We present a generic approach for efficient generation of CW light with a predetermined wavelength within the visible or UV spectrum. Based on sum-frequency generation (SFG), the circulating intra-cavity field of a high-finesse diode pumped CW solid-state laser (DPSSL) and the output from a tapered, single-frequency external cavity diode laser (ECDL) are mixed inside a 10 mm periodically poled KTP crstal (pp-KTP). The pp-KTP is situated inside the DPSSL cavity to enhance conversion efficiency of the nonlinear mixing process. This approach combines different solid state technologies; the tuneability of ECDLs, the high intra-cavity filed of DPSSLs and flexible quasi phase matching in pp-tapered ECDL with a center wavelength of 766 nm in combination with a high finesse Nd:YVo4 laser at 1342 nm. Up to 308 mW of light at 488nm was measured in our experiments. The conversion of te ECDL beam was up to 47% after it was transmitted through a PM fiber, and up to 32% without fiber coupling. Replacing the seed laser and the nonlinear crystal makes it possible to generate light at virtually any desired wavelength withing the visible spectrum.
Distributed temperature sensor based on Raman scattering is investigated. The ratio of intensities in Stokes and anti-Stokes bands reveals the temperature of a fiber section. A spatial resolution of around 1m is obtained by use of Incoherent Optical Frequency Domain Reflectometry. An accuracy of ±2K is demonstrated over a 16km single-mode fiber, which represents a new record. A brief discussion on the choice of the sensing fiber is also given.
A distributed temperature sensor based on spontaneous Raman scattering in a single-mode fiber is demonstrated. A brief theoretical description of the IOFDR technique for spatial resolution of the backscattered waves is given. Measurements on 16 km of SM fiber with spatial resolution of around 2m are presented. To the best of the authors' knowledge, this represents a new record for an IOFDR system. An accuracy of ±2K is achieved.