A passively, Q-switched laser is described. The laser may operate at an eye-safe lasing wavelength of 1.34 microns and use a gain element of Nd:YVO.sub.4 and a saturable absorber element of V:YAG with a space separating the gain element and saturable absorber element. The Q-switched laser is pumped by a grating stabilized laser diode. The laser may be used in laser ranging applications.

There is provided a laser, and/or a reflector for a laser cavity comprising: a ring resonator structure; and a Fabry-Perot filter connected in cascade to the ring resonator structure by a coupling waveguide. The coupling waveguide is configured to propagate light having a frequency corresponding to any of the resonant frequencies of the ring resonator structure to the Fabry-Perot filter, and the Fabry-Perot filter is configured to select one or more frequencies and return light having a frequency matching any of the selected frequencies to the ring resonator structure via the coupling waveguide.

A Raman fiber laser includes a pump light source, a reflective end mirror, a wavelength division multiplexer, a Raman gain fiber, and an output end mirror. The output end mirror is an ultra-low reflectance fiber Bragg grating. The reflective end mirror is connected to a reflective end of the wavelength division multiplexer. The pump light source is connected to an input end of the wavelength division multiplexer. One end of the Raman gain fiber is connected to a common end of the wavelength division multiplexer, and the other end of the Raman gain fiber is connected to the ultra-low reflectance fiber Bragg grating. The laser of the present invention can reduce loss of laser light at the reflective end mirror, thereby increasing laser light optical conversion efficiency and output power, and simultaneously achieving high time domain stability and extremely low coherence.

A passively, Q-switched laser operating at an eye safe wavelength of between 1.2 and 1.4 microns is described. The laser may operate at a lasing wavelength of 1.34 microns and use a gain element of Nd:YVO.sub.4 and a saturable absorber element of V:YAG. The position of the resonator axial mode spectrum relative to a gain peak of the gain element is controlled to yield desired characteristics in the laser output.

A dual-comb measuring system is provided. The dual comb measuring system may include a bi-directional mode-locked femtosecond laser, a high-speed rotation stage, and a fiber coupler. The high-speed rotation stage may be coupled to a pump diode.

A method and a system for measurement of high laser field intensity, the method comprising tight focusing a non-Gaussian azimuthally polarized laser mode beam to a focusing spot, measuring a spectral line shape of a selected ionization state induced by a longitudinal oscillating magnetic field created by the tight focusing in the focusing spot; and determining the laser intensity from the spectral line shape. The system comprises a laser source of a peak power in a range between 100 terawatt and 10 petawatt; a converter unit; a tight focusing optics; and spectral measurement means; wherein the converter unit polarizes a main laser beam from the laser source into a non-Gaussian azimuthally polarized laser mode beam; the tight focusing optics focuses the azimuthally polarized laser mode beam to a focusing spot, yielding a longitudinal oscillating magnetic field of an intensity proportional to the laser intensity, the spectral measurement means measuring a line shape of a selected ionization state induced by the longitudinal oscillating magnetic field in focusing spot.

A multi-wavelength laser system includes a first fiber laser having a first cavity mirror and a first output coupler, a first optical coupler configured to receive light from the first output coupler, a second fiber laser having a second cavity mirror and a second output coupler, and a second optical coupler configured to receive light from the second output coupler. The multi-wavelength laser system also includes a spectral beam combiner configured to receive first output light from the first optical coupler, receive second output light from the second optical coupler, combine the first output light and the second output light, and form a multi-wavelength output beam.

A dual-comb measuring system is provided. The dual comb measuring system may include a bi-directional mode-locked femtosecond laser, a high-speed rotation stage, and a fiber coupler. The high-speed rotation stage may be coupled to a pump diode.

A CO.sub.2 laser that generates laser-radiation in just one emission band of a CO.sub.2 gas-mixture has resonator mirrors that form an unstable resonator and at least one spectrally-selective element located on the optical axis of the resonator. The spectrally-selective element may be in the form of one or more protruding or recessed surfaces. Spectral-selectivity is enhanced by forming a stable resonator along the optical axis that includes the spectrally-selective element. The CO.sub.2 laser is tunable between emission bands by translating the spectrally-selective element along the optical axis.

An electro-optic modulator (EOM) for altering an optical path length of an optical field is described. The EOM comprises first and second Brewster-angle cut nonlinear crystals having a first and second optical axis. The optical axes are orientated relative to each other such that when an optical field propagates through the nonlinear crystals it experiences no overall deviation. The nonlinear crystals are also arranged to be opposite handed relative to the optical field. The EOM has the advantage that its optical losses are lower when compared with those EOMs known in the art. In addition, the EOM can be inserted into, or removed from, an optical system without any deviation being imparted onto the optical field. This reduces the levels of skill and effort required on the part of an operator. The described method and apparatus for mounting the nonlinear crystals also suppresses problematic piezo-electric resonances within the nonlinear crystals.