High Performance Resonance Raman Spectroscopy Using Volume Bragg Gratings As Tunable Light Filters

We designed a near infrared tunable resonance Raman spectroscopy system based on a tandem of thick volume Bragg gratings (VBGs). VBGs are here the constituents of two light filtering units: a tunable laser line filter (LLF) and a tunable notch filter (NF). When adapted in a micro-Raman setup with a single stage monochromator (1800 gr/mm grating), the tandem of LLF and NF allowed measurements of Raman signals down to +/-20 cm⁻¹. The good performance and fast tunability of the VBG Raman system was demonstrated on a sulfur powder and on a bulk single-walled carbon nanotube sample through a series of 22 Stokes and anti-Stokes spectra recorded at excitation wavelengths between 800 and 990 nm. The main drawbacks of the setup are the limited spectral range to the near infrared and the small angular acceptance of the filters (~1 mrad), which causes mainly attenuation problems with the NF. The impact of the main limitations is discussed and solutions are provided.