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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−1with a spectral resolution of ∼8 cm−1for sapphire and ∼10 cm−1for 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−1to 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−1were 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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A Portable, Spectroscope-Inspired Three-Dimensionally Printed Smartphone Spectrophotometer
An inexpensive and simple three-dimensional (3D) printed spectrophotometer that interfaces with smartphone cameras for visualizing and measuring visible wavelength absorbance and analyte quantitation is reported. A conventional spectroscope inspired the spectrophotometer design to maximize visual engagement for educational purposes and functions as a single-beam visible spectrophotometer capable of precise calibration, standard curve generation, and quantitative analysis of real-life samples. Spectrophotometer calibration results using a four-point, red-green-blue coordinate-to-wavelength conversion demonstrate that the 3D-printed device exhibits a linear 5.0 nm/mm dispersion over the 400–700 nm range. Quantitative analysis validation using a smartphone camera and Open Source software (ImageJ) analysis for tartrazine determination demonstrate the molar absorptivity for the external standard tartrazine was significantly lower compared to the literature and commercial instrumentation (0.0062 μM–1cm–1versus 0.0216 μM–1cm–1for the commercial instrument). Still, the accuracy of the device was within the linear range is remarkable, as tartrazine determination in a real-life sample (Mello Yello soft drink) was found to be not statistically different compared to the result obtained on a commercial spectrophotometer (10.6 μM versus 10.5 μM, n = 5, p > 0.05). The device design and computer-aided drafting files are available publicly for Open Access replication and modification, with considerable promise for expanded capabilities and applications beyond visible spectroscopy and educational purposes.
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- Award ID(s):
- 2144453
- PAR ID:
- 10569547
- Publisher / Repository:
- SAGE Publications
- Date Published:
- Journal Name:
- Applied Spectroscopy Practica
- Volume:
- 3
- Issue:
- 1
- ISSN:
- 2755-1857
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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