In an example, a tandem pumped fiber amplifier may include a seed laser, a first section coupled to an output of the seed laser, and a second section coupled to an output of the first section. The first section may operate as an oscillator, and may receive pump light from one or more diode pumps, and may the first section may be arranged to convert the one or more diode pumps into a tandem pump. The second section may operate as a power amplifier, and may include a length of a single or plural active core fiber. The tandem pumped fiber amplifier may be arranged to mitigate spectral broadening related to four-wave mixing.

A method and apparatus for passively synchronising the repetition rate of two or more mode-locked lasers is described. The method and apparatus involve forming a first synchronising optical field (6) by separating a portion of an output field of a first mode-locked laser (2) and thereafter redirecting this synchronising optical field to form a driving signal for a second mode-locked laser (3). Employing these techniques results in systems with timing jitter of less than 1 fs. The method is independent of the wavelength and polarisation at which the mode-locked lasers operate and so is not limited to use with any particular type of mode-locked laser. Since the technique is passive it does not require the employment of electronics, variable time delay paths or additional non-linear optical crystals. Therefore, the method and apparatus are significantly less complex than those known in the art and are not power limited by additional non-linear optical processes. Part of the output (7) of the first mode-locked laser (2) is redirected via a beam splitter (9) and beam steering mirrors (11,12) and a half-wave plate (15) to a polariser (13) in the beam line of the second mode-locked laser (3). The seeding and synchronising signal from the first mode-locked laser (2) may be perpendicularly polarized with respect to the polarization of the second mode-locked laser (3) and may have a different wavelength.

An FEL includes a feedback device for feeding back emitted illumination radiation.

A dual optical frequency comb light-emitting device includes a first optical-frequency-comb laser source that includes a first laser resonator having a first optical path length, a second optical-frequency-comb laser source that includes a second laser resonator having a second optical path length different from the first optical path length, and an optical coupler that causes a first portion of first optical-frequency-comb laser light emitted from the first laser resonator to enter the second laser resonator. The first optical-frequency-comb laser source outputs a second portion of the first optical-frequency-comb laser light to an outside. The second optical-frequency-comb laser source outputs second optical-frequency-comb laser light emitted from the second laser resonator to the outside.

An amplified spontaneous emission (ASE) light source and a method for using the ASE light source are provided. The ASE light source may include a seed stage light source for providing a light beam to be amplified. The apparatus may include a tunable element coupled to the seed stage light source configured for filtering a portion of the light beam from the seed stage light source. The apparatus may include a loopback circuit coupled to the tunable element, the loopback circuit comprising a booster stage element for amplifying light from the tunable element.

A laser device includes: a traveling wave type resonator comprising a first mirror and a second mirror; and a laser medium disposed between the first mirror and the second mirror. The first mirror and the second mirror are disposed such that round-trip light that travels in round trips in the resonator has a focus inside the laser medium. The laser device is configured such that: excitation light incident on the resonator is superimposed on the round-trip light at the focus and narrowed to be thinner than the round-trip light, Z.sub.R×α<0.5 is satisfied, where Z.sub.R is a Rayleigh length of the excitation light and α is an absorption coefficient of the laser medium with respect to the excitation light, and a round-trip Gouy phase shift of the resonator has a value excluding 2π×n/m where m is an integer of less than 15 and n is an integer of equal to or less than m.

A system for generating an energy beam based laser includes an apparatus for receiving an energy beam and for generating an energy beam based laser. The apparatus is configurable or controllable for tuning an output wavelength of the laser generated by the apparatus using the energy beam. The apparatus includes a first component for producing a first magnetic field oriented in a first direction and a second component for producing a second magnetic field oriented in a second direction substantially opposite to the first direction. A channel through the apparatus is defined by the first component and the second component through which the energy beam passes to generate the laser at an output of the apparatus. The apparatus is configurable or controllable for modifying at least one of the first magnetic field and the second magnetic field for tuning the output wavelength of the laser.

A fiber laser producing a beam of ultrashort laser pulses at a repetition rate greater than 200 MHz includes a linear fiber resonator and a fiber branch. Ultrashort laser pulses are generated by passive mode-locking and circulate within the linear fiber resonator. Each circulating laser pulse is split into a portion that continues propagating in the linear fiber resonator and a complementary portion that propagates through the fiber branch and is then returned to the linear fiber resonator. The optical length of the linear fiber resonator is an integer multiple of the optical length of the fiber branch. The repetition rate of the ultrashort laser pulses is the reciprocal of the propagation time of the laser pulses through the fiber branch.

A method and system for combining two or more optical fields is disclosed. A first continuous-wave high powered output field generated by a solid-state master laser is injected into a first solid state optical amplifier to produce a single output field from the laser system that exhibits a high phase-coherence with the output field of the master laser. The power of the output field equals the sum of powers of the master laser and that generated by the first optical amplifier, while exhibiting similar beams characteristics to that produced by the output field of the master laser i.e. it exhibits low noise, in a single transverse and longitudinal mode Gaussian beam, and has a single polarisation. The laser system is highly scalable in that N optical amplifiers may be located in series with the master laser to provide a single low noise, high power output field.

A coherent beam combination (CBC) system (10) includes an array of beam sources (12a, 12b and 12c) generating coherent beams directed towards a target (T). The phase modulators (14a, 14b and 14c) allow adjustment of relative phase offsets of the beams. A detector (16) monitors an intensity of the radiation impinging on an area of the target (T). A controller (18) receives the intensity parameter and controls a phase adjustment of the beams according to a deterministic (i.e., quantitative) measurement of a phase offset of each beam relative to a representative phase of the sum of all the other beams. This is achieved by using interferometric techniques, referred to herein as Target In-the-Loop Interferometry (TILI).