Diffraction-limited, 300-kW peak-power pulses from a coiled multimode fiber amplifier

Abstract

We report a multimode, double-clad, Yb-doped fiber amplifier that produces diffraction-limited, 0.8-ns pulses with energies of 255 muJ and peak powers in excess of 300 kW at a repetition rate of ~8 kHz . Single-transverse-mode operation was obtained by bend-loss-induced mode filtering of the gain fiber.

Efficient second, third, fourth, and fifth harmonic generation of a Yb-doped fiber amplifier

“…The threshold power for the onset of nonlinear birefringence corresponds to a polarization beat length of 25 cm [15], a reasonable value for commercial fiber [17]. This effect would be eliminated by the use of polarization-maintaining DC fiber [18], allowing even higher peak powers [12] and conversion efficiencies to be obtained.…”

“…We used a different seed laser than that described in [12]. For the present experiment, the fiber amplifier was seeded with the 1064 nm output of a passively Q-switched Nd:YAG microchip laser (Poly-Scientific), which was pumped by an 808 nm diode laser.…”

“…The input and output facets were fusion spliced to fused-silica beam expanders to prevent optical damage, and both ends were angle-polished at 8°to eliminate feedback. The amplifier produced diffraction-limited output pulses with a temporal profile identical to that of the seed laser [12]. Half-wave plates were used to adjust the polarization of the seed beam and the amplifier output in order to provide linearly polarized light of the correct orientation for the nonlinear crystals.…”

“…Fiber-based systems have not been widely used for visible and UV generation, however, because of their relatively low pulse energies and peak powers (in comparison to bulk lasers) and consequent low nonlinear conversion efficiency. In the past several years, techniques have been developed for significantly increasing the pulse energy and peak power of fiber sources [7][8][9][10][11][12], opening up the possibility of efficient nonlinear frequency conversion throughout the visible and UV spectral regions using standard nonlinear crystals. In this paper, we report generation of the second, third, fourth, and 15 fifth harmonics of a high-pulse-energy, Yb-doped, double-clad (DC) fiber amplifier seeded by a pulsed Nd:YAG microchip laser.…”

“…1 shows a schematic diagram of the apparatus. The fiber amplifier was similar to that described in [12]. In this system, high pulse energies and peak powers were enabled by the use of multimode gain fiber, but diffraction-limited beam quality was obtained by coiling of the fiber to suppress propagation of transverse modes other than the fundamental mode (LP 01 ) [13].…”