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Optics of Biomedical Instrumentation
Published in Daniel Malacara-Hernández, Brian J. Thompson, Advanced Optical Instruments and Techniques, 2017
Shaun Pacheco, Zhenyue Chen, Rongguang Liang
The pinhole in the confocal microscope determines both the optical sectioning capability and the resolution. The derivation of the PSF for a confocal microscope assumes an infinitely small pinhole. There is an inherent tradeoff in the choice of a pinhole. A smaller pinhole yields better resolution and better optical sectioning; however, there is less signal. In light starved samples, a small pinhole may not yield an appropriate signal-to-noise ratio (SNR). If the pinhole is increased, the signal is higher, but more light is detected outside the focal point. If the pinhole is increased too much, the system is no longer confocal. A further discussion of the pinhole size on the resolution is found in Refs. [3–5].
Imaging Fibrillar Collagen with Optical Microscopy
Published in Jiro Nagatomi, Eno Essien Ebong, Mechanobiology Handbook, 2018
Tong Ye, Peng Chen, Yang Li, Xun Chen
A functioning confocal microscope generally consists of one or multiple laser sources, laser scanning optics, one or multiple sensitive photodetectors, a data acquisition system, and a computer that controls the scan and reconstructs images. A confocal laser scanning microscope is usually equipped with continuous wave lasers at the short visible or ultraviolet wavelength. An Ar-Ion gas laser was traditionally used, as it outputs two emission peaks at 488 and 514 nm. The recent update is diode-pumped solid-state (DPSS) lasers or a supercontinuum laser, which covers the entire visible and near-IR region.
Optical Nanosensors
Published in Vinod Kumar Khanna, Nanosensors, 2021
Even if the sensitivity of the SPR sensors is slightly superior to that of LSPR NSs, a direct comparison is not possible because of the different mechanisms that give rise to their respective sensitivity gains. However, some advantages of LSPR NSs can be cited. The LSPR NSs do not require temperature control, compared with SPR, since the large refractive index sensitivity of SPR induces a strong dependence on the environmental temperature. No specific angular conditions of excitation are required for LSPR. There is no requirement of prism coupler-based, grating coupler-based, or optical waveguide optical accessories. In practice, SPR sensors require at least 10 × 10 μm2 area for a sensing experiment, whereas, for LSPR sensing, the probed zone can be minimized to a large number of individual sensing elements up to a single NP, using confocal or near-field measurement techniques. “Confocal” means having the same focus or foci. Confocal microscopy is an optical imaging technique, offering several advantages over conventional optical microscopy, including a shallower depth of field, and elimination of out-of-focus glare. Resolution and contrast of a micrograph are increased by using point illumination and a spatial pinhole to eliminate out-of-focus light in specimens that are thicker than the focal plane. Near-field measurement techniques include near-field scanning optical microscope, in which the intensity of light focused through a pipette with an aperture at its tip is recorded, as the tip is moved across the specimen in a raster pattern at a distance of much less than a wavelength; this allows for the surface inspection with high spatial, spectral, and temporal resolving power. Finally, the extinction spectroscopy (highly sensitive optical spectroscopic technique that enables measurement of absolute optical extinction by samples that scatter and absorb light) of LSPR does not need a complex device; an ultraviolet (UV)-visible microspectrometer is sufficiently efficient to obtain the spectra.
Assays and enumeration of bioaerosols-traditional approaches to modern practices
Published in Aerosol Science and Technology, 2020
Maria D. King, Ronald E. Lacey, Hyoungmook Pak, Andrew Fearing, Gabriela Ramos, Tatiana Baig, Brooke Smith, Alexandra Koustova
Phase-contrast microscopy is a variant of bright-field microscopy that takes advantage of the variation in the refractive index between a microorganism and its surrounding medium to enhance contrast and provide easier viewing (Zernike 1942; Morris 1995). Phase-contrast microscopy can be used to observe live microorganisms, but is particularly useful for imaging low-contrast specimens. Fluorescence is a powerful tool that can be used in microscopy to examine particular structures or molecules in a microorganism or its surroundings. Fluorescence can be achieved either with fluorescent dyes or with cells that are naturally or artificially fluorescent. A variant of fluorescent microscopy is confocal microscopy, which allows very precise resolution and location of fluorescent molecules in a cell. Epifluorescence microscopy has been used to determine viral abundance in bioaerosols (Michaud et al. 2018).
Imaging resolution and properties analysis of super resolution microscopy with parallel detection under different noise, detector and image restoration conditions
Published in Journal of Modern Optics, 2018
Zhongzhi Yu, Shaocong Liu, Shiyi Sun, Cuifang Kuang, Xu Liu
Confocal microscopy is widely employed as a method that can enhance resolution significantly. However, the trade-off between the signal-to-noise ratio (SNR) and resolution has stymied further improvement of the performance of confocal microscopy. A larger pinhole size allows more incident light on the detector; however, the resolution decreases owing to a more blurred point spread function (PSF) introduced by the larger pinhole size. Although pursuing the sharper PSF theoretically guarantees higher resolution, in this case, most of the light emitted from sample would be blocked by the pinhole, leading to a sharp decrease in SNR (1–4). To surpass this limit, using parallel detection to replace the pinhole could be an effective method to enhance the resolution and improve the SNR. Until now, various parallel detection methods have been proposed, including spinning disc microscopy (5,6), optical photon reassignment microscopy (7), rescan confocal microscopy (8), fluorescence depletion microscopy (9,10), and virtual k-space modulation optical microscopy (11). These methods have been implemented in a variety of applications.
A review on mechanical and tribological characterization of boron carbide reinforced epoxy composite
Published in Advanced Composite Materials, 2021
Sunny Bhatia, Surjit Angra, Sabah Khan
Confocal microscopy is also used to monitor the curing of the clear and filled epoxies. In this method point illumination and a pinhole are used in front of a detector in an optically conjugate plane [45]. Confocal microscopy allows generation of 3D images of the specimen.