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LIGO-G000228-00-D. GEO 600 Laser System as in the optics lab of Callinstraße 38 at 12.08.2000. New Features of GEO 600 Slave Laser. Resonator spacer and base plate made of Invar (FeNi36 / 1.3912) - PowerPoint PPT Presentation
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©LZH
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GEO 600 Laser Systemas in the optics lab of Callinstraße 38 at 12.08.2000
•LIGO-G000228-00-D
©LZH
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New Features of GEO 600 Slave Laser
• Resonator spacer and base plate made of Invar (FeNi36 / 1.3912)– low thermal expansion 8x10-7 / K (average 20-50°C)
(thermal change of optical path length in air at const. pressure - 9x10-7 / K)
• Diode laser power monitor
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GEO 600 Slave Laser
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GEO 600 Slave Laser
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GEO 600 Slave Laser
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“Long Term” Stability
• Maximum power after two mirrors and an adjustable attenuator consisting of
a polarizer a half wave plate and a 2nd polarizer.
• Laser left untouched, attenuator varied for different purposes • 2 % / 1.5 % pump power drop observed over full 21 day period
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“Long Term” stability II(20 h preliminary)
0 180 360 540 720 900 10800,5
0,6
0,7
0,8
0,9
1,0
slav
e pi
ezo
leng
th in
crem
ent
[m
]
time [min]
All other acquired data stableto measurement resolution
– room temperature: 1 K
– pump power: 0.2 %
– output power : 1%
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Slave Intensity Noise Suppression
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Slave Intensity Noise SuppressionTransfer of Pump Current Modulation to Amplitude Modulation
102 103 104 105 106
-70
-60
-50
-40
-30
-20
ampl
itude
a. u
. [dB
]
102 103 104 105 106
-270
-180
-90
0
90
pha
se [d
eg]
frequency [Hz]
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Slave Intensity Noise SuppressionFull Open Loop Transferfunction of AM Servo (preliminary setup)
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Slave Intensity Noise SuppressionFirst Results (of preliminary setup)
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Power Scaling of End Pumped Nd:YAG
0 5 10 15 20 25 30 35 400
2
4
6
8
10
12
14
16
18
GEO Slave with Nd:YAG rods with undoped encaps first data taking second data taking after realingnment
outp
ut p
ower
[W]
pump power [W]
As ta n d a r d r o d s g o o d c o a t in g1 3 .5 W @ 2 x 1 7 W p u m p p o w e r.Bs ta n d a r d r o d s b a d c o t in g11 .5 W @ 2 x 1 7 W p u m p p o w e rCr o d s w ith u n d o p e d e n d c a p ss a m e c o a t in g a s in 1 5 W @ 2 x 2 0 W p u m p p o w e rBDe x p e c ta t io n s fo r r o d s w ith u n d o p e d e n d c a p sg o o d c o a t in gp ro b a b ly 1 7 W a t 2 x 2 0 W p u m pEr e d e s ig n o f c a v ity a n d p u m p o p t ic sm ig h t y ie ld 2 0 W
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Power Scaling of End Pumped Nd:YVO4
0 5 10 15 20 25 30 35 400
2
4
6
8
10
12
14
16
18
GEO slave with standard Nd:YVO4 "rods"
brewsterplates removed
outp
ut p
ower
[W]
pump power [W]
Advantages of Nd:YVO4 1)
• amplifies 1064 nm emission of Nd:YAG(? at what temperature difference ?)
• birerefingence na= 1.96 / nc= 2.17 no depolarization
• emission || = 25x10-19 cm-2 = 7x10-19 cm-2
polarized emission• large product of || sp (sp 90 s)
loss insensitive high gain lasers• 8 nm broad absorption @ 808 nm
low requirements on pump diodes
Disadvantage of Nd:YVO4 1)
• low pump intensity damage threshold58 W / mm2 @ 0.5 % doping29 W / mm2 @ 1.0 % dopingincreased by 50 % by undoped endcaps
1) Data from Y.-F. Chen, IEEE J. Q. E. 35(2), 234 (1999) / Tsunekane et. al. Elt. Lett. 32(1), 41 (1996) / VLOC, Casix, Castech web pages
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Problems of the slave
• Atmospheric pressure changes p dl/(l dp) 2.8x10-7 / hPa
– 50 hPa and 0.5 m 7 m
• Mirrors on single long range piezos tilt 10 rad / m
• Long range piezos have large low frequency resonances
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Possible Solutions
• Sophisticated piezo mountpre tension / damping / thick mirrorsmultiple piezos
• Thermal length actuator30 mm Al/FeNi36 0.5 m / K
pessimistic assumption: f 106 Hz / Hz1/2, fx-over 0.01 Hz
piezo: lRMS 10 nm
• Hermetically airproof resonatorconstant density of air nearly constant optical path length expansion dependent on spacer material only Suprainvar / Zerodur / ULE