Abstract: A Raman fiber laser source (RFLS) is configured with a feeding fiber delivering MM pump radiation to an inner cladding of double-clad MM Raman fiber laser. The MM pump radiation has a sufficient power to produce Raman scattering in the MM Raman fiber converting the pump radiation to a MM signal radiation at a Raman-shifted wavelength ?ram which is longer than a wavelength ?pump of the pump radiation. The RFLS further has a pair of spaced reflectors defining therebetween a resonator for the signal radiation at a 1st Stokes wavelength and flanking at least part of the MM core of the Raman fiber which is provided with a central core region which is doped with impurities for enhancing Raman process. The reflectors and central core region are dimensioned to correspond to the fundamental mode of the MM signal radiation.

Abstract: A Raman fiber laser source is configured with a feeding fiber delivering MM pump radiation to an inner cladding of double-clad MM Raman fiber laser. The MM pump beam radiation has a sufficient power to produce Raman scattering in the MM Raman fiber converting the pump radiation to a MM signal radiation at a Raman-shifted wavelength ?ram which is longer than a wavelength ?pump of the pump radiation. The Raman laser source further has a pair of spaced reflectors defining therebetween a resonator for the signal radiation at a 1st Stokes wavelength and flanking at least part of the MM core of the Raman fiber which is provided with a central core region which is doped with impurities for enhancing Raman process. The reflectors and central core region are dimensioned to correspond to the fundamental mode of the MM signal radiation which is output from the Raman fiber with an M2 factor ?1.1 and in a power range between a few kW and tens of kW.

Abstract: A fiber Raman laser is configured with a microstructured double clad passive fiber which has an inner cladding receiving and guiding a high intensity pump light. The double-clad passive fiber farther has a eon surrounded by the inner cladding and an outer cladding. An arrangement of air holes is configured to define the inner, waveguiding cladding so that an NA of the latter varies between about 0.25-0.9 allowing this to reduce the diameter of the inner cladding. The passive fiber is characterized by a substantial overlap between the pump light and 1st stokes in the care and further includes an absorber operative to substantially suppress the signal light at the 2nd strokes so that the Ge-doped fiber outputs a SM, bright radiation at up to kW levels.

Abstract: A fiber Raman laser is configured with a microstructured double clad passive fiber which has an inner cladding receiving and guiding a high intensity pump light. The double-clad passive fiber farther has a eon surrounded by the inner cladding and an outer cladding. An arrangement of air holes is configured to define the inner, waveguiding cladding so that an NA of the latter varies between about 0.25-0.9 allowing this to reduce the diameter of the inner cladding. The passive fiber is characterized by a substantial overlap between the pump light and 1st stokes in the care and further includes an absorber operative to substantially suppress the signal light at the 2nd strokes so that the Ge-doped fiber outputs a SM, bright radiation at up to kW levels.

Abstract: A high power fiber laser is configured with a multimode active fiber and input and output single mode passive fibers butt-spliced to respective opposite ends of the active fiber. If the input passive and active fibers do not have substantially matched diameters, a SM radiation coupled into the active fiber may excite fundamental and high order modes which, while interfering with one another, create a non-uniform distribution of refractive index in each of forward and backward light propagation directions along the resonator of the laser. The variable longitudinal perturbation components of the refractive index in respective forward and backward directions along an optical path in the active fiber are distributed in accordance with respective cosine functions.