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.

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
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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
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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
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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
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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)
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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)
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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
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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
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9. • Pulse duration 10ns, rep rate 350kHz
• Near diffraction limited output M2 = 1.24
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10. • 1064nm central wavelength, 0.8 nm spectral width
• No sign of SBS or SRS
• Moderate spectral broadening
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11. • Stable 50W output at 50kHz-50MHz pulse repetition rates
• Pulse durations 2.5ns-200ns
• Pulse energies up to 1mJ at 50kHz rep rate
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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
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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
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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
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