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Optical System and Design
Published in Shen-En Qian, Hyperspectral Satellites and System Design, 2020
A beam splitter is an optical device for dividing a beam into two or more separate beams. A simple beam splitter may be a very thin sheet of glass inserted in the beam at an angle to divert a portion of the beam in a different direction. A more sophisticated type consists of two right-angled prisms cemented together at their hypotenuse faces. A dichroic mirror, also referred to as a dichroic filter, is the optical device commonly used as a beam splitter in imaging spectrometers to divert the beam to VNIR and SWIR spectrometers. It spectrally separates light by transmitting and reflecting light as a function of wavelength. A long-pass dichroic mirror is highly reflective below the cutoff wavelength and highly transmissive above it, while a short-pass dichroic mirror is highly transmissive below the cutoff wavelength and highly reflective above it.
All About Wave Equations
Published in Bahman Zohuri, Patrick J. McDaniel, Electrical Brain Stimulation for the Treatment of Neurological Disorders, 2019
Bahman Zohuri, Patrick J. McDaniel
An interferometer is really, a precise scientific instrument designed to measure things with extraordinary accuracy. The basic idea of interferometry involves taking a beam of light (or another type of electromagnetic radiation) and splitting it into two equal halves using what’s called a beamsplitter (also called a half-transparent mirror or half-mirror). This is simply a piece of glass whose surface is very thinly coated with silver. If you shine light at it, half the light passes straight through and half of it reflects back, so the beam-splitter is like a cross between an ordinary piece of glass and a mirror. One of the beams (known as the reference beam) shines onto a mirror and from there to a screen, camera, or other detectors. The other beam shines at or through something you want to measure, onto a second mirror, back through the beam splitter, and onto the same screen. This second beam travels an extra distance (or in some other slightly different way) to the first beam, so it gets slightly out of step (out of phase).
Neutral Mirrors and Beam Splitters
Published in H. Angus Macleod, Thin-Film Optical Filters, 2017
A device that divides a beam of light into two parts is known as a beam splitter. The functional part of a beam splitter generally consists of a plane surface coated to have a specified reflectance and transmittance over a certain wavelength range. The incident light is split into a transmitted and a reflected portion at the surface, which is usually tilted so that the incident and reflected beams are separated. The ideal values of reflectance and transmittance may vary from one application to another. The beam splitters considered in this section are known as neutral beam splitters, because the reflectance and transmittance should ideally be constant over the wavelength range concerned. There are different types of beam splitter, considered in later chapters, that separate the light into different wavelength regions and are usually known as dichroic or that separate the light according to polarization.
Optical coherence tomography systems for evaluation of marginal and internal fit of ceramic reconstructions
Published in Biomaterial Investigations in Dentistry, 2022
Hiba Al-Imam, Ana R. Benetti, Pete Tomlins, Klaus Gotfredsen
Nonetheless, different types of OCT systems have been used to assess the fit of dental reconstructions since 2018 [6–10]. OCT is based on light interference between signals from a sample and a reference mirror [13–15]. Depending on the OCT system, the near infrared light can either be swept source (SS-OCT) or broadband. In the SS-OCT, a tunable laser is used to sweep the wavelengths. Broadband source is applied in the spectral domain OCT (SD-OCT) system and emits a broad range of wavelengths. In both systems, a beam splitter is used to split the light beam in two, propagating to the reference mirror and to the sample. Subsequently, the light backscattered from within the sample and from the reference mirror is coupled through the beam splitter/coupler [13–15]. In the specific SD-OCT system employed in this study, the interference fringes from the reference mirror and sample are detected using a diffraction grating and a single-line photodetector. However, other configurations may be applied in SD-OCT systems [13,15]. For the SS-OCT system, the light is detected using a single-element balanced photodetector. These interference fringes provide a single A-scan, which is a single scanned line in depth from within a sample. Raster scanning across the sample will result in propagation of A-scans, giving rise to a 2D in depth image – known as a B-scan.
Development of a radiative transfer model for the determination of toxic gases by Fourier transform–infrared spectroscopy with a support vector machine algorithm
Published in Instrumentation Science & Technology, 2018
Hyunwoo Nam, Jong-Seon Kim, Hyeon Jeong Kim, Jae Hwan Lee, Young Il Kang, Byeong Hwang Park
An FT-IR sensor scans the entire wavelength range simultaneously by using an interferometer. For example, a Michelson interferometer consists of a beam splitter and stationary and moving mirrors. The beam splitter divides the incoming IR beam of radiation into two optical beams. Some are partially reflected to the fixed mirror, while rest are transmitted to the moving mirror. Then, the two beams that are on different paths recombine and may interfere with each other. The sum of the intensities of the two beams varies as a function of the path difference, which can be expressed as interferogram. The fast Fourier transform (FFT) is applied to convert the time-domain interferogram data into a frequency-domain spectrum. Then, by using Planck’s function, the radiance spectrum is changed to the brightness temperature spectrum that shows the spectral signatures of targeted chemical compounds.