Rupak Changkakoti

High-energy and high-peak-power nanosecond pulse generation with beam quality control in 200-μm core highly multimode Yb-doped fiber amplifiers

We explored high-energy and high-peak-power pulse generation in large-core multimode fiber amplifiers, achieving what is to our knowledge the highest reported energies, up to 82 mJ for 500-ns pulses, 27 mJ for 50-ns pulses, and 2.4-MW peak power for 4-ns pulses at 1064 nm, using 200-microm-diameter and 0.062-N.A. core Yb-doped double-clad fiber amplifiers. The highly multimode nature of the fiber core was mitigated by use of a coiling-induced mode-filtering effect to yield a significant improvement in output-beam quality from M2 = 25 from an uncoiled fiber to M2 = 6.5 from a properly coiled fiber, with the corresponding reduction in number of propagating transverse modes from > or = 200 to < or = 20.

Extreme energy pulsed fiber lasers

In this paper, we experimentally explored high energy and high peak power pulse generation in very large core multimode fiber amplifiers, achieving the highest ever reported energies of up to 82-mJ for 500-ns pulses, of up to 27-mJ for 50-ns pulses, and of up to 2.4-MW peak power for 4-ns long pulses at 1064 nm5. Fiber core sizes used in these studies ranged from 50-mum up to 200-mum, just above the single-transverse mode operation achievable with low-NA fibers with core diameters of up to ~50mum. Highly multimode nature of these very large core fibers was mitigated by using coiling-induced mode-filtering effect

High average power generation of single-transverse mode MW-peak power pulses using 80-μm core Yb-doped LMA fibers

Diffraction-limited nanosecond pulse generation with MW-peak powers and multi-mJ-energies has been explored using 80-mum core Yb-doped fibers, demonstrating 1-MW peak power pulses with 85-W of average power at 100-kHz and 1.56-MW peak at 50-Hz.

High peak power amplification: real limits on pulsed generation in optical fibers

Studies of multi-millijoule pulse generation revealed ultimate peak-power generation limits set by bulk damage and self-focusing in large-core fibers. Ultrashort pulse or narrow-linewidth amplification is more stringently limited by Raman and Brillouin scattering, and self-phase-modulation.