A method includes driving, while producing a burst of pulses at a pulse repetition rate, a spectral feature adjuster among a set of discrete states at a frequency correlated with the pulse repetition rate; and in between the production of the bursts of pulses (while no pulses are being produced), driving the spectral feature adjuster according to a driving signal defined by a set of parameters. Each discrete state corresponds to a discrete value of a spectral feature. The method includes ensuring that the spectral feature adjuster is in one of the discrete states that corresponds to a discrete value of the spectral feature of the amplified light beam when a pulse in the next burst is produced by adjusting one or more of: an instruction to the lithography exposure apparatus, the driving signal to the spectral feature adjuster, and/or the instruction to the optical source.

A folded slab waveguide laser having a hybrid waveguide-unstable resonator cavity. Multiple slab waveguides of thickness t supporting vertical waveguide modes are physically arranged above one another in a stack and optically arranged in series through one or more cavity folding assemblies with curved mirrors. A gain medium such as a gas is arranged in each slab. Each cavity folding assembly is designed to redirect the radiation beam emitted from one slab waveguide into the next waveguide and also at the same time to provide a focus for the radiation beam so that a selected vertical waveguide mode (or modes) is (or are) coupled efficiently into the next slab.

The present invention comprises a core (11) and a primary coating (12) that is lower in refractive index than the core (11) and that covers the side surface of the core (11) except in a coating-removed section (I0). The side surface of the core (11), in at least part of the coating-removed section (I0), is covered with an intermediate-refractive-index resin part (14) that is lower in refractive index than the core (11) and that is higher in refractive index than the primary coating (12).

The present invention comprises a core (11) and a primary coating (12) that is lower in refractive index than the core (11) and that covers the side surface of the core (11) except in a coating-removed section (I0). The side surface of the core (11), in at least part of the coating-removed section (I0), is covered with an intermediate-refractive-index resin part (14) that is lower in refractive index than the core (11) and that is higher in refractive index than the primary coating (12).

An optical configuration including axiconical elements that serve as parts of a resonator or an optical chain of an amplifier for an active laser volume with a large transverse dimension. The system may include a single-fold or multiple-folds axiconical elements. One of the system's advantages is providing the means to produce, even with a stable resonator, a high-quality and well-controlled beam, utilizing efficiently a wide active laser medium.

An optical configuration including axiconical elements that serve as parts of a resonator or an optical chain of an amplifier for an active laser volume with a large transverse dimension. The system may include a single-fold or multiple-folds axiconical elements. One of the system's advantages is providing the means to produce, even with a stable resonator, a high-quality and well-controlled beam, utilizing efficiently a wide active laser medium.

A laser medium unit includes: a plate-shaped laser gain medium which includes a first surface and a second surface opposite to the first surface and generates emission light by the irradiation of excitation light from the first surface; a reflection member that is provided on the second surface so as to reflect the excitation light and the emission light; and a cooling member that cools the laser gain medium. The laser gain medium includes an irradiation area which is irradiated with the excitation light and an outer area which is located outside the irradiation area when viewed from a thickness direction intersecting the first surface and the second surface. The cooling member is thermally connected to the second surface through the reflection member so that a cooling area of the laser gain medium is formed on the second surface.

A system includes: a heat sink module with a plurality of first through-holes linking its top and bottom surfaces and a plurality of grooves on the bottom surface, wherein each groove passes through a respective sequence of the first through-holes; and a driving circuit module with a plurality of conductive connectors and electrical driving surfaces that are disposed substantially perpendicular to the top and bottom surfaces of the heat sink module, wherein each conductive connector lies partially within a respective groove in the bottom surface of the heat sink module, the conductive connectors include internal connectors that each links at least two of the first through-holes in a respective sequence of first through-holes, and external connectors that each links at least one of the first through-holes in a respective sequence of first through-holes to an electrical driving surfaces of the driving circuit module.

External cavity laser systems are described that can operate with essentially no mode hopping. One example configuration of the laser system includes a semiconductor laser device, a folded cavity external to the semiconductor laser device, where at the semiconductor laser device is positioned at a fold in the folded cavity. In this configuration, at least one mirror is positioned in the folded cavity to enable sustained propagation of light within the folded cavity, and at least two polarization elements are positioned in the folded external cavity. The polarization elements cause a polarization state of the light that impinges in different directions on each semiconductor laser device that is positioned at a fold to be orthogonal to one another, thus eliminating or substantially reducing mode hopping in the laser output.

A laser oscillator includes: an external resonator configured to include laser media to emit laser beams having different wavelengths; and a partially reflective mirror to transmit part of the laser beams and reflect and return a remainder toward the laser media. The external resonator includes therein: a diffraction grating to perform wavelength coupling on the laser beams having different wavelengths emitted from the laser media so as to superimpose the laser beams into one laser beam and to emit, to the partially reflective mirror, the one laser beam; and a prism that is placed between the laser media and the diffraction grating and that superimposes the laser beams into one laser beam on the diffraction grating, the prism including two surfaces forming an apex angle, one of the two surfaces being an incident surface and another of the two surfaces being an exit surface.