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In this paper it is verified, from experimental results, that the Raman susceptibility asymmetry is found as a key factor to improve dynamic range in distributed anti-Stokes Raman thermometry sensor which operates in stimulated regime. Improvements are discussed from experimental results of the spatial evolution of the anti-Stokes and Stokes branches for different Raman anti-Stokes wavelengths.Stimulated Raman scattering, anti-Stokes Raman scattering, Raman susceptibility, Distributed sensor, Standard optical fiber, OTDR.

Fiber sensors are the state of the art in distributed sensors. The basic effects for distributed sensors of temperature and strain are related with nonlinear optics. However, the development of this equipment require a well established knowledge about the characteristics effects involved and how they change the spectral distribution of the light: its intensity and frequency; in this way the work shows up spontaneous Raman measurement in optical fiber and discuss its mainly characteristics. The measurements were taken with a 1319 nm wavelength from a Nd-YAG CW laser coupled in a 2,7 km monomode optical fiber. Several spectrum were taken in the range of 20 mW till 100 mW, also the ratio power output/power input was observed in that range. The Raman shift measured in this experiment, about 12 THz, is in a good agreement with the literature. Raman peaks were observed only in the 20mW - 90mW range, it has been observed that the higher the power input, the lower is the spontaneous Raman peaks intensity, and at 100 mW it vanishes completely. The power ratio analyses shows the power transmission loss; it is discussed the pump depletion due to nonlinear backscattering and the Raman beam depletion for higher power input values are also discussed.

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