Progress in ultrafast Cr:ZnSe Lasers Evgueni Slobodtchikov, Peter Moulton
Topics Diode-pumped Cr:ZnSe femtosecond oscillator CPA Cr:ZnSe laser system with 1 GW output This work was supported by SBIR Phase II programs from AFRL and DoE
Motivation Goals: Development of a low-noise, mode-locked femtosecond laser source at 2.5 m Development of high-energy, high-peak-power femtosecond laser source at 2.5 m Some applications: High-power amplifier seeding (for oscillator) Mid-IR super-continuum generation High-harmonic generation
Ti:Sapphire of infrared, courtesy Sorokin(a) Cr:ZnSe Ti:Sapphire Crystal structure Cubic Uniaxial Thermal conductivity 18 W/m C 28 W/m C Thermooptics dn/dt 70 10-6 1/ C 12 10-6 1/ C Third order nonlinearity n 2 180 10-20 m 2 /W at 1.6 µm*) 3 10-20 m 2 /W Two-photon absorption band gap 2.83 ev ~8 ev Second-order nonlinearity very high: 30 pm/v absent Peak emission cross-section em at 0 13 10-19 cm 2 2450 nm 4.5 10-19 cm 2 780 nm Fluorescence bandwidth 1000 nm (50 THz) 300 nm (130 THz) Relative bandwidth 0 0.49 0.57 Lifetime at room temp. 6 µs 3 µs E sat = h / em 0.06 J/cm 2 0.6 J/cm 2 I sat = h / em 11 kw/cm 2 210 kw/cm 2 Direct diode pumping Yes (cw) Emerging (cw)
Pumping options for Cr 2+ -doped lasers Er:fiber Tm:YALO Tm:YAG Tm:fiber Ho:YLF InGaAsP diodes Co:MgF 2 GaSb diodes Cr:ZnS Cr:ZnSe 1200 1400 1600 1800 2000 2200 2400 2600 Wavelength, nm
Diode-pumped Cr:ZnSe femtosecond oscillator SESAM M5 M4 M1 output 4 mm xtal 50 um spot 60% abs. sapphire M3 M2 Cr 2+ :ZnSe L4 L3 L2 L1 wavelength 1550 nm 3.5 W, diode laser M1-2% T output coupler; M2 ROC=100 mm; M3 ROC=150 mm; M4 flat HR; M5 ROC=100 mm; L1-4 collimating-focusing telescope.
Photograph of oscillator in enclosure
Characterization of the laser output autocorrelation intensity, a.u. 0.025 0.02 0.015 0.01 0.005 180 fs x 1.47 0-600 -400-200 0 time, fs 200 400 600 intensity, a.u. 1.7 1.6 1.5 1.4 1.3 2425 2475 2525 2575 wavelength, nm Autocorrelation trace of 180 fs pulse Spectrum of the laser output centered at 2520 nm with 30 nm bandwidth Pave = 50 mw
RF spectra of Cr:ZnSe femtosecond lasers Output of laser pumped by cw Er:fiber-pumped Tm:fiber laser Output of laser pumped by 1550-nm diode laser
Topics Diode-pumped Cr:ZnSe femtosecond oscillator CPA Cr:ZnSe laser system with 1 GW output This work was supported by SBIR Phase II programs from AFRL and DoE
Setup of typical CPA Ti:Sapphire system SHG CW Nd:doped pump laser 5 W at 532 nm SHG Nd:doped Q-switched pump laser 5 mj, 532 nm femtosecond KLM mode-locked Ti:S laser 10-50 fs, 10 nj, 800 nm 100 MHz Pulse stretcher Ti:S regenerative amplifier 1 mj, 800 nm output 800 nm, 30-100 fs, mj-j Pulse compressor Ti:S amplifier 800 nm SHG Nd:doped Q-switched pump laser
Fiber-laser-pumped Cr:ZnSe CPA system Tm:fiber 1940-nm polarized laser Tm:fiber 1940-nm laser 40 W 2050 nm Q-switched Ho:YLF laser 4.6 W 11 mj, 20 ns pulses 1 khz PRR Cr:ZnSe 2500 nm mode-locked laser 150 fs, 2.3 nj, 100 MHz CVBG Pulse stretcher 150 fs 300 ps Cr:ZnSe regenerative amplifier gain 6 x 10 5 0.7 mj pulses 1 khz PRR 2475 nm 0.35 mj pulses 346 fs Grating pulse compressor
Ho:YLF MOPA output Ho:YLF AMP DM HR Output power 11 W L1 DM L2 OC Ho:YLF OSC DM λ/2 Repetition rate 1 khz Pulse duration 20 ns 40 W Tm:fiber laser TFP DM HR AOM L3 12 10 HR output power, W 8 6 4 2 0 10 20 30 40 pump power, W
Regenerative amplifier Ho:YLF MOPA M1 λ = 2050 nm 11 W (1kHz) M3 L2 L1 M4 Cr 2+ :ZnSe M2 l/4 M6 RTP Regenerative amplifier TFP l/2 FR TFP Seed ~300 ps 1.2 nj M2 M5 Output 0.7 mj 1.5 cm single crystal 10 round trips
Stretcher-compressor pair ps out REGEN fs out seed M M AMP out TFP CVBG λ/2 M M G2 G1 M Stretcher CVBG 150 fs -> 300 ps Compressor (ruled diffraction gratings) 300 ps -> 350 fs
CPA system photograph
CPA output characterization 0.035 0.6375 autocorrelation intensity, a.u 0.03 0.025 0.02 0.015 0.01 experiment gaussian fit 346 fs X 1.47 intensity, a.u. 0.6325 0.6275 0.6225 0.005 0.6175 0-800 -600-400 -200 0 time, fs 200 400 600 800 0.6125 2400 2450 2500 2550 wavelength, nm Autocorrelation trace of 346 fs pulse Spectrum of the CPA output centered at 2475 nm with 30 nm bandwidth
> 1 kw of Tm:fiber power output at 2045 nm MOPA output power (W) 1200 1000 800 600 400 One stage Fiber #1 One stage Fiber #2 Two stage 61.6% slope efficiency 53.2% slope efficiency 200 0 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Pump power (W)
2.05- m Ho:YLF MOPA scaling (Dergachev) Tm-pump #1 ~120 W at 1940 nm Osc/ Amp #1 Ho-stage/ Regime CW 100 Hz 500 Hz Tm-pump #2 ~120 W at 1940 nm Tm-pump #3 ~120 W at 1940 nm Amp #2 Amp #3 Osc/Amp #1 39 W 55 mj 50 mj Amp#2 76 W 110 mj 95 mj Amp#3 115 W 170 mj 140 mj Tm-fiber laser TLR-100-1940 IPG Photonics www.ipgphotonics.com Operation regime Beam Profile Output power Wavelength Polarization Linewidth CW TEMoo 120 W 1940 nm Random 2 nm
Summary We have developed a directly diode-pumped femtosecond Cr:ZnSe oscillator 180 fs pulsewidth We have built and operated the first Cr:ZnSe-based CPA system 1 GW peak power (350 fs, 0.35 mj) at a 1-kHz rate 2475 nm center wavelength Future: Improved SESAMs with broader spectral coverage Further CPA scaling with Q-switched Ho:YLF pumps