China
Africa
Explore chapters and articles related to this topic
Imaging Fibrillar Collagen with Optical Microscopy
Published in Jiro Nagatomi, Eno Essien Ebong, Mechanobiology Handbook, 2018
Tong Ye, Peng Chen, Yang Li, Xun Chen
The point spread function is the key system function that determines the spatial resolution of any microscopy. Due to light diffraction, a point-like object cannot be imaged as a true point through an optical system, but spread to a diffraction pattern (Airy disc), called the point spread function. In an ideal diffraction limited system (no aberration, homogeneous illumination of the pupils), the 3D-PSF is a comet-like rotationally symmetric shape, as shown in Figure 6.9. The lateral diameter is defined as Airy unit representing the size of the Airy disc: 1AU=1.22λNA
Diffraction
Published in Rajpal S. Sirohi, Optical Methods of Measurement, 2018
The intensity distribution in the image of point source at infinity is given by [2J1(x)/x]2, where the argument x of the Bessel function J1(x) depends on the f -number of the lens, the magnification, and the wavelength of light. This distribution is plotted in Figure 3.4b. Figure 3.4a shows a photograph of an Airy pattern. It can be seen that the image of a point source is not a point but a distribution, which consists of a central disk, called the Airy disk, within which most of the intensity is contained, surrounded by circular rings of decreasing intensity. The radius of the Airy disk is 1.22λf/2a, where 2a is the lens aperture and f is the focal length of the lens. The Airy disk defines the size of the image of a point source. It should be kept in mind that if the beam incident on the lens has a diameter smaller than the lens aperture, then 2a in the expression for the disk radius must be replaced by the beam diameter. The intensity distribution in the diffraction pattern outside the Airy disk is governed by the shape and size of the aperture.
Basic Concepts of Laser Imaging
Published in Helmut H. Telle, Ángel González Ureña, Laser Spectroscopy and Laser Imaging, 2018
Helmut H. Telle, Ángel González Ureña
The image in confocal (laser) microscopy is an Airy disk, generated by the confocal aperture; a smaller aperture means better resolution, but the caveat is reduced transmitted light intensity. Both light throughput and spatial resolution can be improved by using a novel detector geometry, the so-called Airy-scan detector. It consists of a multielement (typically 32 elements) device recording the confocal Airy disk (its size is defined in Airy units, AU). Each detector element of size 0.2 AU acts like a pinhole, with a full detector diameter for light capture of 1.25 AU. This means that this detector array will produce 32 images with different, small displacements. As the sample is scanned, so is the Airy disk of the PSF. Then, mathematically one shifts all individual pixel images, with well-known displacement, back to the center position. As in the subpixel-shift approach for superresolution (discussed in Section 17.3), the composite image exhibits improved resolution in comparison to a classical confocal imaging. Together with image deconvolution algorithms, the spatial resolution can be improved by as much as a factor ×1.7. The overall concept of Airy scanning and the framework for image reconstruction are discussed in detail in Weisshart (2014), Huff (2015), and Huff et al. (2015). The process of Airy-scan imaging is shown schematically in Figure 17.20.
Application of extension rings in thermography for electronic circuits imaging
Published in Quantitative InfraRed Thermography Journal, 2022
For the camera without any extension ring and the minimum focusing distance given by the manufacturer, i.e. 30 cm, a resolution of 90 µm per pixel was obtained. As the camera’s FPA pixel pitch was 15 µm, it gave a magnification of 0.17. For configurations with an extension ring from, R1 to R9, a resolution from 50 µm/pixel to 5.5 µm/pixel was obtained (no diffraction taken into account) and magnification from 0.3 to 2.72 was achieved. The measured magnifications were compared with the values calculated using Equation (4), giving comparable results. It must be emphasised that for each of those measurements, because of the weight and the size of the camera, and the need to change the rings, the measurement setup had to be remade each time and the camera lens refocused. Thus, repeating the measurements with a different position of the lens focusing ring would give slightly different resolution values, especially for shorter rings, when larger values of depth of focus were possible. The measured spatial resolutions were compared with the Airy disk diameters calculated based on Equation (6), using λ = 4 µm as wavelength. For all but R0 and R1 configurations, the Airy disk diameter was higher than the measured geometrical resolution, thus suggesting that those configurations could be diffraction limited.