Development of high-power and stable laser
for gravitational wave detection
Mio Laboratory
Kohei Takeno
2003-Feb-07 The 3rd TAMA symposium 2
Nd:YAG30WTEM00
Injection lock??×
Aims of My Work
Nd:YAG ( 1.064m )Output Power > 100WSingle Transverse ModeSingle Longitudinal ModeLow Intensity NoiseLow Frequency NoiseLinearly Polarized
Final Goal Current Status
2003-Feb-07 The 3rd TAMA symposium 3
Mode / Thermal Effects
Rd
Laser Cavity
Laser Medium
OC HR
Output
Optimum Coupling
Pump
2003-Feb-07 The 3rd TAMA symposium 4
Mode
Transverse Mode : Spatial DistributionMulti-mode oscillation depends on the
mode of the laser cavity
Longitudinal Mode : Frequency Difference The spatial hole burning causes multi-mode
oscillation
In progress now
Succeeded in controlling!
2003-Feb-07 The 3rd TAMA symposium 5
Transverse Mode
Lowest Order TEM00
Higher Order TEM10
Higher order modes spread compared to the lowest
2003-Feb-07 The 3rd TAMA symposium 6
Beam Quality : M2
M2 =1 : Diffraction-Limited (TEM00)
M2 = D0/ d0
2003-Feb-07 The 3rd TAMA symposium 7
Thermal Effects
Energy which is stored in the laser medium causes…Thermal Lens
Thermal Birefringence
Thermal lens affects
stability of the laser cavity
2003-Feb-07 The 3rd TAMA symposium 8
Strategy forHigh Power Laser
Two points: Give gain to the lowest-order mode Give loss to higher-order modes
How to design the laser cavity? Clip higher-order modes with rod hard aperture
→ Long cavity Stable cavity by use of thermal lens → Flat mirrors
2003-Feb-07 The 3rd TAMA symposium 9
Strong thermal lens/Too long cavity
Long cavity
Rd
Flat mirrors + Thermal lens
Cavity Modes
Laser MediumOC HRunstable
Rd
Laser MediumOC HR
2003-Feb-07 The 3rd TAMA symposium 10
My Experiment
Design of Optimum Laser CavityTransverse mode controlMake use of thermal lensLaser module
Specification : 35W Output @ 25A LD Current
( Short cavity / Multi transverse mode oscillation )
2003-Feb-07 The 3rd TAMA symposium 11
Laser Module
Cutting Edge Optronics Nd:YAG Rod (2mm diameter, 63mm lengt
h)0.6% Nd3+ dopedLD pumped Water-cooled
2003-Feb-07 The 3rd TAMA symposium 12
Thermal Lens
Measurement of the Focal Length
2003-Feb-07 The 3rd TAMA symposium 13
Linear Cavity(L 1 , L 2 ) Cavity and Mode Simulation
2003-Feb-07 The 3rd TAMA symposium 14
Power vsOC Transmittance
Laser Output→“Loss” of the cavityOptimum coupling
2003-Feb-07 The 3rd TAMA symposium 15
Power vsOC Transmittance
2003-Feb-07 The 3rd TAMA symposium 16
Power vs Cavity Length
Short cavity→Multi transverse mode
Long cavity→Causes loss for TEM00
2003-Feb-07 The 3rd TAMA symposium 17
Power vs Cavity Length
2003-Feb-07 The 3rd TAMA symposium 18
M2 = 1.1 (Horizontal)
M2 = 1.2 (Vertical)
Flat mirrors
Long cavity ( 71cm )Output Power 30W
Optimum Laser Cavity
TEM00
2003-Feb-07 The 3rd TAMA symposium 19
TEM00 ・ 30W Laser
2003-Feb-07 The 3rd TAMA symposium 20
Ring Cavity
Traveling-wave cavity
Bi-directional output(3 W / path )
2003-Feb-07 The 3rd TAMA symposium 21
Summary
Measure the thermal effects
Succeeded in controlling transverse modes
TEM00 30W laser output with linear cavity
Bi-directional lasing with ring cavity
2003-Feb-07 The 3rd TAMA symposium 22
Further Work
Thermal birefringence compensation Insert a QWP in the laser cavity
Injection lockingControl the laser cavityMeasure the noise characteristics
New laser head has arrived!!
2003-Feb-07 The 3rd TAMA symposium 23
CIDER
Close-coupled Internal Diffusive Exciting Reflector60W ・ TEM00 (M2 = 1.07)
2003-Feb-07 The 3rd TAMA symposium 24
Thermal Birefringence
Image of the thermal birefringence
20.3A 25.4APumpingPower
Image
2003-Feb-07 The 3rd TAMA symposium 25
Further Work II
Cascade Laser Cavity
MOPA
Coherent Addition
Injection-locking Chain
2003-Feb-07 The 3rd TAMA symposium 26
Laser Development
My Work
+Stable,
High Quality
M2<1.1 100W