Adaptive design of dual excitation ultra‐low wavenumber Raman spectroscopy system

Abstract Ultra‐low wavenumber or ultra‐low frequency (ULF) Raman spectroscopy using holographic optics is an emerging technique to obtain spectral signatures of chemicals in low energy corresponding to their phases, crystallinity, isomerism, and environmental conditions such as temperature. Commercial turn‐key systems employ mechanical turrets and other such optomechanical moving elements to accommodate multiple laser excitations, which are incident normally on the sample, and the Raman signal is collected in a 180° backscattering configuration. Here, we have developed a system consisting of two single‐longitudinal mode (SLM) lasers and a single‐stage spectrometer. Selected notch filters were based on the volume holographic grating technology providing output beam at a certain angle, which facilitates the possibility of different angles of incidence of the excitation laser on the sample. This adaptive ULF Raman system, therefore, is not only able to acquire high‐quality low‐wavenumber spectral fingerprints of various chemicals but can also be easily reconfigured for differential spectral studies.