Present status of the laser system for KAGRA Univ. of Tokyo Mio Lab. Photon Science Center SUZUKI,...

Present status of the laser system for KAGRA

Univ. of Tokyo Mio Lab.

Photon Science Center

SUZUKI, Ken-ichiro

2014/06/20 6th KAGRA Workshop 2

Outline

• Laser system– Fiber laser amplifier– Coherent addition

• Previous work

• Present status

• Summary & Future work


Laser System & Requirements

• MOPA (Fiber and Solid-state laser amplifiers) + Coherent Addition

Nd:YAG NPRO400mW

40W

80W180W

Fiber laser amplifiers

Solid-state laser amplifiers

Coherent addition on the beam splitter

40W

Requirements・ Laser power 180W・ Single frequency 1064nmSingle transverse mode TEM00

・ Linear polarization・ Low intensity noise・ Low frequency noise

Setup

• Widen dynamic range – Fiber stretchers• Same path length – good spatial mode matching

• Change water chiller

HWP HWPIsolator

15MHz

EOM

Nd:YAG NPRO400mW

Fiberstretcher

CollimatorFiber amplifier

Photo detector

MixerServo

Optical fiber system Free space optical system

Beam splitter

output

+ -

Previous work

78.9W was observed from two 40-W incident beams


Optical System – fiber system

Fiber amplifiers

Seed laser (NPRO 400mW)

Fiber componentsIsolatorcouplerEOMstretcher

Power supply for NPRO

19 inch rack mounted


Optical System – addition stageCollimators(Fiber amp. output) Isolators Beam splitter

Bright port

Dark port

Dark port optical system


Experimental Result – long term operation

• Operation itself lasted 5 hours (Output power: 77 ～ 78W)

• The fiber stretchers had enough margin of control

• Large power fluctuation was observed for the first one hour

• Further brush-up is needed

0

10

20

30

40

50

60

70

80

0 1 2 3 4 5 6

Pow

er[W

]

Time[hour]

Bright portDark port

-15

-10

-5

0

5

10

15

0 1 2 3 4 5 6

Vol

tage

[V]

Time[hour]

Stretcher1Stretcher2

Stable operation

output power of bright and dark port applied voltage of the fiber stretchers

Experiment Result – polarization fluctuation

• Power fluctuation results from polarization fluctuation

• Isolator is polarization dependent

• Polarization stability is important for power stability

0

5

10

15

20

25

30

35

40

0 0.05 0.1 0.15 0.2

Pow

er[W

]

Time[hour]

transmitted powercut off power

Collimator

HWP IsolatorTransmitted power

Cut off power

an example of power fluctuation

Experiment Result – fiber stretcher


NPRO

Polarization rotation was seen at fiber stretcher.This may causes power fluctuation.

Fiber stretcher

Oscillo scope

PD

oscillator

Signal: 10Vp-p @100Hz

Setup


Next Step – solid amplifier stage

• Use three Mitsubishi laser amplifiers

• Strong thermal lensing ( ～ 50cm/rod)

• Amplification of up to 180W is expected.

180W

Three solid-state laser amplifiers

80W


Summary & Future work

• Coherent addition in new system was done

• Operation lasted 5 hours

• Longer operational term can be expected

• Control system worked well

• Noise evaluation of coherent addition

• Solid amplifier stage ( ～ 180W)

• Stabilization of intensity and frequency

Present status of the laser system for KAGRA Univ. of Tokyo Mio Lab. Photon Science Center SUZUKI,...

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