Patent ID: 7936796

Claim:
An apparatus for providing optical radiation having a first bandwidth, which apparatus comprises: a seed laser configured to provide seeding radiation; at least one amplifier configured to amplify the seeding radiation, wherein in use the amplifier emits a pulse having a peak power greater than 1 kW when seeded by the seed laser; a reflector; and wherein: the seed laser is a Fabry Perot semiconductor laser which is defined by an effective optical transit time, a spectrum, and a second bandwidth; the reflector is characterized by a third bandwidth; the seed laser is connected to the amplifier via the reflector; the reflector is arranged to reflect a proportion of the seeding radiation emitted by the seed laser back into the seed laser; and the amplifier comprises an optical fibre which comprises a core having a refractive index n 1 and a pedestal having a refractive index n 2 , and wherein the optical fibre includes a first cladding made of glass having a refractive index n 3 surrounding the pedestal, wherein: n 1 is greater than n 2 ; n 2 is greater than n 3 ; and the pedestal is adapted to guide optical radiation that escapes from the core; and wherein the amplifier is cladding pumped by coupling pump radiation into the first cladding, and the optical feedback from the reflector is such that the first bandwidth is less than the second bandwidth.