Chapter 9
NIR Optics and Measurement Methods
Akifumi Ikehata
Abstract What type of components does a NIR spectrometer consist of? How do
these parts determine the performance of the instruments? The measurement targets
of NIR spectroscopy span a wide variety from transparent liquids to opaque solid
samples, and as described in Chap. 8, the NIR spectrometers are characterized by a
wide variety of device specifications and shapes. Consequently, what are the criteria
for choosing a spectrometer? In the first half of this chapter (9.1), the basics of the
optics that comprise the NIR spectrometer, such as the light source, spectroscopic
element, and detector, are explained. This will allow the reader to understand the
specifications, that control the functions of the spectrometer. Next, in the latter half
of this chapter (9.2), the measurement method is explained for each sample form,
namely liquid, solid, and paste. The most characteristic feature of NIR spectroscopy
is the use of diffuse reflected light, and the “interactance” method, which is a unique
application. It can be inferred that diffuse reflectance method contributes to the
expansion of the range of sample forms that are measurable by NIR spectroscopy.
Keywords Light sources · Spectrometers · Detectors · Sample cells ·
Interactance · Transflectance
9.1 Optics
9.1.1 Device Configuration
Near-infrared (NIR) spectrometers are composed of a light source, a sample optical
system, a spectrometer, and a detector. The configuration of NIR spectrometers is
largely confined to two types, as shown in Fig. 9.1a and b. In type (a), the sample is
positioned after the spectrometer and thereby irradiated with monochromatic light.
This configuration is often used for standard desktop UV–VIS spectrometers. In type
A. Ikehata (B)
Food Research Institute, National Agriculture and Food Research Organization (NARO),
2-1-12 Kannondai, Tsukuba 305-8642, Japan
e-mail: ikehata@affrc.go.jp
© Springer Nature Singapore Pte Ltd. 2021
Y. Ozaki et al. (eds.), Near-Infrared Spectroscopy,
https://doi.org/10.1007/978-981-15-8648-4_9
211
NIR Optics and Measurement Methods
Akifumi Ikehata
Abstract What type of components does a NIR spectrometer consist of? How do
these parts determine the performance of the instruments? The measurement targets
of NIR spectroscopy span a wide variety from transparent liquids to opaque solid
samples, and as described in Chap. 8, the NIR spectrometers are characterized by a
wide variety of device specifications and shapes. Consequently, what are the criteria
for choosing a spectrometer? In the first half of this chapter (9.1), the basics of the
optics that comprise the NIR spectrometer, such as the light source, spectroscopic
element, and detector, are explained. This will allow the reader to understand the
specifications, that control the functions of the spectrometer. Next, in the latter half
of this chapter (9.2), the measurement method is explained for each sample form,
namely liquid, solid, and paste. The most characteristic feature of NIR spectroscopy
is the use of diffuse reflected light, and the “interactance” method, which is a unique
application. It can be inferred that diffuse reflectance method contributes to the
expansion of the range of sample forms that are measurable by NIR spectroscopy.
Keywords Light sources · Spectrometers · Detectors · Sample cells ·
Interactance · Transflectance
9.1 Optics
9.1.1 Device Configuration
Near-infrared (NIR) spectrometers are composed of a light source, a sample optical
system, a spectrometer, and a detector. The configuration of NIR spectrometers is
largely confined to two types, as shown in Fig. 9.1a and b. In type (a), the sample is
positioned after the spectrometer and thereby irradiated with monochromatic light.
This configuration is often used for standard desktop UV–VIS spectrometers. In type
A. Ikehata (B)
Food Research Institute, National Agriculture and Food Research Organization (NARO),
2-1-12 Kannondai, Tsukuba 305-8642, Japan
e-mail: ikehata@affrc.go.jp
© Springer Nature Singapore Pte Ltd. 2021
Y. Ozaki et al. (eds.), Near-Infrared Spectroscopy,
https://doi.org/10.1007/978-981-15-8648-4_9
211