Limits of IR-spectrometers based on linear variable filters and detector arrays

Wiesent, Benjamin R.; Dorigo, D.G.; Koch, Alexander W.

doi:10.1117/12.860532

Cited by 12 publications

(13 citation statements)

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“…241 Linear variable filters are commercially available from a number of vendors. 242 Wilks Scientific (later Wilks Enterprise and now Spectro Scientific) 243 offered compact mid-IR spectrometers employing an LVF for many years. 244 One example incorporated uncooled 64-element pyroelectric array giving a resolution of 40 cm -1 , and had a built-in ATR sample interface, targeted at a limited number of liquidphase industrial applications, for instance, in oil-condition monitoring.…”

Section: Linear Variable Filtersmentioning

confidence: 99%

Portable Spectroscopy

Crocombe¹

2018

Appl Spectrosc

373

233

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Until very recently, handheld spectrometers were the domain of major analytical and security instrument companies, with turnkey analyzers using spectroscopic techniques from X-ray fluorescence (XRF) for elemental analysis (metals), to Raman, mid-infrared, and near-infrared (NIR) for molecular analysis (mostly organics). However, the past few years have seen rapid changes in this landscape with the introduction of handheld laser-induced breakdown spectroscopy (LIBS), smartphone spectroscopy focusing on medical diagnostics for low-resource areas, commercial engines that a variety of companies can build up into products, hyphenated or dual technology instruments, low-cost visible-shortwave NIR instruments selling directly to the public, and, most recently, portable hyperspectral imaging instruments. Successful handheld instruments are designed to give answers to non-scientist operators; therefore, their developers have put extensive resources into reliable identification algorithms, spectroscopic libraries or databases, and qualitative and quantitative calibrations. As spectroscopic instruments become smaller and lower cost, ''engines'' have emerged, leading to the possibility of being incorporated in consumer devices and smart appliances, part of the Internet of Things (IOT). This review outlines the technologies used in portable spectroscopy, discusses their applications, both qualitative and quantitative, and how instrument developers and vendors have approached giving actionable answers to non-scientists. It outlines concerns on crowdsourced data, especially for heterogeneous samples, and finally looks towards the future in areas like IOT, emerging technologies for instruments, and portable hyphenated and hyperspectral instruments.

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Section: Linear Variable Filtersmentioning

confidence: 99%

Portable Spectroscopy

Crocombe¹

2018

Appl Spectrosc

373

233

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“…The detector resolution should suit the resolution of the LVF. 11 The LVF has a spectral resolution (FWHM) of less than 1.5% centre wavelength. At a wavelength of 620 nm, the resolution was 9.3 nm, equivalent to 259 µm in terms of distance along the LVF.…”

Section: Optical Designmentioning

confidence: 99%

Development of a Handheld Spectrometer Based on a Linear Variable Filter and a Complementary Metal-Oxide-Semiconductor Detector for Measuring the Internal Quality of Fruit

Gao

et al. 2016

Journal of Near Infrared Spectroscopy

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Visible and near infrared spectroscopy has long been used to predict fruit internal quality, with portable instrumentation advantageous for in-field use. We developed a handheld spectrometer using a linear variable filter (LVF) and a complementary metal-oxidesemiconductor (CMOS) linear detector array. The LVF is a bandpass filter with a centre wavelength changing linearly in one direction and can replace a grating as the light-dispersion component. An LVF was designed and fabricated specifically to work in the 620-1080 nm region and for the analysis of fruit. The optical design used an improved collimator and an LVF to yield a compact, stable and low-cost optical engine. By using a CMOS detector and other suitable electronics, the spectrometer achieved a low power consumption. The spectrometer can analyse spectral data using an onboard prediction model and can be operated from a remote smartphone, tablet or laptop computer. This paper details the design of the spectrometer and the results of its resolution and stability tests. The spectrometer operated with a resolution of less than 1.5% centre wavelength and a signal-to-noise ratio of up to 5000. The spectrometer was then used to predict the sugar content in pears. The optimised model provided an R 2 c value of 0.96, standard error of calibration value of 0.29 °Bx and standard error of prediction value of 0.46 °Bx. The results indicated that this LVF-based spectrometer is promising for measuring the internal quality of fruit.

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“…LVF refers to a narrow band filter corresponding to the linear variation passband spectrum at each spatial position in the gradient direction of the filter [7,8]. LVF has a high integration level (low weight, simple structure, and miniaturized), and its spectral coefficient can be adjusted according to the design requirements [9,10]. The efficiency of LVF beam splitting is higher than that of traditional dispersion devices, which is of great significance for the miniaturization and integration of optical systems in space applications [11,12].…”

Section: Introductionmentioning

confidence: 99%

Preparation and Spectrum Characterization of a High Quality Linear Variable Filter

et al. 2018

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To meet the requirements for lightweight, miniaturized dispersive optical systems for space applications, linear variable filters with a high transmittance and spatial dispersion coefficient are proposed. The filters were produced with dual ion beam sputtering, where a single layer thickness variation was achieved with a deposition rate adjustment based on a linear variable correction formula. A linear variable trend matching method was used to correct the film thickness based on the reduction of the mismatch error between two materials: Ta2O5 and SiO2. The influence of the spectral and spatial measuring average effects was addressed by sampling the spot size optimization. This paper presents an all-dielectric linear variable filter that operates between 520 and 1000 nm, with an excellent linear dependence of 40 nm/mm over 12 mm. The linear variable filter possessed a 2.5% bandwidth, and its transmittance was found to be >80% at the central wavelength of the band, with a 0.1% transmittance in the cut-off region. These results indicate great potential for optical devices for space applications, and the developed process has good reproducibility and stability.

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Limits of IR-spectrometers based on linear variable filters and detector arrays

Cited by 12 publications

References 0 publications

Portable Spectroscopy

Portable Spectroscopy

Development of a Handheld Spectrometer Based on a Linear Variable Filter and a Complementary Metal-Oxide-Semiconductor Detector for Measuring the Internal Quality of Fruit

Preparation and Spectrum Characterization of a High Quality Linear Variable Filter

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