1. Current status of Laser development 2nd Korea - Japan Workshop on KAGRA 2012/5/28(Mon)

2. Collaboration items High power amplifier Pre-stabilization with fiber ring cavity 2

3. Current status of the collaboration To start definite collaboration, we need some financial support. Prof. Yoon submitted his proposal concerning a high-power PCF fiber amplifier to Korean government. Mio submitted his proposal to Mitsubishi foundation with Prof. Yoon. 3 We are waiting for good news!

4. Overview: Definition of Laser Subsystem Laser subsystem consists of a laser oscillator, a power supply, a tiller, control systems and monitor systems and an optical table. 4 Laser output Laser Oscillator Power supply Chiller Monitor signals Control signals Circulating cooling water DC/AC Cooling water 3  AC200V 1  AC200V 1  AC100V 3  AC200V Input Optics Clean room

5. bKagra: Target specifications ItemValue Wave length1064 nm Power180 W Oscillation modeSingle (longitudinal and transversal) PolarizationLinear Line-width< a few kHz Frequency noise at 100 Hz Frequency Control band- width >800 kHz with an external EOM Intensity noise (RIN) at 100 Hz 5

6. 6 Schematic diagram Mitsubishi laser modules Fiber laser amplifiers NPRO(500mW) 40 W 80 W 200 W The output of the NPRO is lead to two fiber amplifiers. Two outputs of the amplifiers are coherently added to obtain 80-W power. The laser light is introduced into three-stage solid-state amplifiers in order to obtain 180-W output power.

7. 7 Current Status for parts preparation Mitsubishi laser modules Fiber laser amplifiers NPRO(500mW) 40 W 80 W 200 W Power Supply Chiller All components have been obtained and will be tested. Delivery of the amplifiers is delayed because of a trouble on Faraday isolators that are set at the output fibers. FR

8. bKAGRA:Prototype test Performance of the fiber amplifier – 40-W one is being tested. Performance of the coherent addition system – The fringe contrast, phase stability and so on will be tested sonn. Performance of the laser module when used as an amplifier. – Optimization of the beam profile for obtaining the best amplification performance. – Polarization stability, noise level should be tested; not started. Fix the specifications for the control system (interfaces to a PC and other systems) – Discussion about the assembling with a company is necessary. 88

9. After the 1 st Workshop No fiber amplifiers have not been delivered to us at the first workshop. One laser system was delivered to our lab in the middle of Feburuary. We have tested its phase noise using an interferometer. 9

10. Intensity Noise 10 Relative Intensity Noise Frequency (Hz) 10-W Amplifier

11. Phase Noise Measurement 11

12. Measurement System 12 Amplified laser light Seed laser light PZT Mirror Control Circuit

13. Phase Noise 13 Phase Noise Frequency (Hz)

14. New lab@Hongo 14 We moved our lab from Kashiwa to Hongo in March. Most of our experimental systems are still in boxes.

15. Laser Development @ Hongo Phase noise measurement has been started. We decided not to use a fiber-coupled Faraday isolator. Two lasers will be available in June; a coherent addition system can be tested soon. 15

16. Summary The performance of the 40-W fiber amplifier is not so good as 10-W one; we need further investigation. Choice of fiber coupled optical devices for high power laser should be careful ; the heat due to the light loss is quite serious. 16