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Spectral Beam Combining (SBC) of fiber lasers provides a simple, robust architecture for high brightness power scaling beyond the limit of a single fiber. We review recent progress in power scaling and describe what we believe is the highest power SBC fiber demonstration and largest number of fiber lasers combined to date. Here we report results on a fiber SBC system where we achieved > 30 kW by combining 96 individual fiber lasers into a single high brightness beam with a beam quality of M2 = 1.6 x 1.8. The potential for further power scaling at the system level is highlighted with examples of beam combinable fiber laser power scaling.

The transient theory of stimulated Brillouin Scattering (SBS) in optical fibers is used to investigate the effects of weak feedback of an incident broadband laser field. When the linewidth of the laser approaches the Brillouin frequency shift, a weak reflection of the laser field overlaps with the SBS gain and can be amplified in the fiber resulting in an apparent reduction in SBS threshold. We show that a reflection of 0.01% (-40 dB) of a laser field with a linewidth equal to the Brillouin shift can reduce the SBS threshold by a factor of 2. These results have implications on the design of high power fiber laser systems that utilize spectral broadening to suppress SBS.

We report a master-oscillator/power-amplifier laser system featuring a polarizing and coilable 40-micron-core Yb-doped photonic crystal fiber as the final-stage amplifier. The laser source generates 3.4 ns pulses at a repetition rate 19 kHz, with maximum pulse energy 1.2 mJ, maximum average power 22.8 W, near diffraction-limited (M 2 < 1.1) beam quality, and 20% electrical to optical efficiency in a compact package. This pulsed-fiber laser flight system provides high pulse energy, average power, peak power, diffraction limited beam quality, and high efficiency all in a thermally and mechanically stable compact package.

Spectrally Beam Combined fiber laser provide a superior architecture for power scaling laser to high power. We present experimental results where we achieved < 3 kW, M2 = 1.35 with < 39% E-O efficiency by combining 12 individual fiber lasers into a single high brightness beam.

We describe our work on Spectral Beam Combining geometries and design implementations using multilayer dielectric gratings. With appropriate designs, power scaling beyond the single fiber limit can be achieved while maintaining near diffraction limited beam quality.

We have demonstrated and characterized a Q-switched Nd:YAG laser under continuous operation for over 7 billion shots. Through periodic monitoring of the laser's vital signs, the system dynamics were decoupled to identify the sources of degradation. The initial and the final pump-laser diode wavelengths and powers were measured and compared. No evidence of an accumulative effect leading to optical damage at a fluence lower than the single-shot threshold was observed.

Simple modifications were made to a commercial microscope to enable injection of light from a diode laser, and demonstrate optical tweezers action. The basic properties of microscope optics are presented together with discussion of principles to be followed in arranging the external optics for achieving useful tweezers. Procedures using a single‐mode diode laser along with experimental results are presented in enough detail to permit readers to make their own system for trapping and manipulating single cells. It is surprisingly easy to demonstrate tweezers action once some basic concepts are understood.

Solid-state lasers have been in use for space applications since the early days of the space program. To date most of the lasers have been pulsed Nd:YAG lasers and with the development of diode laser technology as pump sources, performance improvements in lifetime, weight and efficiency have been the key drivers to enable space missions. This paper will review the lasers used on various missions and discuss their designs and performance in light of their mission requirements.

We present tests of 100 W/bar quasi-CW laser diode arrays conducted, at SDL Inc. (at various deratings with constant junction temperature) and NASA Goddard, to assist in designing lasers for use in space.

NASA's Goddard Space Flight Center is developing the Geoscience Laser Altimeter System (GLAS) employing a diode pumped, Q-switched, Nd:YAG laser operating at 40 Hz repetition rate. To meet the five-year mission lifetime goal, a single transmitter would accumulate over 6.3 billion shots. Cr 4+ :YAG is a promising candidate material for passively Q- switching the laser. Historically, the performance of saturable absorbers has degraded over long-duration usage. To measure the multi-billion shot performance of Cr 4+ :YAG, passively Q-switched GLAS-like oscillator was tested at an accelerated repetition rate of 500 Hz. The intracavity fluence was calculated to be approximately 2.5 J/cm 2 . The laser was monitored autonomously for 165 days. There was no evidence of change in the material optical properties during the 7.2 billion shot test. All observed changes in laser operation could be attributed to pump laser diode aging. This is the first demonstration of multi-billion shot exposure testing of Cr 4+ :YAG in this pulse energy regime.

We describe a narrow band (16 pm FWHM), passive, holographic 532 nm optical filter for use with frequency stabilized doubled Nd:YAG lasers.

We have demonstrated an efficient, compact, 1.5-mJ, 3.9-ns, passively Q-switched, single mode, diode pumped Nd:YAG laser using Cr4+:YAG as a saturable absorber.

We have developed a unique numerical laser model by use of a commercial physical optics software package. The experimentally measured lasing threshold, slope efficiency, power output distribution, and phase front have been derived. This model is particularly powerful for monitoring the effects caused by thermal distortions encountered in power scaling lasers. Extrapolations have been made through parametric studies to predict changes required in the laser design that would optimize the performance of the laser.

A simple, efficient diode-laser-pumped Q-switched Nd:YAG laser is described that produces 2.25-mJ, TEM(00), 4-ns pulses up to 90 Hz with only 20 mJ of pump power. The laser has a zigzag slab geometry, side pumped with only one high-power quasi-cw diode bar. This performance approaches that of longitudinal pumping, demonstrating TEM(00) mode operation with long-pulse and Q-switched slope efficiencies of 28% and 19%, respectively. Secondand fourth-harmonic efficiencies of >50% and >20% from 1064 nm without the use of external focusing optics were also demonstrated.

Optical amplification of 11 orders of magnitude in a microlens-collimated, diode-laser-pumped regenerative amplifier has been demonstrated. The amplifier was seeded with 20-ps pulses from an FM mode-locked oscillator and with 0.9-ns pulses from a modulated diode laser. Seed pulses from both sources were amplified to energies exceeding 2.5 mJ. With the thermoelectric coolers and the Pockels cell electronics neglected, the diode-seeded system exhibited an electrical-to-optical efficiency of 2.2%.