We report a passively Q-switched all-fiber laser using a large mode area Yb3+-doped fiber cladding-pumped at 915 nm and an unpumped single-mode Yb3+-doped saturable absorber fiber. 60 μJ 80 ns pulses at 1030 nm are reported.

We report a passively Q-switched all-fiber laser using a large mode area (LMA) Yb3+-doped fiber cladding-pumped at 915 nm and an unpumped single-mode Yb3+-doped fiber as the saturable absorber (SA). The saturable absorber and gain fibers were first coupled with a free-space telescope to better study the composite system, and then fusion spliced with fiber tapers to match the mode field diameters. ASE generated in the LMA gain fiber preferentially bleaches the SA fiber before depleting the gain, thereby causing the SA fiber to act as a passive saturable absorber. Using this scheme we first demonstrate a Q-switched oscillator with 40 mu J 79 ns pulses at 1026 nm using a free-space taper, and show that pulses can be generated from 1020 nm to 1040 nm. We scale the pulse energy to 0.40 mJ using an Yb3+-doped cladding pumped fiber amplifier. Experimental studies in which the saturable absorber length, pump times, and wavelengths are independently varied reveal the impact of these parameters on laser performance. Finally, we demonstrate 60 mu J 81 ns pulses at 1030 nm in an all fiber architecture using tapered mode field adaptors to match the mode filed diameters of the gain and SA fibers.

Sandia National Laboratories' program in high-power fiber lasers has emphasized development of enabling technologies for power scaling and gaining a quantitative understanding of fundamental limits, particularly for high-peak-power, pulsed fiber sources. This paper provides an overview of the program, which includes: (1) power scaling of diffraction-limited fiber amplifiers by bend-loss-induced mode filtering to produce >1 MW peak power and >1 mJ pulse energy with a practical system architecture; (2) demonstration of a widely tunable repetition rate (7.1-27 kHz) while maintaining constant pulse duration and pulse energy, linear output polarization, diffraction-limited beam quality, and <1% pulse-energy fluctuations; (3) development of microlaser seed sources optimized for efficient energy extraction; (4) high-fidelity, three-dimensional, time-dependent modeling of fiber amplifiers, including nonlinear processes; (5) quantitative assessment of the limiting effects of four-wave mixing and self-focusing on fiber-amplifier performance; (6) nonlinear frequency conversion to efficiently generate mid-infrared through deep-ultraviolet radiation; (7) direct diodebar pumping of a fiber laser using embedded-mirror side pumping, which provides 2.0x higher efficiency and much more compact packaging than traditional approaches employing formatted, fiber-coupled diode bars; and (8) fundamental studies of materials properties, including optical damage, photodarkening, and gamma-radiation-induced darkening.