Raman probes based on optically-poled double-clad fiber and coupler

Anna Chiara Brunetti,Walter Margulis,Karsten Rottwitt

doi:10.1364/oe.20.028563

Abstract

Two fiber Raman probes are presented, one based on an optically-poled double-clad fiber and the second based on an optically-poled double-clad fiber coupler respectively. Optical poling of the core of the fiber allows for the generation of enough 532nm light to perform Raman spectroscopy of a sample of dimethyl sulfoxide (DMSO), when illuminating the waveguide with 1064nm laser light. The Raman signal is collected in the inner cladding, from which it is retrieved with either a bulk dichroic mirror or a double-clad fiber coupler. The coupler allows for a substantial reduction of the fiber spectral background signal conveyed to the spectrometer.

Highlights

Raman spectroscopy is a powerful technique for the rapid and non-destructive identification of the molecular composition and structure of substances
Two fiber Raman probes are presented, one based on an optically-poled double-clad fiber and the second based on an opticallypoled double-clad fiber coupler respectively
Optical poling of the core of the fiber allows for the generation of enough 532nm light to perform Raman spectroscopy of a sample of dimethyl sulfoxide (DMSO), when illuminating the waveguide with 1064nm laser light

Summary

Introduction

Raman spectroscopy is a powerful technique for the rapid and non-destructive identification of the molecular composition and structure of substances. Three desired functions can be identified: (a) generation of the excitation light; (b) its delivery to the sample and the efficient collection of Raman scattering; and (c) guidance of the latter to a suitable detector. Frequency doubling by thermal poling followed by periodic erasure allows for generation of red [9], green [10] and blue [11] wavelengths and recently as much as 236mW of green light were produced in a fiber with this technique [12]. The peak conversion efficiency of optical poling does not exceed a couple of percent, the technique is considerably simpler to implement since it relies on the creation of a self-organized grating [15] through the interaction of high-power radiation at 1064nm with the SH light at 532nm, requiring neither internal electrodes nor periodic UV exposure. The process is accelerated by briefly seeding the fiber with SH light, together with the fundamental IR [16]

Methods

Results

Conclusion