A desired N.sup.th-order Stokes output and zeroth-order Stokes pump input are seeded into a rare-earth doped amplifier where the power of the zeroth-order Stokes signal is amplified prior to both signals entering a Raman amplifier comprised of N1 Raman resonators, each uniquely tuned to one of the N1 Stokes orders, in various configurations to include one or more nested and/or in-series Raman resonators. The zeroth-order Stokes signal is converted to the N.sup.th1-order Stokes wavelength in steps and the power level of the N.sup.th-order Stokes wavelength is amplified as the two signals propagate through the Raman resonators. Each Raman resonator includes a photosensitive Raman fiber located between a pair of Bragg gratings. The linewidths of the Stokes orders can be controlled by offsetting the reflectivity bandwidths of each pair of Bragg gratings respectively located in the Raman resonators.

Modelocked fiber laser resonators may be coupled with optical amplifiers. An isolator optionally may separate the resonator from the amplifier. A reflective optical element on one end of the resonator having a relatively low reflectivity may be employed to couple light from the resonator to the amplifier. Enhanced pulse-width control may be provided with concatenated sections of both polarization-maintaining and non-polarization-maintaining fibers. Apodized fiber Bragg gratings and integrated fiber polarizers may also be included in the laser cavity to assist in linearly polarizing the output of the cavity. Very short pulses with a large optical bandwidth may be obtained by matching the dispersion value of the grating to the inverse of the dispersion of the intra-cavity fiber. Frequency comb sources may be constructed from such modelocked fiber oscillators. Low dispersion and an in-line interferometer that provides feedback may assist in controlling the frequency components output from the comb source.

A wavelength-stabilised narrow-linewidth mode-locked picosecond laser system comprises a laser cavity which includes an amplifier, a mode-locking element, and a fiber Bragg grating which acts as a narrowband reflector. The system includes a mount to which the fiber Bragg grating is mounted under tension, a tension control system to adjust the tension, and a measurement device to provide a measurement output related to a current operating wavelength of the fiber Bragg grating. A microcontroller or other controller wavelength-stabilises the laser by controlling the tension control system responsive to the measured wavelength.

The invention relates to an apparatus for generating temporally spaced apart light pulses, comprising a first laser (11) which generates a first sequence (I) of light pulses at a first repetition rate, a second laser (12) which generates a second sequence (II) of light pulses at a second repetition rate, and at least one actuating member which influences the first repetition rate and/or the second repetition rate. It is an object of the invention to provide an apparatus for generating temporally spaced apart light pulses which is improved in relation to the prior art. This object is achieved by the invention by a control element (23) which applies a periodic modulation signal (24) to the actuating member for periodic variation of the first repetition rate and/or the second repetition rate, wherein the actuating member comprises a mechanical oscillator excited by the modulation signal (24), the deflection of said oscillator causing an adjustment in the resonator length of the first laser (11) and/or second laser (12), wherein the mechanical oscillator oscillates in resonant fashion at the frequency of the modulation signal (24). In accordance with the invention, an actuator (e.g. a piezo-actuator) which adjusts the resonator length of the laser is operated in resonant fashion. As a result, a large maximum time offset of the light-pulse sequences (I, II) with, at the same time, a high scanning speed is rendered possible. Moreover, the invention relates to a method for generating temporally spaced apart light pulses.

A light source apparatus includes: a light source configured to output light; a reflection unit (spatial light modulator) having an input unit of a control signal and configured to be able to control distribution of angles at which incident light is reflected based on the control signal; and a diffraction grating configured to disperse the light output from the light source, cause the light to be incident on the spatial light modulator, and return at least a part of the light reflected by the spatial light modulator to the light source. An optical cavity is formed by the light source and the spatial light modulator, and a bandwidth of the light returned from the diffraction grating to the light source is controlled by controlling the distribution of angles of the light reflected by the spatial light modulator based on the control signal.

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 radiation field generating system comprising an optical unit with an optical assembly which defines an optical path is provided, wherein the optical unit is operable in several different operation conditions and the optical assembly comprises at least one optical switching component with which switching between at least two different operation conditions of the several operation conditions can be performed.