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High-power and high-stable Yb fiber laser for KAGRA

High-power and high-stable Yb fiber laser for KAGRA. Department of Physics Korea University. Jeongmin Lee, Gwang Hoon Jang and Tai Hyun Yoon thyoon@korea.ac.kr. 2 nd Korea-Japan Workshp on KAGRA May 29, 2012, ICRR, Japan. Laser Physics Laboratory. KAGRA Input Optics.

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High-power and high-stable Yb fiber laser for KAGRA

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  1. High-power and high-stable Yb fiber laser for KAGRA Department of Physics Korea University Jeongmin Lee, GwangHoon Jang and Tai Hyun Yoon thyoon@korea.ac.kr 2nd Korea-Japan Workshp on KAGRA May 29, 2012, ICRR, Japan Laser Physics Laboratory

  2. KAGRA Input Optics Isolator for backward light Mode Cleaner ETMy Pre Mode Cleaner Intensity stabilization ITMy PRM PR2 Laser ITMx ETMx BS PR3 SR2 Mode matching Alignment Modulator SR3 AOM SRM Beam shutter Variable attenuator EOPM AOM Laser AOM Laser Reference Cavity Mode cleaning Phase lock

  3. KGWG-LCGT Laser Experiments • Master laserfrequency stabilization: frequency stabilization of NPRO with a fiber ring cavity • High power Yb fiber laser & amplifier • Optical frequency comb metrology: Absolute long distance measurement

  4. Fiber ring cavity for laserfrequency stabilization r = coupler insertion loss k = coupling coefficient a = splice loss α = fiber loss per unit length L = length of the fiber ring resonator n = refractive index in the fiber core Ei Et Er E1 E3 - 2×2 fiber coupler E1 E3 coupler - Fabry-Perot cavity 1 3 E2 E4 Ei 2 4 coupler E4 E2 Er - Fiber ring cavity splice - Fiber ring cavity E. Her and T. H. Yoon, MOC 2011

  5. High Finesse fiber ring cavity for laser frequency stabilization: F = 1000 (b) (a) Thermistor Input Coupler Insulated package TEC Output Coupler Thermistor TEC Thermal insulator (c) Cavity Optical fiber protection sleeve Acrylic cover cavity (d) Vibration isolating rubber plate Aluminum plate Rubber plate TEC

  6. Frequency stabilization of NPRO Nd:YAG laser Signal generator 2 DC voltage controller AOM 8 V → 130 MHz 0 V → 160 MHz -8 V → 190 MHz sweep in Laser driver Loop Filter AOM driver Error in FM HWP PBS BS Nd:YAG laser (λ=1064 nm) AOM Block QWP PD 2 BS BS M Temperature controller AOM : acousto-optic modulator EOM : electro-optic modulator PD : fast photo diode QWP : quarter-wave plate HWP : half-wave plate PBS : polarization beam splitter BS : beam splitter CL : collimation lens QWP CL EOM Cavity M PD Signal generator Power splitter Lock-in amp.

  7. Pound-Drever-Hall error signal Before environmental isolation, modulation frequency = 6.15 MHz S/N ratio 20 : 1 After environmental isolation, acoustic noise, temperature stabilization S/N ratio 100 : 1 Slope of central error signal: 7.92 V/MHz

  8. Short-term frequency stability Out of tuning range Allan deviation of beat frequency at 160 MHz 8×10-4 @ 1 s

  9. Chirped pulse amplifier: Ti:Sapphire Laser • In CPA systems the effect of self-phase modulation on the pulse is small. However, recompression of the amplified, stretched pulses can affected by phase modulation.

  10. Yb fiber mode-locked laser with a SESAM Chip PZT 976 nm Pump laser Multi-pulsing SESAM R = 70 ~ 90 % Single-pulsing AQWP Saturation fluence All PM fiber CFBG R= 12.5 % WDM YDF Output 1030 nm Nonlinear Reflectance of SESAM Modulation depth () = 0.10562 Non-saturation loss (Lns) = 0.0679 Saturation fluence (Fs) = 70.7 μJ/ TPA fluence (Ftp) = 7 - Self-starting mode-locking via SESAM without Q-switching operation - In-line fiber output coupler (CFBG) - All-normal-dispersion (~ 0.08 ps2) - Environmentally-stable operation (single polarization operation by controlling AQWP angle G. H. Jang and T. H. Yoon, Laser Phys. 20, 1463 (2010)) - Temperature controlled compact system (All system can be integrated within A4 size plate) Two-photon absorption regime

  11. Operation of Yb fiber mode-locked laser - Out pulse energy of Yb fiber mode-locked laser vs. Pump power - Interferometric autocorrelation output pulse Chirped Gaussian Self-starting mode-locking - Optical spectrum of Yb fiber mode-locked laser Gaussian - Self-starting mode-locking at 200 mW pump - Picosecond chirped gaussian pulse shape - Gaussian spectrum with over 20 nm width - Pulse width and spectral width is increased by increasing pulse energy

  12. Environmentally-stable operation - Measured RF spectra of Yb mode-locked fiber laser - The fundamental carrier of 186 MHz repetition frequency - Allan deviation of 186 MHz fundamental carrier - Single polarization laser operation (Polarization maintaining fiber) - Fundamental RF carrier was 186 MHz, and it’s stability is 2.8×10-11 at 1-s averaging time with phase lock circuit. - High repetition frequency achievable (210 MHz)

  13. YbOptical Frequency Comb at Korea University GPS Synthesizer

  14. Yb doped fiber amplifer PL L C M C M M DM YDF L L FCMAS M I L SL PL: 25 W, 976 nm pump laser, SL: 300 mW, 1030 nm seed laser, M: Mirror, DM: Dichroic mirror, I: Isolator, L: Lens, FCMAS: Fiber chuck multi axis stage, YDF: Ytterbium doped fiber, C: Clamp.

  15. Characteristics of single-stage18-W Yb fiber amplifier collimation lens 25 W, 976 nm Pump mirror coupling lens mirror output Double cladding Yb doped fiber collimation lens multi axis stage optical isolator dichroic mirror 300 mW, 7.7 MHz Yb fiber mode -loced laser mirror Amplified laser Pout=18 W λc=1035 nm Δλ=8.9 nm collimation lens for seed oscillator Seed laser λc=1032 nm Δλ=5.1 nm seed oscillator Pout = η (Ppump- Pth) η = 0.81 Pth= 1.83 W

  16. High power Yb-doped fiber amplifier (Y.-H. Cha, KAERI) Structure of rod-type PCF Glass support - f = 1.7 mm - No outer coating 55 or 80 cm Pump clad, air gap - f= 285 mm - NA ~ 0.6 Signal core, Yb-doped, PM - f= 100 mm, MFD = 76 mm - NA ~ 0.02 - Pump absorption@ 976 nm ~ 30 dB/m (small signal) End capped on both ends - Material: fused silica - Length: 8 mm - Diameter: 8.2 mm - AR coated

  17. Yb-fiber MOPA system Main Amplifier (Rod-PCF) DFB 20 mW, 1056 nm Allfiber set-up Easy to handle DL Master Laser NPRO Nd:YAG Absolute frequency stabilization Line-width reduction by ULE(or fiber) ring cavity LD 0.5 W LD 5 W LD 25W OI Free Space Coupling x x BPF BPF 2 m x x x x AOM O.I. O.I. BPF 3m 7m PM-SC Yb Fiber (6/125) PM-PCF Yb Fiber (40/200) PM-DC Yb Fiber (5/130) Pulse Generation & Pre-Amplifier Mid-Amplifier

  18. Main amplifier with a rod PCF For 200 W cw laser Need to activeresearch - Wavelength: 1056 nm - Repetition rate: 150 kHz - Max. amp. Power: 230 W (Ep = 1.5 mJ) - Pump absorption decreases at high-power - Max. SBS power: ~ 8 W at 230 W power - Pulse width: ~ 5 ns SBS monitor 1056 nm 5-6 W (150 kHz) Pump LD - 976 nm - 450 W F=300 mm NA: 0.22 Isolator Isolator Amplified output Lens Transmitted Pump Rod PCF (80 cm) Lens SWP SWP Lens

  19. Conclusion • We have developed mode-locked Yb fiber laser oscillator with high stability & efficiency: 200 MHz & 7.7 MHz. • Optical frequency comb generation with more than one octave is almost completed. • 18-W stretching-free amplification has been demonstrated for positively chirped dissipative soliton laser.

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