Development of high-power
and stable laser
for gravitational wave
detection
Mio Laboratory
Kohei Takeno
Aims of My Work
Current Status
Final Goal
Nd:YAG （1.064mm）
 Output Power＞100W
 Single Transverse Mode
 Single Longitudinal Mode
 Low Intensity Noise
 Low Frequency Noise
 Linearly Polarized

2003-Feb-07
The 3rd TAMA symposium
Nd:YAG
 30W
 TEM00
 Injection lock
 ？
 ？
 ×

2
Laser Cavity
Optimum Coupling
Mode / Thermal Effects
OC
Pump
HR
Rd
Output
2003-Feb-07
Laser Medium
The 3rd TAMA symposium
3
Mode
Transverse Mode : Spatial Distribution

Multi-mode oscillation depends on the
mode of the laser cavity
Succeeded in controlling!
Longitudinal Mode : Frequency Difference

The spatial hole burning causes multi-mode
oscillation
In progress now
2003-Feb-07
The 3rd TAMA symposium
4
Transverse Mode
Lowest Order
TEM00
Higher Order
TEM10
Higher order modes spread compared to the lowest
2003-Feb-07
The 3rd TAMA symposium
5
Beam
2
Quality：M
M2 =1 : Diffraction-Limited (TEM00)
M2 = D0Q / d0q
2003-Feb-07
The 3rd TAMA symposium
6
Thermal Effects
Energy which is stored in the laser
medium causes…
 Thermal
Lens
Thermal lens affects
stability of the laser cavity
 Thermal
2003-Feb-07
Birefringence
The 3rd TAMA symposium
7
Strategy for
High 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
8
Cavity Modes
Flat mirrors + Thermal lens
Long cavity
Strong thermal lens/Too long cavity
OC
Laser Medium
unstable
HR
Rd
2003-Feb-07
The 3rd TAMA symposium
9
My Experiment
Design of Optimum Laser Cavity
Transverse mode control
 Make use of thermal lens
 Laser module


2003-Feb-07
Specification：35W Output @ 25A LD Current
（Short cavity / Multi transverse mode
oscillation）
The 3rd TAMA symposium
10
Laser Module
Cutting Edge Optronics
Nd:YAG Rod (2mm diameter, 63mm
length)
3+
 0.6% Nd doped
 LD pumped
 Water-cooled

2003-Feb-07
The 3rd TAMA symposium
11
Thermal Lens
Measurement of the Focal Length
2003-Feb-07
The 3rd TAMA symposium
12
Linear Cavity
(L１, L２ ) Cavity and Mode Simulation
2003-Feb-07
The 3rd TAMA symposium
13
Power vs
OC Transmittance
Laser Output→“Loss” of the cavity

Optimum coupling
2003-Feb-07
The 3rd TAMA symposium
14
Power vs
OC Transmittance
2003-Feb-07
The 3rd TAMA symposium
15
Power vs Cavity Length
Short cavity→Multi transverse mode
Long cavity→Causes loss for TEM00
2003-Feb-07
The 3rd TAMA symposium
16
Power vs Cavity Length
2003-Feb-07
The 3rd TAMA symposium
17
Optimum Laser Cavity
Flat mirrors
Long cavity（71cm）
Output Power 30W
M2 ＝1.1 (Horizontal)
M2 ＝1.2 (Vertical)
TEM00
2003-Feb-07
The 3rd TAMA symposium
18
TEM00 ・30W Laser
2003-Feb-07
The 3rd TAMA symposium
19
Ring Cavity
Traveling-wave cavity
Bi-directional output
（３W / path）
2003-Feb-07
The 3rd TAMA symposium
20
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
21
Further Work
Thermal birefringence compensation

Insert a QWP in the laser cavity
Injection locking
Control the laser cavity
 Measure the noise characteristics

New laser head has arrived!!
2003-Feb-07
The 3rd TAMA symposium
22
CIDER
Close-coupled Internal Diffusive
Exciting Reflector

60W・TEM00 (M2 = 1.07)
2003-Feb-07
The 3rd TAMA symposium
23
Thermal Birefringence
Image of the thermal birefringence
Image
Pumping
Power
2003-Feb-07
20.3A
25.4A
The 3rd TAMA symposium
24
Further Work II
Cascade Laser Cavity
MOPA
Coherent Addition
Injection-locking Chain
2003-Feb-07
The 3rd TAMA symposium
25
Laser Development
My Work
M2<1.1
100W
+
Stable,
High Quality
2003-Feb-07
The 3rd TAMA symposium
26

Undulators to Free Electron Lasers

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