A method for realizing precise gain control for a hybrid fibre amplifier, and a hybrid fibre amplifier, in which by an erbium-doped fibre amplifier firstly outputting a constant power, a comparable source signal optical power is provided for a raman fibre amplifier of a next stage. A feedback for the gain control may be formed by comparing a source signal optical power calculated after starting pumping of the Raman fibre amplifier and a source signal optical power detected after pumping stops, thereby greatly improving gain control precision of the Raman fibre amplifier. Moreover, the erbium-doped fibre amplifier parts of all the hybrid fibre amplifiers may simultaneously output a constant optical power, and the Raman amplifier parts of all the hybrid fibre amplifiers may simultaneously start calibration, so that the time for starting operation of the entire system may be improved greatly.

Operating an optical frequency comb assembly includes operating an optical frequency comb source to generate laser light constituting an optical frequency comb and introducing the laser light into a common light path and seeding at least one branch light path by the laser light from the common light path, the branch light path comprising at least one optical element. For the branch light path, a phase difference of a first frequency mode ν.sub.1 of the optical frequency comb is determined between laser light coupled out at a reference point within the frequency comb assembly upstream of the at least one optical element and laser light coupled out at a measurement point provided in the branch light path downstream of the at least one optical element. Phase correction for the laser light from the branch light path is based on a deviation of the determined phase difference from a target value.

A MOPA laser system that includes a seed laser configured to output pulsed laser light, an amplifier configured to receive and amplify the pulsed laser light emitted by the seed laser; and a pump laser configured to deliver a pump laser beam to both the seed laser and the amplifier.

An apparatus for generating electromagnetic radiation includes a pump laser so adapted that in operation of the apparatus it generates electromagnetic continuous-wave pump radiation; an optical parametric oscillator which is arranged in the beam path of the pump radiation and has a non-linear optical crystal, and is so adapted that in operation of the apparatus it generates signal and idler radiation from the pump radiation, and a non-linear optical device having a non-linear optical crystal, being arranged at least in a beam path of the signal radiation or idler radiation, and being so adapted that in operation of the apparatus it generates from the signal or idler radiation electromagnetic radiation at a frequency greater than a frequency of the signal or idler radiation. The non-linear optical crystal being heated in a furnace so that the crystal has a temperature gradient in the beam direction of the signal or idler radiation.

According to the invention, a plurality of elementary laser beams (f.sub.i) are generated, the phases of which are adjusted by an electro-optical feedback loop (6, 7i, 8i, 9) implementing the matrix equation of a phase-contrast filtering device (6).

A device includes: at least one laser element with light emitting points to output fundamental waves in a one-dimensional array; a wavelength converting element to carry out wavelength conversion of the incident fundamental waves, and to output wavelength converted light rays; and an output mirror to reflect the fundamental waves, and to transmit the wavelength converted light rays resulting from the wavelength conversion by the wavelength converting element. The wavelength converting element is disposed between the laser element and the output mirror, and the distance between the position of a waist of the fundamental waves output from the laser element and the output mirror is set in accordance with a Talbot condition under which the adjacent light emitting points cause phase synchronization with each other.

A method of spectrally multiplexing diode pump modules to increase brightness includes generating one or more pump beams from respective diode lasers at a first wavelength in a diode laser package, generating one or more pump beams from respective diode lasers at a second wavelength different from the first wavelength in the diode laser package, wavelength combining at least one of the pump beams at the first wavelength with at least one of the pump beams at the second wavelength to form one or more combined pump beams, and receiving the combined pump beams in a pump fiber coupled to the diode laser package. Laser systems can include multi-wavelength pump modules and a gain fiber having a core actively doped so as to have an absorption spectrum corresponding to the multiple wavelength, the gain fiber situated to receive the pump light and to produce an output beam at an output wavelength.

There is provided a laser system that may include a Raman cell, a pumping light generator, and a Raman cell laser unit. The pumping light generator may include one or more optical parametric amplifiers (OPAs), and may be configured to output first Raman-cell pumping light and second Raman-cell pumping light to the Raman cell. The Raman cell laser unit may be configured to output probing light as a target of wavelength conversion to the Raman cell.

A method (10) of changing operating mode of an optical amplifier in an amplifier chain in an optical network, the optical amplifier initially configured to operate in a first mode to apply a substantially constant first gain to an optical signal comprising a plurality of optical channels, the method comprising, after a time period unique to the optical amplifier within the amplifier chain (12), configuring the optical amplifier to operate in a second mode to apply a second gain to the optical signal so that the optical power of the optical signal is maintained at a target optical power dependent on a current plurality of optical channels in the optical signal (14).

An example of the disclosure is a laser apparatus including a master oscillator capable of outputting a pulse laser beam, a plurality of optical amplifiers disposed on an optical path of the pulse laser beam outputted from the master oscillator and configured to sequentially amplify the pulse laser beam, an optical reflector capable of passing the pulse laser beam therethrough and reflecting a self-oscillation beam generated in one of the plurality of optical amplifiers, and an optical absorber capable of receiving and absorbing the self-oscillation beam reflected by the optical reflector.