New Conference publication: Pittcon 2020

Lasers for low frequency Raman spectroscopy

Title: Novel narrow linewidth 785 nm diode laser with enhanced spectral purity facilitates low-frequency Raman spectroscopy.

We are happy to be granted permission from Pittcon to share our poster from the 2020 Conference.

Raman Spectroscopy enables fast, sensitive and label-free chemical analysis of a large range of materials and has become a routine analytical tool in a wide range of material science and process-control applications. As the Raman signal is weak it is critical that the illumination laser has a very high level of spectral purity, for efficient detection of the Raman signal. Most materials can be characterized by studying Raman shifts down to 100 cm-1, but in some cases, for instance for determining the crystallinity of pharmaceutical compounds, it is required to study Raman shifts in the low-frequency regime; <100 cm-1 . 785 nm is the most common illumination wavelength for Raman spectroscopy as it offers the best compromise between Raman signal strength and fluorescence background suppression.

In this paper, we present a novel design for a frequencystabilized 785 nm diode laser using a highly reflective volume Bragg grating (VBG) element that offers not only a narrow spectral linewidth and low wavelength drift, but also a very high level of spectral purity. Using the VBG reflected light as output from the laser suppresses Amplified Spontaneous Emission (ASE) from the diode so that a very high level of sidemode suppression ratio (SMSR) in the laser output is reached within just a few cm-1 away from the main peak without any external spectral filtering. This enhanced spectral purity directly from the laser enables simpler, more compact and more cost-efficient detection of Raman shifts in the very low frequency range.

Lasers for Raman spectroscopy

Authors: Magnus Rådmark, Gunnar Elgcrona, Håkan Karlsson
Part of Pittcon 2020 Proceedings: Vibrational Spectroscopy, 614-15P, (3 March 2020).