58th Fujihara seminar 1

Laser system Laser system for LCGTfor LCGT

Norikatsu Mio* and Noriaki Ohmae* and the LCGT coNorikatsu Mio* and Noriaki Ohmae* and the LCGT collaborationllaboration

*Department of Advanced Materials Science, Univers*Department of Advanced Materials Science, University of Tokyoity of Tokyo

58th Fujihara seminar 2

OutlineOutline• Power requirement for laser system

of LCGT• Design of the laser system• Development of the prototype

system– Injection locked laser– Stabilization system

• Summary

58th Fujihara seminar 3

Power requirement for laser Power requirement for laser system of LCGT system of LCGT

780 W

G=11

75 W150 W

50 %

Laser

58th Fujihara seminar 4

Laser system of LCGTLaser system of LCGT

2W

Plan of a Pre-Stabilized Laser System for LCGT

NPROFI FI

EOM

Piezoelectric transducer

PD

Slave Laser (Injection Locking)

100W

FIFI

EOM

MOPAPre-Mode Cleaner

170WWideband EOM

Frequency Stabilization

to crystal temperature (< 1 Hz)to piezoelectric transducer (1 Hz - 10 kHz)

to wideband EOM(10 kHz - 1MHz)

Intensity Stabilizationto current control

58th Fujihara seminar 5

Design conceptDesign concept• Injection-locked laser: Clean and

Stable optical mode

• Power amplifier: Easy operation, possible expansion for higher power operation

Intensity control element

Frequency control element

58th Fujihara seminar 6

Injection locked laserInjection locked laser• Master laser ：２ -W NPRO

– Innolight Mephisto• Slave ： 100-W ring laser

– Laser module ： Mitsubishi– Resonator and Controller ： U-Tokyo

58th Fujihara seminar 7

Laser module Laser module （（ MitsubishiMitsubishi ））

Two rods and rotator Diffusive reflector +LD

58th Fujihara seminar 8

100-W Injection locked laser100-W Injection locked laser

• 100 W• Continuous wave(cw)• Single frequency

~ 1kHz

• M2 ~ 1.1• Linear polarization

Innolight NPROMephisto 2000NE

FI FI

EOM

lens

HRHRHR

HR

HR,0.2mCX

85%,0.2mCX

Nd:YAG rod 　 (Side-pumped)=4mm, L=70mm

Quartz rotator

Piezoelectric transducer

PD

Slave Laser

2W

100W

2W

100W

58th Fujihara seminar 9

Output power of the slave Output power of the slave laserlaser

•１２１W by bidirectional oscillation

M 2～ 1.1

58th Fujihara seminar 10

Realization of single Realization of single frequency oscillationfrequency oscillation

• Scanning Fabry-Perot output

Free

Injection Locking

100-W Single Frequency oscillation by injection locking

58th Fujihara seminar 11

Long term stabilityLong term stability

Continuous operation for more than 6 hours

58th Fujihara seminar 12

Frequency stabilizationFrequency stabilization

100W

EOM

100-W injection-locked Nd:YAG laser

Reference cavity

0.1W

Wideband EOM(Stoichiometric LiNbO3)

To crystal temperatureTo piezoelectric transducer

OSC

Mixer

Pound-Drever-Hall technique

Old EOM (RTA)Old EOM (RTA)Special EOMSpecial EOM

(Stoichiometric LiNbO(Stoichiometric LiNbO33))

58th Fujihara seminar 13

EOM loop

Piezo loop

Bode plot of frequency controlBode plot of frequency control

“Wideband (UGF=100 kHz)” and “high-gain (170dB at 1 kHz)” control

330dB at 100Hz

170dB at 1kHz

58th Fujihara seminar 14

Intensity stabilization using Intensity stabilization using a current shunta current shunt

• Current Shunt controlMasterlaser

Amplifier

Current shunt

Currentsource

Laser Module

Opt-couplerSeparate high current circuit and small control signal circuit

58th Fujihara seminar 15

Transfer function and Transfer function and noise suppressionnoise suppression

Frequency (Hz)

gain

phase (degre

es)

gain

phase

CEO

Mitsubishi

Transfer function of Amplifier

Frequency (Hz)

RIN

(1/

Hz1

/2)

free-run

Out-of-loop

In-loop

Noise spectrumUFG=30 kHz

58th Fujihara seminar 16

SummarySummary• Basic components for the LCGT laser

have been completed.– 100-W single frequency operation has

been achieved.– Wide range frequency and intensity

control have been done.

For a real interferometer, the laser must work for 24 hours a day, 365 days a year

Further engineering work is necessary

58th Fujihara seminar 17

Thank you very much

58th Fujihara seminar 18

Frequency referenceFrequency reference

• Ring resonator– Superinvar spacer– Tunable with PZT

• FSR = 714MHz• Finesse~ 2900 （ S)

~ 220 （ P ）• Linewidth （ S ） ~ 250 kHz • Transmission~ 80%

（ P-polarization）