Abstract: 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.

Abstract: A laser system comprising a laser configured to emit a laser beam wherein the laser beam is linearly polarized in a polarization plane and an optical assembly comprising a partial reflector having a refractive index and comprising a partially reflective surface. The partially reflective surface is arranged to receive the laser beam at an angle of incidence which lies in a plane of incidence and reflect a portion of the laser beam such that the reflected portion is output from the optical assembly. The partially reflective surface is arranged such that the plane of incidence forms a polarization angle with the polarization plane of the laser beam and the laser beam includes a p-polarized component and an s-polarized component.

Abstract: A laser system comprising a laser configured to generate a laser beam, a power supply arranged to provide a drive power to the laser, a photodetector arranged to detect the power of the laser beam and provide a detection signal from the power of the laser beam and a feedback loop arranged to form a feedback signal by subtracting a target signal from the detection signal wherein the feedback signal has a high bandwidth, amplify the feedback signal and adjust the drive power according to the amplified feedback signal, thereby reducing noise in the laser beam.

Abstract: An optical fiber laser or amplifier comprising an optical fiber and a pump radiation source configured to generate pump radiation which is received through an input end of the optical fiber. The optical fiber may include a doped core which is configured to guide the pump radiation and to generate or amplify and guide signal radiation when pump radiation passes through it. The optical fiber laser or amplifier may include a first reflector configured to reflect pump radiation and further comprises a second reflector configured to selectively reflect a portion of pump radiation. The selection of the portion of pump radiation to be reflected by the second reflector depends upon one or more of: the spatial position of the pump radiation, the direction of the pump radiation, and the polarization of the pump radiation.

Abstract: An optical fibre laser or amplifier comprising an optical fibre and a pump radiation source configured to generate pump radiation which is received through an input end of the optical fibre. The optical fibre may include a doped core which is configured to guide the pump radiation and to generate or amplify and guide signal radiation when pump radiation passes through it. The optical fibre laser or amplifier may include a first reflector configured to reflect pump radiation and further comprises a second reflector configured to selectively reflect a portion of pump radiation. The selection of the portion of pump radiation to be reflected by the second reflector depends upon one or more of: the spatial position of the pump radiation, the direction of the pump radiation, and the polarisation of the pump radiation.