Abstract: A system and method for controlling polarization in a fiber amplifier is disclosed. A polarization dither waveform is applied to a polarization controller so that dithering does not trigger PI-HOMI (Polarization-Induced High Order Mode Instability). The dither waveform may have a period that is much less than the thermal diffusion time across the fiber amplifier core. The dither waveform may also have a slew rate (defined in degrees/second on the Poincaré sphere) that is much slower than the thermal diffusion time across the fiber amplifier core.

Abstract: A high power laser system is provided having a master oscillator for generating a reference laser beam of desired beam quality, means for dividing the reference beam into multiple sub-beams, a multi-slab gain module positioned to receive the multiple sub-beams as input beams, and means for adjusting the sub-beams in phase to allow the output sub-beams to be coherently combined as a single composite output beam. Optionally, additional multi-slab gain modules similar to the first multi-slab gain module may be positioned to receive amplified output sub-beams from the first multi-slab gain module. The additional multi-slab gain modules generate further amplified output sub-beams of high aggregate power.

Abstract: An optical beam combiner and a related method for its operation, in which multiple coherent input beams are directed onto a diffractive optical element (DOE) along directions corresponding to diffraction orders of the DOE, such that the DOE generates a single output beam in a direction corresponding to a desired diffraction order, and suppresses outputs in directions corresponding to unwanted diffraction orders. The phases of the input beams are actively controlled to ensure and maintain the condition that only a single diffraction mode is present in the output of the DOE.

Abstract: A fiber laser system and a related method for its use, in which one or more fiber laser amplifiers are cryogenically cooled and optimized to operate at a desirably high efficiency. Versions of the laser system using either thulium or erbium doped fibers are disclosed. In a high power version of the system, the outputs of multiple fiber lasers are coherently combined. Cooling by a selected liquefied gas, such as nitrogen, is applied to the fiber laser amplifiers and, optionally, to pump diodes and to optical elements used to combine the outputs of the fiber laser amplifiers.

Abstract: A method for combining beams from multiple laser emitters, which may be optical fibers or bulk amplifiers, to form a composite output beam with desirable beam characteristics, as measured, for example, by Strehl ratio. Beams from the multiple emitters are interferometrically combined in the near field, and the phases of the beams are controlled to provide optimal phase coherence, and thereby to minimize losses. Various techniques are disclosed for controlling the phase angles of the emitted beams, using either a separate phase detector for each emitter beam, or a single detector for the composite output beam, or nulling detectors in spurious outputs from the beam combining optics. All of these techniques achieve an improvement in Strehl, largely because the interferometric combination of beams is independent of the array fill factor.

Abstract: A technique for suppressing stimulated Brillouin scattering (SBS) in fibers intended to handle high powers. A fiber is embedded in an elongated embedding material to form an embedded fiber structure. The embedded fiber structure is formed either as a cantilevered beam or as one or more turns around a circular or elliptical path, and then the entire structure is deformed to apply a desired strain that varies along the fiber length and results in suppression of SBS. In one embodiment, the embedded fiber structure is deformed by applying lateral and generally diametric force across the turns of the structure, resulting in changes to its curvature. In another embodiment the embedded fiber structure initially has a helical shape, which is deformed by stretching or twisting to change its radius. In either embodiment, a desired strain profile is obtained by selecting the position of the fiber with respect to a neutral axis.

Abstract: A solid state laser amplifier architecture in which multiple zig-zag slab laser amplifiers (50) are stacked together, side-pumped using a common pump source (52, 54), and cooled with a common cooling system. The stack of zig-zag slabs (50) produces an array of sub-beams (62) that can be combined coherently into a single composite output beam. Variations in pump power absorption through the stack are mitigated by selection of doping levels for the slabs (50). The composite output beam is sufficiently symmetrical to be directed through conventional optics of circular cross section. Multiple stacks may be arranged in a two-dimensional array to obtain even higher output powers.

Abstract: A solid state zig-zag slab laser amplifier in which depolarization occurring at total internal reflection from opposed lateral faces of the amplifier slab is controlled by selecting a complex evanescent coating that provides a selected phase retardance that results in minimization of depolarization. Without use of the complex coating, small changes in incidence angles can result in phase retardance changes large enough to increase depolarization significantly, especially when the amplifier is operated at higher powers. Appropriate selection of the complex evanescent coating allows a desired phase retardance angle to be maintained relatively constant over a small range of angles of incidence, at a given wavelength, and therefore permits minimization of depolarization and birefringence effects.

Abstract: A laser array architecture scalable to very high powers by closely stacking fiber amplifiers, but in which the output wavelength is selectable to be in the visible or ultraviolet region, without being restricted by the wavelengths usually inherent in the choice of fiber materials. A pump signal at a fundamental frequency is amplified in the fiber amplifier array and input to an array of nonlinear crystals that function as harmonic generators, producing an output array at a desired harmonic of the fundamental frequency. A phase detection and correction system maintains the array of outputs in phase coherency, resulting in a high power output with high beam quality, at the desired frequency. The array of nonlinear crystals may a single array to produce a second harmonic output frequency, or a combination of multiple cascaded arrays configured to produce a selected higher order harmonic frequency.

Abstract: A laser array architecture scalable to very high powers by fiber amplifiers, but in which the output wavelength is selectable, and not restricted by the wavelengths usually inherent in the choice of fiber materials. A pump beam at a first frequency is amplified in the fiber amplifier array and is mixed with a secondary beam at a second frequency to yield a frequency difference signal from each of an array of optical parametric amplifiers. A phase detection and correction system maintains the array of outputs from the amplifiers in phase coherency, resulting in a high power output at the desired wavelength. A degenerate form of the architecture is disclosed in an alternate embodiment, and a third embodiment employs dual wavelength fiber amplifiers to obtain an output at a desired difference frequency.