Transcript Pumping scheme for nd-yag.... - ego

Lasers for Advanced Interferometers
Benno Willke
ILIAS WG3
Hannover, October 2004
Requirements - Topology
• Sagnac:
– broadband source to reduce scattered light noise
– power control
• recycled Michelson:
– coherence control
– power control
– spatial control
• squeezed light IFOs
• different wavelength
Prestabilized Laser System
(PSL)
Requirement – High Power
Laser Limits
•
•
•
•
•
stress fracture
birefringence / depolarization
spatial distortions
cavity stability / thermal lens
spurious oscillations in high gain
material
IFO Limits
• thermal problems due to heating of
surface/bulk (cavity stability, limit in
cooling for cryogenic detectors)
• scattered light noise
• radiation pressure fluctuations in IFO
and in frequency reference (low f
performance)
trade off:
high input power
• easier control problem
• easier lock acquisition
(radiation pressure dynamics)
high power recycling gain
• spatial and temporal filtering
• good frequency reference
Requirement – Noise
Frequency Noise
Coupling
• via arm asymmetry
• options: change IFO readout (DC
readout / external modulation)
Limits
• sensing noise
– shot noise in PDH signal
– discriminator slope
Intensity Noise
Coupling
• via radiation pressure noise
– technical RIN sees common mode
rejection (same pendulum TFs) in IFO
– quantum noise can be reduced by
squeezing techniques and QND
• via RIN on photo detectors
– non perfect dark fringe contrast
– requires passive filtering for rf readout
• via rad. press. in frequency reference
Limits
• sensing noise
– shot noise
– pointing combined with detector
inhomogeneity
Requirement – Noise / Design
Spatial Fluctuations
Coupling
• via RIN caused by cavities
• via higher order mode “waste light” on
IFO photodiodes
Limits
• finesse of modecleaners
– additional shot noise on PDH detector
– fluctuations in spurious
interferometers
Design Requirements
• stability / reliability
• soft failure mode
• easy to maintain / rare maintenance interval
• good efficiency
• good stationarity / low glitch rate
• high bandwidth / large range actuators
– thermal problems in modecleaner
– noise introduced by modecleaner
Laser Design
• common concept:
– laser diode pumped solid state lasers
– transfer frequency stability of low power master
laser to high power stage
• Maser Laser Power Amplifier (MOPA)
• injection locked oscillator
• different power stage concepts:
–
–
–
–
rods
zig-zag slabs
fibers
thin disc lasers / active mirror laser
Nd:YAG Master-Laser
NPRO (non-planar ring
oscillator)
• output power: 800mW
• frequency noise:
[ 10kHz/f ] Hz/sqrt(Hz)
• power noise:
10-6 /sqrt(Hz)
High Power Stage
• main problem: thermal design
– stress fracture
– thermal lensing – spatial profile
– birefringence with tangential and
radial principle axis
• solutions
– reduce deposited heat – Yb:YAG, high efficiency
– propagate beam perpendicular to temperature gradient –
zig-zag, thin disc lasers
– increase interaction length – fiber lasers
– compensate birefringence
Face-pumping - Edge-pumping
Pumping
zig-zag
slab
Facepumping
zig-zag
plane
Cooling
Edgepumping
zig-zag
plane
Pumping
Cooling
Stanford High Power Laser Lab
Adelaide University
End pumped slab geometry
808nm
Pump
undoped end
signal
OUT
3.33cm
1.51cm
1.51cm
0.6% Nd:YAG
signal
IN
808nm
Pump
undoped end
1.1mm X 0.9mm
Stanford High Power Laser Lab
Stanford High Power Concept
10W LIGO
MOPA
System
Pump Power = 130
Output TEM00Power = 50 W
Mode-matching
optics
20 W
Amplifier
ISOL
ATOR
Lightwave Electronics
2-pass End Pumped
Slab #1
Mode-matching
optics
2-pass End
Pumped Slab #2
TO PRE MODE
CLEANER
Pump Power = 430 W
Expected TEM00
Output Power = 160W
End Pumped Rods
Nd:YAG - GEO600 Laser (14W)
Nd:YVO4 - Virgo Laser (20W)
Laser Zentrum Hannover
LZH High Power Concept
output
f QR
f
BP
from Master
f QR
f
20% OC
HR
20% OC
HR
Brewster Plate
Brewster Plate
f QR
f
80 150 50
fiber bundle
10 X 30 W 80 150 50
fiber bundle
10 X 30 W
HR@1064
HT@808
f
2f
f
f
2f f
54 mm laser rod
f QRrelay optics f
with two undoped
end caps
2f f
54 mm laser rod
relay optics
with two undoped
end caps
f
Fiber Lasers
Pump light
Active fiber
HR-mirror
Coupling optics
courtesy H. Zellmer
Laser radiation
Collimator
Outcoupler
Fiber Laser Result of Jena Group
NPRO
Backscattered
signal
9.4 m Yb-doped
LMA-fiber
Dichr. mirror
Fiber coupled
laser diode
Isolator
Input-output diagram
Backscattered signal [a.u.]
Output power [W]
120
100
80
60
8
Yb-doped LMA-Fiber
6
4
2
0
0
20
40
60
80
100
120
Output power [W]
40
20
Opt. efficiency = 70%
0
0
To experiment
20
40
60
80 100 120 140 160 180
Launched power [W]
Core:
MFD
Doping.
Pumpc.:
 = 28.5 µm, NA = 0.06
23 µm
700 ppm (mol) Yb2O3
 = 400 µm, NA = 0.38, D-Form
Seed:
800 mW
• Diffraction limited (M2 = 1.1)
• Polarization 82% (10:1)
Advanced LIGO Laser – Requirements
Power / Beamprofile:
– 165W in gausian TEM00 mode
– less than 5W in non- TEM00 modes
Drift:
– 1% power drift over 24hr.
– 2% pointing drift
Control:
– tidal frequency acuator +/- 50 MHz, time
constant < 30min
– power actuator 10kHz BW, +/-1% range
– frequency actuatot BW:<20o lag at
100kHz, range:
DC-1Hz: 1MHz,
1Hz-100kHz: 10kHz
Injection Locked Oscillators - Hannover
output
f QR
NPRO
f
FI
BP
EOM
FI
modemaching
optics
f QR
HR@1064
HT@808
f
YAG / Nd:YAG
3x2x6
f
2f
f
YAG / Nd:YAG / YAG
3x 7x40x7
High Power Slave
key elements:
• undoped bonded end-caps
• birefringence compensation
• pumplight homogenization
20 W Master
Prestabilized Laser PSL
• frequency stability:
– stabilize master laser to
rigid or suspended-mirror
cavity
• power stability:
– feed-back to pump source
of high power stage
– passive filtering at rf
• spatial profile
– passiver modecleaning
– active mode compesation
frequency noise requirement
intensity noise requirement
Adv LIGO - PSL optical layout
high power
ring laser
200W
GEO typ
ring laser
15W
spatial filter
resonator
(PMC)
NPRO
1W
frequency
reference
resonator
AOM
PSL – stabilization scheme
intensity stabilization
outer loop
injection locking
intensity stabilization
inner loop
PMC loop
frequency stabilization
inner loop
frequency stabilization
outer loop
Power Noise Reduction
Relock Time
2
1
Slave
12 W Master
Piezo Ramp:
Master 1,3 Hz (770ms)
Slave 2.5 Hz (400ms)
0
PD Signal [V]
-1
-2
-3
-4
-5
-6
-7
-8
-0,4
-0,3
-0,2
-0,1
0,0
0,1
0,2
0,3
0,4
t [s]
relock time < 500 ms
faster relock possible depending on piezo ramp
Birefringence Compensation
End-Pumped Rods
output
f QR
f
BP
from Master
f QR
f
20% OC
HR
20% OC
HR
Brewster Plate
Brewster Plate
f QR
f
80 150 50
fiber bundle
10 X 30 W 80 150 50
fiber bundle
10 X 30 W
HR@1064
HT@808
f
2f
f
f
2f f
54 mm laser rod
f QRrelay optics f
with two undoped
end caps
2f f
54 mm laser rod
relay optics
with two undoped
end caps
f
high power stage status Feb 2004
250
no re-alignment
re-optimized @ 40A
linear polarized
with birefringence
compensation
output power [W]
200
150
100
50
0
20
25
30
Diode current
35
40
45
Summary
• different high power stages:
- end-pumped slabs
- end-pumped rods
- fiber amplifier
• different topologies:
- MOPA
- injection locking
• Advanced LIGO pre-stabilized laser system
• status of laser development
• possible stabilization schemes