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Spectroscopy
Published in C. R. Kitchin, Astrophysical Techniques, 2020
A practical device for producing spectra by diffraction uses a large number of closely spaced, parallel, narrow slits or grooves and is called a ‘diffraction grating’. Typical gratings for astronomical use have between 100 and 1,000 grooves per millimetre and 1,000–50,000 grooves in total. They are used at orders ranging from one up to 200 or so. Thus, the spectral resolutions range from 102 to 105. Although the previous discussion was based upon the use of clear apertures, a narrow plane mirror can replace each aperture without altering the results. So, diffraction gratings can be used either in transmission or reflection modes. Most astronomical spectroscopes are in fact based upon reflection gratings. Often the grating is inclined to the incoming beam of light, but this changes the discussion only marginally. There is a constant term, d sin i, added to the path differences, where i is the angle made by the incoming beam with the normal to the grating. The whole image (Figure 4.3) is shifted at an angular distance i along the image plane. Equation 4.13 then becomes() θ=sin−1[(mλd)−sini]
Diffraction
Published in Myeongkyu Lee, Optics for Materials Scientists, 2019
A diffraction grating is an optical element that splits and diffracts light into several beams traveling in different directions. A repetitive array of diffracting elements (apertures, obstacles, refractive index variations, etc.) has the effect of producing periodic alterations in the amplitude, phase, or both of the light. This makes constructive interference occur along certain well-defined directions. The multi-slit system described in Section 5.2.2 is a simple example showing the effect. Suppose that the width of each slit is much smaller than the inter-slit separation a. When a plane wave is incident, the slits become coherent sources as illustrated in Figure 5.19. Wavelets emanating at an angle θ from two adjacent slits have a path length difference of a sin θ. Obviously, constructive interference occurs at this angle when the path length difference equals an integral multiple of wavelengths, that is, () asinθm=mλ.
Diagnostic Methods
Published in Ranjeet Kumar Sahu, Somashekhar S. Hiremath, Corona Discharge Micromachining for the Synthesis of Nanoparticles, 2019
Ranjeet Kumar Sahu, Somashekhar S. Hiremath
The absorption spectra of the colloidal suspension of nanoparticles could be measured at room temperature using a double beam UV-vis spectrophotometer. Figure 3.1 shows the schematic diagram of a double beam UV-vis spectrometer. This spectrometer works in the wavelength range of 190–1100 nm. The spectrometer consists of a light source, diffraction grating, monochromator with a slit, sample holder (i.e. rectangular type quartz-cuvette), series of mirrors, and detector. The light source has two lamps—halogen lamp and deuterium lamp—which give an entire visible spectrum plus the near UV so that the wavelength range of about 190–1100 nm can be covered. A diffraction grating splits the light beam at various wavelengths in different directions. The monochromator with a slit separates and allows the light into a very narrow range of wavelengths that will reach the cuvette containing the sample. The cuvette which contains the sample has an internal width of 10 mm (i.e. path length of 10 mm) and a volume capacity of 3.5 ml.
Steering light in fiber-optic medical devices: a patent review
Published in Expert Review of Medical Devices, 2022
Merle S. Losch, Famke Kardux, Jenny Dankelman, Benno H. W. Hendriks
One patent describes a distal end design with a modified optical fiber core to induce diffraction [90]. This patent discloses a device that includes an optical fiber with a diffraction grating. A diffraction grating is an optical element with evenly spaced slots or grooves that divide the element into sections. Between the boundaries of the individual sections, there are small openings. If the size of these openings is in the range of the wavelength of the incident light, diffraction of light occurs. The diffraction direction is strongly dependent on both the shape of the diffraction grating and the wavelength of the incident light. As a result, well-defined diffraction gratings can steer light of specific wavelengths in the desired direction. In the device described by Zerfas [90], the diffraction grating is an angled optical grating aligned along a plane non-normal to the longitudinal axis of the optical fiber. This grating can be a fiber Bragg grating that is designed to redirect light of a specific wavelength off the fiber axis while transmitting light of other wavelengths, see Figure 4a.
MEMS gratings and their applications
Published in International Journal of Optomechatronics, 2021
Guangcan Zhou, Zi Heng Lim, Yi Qi, Fook Siong Chau, Guangya Zhou
In recent years, the continuous development of optical techniques has made it more efficient and effective to understand and explain scientific knowledge in different fields, such as in modern life science and remote sensing. Therefore, novel and innovative optical systems attract wide research and industrial interest to meet the increasing demand for various applications. The diffraction grating plays an essential role in numerous functional optical systems to disperse the incident light to a spectrum of associated lines or steer the incident light to a specified direction by employing a periodic structure. Many methods have been explored to construct an efficient grating architecture, and microelectromechanical system (MEMS) seems to be a promising technology considering the trend of miniaturizing optical systems. MEMS technology typically allows the integration of multiple electrical and mechanical functionalities within a small chip, and thus MEMS gratings become a potential candidate for future portable devices. Advanced manufacturing technology, such as ion etching, also permits the fabrication of grating structures on glass with compact size and low cost, but the produced gratings has fixed and limited functionalities. Compared with MEMS gratings, external driving sources are required to modulate the properties of these traditional gratings for different application scenarios, hence increasing the overall size of resulted systems. Till now, MEMS diffraction gratings have mainly been explored in two research architectures, namely the scanning grating and the tunable grating.
Ruling engines and diffraction gratings before Rowland: the work of Lewis Rutherfurd and William Rogers
Published in Annals of Science, 2018
Spectroscopy has been one of the most productive tools for research in the physical sciences. Diffraction gratings are an essential component of many spectroscopic instruments. During the last twenty years of the nineteenth century, Henry Rowland, Professor of Physics at Johns Hopkins University in Baltimore, was the sole source of diffraction gratings, and the ruling engines he built at Johns Hopkins continued to have a near-monopoly of diffraction grating supply for decades after his death in 1901.1 Rowland’s dominance has overshadowed the work of others in this field.