A laser comprises a first end mirror and a second end mirror defining an optical cavity therebetween, a first gain medium and a second gain medium positioned in the optical cavity, at least one radiation source configured to provide pump radiation to the first and second gain media, wherein the pump radiation comprises a first pump beam directed to be incident on the first gain medium and a second pump beam directed to be incident on the second gain medium so as to stimulate emission of radiation from the first and second gain media thereby establishing a laser beam in the optical cavity and a control apparatus operable to adjust a property of at least one of the first and second pump beams and thereby control a thermal lens of at least one of the first and second gain media so as to substantially remove an instability zone from the power curve of the laser.

A vertical external cavity surface emitting laser (VECSEL) based system in a linear single cavity configuration is configured to deliver light in higher-order Hermite-Gaussian transverse modes with Watt-level output power. Simultaneous and independent lasing of spatially-restructurable multiple high-order transverse modes that are collinearly-propagating at the output of such laser cavity is facilitated with the use of an optical pumping scheme devised to control positions of location at which the gain medium of the system is pumped (e.g., locations of focal spots of multiple pump beams on the gain-medium chip). An external astigmatic mode converter is utilized to convert such high-order Hermite-Gaussian modes into corresponding Laguerre-Gaussian modes.

A method for generating a spatially transformed optical output from a laser system, the method comprising: disposing a laser gain medium within a laser cavity structure; arranging an interferometric device to complete the laser cavity structure, wherein the interferometric device receives an input beam from laser oscillation in the laser cavity structure, splits the input beam into two sub-beams, and recombines the two sub-beams to provide an optical feedback beam to sustain laser oscillation; configuring the optical components that comprise the interferometric device to provide relative misalignment of the two sub-beams that are produced internally to the interferometric device; using at least a first output port of the interferometric device to provide an output beam of the laser system that due to the misalignment is a spatial transformation of the internal mode structure of the laser; and using at least a second output port of the interferometric device to provide the optical feedback beam to the laser cavity structure that sustains laser oscillation with a spatial structure that substantially preserves the internal mode structure of the laser. An apparatus which implements such a method is also provided.

Large mode area optical fibers include cores that are selected to be smaller than a core size associated with a minimum mode field diameter of a lowest order mode. Cross-sectional shape of such cores can be circular or annular, and a plurality of such cores can be used. Gain regions can be provided in cores or claddings, and selected to produce a selected state of polarization.

The laser device includes a first mirror and a second mirror forming a resonator, a gain medium disposed between the first mirror and the second mirror and having a light emitting surface, an antireflection film provided on the light emitting surface of the gain medium, at least one optical element disposed between the gain medium and the second mirror, and a diffraction grating disposed between the optical element and the second mirror. The gain medium is a semiconductor layered body including an active layer and having a varying gain distribution in at least a first direction within the light emitting surface, and includes no waveguide.

A high average and peak power single transverse mode laser system is operative to output ultrashort single mode (SM) pulses in femtosecond-, picosecond- or nanosecond-pulse duration range at a kW to MW peak power level. The disclosed system deploys master oscillator power amplifier configuration (MOPA) including a SM fiber seed, outputting a pulsed signal beam at or near 1030 nm wavelength, and a Yb crystal booster. The booster is end-pumped by a pump beam output from a SM or low-mode CW fiber laser at a pump wavelength in a 1000-1020 nm wavelength range so that the signal and pump wavelengths are selected to have an ultra-low-quantum defect of less than 3%.

An amplification fiber includes a core which is doped with an erbium ion and a cladding which surrounds the core and has a refractive index lower than a refractive index of the core, and a relative refractive index difference Δn.sub.51 between the core and the cladding is not more than a smaller one of values of a relative refractive index difference Δn.sub.1 expressed as a predetermined expression related to a radius a of the core and a relative refractive index difference Δn.sub.2 expressed as a predetermined expression related to the radius a of the core.

The present technology provides large mode area optical fibers engineered to have normal dispersion around 1600 nm, enabling high power Raman amplification at eye safer wavelengths. The fibers can have a main core and one or more side cores disposed relative to the main core so that modes of the main core and the one or more side cores hybridize into supermodes with modified dispersion.

An optical apparatus includes one or more pump sources situated to provide laser pump light, and a gain fiber optically coupled to the one or more pump sources, the gain fiber including an actively doped core situated to produce an output beam, an inner cladding and outer cladding surrounding the doped core and situated to propagate pump light, and a polymer cladding surrounding the outer cladding and situated to guide a selected portion of the pump light coupled into the inner and outer claddings of the gain fiber. Methods of pumping a fiber sources include generating pump light from one or more pump sources, coupling the pump light into a glass inner cladding and a glass outer cladding of a gain fiber of the fiber source such that a portion of the pump light is guided by a polymer cladding surrounding the glass outer cladding, and generating a single-mode output beam from the gain fiber.

A multi-clad optical fiber design is described in order to provide low optical loss, a high numerical aperture (NA), and high optical gain for the fundamental propagating mode, the linearly polarized (LP) 01 mode in the UV and visible portion of the optical spectrum. The optical fiber design may contain dopants in order to simultaneously increase the optical gain in the core region while avoiding additional losses during the fiber fabrication process. The optical fiber design may incorporate rare-earth dopants for efficient lasing. Additionally, the modal characteristics of the propagating modes in the optical core promote highly efficient nonlinear mixing, providing for a high beam quality (M.sup.2<1.5) output of the emitted light.