University of Tokyo

1
Development of a 100-W,single-frequency NdYAG
laser for large-scale cryogenic gravitational
wave telescope

• University of Tokyo
• Kohei Takeno, Takafumi Ozeki,
• Shigenori Moriwaki and Norikatsu Mio

2
Overview

• 101W, single-frequency oscillation of NdYAG
  laser (l 1.064mm)
• Side-pumped NdYAG rod
• Frequency-stabilized with injection locking
• Beam quality
• TEM00 (diffraction-limited)
• Linearly polarized

3
Background

• Gravitational wave detection project
• Detect tiny distortion of space-time caused by a
  gravitational wave (GW)

4
Japanese next-generation interferometer

• Large-scale cryogenic gravitational wave
  telescope (LCGT)
• Michelson interferometerwith 3-km arms
• Fabry-Perot cavityin each arm
• Power recycling technique
• RSE technique
• Will be located under the ground of Kamioka mine

Talk by K. Kuroda
5
Design sensitivity of LCGT
Target
Shot noise
6
Requirements

• Output power
• 150 W for the first phase
• Beam quality
• Single longitudinal mode
• Single transverse mode (M2 lt 1.1)
• Linearly polarized
• Noise characteristics
• Frequency noise
• Relative intensity noise

7
Optical layout

• Injection locking MOPA

8
Laser module

• LD side-pumped NdYAG rod
• Thermal birefringence compensation
• Water cooling

Made by Mitsubishi Electric Corporation
9
Slave laser

• Ring cavity with two laser modules
• 121 W in bidirectional operation
• 13- optical-to-optical efficiency

10
Slave laser

• Ring cavity with two laser modules

11
Experimental setup

• Injection locking with 2-W master laser (NPRO)
• Two Faraday isolators
• Phase modulation by an electro-optic
  modulator(Pound-Drever-Hall technique)

12
Frequency spectrum

• Single-frequency oscillation over an hour was
  achieved

Free running
Injection locked
13
Beam quality

• M2
• M2 horizontal 1.14
• M2 vertical 1.09
• Polarization ratio 221

TEM00 oscillation
Free running
Injection locked
14
Intensity noise

• Spectrum density of RIN

15
Slave laser fluctuation

• Slave cavity fluctuation estimated from the
  signal applied to the PZT actuator of the slave
  laser

Phase locking below threshold
Phase locking above threshold (injection locking)
16
Summary

• 101W, single-frequency operation of NdYAG laser
• TEM00, linearly polarized output mode
• Intensity noise in injection locking operation
  was comparable to that in linear cavity
  oscillation
• Slave cavity fluctuation was independent of laser
  oscillation

Achieved the specification required for the
injection locking part of the LCGT laser
17
Future work

• Frequency stabilization experiments
• Improve the mechanical stability
• Stabilize to a frequency reference
• Intensity stabilization experiments
• Intensity control with a current-modulated NdYAG
  amplifier
• Preliminary experiments in progress

18
Comparison to other works
Development of single-frequency NdYAG lasers
1989 Stanford (13W) CNRS (18W)
19
Comparison to other works
Development of single-frequency NdYAG lasers
1989 Stanford (13W) CNRS (18W)
1989 Stanford (13W) CNRS (18W) 1995 LZH
(20W) 2000 New Mexico (30W)
20
Comparison to other works
Development of single-frequency NdYAG lasers
1989 Stanford (13W) CNRS (18W) 1995 LZH
(20W) 2000 New Mexico (30W) 2003 Friedrich-Schill
er (MOPA,118W) 2004 LZH (87W)
1989 Stanford (13W) CNRS (18W) 1995 LZH
(20W) 2000 New Mexico (30W)
21
Comparison to other works
Development of single-frequency NdYAG lasers
1989 Stanford (13W) CNRS (18W) 1995 LZH
(20W) 2003 Friedrich-Schiller
(MOPA,118W) 2004 LZH (87W) 2005 This work
(101W) LZH (195W)
1989 Stanford (13W) CNRS (18W) 1995 LZH
(20W) 2000 New Mexico (30W) 2003 Friedrich-Schill
er (MOPA,118W) 2004 LZH (87W)