China
Africa
Explore chapters and articles related to this topic
The Diffraction Grating
Published in Abdul Al-Azzawi, Photonics, 2017
A spectrograph is a spectrometer that images a range of wavelengths simultaneously, either onto photographic film or a series of detector elements, or through several exit slits (sometimes called a polychromator). The defining characteristic of a spectrograph is that an entire section of the spectrum is recorded at once.
Raman spectroscopy in biomineralization
Published in Elaine DiMasi, Laurie B. Gower, Biomineralization Sourcebook, 2014
Karen Esmonde-White, Francis Esmonde-White
5.2.1 RAMAN SPECTROGRAPH e instrument used to collect Raman spectra (interchangeably called a spectrometer or spectrograph) includes a light source, optics, and a detector. Modern Raman instrumentation almost exclusively uses lasers as excitation light sources due to the high-intensity monochromatic light that can be produced. The excitation light is delivered to the sample and Raman-scattered light is collected back into the spectrograph by some intermediate optics. These intermediate optics can include lenses, mirrors, and lters. Only a small fraction of the light used to excite the sample is Raman scattered. The majority of the excitation light is scattered inelastically. One or more optical lters are used to reject elastically scattered excitation light to minimize stray light that otherwise overwhelms the detector. The spectrograph is the detection module. The spectrograph includes an optical detector to record intensity with respect to wavelength (in nanometers or micrometers). Raman scattering causes photons to gain or lose speci c amounts of energy based on molecular vibrations—regardless of the excitation energy. Raman spectra are reported with wavenumber units (photon energy in inverse centimeters, or cm-1), which are independent of the excitation frequency. This allows spectra collected at different excitation frequencies to be compared. After correcting for variable detector e ciency, spectra collected using different excitation frequencies will usually be similar in shape, though at some excitation frequencies, resonance enhancement can lead to ampli cation of particular bands (resonance Raman spectroscopy). Spectrographs use either dispersive (with re ective or transmissive gratings) or interferometric (Fourier transform, or FT) methods for resolving light of different frequencies. Re ective gratings have the bene t of not having chromatic aberration, while transmissive systems have a higher throughput (greater e ciency). Early Raman systems used scanning systems to turn re ective gratings, measuring each point in the spectrum sequentially using a single detector element. Single-point detectors are less expensive but require that the spectral data be collected sequentially. Scanning dispersive Raman systems are no longer widely used because there is an advantage in collecting light for longer periods of time. Line and array imaging detectors allow light of different wavelengths to be measured simultaneously. Instead of spending a small amount of time at many separate points, these systems allow light to be collected across the
A spectroscopic bandwidth correction method based on multi-bandwidth functions
Published in Journal of Modern Optics, 2022
As an important part of optical instruments, the spectrograph is a basic optical detection instrument for spectroscopy research and material spectral analysis. It has the advantages of stable performance, accurate detection, and fast analysing speed over ordinary optical detection instruments. With the rapid development of optoelectronics, advanced manufacturing and other new technologies, the performance of the spectrograph is continuously improved. The development of spectroscopy and spectral analysis technology also makes the application of the spectrograph develop widely. At present, they are widely used in agriculture, industrial automatic monitoring, astronomy, environmental detection, food safety, colour measurement and other fields [1–5]. However, the bandwidth function [6] of the spectrograph affects the spectral resolution of the instrument and can result in measurement errors. To obtain accurate measurement results, a practical scheme is to use a bandwidth correction algorithm to correct the measured spectrum.
Soot Pyrometry by Emission Measurements at Different Wavelengths in Laminar Axisymmetric Flames
Published in Combustion Science and Technology, 2022
J. J. Cruz, Luis Fernando Figueira da Silva, F. Escudero, F. Cepeda, J. C. Elicer-Cortés, A. Fuentes
When thermal radiation is transported throughout a flame, soot emission may be absorbed by the adjacent participating medium. Considering the classical particle cloud model, the exponential term that describes this self-absorption process poses an important problem to the solution of the associated integral equation (Liu, Thomson, Smallwood 2013). This solution requires the knowledge of the soot absorption coefficient, , the determination being subject of several proposed techniques. For instance, the Modulated Absorption/Emission technique (MAE) (Jenkins and Hanson 2001; Legros et al. 2015) relies on light extinction measurements to determine this coefficient. The multi-spectral soot emission technique (De Iuliis et al. 1998; Snelling et al. 2002) determines the soot temperature via a curve fitting between the measured emission and its corresponding detection wavelengths. These approaches require external light sources (e.g. a laser) or careful independent spectrograph calibration at several detection bands, which could constitute a source of uncertainties. These uncertainties are over-layered to other error sources, such as the soot refractive index function value (Goulay et al. 2009) and the experimental noise (Li and He 2019). Different methods have been proposed to solve the integral equation when the self-absorption term is not accounted for, but which correct the attenuated measured signals by modeling the projected signal ratio without and with self-absorption (Freeman and Katz 1960; Snelling et al. 2002). However, these methods also require the knowledge of soot properties, such as the absorption coefficient (). The ratio color pyrometry technique involves a function that relates the soot temperature with the ratio of soot emission measured at different wavelengths (Escudero et al. 2016; Jakob et al. 2014; Jenkins and Hanson 2001; Legros et al. 2015; Panagiotou, Levendis, Delichatsios 1996). In cases where self-absorption is neglected, the radiative model is simplified to an Abel integral equation. Errors of around tenths of Kelvin have been reported (Kempema and Long 2018; Liu, Thomson, Smallwood 2013) when the ratio of two wavelengths emission is used.