Optical Isolation
• Distribution of Control Beams
• Self Diagnostics

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The Challenge

• Advanced LIGO will operate at 180W CW powers -
  presents some challenges
• Thermal Lensing --gt Modal Degradation
• z z 1
  i z
• Thermally induced birefringence
• FI- loss of isolation
• EOM - spurious amplitude
• modulation
• Damage
• Other (nonlinear) effects (SHG, PR)

LiNbO3 at 30W
5 x 5 x 40 mm LiNbO3 EOM - thermal lensing is
i) severe ii) position dependent
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Characterization of thermal lensing
Samples TGG Litton 111 10 mm
diameter, 20 mm length LiNbO3
Leysop, 5 x 5 x 40 mm
Power Meter
Lensing Measurement
Dz
HRM
HRM
l/2
Sample
Glan Pol.
Beam Scan
l/4
HRM
50 W NdYLF
Beam Dump
HRM
Power Meter
D Sag Measurement
l 1053 nm
NeNe
PD -Ref.
HRM
DM
l/2
Glan Pol.
DM
l/4
HRM
PD - Signal
Beam Dump
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Optical Path Difference Measurements
Theory Hello-Vinet
P50 W Absolute DL (hot - cold) 10 mm DOPD (1/e
intensity) 100 nm 250 nm _at_ 125W
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Optical Path Difference Measurements
Mansell, et al., Appl. Opt., 2001
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Propagation Measurements I
w(z)
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Propagation Measurements II
50 W
Effective Thermal Lens
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Thermal Lensing in LiNbO3

• KTP does work 300 W CW power, 1064 nm (H.
  Injeyan, TRW)
• RTA should also work (lower loss tangent)

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E-O Modulation in Advanced LIGO
Alternative Method Mach-Zehnder modulation --gt
architecture problem
Prototype developed for initial LIGO detectors,
but not well characterized gtgt RD effort
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Power Independent Compensation of Thermal Lensing
a L P / 2 K l

z
z 1 iz
a absorption coefficient
K thermal conductivity
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Thermal Lensing Compensation
Modeled using Melody
150 W
FI or EOM
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Thermal Lensing Telescope

• Similar to current LIGO Telescope
• 2 mirror design (vacuum envelope constraints)
• Accommodates wide range of mode matching
  parameters
• All large (20 cm) optics
• in-situ adjustment with feedback

532 nm
1064 nm
Wide Bandgap Glass
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RD Issues Still to be Faced

• Modulator Development
• RTA performance
• MZ modulation
• Isolator Development
• Full FI system test (TCFI, EOT)
• Possible thermal compensation (-dn/dT materials)
• Telescope Development
• in-situ mode matching adjustment