Raman measurements using a field‐widened spatial heterodyne Raman spectrometer

Abstract

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.

A Monolithic Spatial Heterodyne Raman Spectrometer: Initial Tests

“…The basic design and operation of the SHRS has been discussed previously. 1–11,20–41 In the interferometer, collimated light is passed through a 50:50 beam splitter, dividing the beam into two parts which are directed onto tilted diffraction gratings. After being diffracted off the gratings, the beams recombine at the beamsplitter as crossing wave fronts.…”

Raman Spectroscopic Investigation of Sulfates Using Mosaic Grating Spatial Heterodyne Raman Spectrometer

“…We have used a mercury lamp for the purpose of wavelength calibration. Using the measured fringe cycles across the detector and the known wavelengths from the calibration source, the wavelengths corresponding to each spatial frequenies can be calculated [12]- [14].…”

“…The MGSHRS breadboard instrument performance parameters can be estimated by a calibration procedure. This procedure establishes the spectral response of the instrument based on the spatial frequency respond from the known input lines (576.964 nm, 579.588 nm) of a mercury lamp [12]- [14]. The Littrow wavelength equals to 535.587 nm.…”

Recent advances in linear and nonlinear Raman spectroscopy. Part XIV

“…The HSRI showed superior spectral resolution and signal‐to‐noise ratio, while more than doubling the field of view of the pointwise imaging with laser power densities reduced by a factor if more than 250 at the target. Qiu et al [ 199 ] described Raman measurements using a field‐widened spatial heterodyne Raman spectrometer (SHRS). Their results show that the field‐widened SHRS exhibits sufficiently good performance to allow successful performance of wide‐field Raman measurements.…”