Picosecond Crystal Fiber Amplifier for High Average and Peak Power Compact Lasers with Diffraction Limited Output

For generating <;1 ns diffraction limited laser pulses, at a kilohertz repetition rate in the recent decade a significant amount of effort was focused on the development of compact passively Q-switched microchip lasers [1-2]. However, they have significant drawbacks - the output energies are typically in the range of few to hundred microjoules, which is not enough to reach saturation of the amplification in a Nd/Yb power amplifiers, required for efficient extraction of the stored energy. Hence, a pre-amplifier must be employed in order to boost the oscillator pulse energy to the few milijoules [3]. Good candidates of such preamplifier, are thin rods amplifiers (diam. ~1mm) based on pulled YAG single crystal fibers [4] or mechanically fabricated YAG rods [5]. In most of the proposed amplifiers, the studies ware focused on configurations ensuring maximum output average power until the output beam polarization is not taken into account even though the Nd:YAG crystal possesses a thermally induced depolarization of the laser beam passed through it.