50W single-mode linearly polarized high peak power pulsed fiber laser

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We demonstrate 50W single-mode linearly polarized high peak power pulsed fiber laser with tunable ns–µs pulse durations and kHz–MHz repetition rates capable to address a wide range of applications: frequency conversion, LIDAR and others.

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50W single-mode linearly polarized high peak power pulsed fiber laser

  1. 1. 50W single-mode linearly polarized high peak power pulsed fiber laser with tunable ns-µs pulse durations and kHz-MHz repetition rates V. Khitrov*, B. Samson, D. Machewirth, K. Tankala * Presenting author www.nufern.com 1 1 www.nufern.com
  2. 2. • 10 ~ 100W linearly polarized pulsed fiber lasers have been demonstrated (IPG Photonics, Aculight, Sandia Labs and others) – 0.1~0.5mJ pulse energies, 1~10ns pulse durations – Near diffraction limited beam (M2 < 1.5) – Yb-doped large mode area (LMA) double clad fiber – Operating wavelengths 1060-1080nm – Limited set of parameters per device, typical sets • High rep rate ~1MHz, low energy <0.1mJ, high average power 50~100W • Low rep rate <50kHz, high energy ~0.5mJ, low average power ~10W • We demonstrate 50W single-mode linearly polarized high peak power pulsed fiber laser with tunable ns-µs pulse durations and kHz-MHz repetition rates capable to address a wide range of applications: frequency conversion, LIDAR and others www.nufern.com 2 2
  3. 3. PM LMA Yb-doped double clad fiber – key component Glass Cladding • Silica fiber with high optical damage threshold • 20-40μm core, low NA<0.1 for good beam quality • 200-400μm cladding, high NA~0.5 for efficient pump coupling LMA core High NA • High Yb concentrations for short fiber lengths cladding • Hi birefringence for single polarization Challenges for high power pulsed polarized fiber lasers • Nonlinear effects: SBS, SRS, Self Phase Modulation, Four Wave Mixing – limiting output power, broadening narrow spectral linewidth and destroying integrity of output spectrum • Polarization control problems – power de-coupling from fundamental linearly polarized mode to parasitic higher order modes www.nufern.com 3
  4. 4. Principal design High power isolator High Master Low power power oscillator pre-amp amplifier • Master Oscillator Power Fiber Amplifier (MOPFA) design – flexible all-fiber format • Low power semiconductor laser diode as seed source • High power PM LMA fiber based amplifier www.nufern.com 4
  5. 5. Fiber Design Coil Technique • Yb-doped LMA 30/250μm fiber • Utilizes differential bend loss of • Low core NA (0.06) fundamental and higher order modes • 0.46 NA cladding • 8 cm coil maintains single-mode linear • High birefringence (2.5x10-4) polarization operation Bend Loss at 1060 nm 1.E+03 1.E+01 1.E-01 (dB/m) Fast Pol 1.E-03 1.E-05 1.E-07 Slow Pol 1.E-09 50 100 150 200 Coil Diameter (mm) www.nufern.com 5 5
  6. 6. Choice of seed pulsed lasers • Pulsed Nd:YAG, Yb:YAG lasers • Microchip lasers • Semiconductor diode seeded multi-stage fiber amplifiers • Q-switch fiber lasers Semiconductor diode advantages • Robust PM fiber-coupled output • Flexible pulse repetition rates 10kHz-50MHz • Flexible pulse durations 2ns-10µs • Suitable output for seeding the multi-stage fiber amplifier (~0.5W peak power) www.nufern.com 6
  7. 7. S M P M Yb -dope d fib e r P M LMA Yb -dope d 30/ 0 μ fib e r 25 m 1064nm S ig na l/pump S ig na l/pump puls e d fibe r fibe r MO m ultiple xe r m ultiple xe r P M is o P M is o P M is ola tor 1064nm puls e d s ig na l 976nm pump 976nm pump 976nm pump 976nm pump • 0.5W peak power seed laser • 2-stage SM preamplifier • High power amplifier based on 3m of PM-LMA-YDF-30/250 fiber • Up to 92 W of coupled pump power (at 976nm, ~3nm line width) through signal/pump multiplexers www.nufern.com 7 7
  8. 8. • Output power increases linearly with pump power • 51 W (10ns, 350kHz) output achieved with 92 Wcoupled pump • Slope efficiency 60%, overall optical efficiency 56% • Polarization Extinction Ratio 15dB www.nufern.com 8 8
  9. 9. • Pulse duration 10ns, rep rate 350kHz • Near diffraction limited output M2 = 1.24 www.nufern.com 9 9
  10. 10. • 1064nm central wavelength, 0.8 nm spectral width • No sign of SBS or SRS • Moderate spectral broadening www.nufern.com 10
  11. 11. • Stable 50W output at 50kHz-50MHz pulse repetition rates • Pulse durations 2.5ns-200ns • Pulse energies up to 1mJ at 50kHz rep rate www.nufern.com 11
  12. 12. Pulse shapes at 200ns duration and 50kHz rep rate from MO (left) and amplifier output (right) • Strong pulse distortion (collapsing towards leading edge) at the output at low repetition rates • Due to Yb inversion depletion • Results in extremely high peak power in the beginning of the pulse causing detrimental non- linear effects like SBS, SRS, etc. • Pulse engineering applied to seed laser is required to correct pulse distortion * • >1mJ possible to achieve with corrected pulse shapes * - K.T.Vu, A.Malinowski, D.J.Richardson, F.Ghiringhelli, L.M.B.Hickey, M.N.Zervas “Adaptive pulse shape control in a diode-seeded nanosecond fiber MOPA system”, Optics Express, Vol 14, No 23, 2006, pp. 10996- 11001 www.nufern.com 12
  13. 13. 532nm power (W) 18 16 14 12 10 8 34% SHG efficiency 6 4 2 0 0 10 20 30 40 50 60 1064nm power (W) • 3x3x15mm LBO crystal operating at room temperature, single-pass SHG, ~70µm beam size • 17 W (10ns, 350kHz) output at 532nm achieved with 50W 1064nm input • 34% SHG efficiency close to 40% theoretical efficiency www.nufern.com 13
  14. 14. Summary • Demonstrated high power pulsed, monolithic fiber laser – Robust all-fiber MOPFA design – 51W average output power – 1064nm wavelength, 0.8nm linewidth – Flexible 2ns-0.2µs pulse durations, 50kHz-50MHz repetition rates, up to 1mJ pulse energy – PER = 15dB, M2 = 1.24 – 56% optical efficiency – 17W at 532nm, 34% frequency doubling efficiency limited by available crystal • Practical design to address a number of applications: frequency conversion, LIDAR and other applications www.nufern.com 14 14

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