Spatial-heterodyne spectrometer for transmission-Raman observations

Foster, Michael J.; Storey, Jonathan; Zentile, Mark A.

doi:10.1364/oe.25.001598

Cited by 18 publications

(11 citation statements)

References 11 publications

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“…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.…”

Section: Resultsmentioning

confidence: 99%

A Monolithic Spatial Heterodyne Raman Spectrometer: Initial Tests

et al. 2020

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Section: Resultsmentioning

confidence: 99%

A Monolithic Spatial Heterodyne Raman Spectrometer: Initial Tests

et al. 2020

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“…Foster et al developed an SHRS that was designed to be fiber coupled for transmission‐Raman observations to test paracetamol tablet samples. However, the non‐filed‐widening SHS was limited by the fiber diameter because the larger diameter produces a larger range of angles through the SHS . Field widening is needed to increase the useable field of view without sacrificing the resolving power.…”

Section: Introductionmentioning

confidence: 51%

“…The field‐widened SHRS is based on a stationary diffraction grating interferometer where selected prisms have been placed in the arms of the device. In our present work, the groove density of the diffraction gratings was 150 groove/mm, which is the same as the groove density of gratings used by Hu et al and Foster et al However, it requires lower laser powers and shorter integration times than those used by Hu et al and Foster et al The fundamental principles of field‐widened SHRS are provided in Section . Then, the calibration results are reported in Section .…”

Section: Introductionmentioning

confidence: 88%

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Raman measurements using a field‐widened spatial heterodyne Raman spectrometer

Qiu

et al. 2019

J Raman Spectroscopy

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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.

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“…In this work, we evaluate and compare the performance of the SHRS with a spectrally filtered, lensed silica fiber Raman probe and a custom unfiltered, non-lensed, SC sapphire probe. To the best knowledge of the authors, this is the first demonstration of an SHRS chemical sensor using optical fiber Raman probes, which differs from other reports 24,25 involving the use of silica fibers only for light collection. The utility of the fiber-coupled SHRS chemical sensor is demonstrated using 532 nm excitation for measuring a variety of solid and liquid Raman standards and real-world samples of high explosive (HE) formulations while simultaneously characterizing spectral resolution, throughput, and signal-to-noise ratio (SNR).…”

Section: Introductionmentioning

confidence: 66%

Spatial Heterodyne Raman Spectrometer (SHRS) for In Situ Chemical Sensing Using Sapphire and Silica Optical Fiber Raman Probes

et al. 2019

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A spatial heterodyne Raman spectrometer (SHRS), constructed using a modular optical cage and lens tube system, is described for use with a commercial silica and a custom single-crystal (SC) sapphire fiber Raman probe. The utility of these fiber-coupled SHRS chemical sensors is demonstrated using 532 nm laser excitation for acquiring Raman measurements of solid (sulfur) and liquid (cyclohexane) Raman standards as well as real-world, plastic-bonded explosives (PBX) comprising 1,3,5- triamino- 2,4,6- trinitrobenzene (TATB) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) energetic materials. The SHRS is a fixed grating-based dispersive interferometer equipped with an array detector. Each Raman spectrum was extracted from its corresponding fringe image (i.e., interferogram) using a Fourier transform method. Raman measurements were acquired with the SHRS Littrow wavelength set at the laser excitation wavelength over a spectral range of ∼1750 cm−1 with a spectral resolution of ∼8 cm−1 for sapphire and ∼10 cm−1 for silica fiber probes. The large aperture of the SHRS allows much larger fiber diameters to be used without degrading spectral resolution as demonstrated with the larger sapphire collection fiber diameter (330 μm) compared to the silica fiber (100 μm). Unlike the dual silica fiber Raman probe, the dual sapphire fiber Raman probe did not include filtering at the fiber probe tip nearest the sample. Even so, SC sapphire fiber probe measurements produced less background than silica fibers allowing Raman measurements as close as ∼85 cm−1 to the excitation laser. Despite the short lengths of sapphire fiber used to construct the sapphire probe, well-defined, sharp sapphire Raman bands at 420, 580, and 750 cm−1 were observed in the SHRS spectra of cyclohexane and the highly fluorescent HMX-based PBX. SHRS measurements of the latter produced low background interference in the extracted Raman spectrum because the broad band fluorescence (i.e., a direct current, or DC, component) does not contribute to the interferogram intensity (i.e., the alternating current, or AC, component). SHRS spectral resolution, throughput, and signal-to-noise ratio are also discussed along with the merits of using sapphire Raman bands as internal performance references and as internal wavelength calibration standards in Raman measurements.

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Spatial-heterodyne spectrometer for transmission-Raman observations

Cited by 18 publications

References 11 publications

A Monolithic Spatial Heterodyne Raman Spectrometer: Initial Tests

A Monolithic Spatial Heterodyne Raman Spectrometer: Initial Tests

Raman measurements using a field‐widened spatial heterodyne Raman spectrometer

Spatial Heterodyne Raman Spectrometer (SHRS) for In Situ Chemical Sensing Using Sapphire and Silica Optical Fiber Raman Probes

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