Near‐Infrared Array Spectrometers

Abstract

Diode‐array spectrometers have become well established for use in the near‐infrared (NIR) spectral region, particularly with fiber‐optic probes. This article discusses the advantages of array spectrometers, specifically, photometric performance, measurement speed, wavelength resolution, stability and accuracy, environmental ruggedness, and reduced cost. The spectral signal, optical throughput, noise sources, and resolution and the spectral response performance parameters of array spectrometer systems are described. The properties of diffraction grating polychromators are discussed in detail starting with diffraction grating principles, spectral resolution, and throughput. Stray radiant energy, absorbance linearity, and dynamic range are considered. Specific grating related issues, including multiple diffraction orders, grating efficiency, and Wood’s anomalies, are defined. The properties of the concave holographic grating and its unique geometry are described. Array detectors for NIR spectroscopy have different requirements than those for Raman spectroscopy due to the larger optical signal and dynamic range typical of NIR transmittance and reflectance measurements. The principles of photon detectors, the operational theory of photodiodes, particularly InGaAs, and the responsivity of various NIR detectors are reviewed. Resistive and capacitive transimpedance preamplifier circuits are compared, with an emphasis on dynamic range and signal amplitude resolution. Discussion of the sources of visible and NIR array spectroscopy completes the review of the principle elements of an array spectrometer system. The spectral radiance of tungsten‐halogen lamps and its temperature sensitivity are described, as are the halogen cycle and the issues of lamp life and failure modes. Finally, deuterium arc lamps and xenon arc and flash lamps are discussed in brief.

Assessment of Lignocellulosic Biomass Using Analytical Spectroscopy: an Evolution to High-Throughput Techniques

“…• Lower cost, simple instrumentation [122,129,254] • Spectra are less intense those from FTIR analysis [113] • Little to no sample preparation required [254] • Only C-H, O-H, N-H, and S-H moieties measured [122] • Water compatible [124] • Requires deconvolution, often with chemometrics [108,113,254] • Field-portable [113] • Calibration [113] • Amenable to process analytics, fiber optics [113,130,254] • High-throughput [29,215,227,248] • Nondestructive [248,254] NMR spectroscopy…”

“…Although applications of common spectroscopic instrumentation such as NMR are discussed, the emphasis will be on methods with highthroughput capabilities. For a detailed analysis of spectroscopic fundamentals and instrumentation, the reader is referred to various informative resources [80,105,108,113,116,117,[119][120][121][122][123][124][125][126][127][128][129][130][131].…”

A Study on the Spectral Change in a Chlorophyll Absorption Band Monitored During the Growth of Japanese Tea Leaves

“…The polychromator is typical spectrometer type (Stark, 2002) and uses a diffraction grating and a collimate lens for the focusing and dispersing of light. The detector for KE-1 is equipped with 256 silicon photo diodes.…”

A polychromator-type near-infrared spectrometer with a high-sensitivity and high-resolution photodiode array detector for pharmaceutical process monitoring on the millisecond time scale

“…[5][6][7][8][9][10] The Fourier transform method is widely used in NIR spectrometers; this method obtains the spectrum by the Fourier transform of interference signal data acquired while changing the optical path length. 7 It needs a wavelength standard, and therefore, it has very high wavelength accuracy.…”

“…This method has advantageous features such as high-speed measurement, robustness, and compactness owing to the non-mechanical moving architecture. 9 These methods involve specific advantages and disadvantages, and it is necessary to select one that is most suitable for use as an in-line analyzer. Generally speaking, this PAT application requires features such as high-speed measurement, compact size, and maintainability (if possible, maintenancefree).…”