We present highly efficient and reproducible Raman converters built with a silica nanofiber immersed in ethanol. The converters are pumped at 532 nm in the sub-nanosecond regime and the first Stokes order photons are generated in the evanescent field probing the liquid at 630 nm. Two standard fibers (SMF28, 460HP) are tested and compared. The Raman conversion operating range limited by the damage threshold is optimized, leading to an external Raman conversion efficiency up to 60% with a nanofiber radius of 300 nm and a length of 8 cm. The extracted Stokes energy is 0.29 µJ, which is three times higher than the previous result. We give guidelines for the design of other efficient evanescent Raman converters, opening the way for a new family of all-fibered compact Raman sources.
Thanks to their unique optical properties, silica nanofibers are used in a growing number of applications. Moreover, the possibility of immerging them in various media adds another interesting feature to these devices. However, as for all optical components, nanofibers are limited by the optical damage that can be induced by a laser. In this Letter, we present for the first time to our knowledge Laser-Induced Damage Threshold (LIDT) measurements of silica nanofibers in air and in three common liquids (ethanol, isopropanol, and water). The experiments were performed in the nanosecond regime with a pump source emitting at the wavelength of 532 nm. Different nanofiber radii (from 220 nm to 450 nm) and two nanofiber lengths (2 cm and 8 cm) were tested. We firstly present the experimental setup and protocol. A significant number of samples were realized, and the results were highly repeatable. We also showed that immerging a nanofiber in a liquid substantially enhanced the LIDT, the most important increase having been obtained for nanofibers immersed in water for which the LIDT energy was almost multiplied by a factor of 2 compared with air (0.38 µJ in air vs 0.71 µJ in water for a radius of 350 nm). This property offers a new degree of freedom to widen the field of applications of nanofibers, where high peak powers are needed.
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