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Optical Crystals
Published in Marvin J. Weber, and TECHNOLOGY, 2020
Optical windows and lens are most frequently made of amorphous materials, such as glasses and plastics, because these materials are relatively inexpensive and can be made in large quantities with excellent reproducibility of material properties. Moreover, for many types of applications it is necessary to retain optical isotropy. Both glass and plastics are isotropic materials. In the case of crystalline solids only those with cubic symmetry are optically isotropic. They are rare compared with most known crystalline materials, which have lower crystallographic symmetry and therefore are optically anisotropic.
Materials for Optical Systems
Published in Anees Ahmad, Handbook of Optomechanical Engineering, 2018
The refractive materials commonly used for making lenses, prisms, optical windows, and filters can be broadly classified into three distinct categories, namely: glasses, optical crystals, and plastics and semiconductor materials. The physical, mechanical, and thermal properties of selected materials, which are most commonly used for optical and mechanical components, are covered in the subsequent sections. To keep the material property tables concise, only the nominal values at room temperature are listed, and therefore must only be used for preliminary evaluation and comparison purposes. Since the mechanical and thermal properties of materials can vary from one manufacturer to another and even from lot to lot for the same material from the same manufacturer, it is advisable to contact the manufacturer for obtaining more exact values of these properties for critical applications.
Optomechanical Design Principles
Published in Anees Ahmad, Handbook of Optomechanical Engineering, 2017
An optical window is a zero power element, in the form of a plane parallel plate. When subject to a uniform or soak temperature change, the window size changes, but geometry remains the same. Hence, there is no change in power or focus. If there is a temperature gradient ΔT through the thickness h of the window, the effect of the gradient is to distort the window. The hot side expands, while the cold side contracts, causing a spherical curvature, which is convex toward the hot side. The window becomes a weak lens with a power 1/f′ given by27
Past, present, and the future of the research and commercialization of CVD diamond in China
Published in Functional Diamond, 2022
Diamond domes and windows for high-speed guided missiles have been of great concern from the very beginning of the history of the CVD diamond films in abroad [61–63]. The related preparation and processing technologies had reached the state very close to the practical applications in the period from late 1990s to the 2010s [64]. This is because diamond is an ideal multi-spectrum optical window material which is capable of working in the LWIR (Long Wave Infrared, 8-12µm) and the millimeter wave (Radar Wave) range simultaneously. Most of all, it is most robust amongst all the IR window materials. In fact, it is the only one that can be used in the case of hypersonic missiles. The stagnant temperature for a hypersonic missile flying at 5-7 Ma in the dense atmosphere would reach 3000oK, which would induce a serious thermal shock that no window material except diamond could survive. Zinc sulfide (ZnS) is also an excellent multi-spectrum window material which could be used in the 3-5µm MWIR (Medium Wave Infrared) and 8-12µm LWIR (Long Wave Infrared) as well as in the Radar wave spectra ranges. Unfortunately, due to the extremely serious thermal shock, ZnS dome and windows would be damaged within 0.4 s at 4 Ma in the dense atmosphere [65].
Measuring aerosol active surface area by direct ultraviolet photoionization and charge capture in continuous flow
Published in Aerosol Science and Technology, 2019
R. T. Nishida, T. J. Johnson, A. M. Boies, S. Hochgreb
In parallel to the SMPS, a portion of the aerosol sample was passed through a UV photoionization chamber and irradiated with UV light while simultaneously being exposed to a constant electric field between two concentric electrodes. A 3 W UV lamp (Dinies Technologies GmbH, Germany: Model Mini3W-52ozon) provided ultraviolet light through a UV-extended fused silica optical window at wavelengths of 185 and 254 nm. A DC voltage in series with an amperometer was applied to the electrodes using a Keithley electrometer (Keithley Instruments Inc., Cleveland, OH, USA: Model 6517B). A constant applied voltage of 30 V (24 V cm−1) was chosen to capture the highly mobile ions created from the photoemission process without significantly capturing the charged particles (Nishida, Boies, and Hochgreb 2017, 2018). The electrometer measured the electrode current dominated by the photoemitted electrons () with a noise level lower than ±1 fA (Keithley Instruments Inc. 2009). However, significant electrical noise from other sources increased the signal uncertainty and the results from the electrode current () were not included in this work. A flow rate of 1.5 std L min−1 through the photoionization chamber was provided by the aerosol electrometer which measured the electrical current due to particle filtration in a Faraday cup electrometer () with a noise level lower than 1 fA at one second averaging time (TSI Inc. 2006a). Further specifications of the photoionization chamber and photoelectric current measurement may be found in Nishida, Boies, and Hochgreb (2018).
Determination of methane during anaerobic digestion by tunable diode laser absorption spectroscopy (TDLAS)
Published in Instrumentation Science & Technology, 2023
Haibin Cui, Fei Wang, Shengyu Hu, Wenyuan Wang, Jinhui Fan
The laser beam projected from the collimator is reflected by a protected gold mirror (PF05-03-M01, reflectance > 96%, Thorlabs, United States) and transmitted along the optical axis from the proximal end of the optical probe through an optical window. A flat optical window was initially used to isolate the internal measurement environment and external atmosphere. To eliminate the influence of optical fringes on the results, a wedged window (WW41050, transmission > 93%, Thorlabs, United States) was used to replace the flat optical window.