Raman measurements using a field-widened spatial heterodyne Raman spectrometer

Spatial heterodyne Raman spectroscopy has become a useful spectroscopic detection technique that is particularly suitable for Raman measurements. This method uses the Fourier transform of the interferogram imaged on the detector by stationary diffraction gratings. Spatial heterodyne Raman spectroscopy has the same characteristic of conventional Fourier-transform spectroscopy, which is that the field of view is limited. We propose a two-dimensional spatial heterodyne Raman spectrometer (SHRS) that uses a field widening prism to effectively increase the throughput or sensitivity without sacrificing the spectral resolution for Raman measurements while broadening the bandpass. The signal-to-noise ratio is measured under different integrations or laser powers and shows that the system exhibits good stability and fair repeatability. Raman spectra obtained from the field-widened SHRS and a commercialized Raman instrument are compared, and the field-widened SHRS and the SHRS using the same instrumental parameters without field widening are also compared. A higher signal-to-noise ratio can be achieved using the field-widened SHRS. In our measurements, the field-widened SHRS can be operated under the slightly more complex conditions required for wide-field measurements with short integration times and low laser power. Raman spectra of a pure inorganic target or a target contained in glass and a plastic bottle are observed. A sulfate is investigated in two states: solid salt and aqueous solution. Several mixture liquids, mixture solids, minerals, and anti-Stokes Raman shifts are also investigated. The results show that the field-widened SHRS exhibits a good performance to successfully perform wide-field Raman measurements.