Kevin F. Wall

Tm-Doped Fiber Lasers: Fundamentals and Power Scaling

We describe fundamental measurements of the properties of thulium (Tm)-doped silica and power scaling studies of fiber lasers based on the material. Data on the high-lying Tm:silica energy levels, the first taken to our knowledge, indicate that pumping at 790 nm is unlikely to lead to fiber darkening via multiphoton excitation. Measurement of the cross-relaxation dynamics produces an estimate that, at the doping levels used, as much as 80% of the decay of the Tm level pumped is due to cross relaxation. Using a fiber having a 25-mum-diameter, 0.08 numerical aperture (NA) core, we observed fiber laser efficiencies as high as 64.5% and output powers of 300 W (around 2040 nm) for 500 W of launched pump power, with a nearly diffraction-limited beam. At these efficiencies, the cross-relaxation process was producing 1.8 laser photons per pump photon. We generated 885 W from a multimode laser using a 35-mum, 0.2-NA core fiber and set a new record for Tm-doped fiber laser continuous-wave power.

Review of Multipass Slab Laser Systems

The multipass slab (MPS) solid-state laser design is a diode-laser, side-pumped configuration that combines high efficiency with high beam quality. Because of a relatively low volumetric thermal loading, the MPS configuration can be used with a wide variety of laser crystals to operate at relatively high powers, and in this paper, we review the MPS lasers based on the materials Nd:YLF, Nd:YVO, Tm:YLF, Er:YLF, Yb:S-FAP, and Cr:LiSAF.

A CW side-pumped Tm:YLF laser

We report on a broadly tunable (1905 - 2067 nm) diode-pumped Tm: YLF laser producing cw output powers of >18 W (37% slope efficiency) in multimode operation and 12 W in the TEM00 mode.

A quasi-continuous-wave deep ultraviolet laser source

We have developed a quasi-CW, deep ultraviolet source producing >250 mW of 205-nm radiation. The source consists of a 100-MHz, mode-locked, 15-W, 1047-nm master-oscillator/power-amplifier, a synchronously pumped optical parametric oscillator, and three nonlinear conversion stages.

Diode-pumped, High-Power CW and Modelocked Nd:YLF Lasers

Using a side-pumped, Nd:YLF slab laser design, we have obtained a TEM00- mode output power of 25.7 W with 43.5% optical efficiency and a multimode output of nearly 36 W with 46% efficiency. As an amplifier of a SESAM-mode-locked laser, the same design has allowed us to generate, with 4.5-ps pulses at a 100-MHz rate, 15.7 W of average power in the fundamental and 2.9 W of power at the fourth harmonic.

Passively Q-Switched Nd:YLF Laser in a D-rod configuration

We have developed a compact, efficient, passively Q-switched, solid-state-laser, producing 7-mJ, < 10 ns pulses, and a near TEM00 beam. The cross section of the laser crystal was D-shaped and it was side pumped.

A Diode-Pumped, Q-Switched, Nd:YLF Laser Using a Prismatic Pump Cavity

We report an energy of 110 mJ per pulse from a diode-pumped, double-pulse, Q-switched, conduction-cooled, 1053-nm, Nd:YLF laser designed for space-based applications. We obtained a slope efficiency of 23% and used heat pipes for laser-head cooling.

Yb:S-FAP Multipass Side-Pumped Amplifier

We report a diode side-pumped, single-stage, multi-pass Yb:S-FAP amplifier designed to achieve high pump brightness, uniform absorption, and high amplification. We demonstrate highly efficient operation of the amplifier with an input signal from a Nd:YLF oscillator.

A 40-W, Single-Frequency, Nd:YLF Master Oscillator/Power Amplifier System

We report on the operation of a high beam quality (M2 < 1.2), 40-W, single-frequency, Q-switched Nd:YLF master-oscillator/power-amplifier system based upon transversely-pumped Nd:YLF gain modules.

High-power, short-pulse, compact SLR2000 laser transmitter

This paper reports on the design and performance of a satellite-ranging transmitter consisting of a Cr:YAG passively Q-switched Nd:YAG microlaser and an air-cooled Nd:YVO4 power amplifier, generating 235-µJ, 270-ps pulses at a 2-kHz rate.