An ultrastable laser system is based on a polarization-maintaining optical fiber. The ultrastable laser system comprises a laser device; acousto-optic modulators, a first beam splitter, a polarizer, an optical fiber interferometer comprising a second beam splitter, an optical fiber delay line, a third acousto-optic modulator, and a beam combiner; a beam combiner, a polarization beam splitter, photoelectric detectors, a frequency synthesizer, frequency mixers, a servo feedback circuit and a piezoelectric ceramic. The temperature interference is eliminated based on the characteristic that refractive indexes of a fast axis and a slow axis of the polarization-maintaining optical fiber differently change with a temperature, a vacuum structure can be avoided, and the ultrastable laser system has low cost, small system, simple structure and high signal stability.

A laser apparatus includes: an oscillator configured to output seed light; an amplifier including a laser chamber provided in an optical path of the seed light and a pair of discharge electrodes provided inside the laser chamber; and a transform optical system provided in the optical path of the seed light between the oscillator and the amplifier and configured to transform the seed light in a way that suppresses a decrease in purity of polarization of a laser beam that is outputted from the amplifier.

A coherent fiber array laser power projection system scalable to large number of subapertures and includes sensors that produce signals dependent upon beam characteristics, and controllers configured to control beam characteristics to achieve either phasing of outgoing beams at transmitter plane or coherent beam combining at a remote target or both.

A method is presented for mitigation of thermal depolarization in laser systems, which uses a spatially variable 180 degree phase retarder to transition the native uniformly linear polarization of the laser to a spatially dependent polarization pattern which matches the birefringence of the gain media prior to the beam encountering the gain media. A second phase retarder converts the polarization back to uniform linear after the beam exits the gain media. The invention includes two phase retarder apparatus which consist of nano-structured, meta-surfaces etched into a monolithic glass optic. The meta-surfaces are designed to provide the required phase retardance pattern as well as an anti-reflective property negating the need for additional coatings and increasing the power handling capability of the optic.