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