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The influence of thermal blooming on characterizations of focused general astigmatism Gaussian beams (GAGBs) propagating through the atmosphere is studied analytically and numerically. The analytical formula of distortion number of focused GAGBs is derived. It is found that a GAGB with smaller value of the rotation parameter has greater resistance to the thermal blooming effect, and a GAGB has greater resistance to the thermal blooming effect than a simple astigmatism Gaussian beam (SAGB), which may be useful in practice. On the other hand, there exists a maximum of the distortion number as the astigmatism parameter varies, i.e., the GAGB is most affected by thermal blooming when a certain value of the astigmatism parameter arrives, which should be avoided in practice. In addition, it is shown that the orbital angular momentum and the gradient force of GAGBs decrease because of thermal blooming effect in the atmosphere. [ABSTRACT FROM AUTHOR]

We report a method for characterizing the focussing laser beam exiting the objective in a laser scanning microscope. This method provides the size of the optical focus, the divergence of the beam, the ellipticity and the astigmatism. We use a microscopic-scale knife edge in the form of a simple transmission electron microscopy grid attached to a glass microscope slide, and a light-collecting optical fibre and photodiode underneath the specimen. By scanning the laser spot from a reflective to a transmitting part of the grid, a beam profile in the form of an error function can be obtained and by repeating this with the knife edge at different axial positions relative to the beam waist, the divergence and astigmatism of the postobjective laser beam can be obtained. The measured divergence can be used to quantify how much of the full numerical aperture of the lens is used in practice. We present data of the beam radius, beam divergence, ellipticity and astigmatism obtained with low (0.15, 0.7) and high (1.3) numerical aperture lenses and lasers commonly used in confocal and multiphoton laser scanning microscopy. Our knife-edge method has several advantages over alternative knife-edge methods used in microscopy including that the knife edge is easy to prepare, that the beam can be characterized also directly under a cover slip, as necessary to reduce spherical aberrations for objectives designed to be used with a cover slip, and it is suitable for use with commercial laser scanning microscopes where access to the laser beam can be limited. [ABSTRACT FROM AUTHOR]

Abstract: X-ray lasers represent a powerful tool to explore matter under extreme conditions. A rigorous characterization of their output parameters is, therefore, of substantial importance for the purposes of the experiments being conducted at these sources. A profound knowledge of the spatial, temporal, spectral, statistical, coherence, and wavefront beam properties may protect us from an unwanted misinterpretation of the experimental data. We present an experimental technique of the spatial (transverse and longitudinal) characterization of the beam profile. Investigating ablative imprints in various materials, we evaluate the spatial properties of the incident beam, namely, the beam waist radius and position, the Rayleigh range, M 2 parameter, and divergence. In this paper, we recall briefly our recent work at the transverse beam profile reconstruction. A newly developed method of the longitudinal beam profile characterization is the main subject of this work. [Copyright &y& Elsevier]

On the basis of well-known methods to obtain the standard Stokes parameters, two simple experimental procedures are analysed to measure the so-called generalized degree of polarization, P, defined elsewhere [Opt. Commun., 149 (1998) 230]. After discussing the accuracy of the methods, the generalized degree of polarization of a non-uniformly polarized beam emerging from an optically pumped birefringent Nd:YAG rod optically pumped is experimentally investigated in terms of the pumped power. [ABSTRACT FROM AUTHOR]

The International Organization for Standardization (ISO), in collaboration with the academic community, has developed and published a comprehensive system of standards for the characterization of optical components and laser beams. Our study offers a pedagogical introduction to the theory and application of laser beam characterization in accordance with ISO 13694:2018 and ISO 11145:2018. The characterizing parameters of each ISO standard are presented, defined mathematically, and explained in detail through the use of a minimum working example. A laser beam applied to an actual industrial process [laser-assisted bonding (LAB) process in the semiconductor packaging industry] is thoroughly analyzed to help the reader understand and interpret the characterizing results. Background noise correction and unit conversion methods are also discussed. We target researchers new to the field of laser beam analysis who want the acquire background knowledge, as well as more experienced researchers who want to implement their own laser beam analysis software and propose new definitions for their specific application. Although our study deals with only two ISO standards, the methods covered in our study can be easily applied to other norms that fit the reader's application. Our study should not be treated as a full review of the LAB process nor of the beam profiling instruments and measurement principles. These are only mentioned to enhance the reader's learning experience. [ABSTRACT FROM AUTHOR]

The minimum size of objects or geometrical features that can be distinguished within a laser scanning point cloud is called the resolution capability (RC). Herein, we develop a simple analytical expression for predicting the RC in angular direction for phase-based laser scanners. We start from a numerical approximation of the mixed-pixel bias which occurs when the laser beam simultaneously hits surfaces at grossly different distances. In correspondence with previous literature, we view the RC as the minimum angular distance between points on the foreground and points on the background which are not (severely) affected by a mixed-pixel bias. We use an elliptical Gaussian beam for quantifying the effect. We show that the surface reflectivities and the distance step between foreground and background have generally little impact. Subsequently, we derive an approximation of the RC and extend it to include the selected scanning resolution, that is, angular increment. We verify our model by comparison to the resolution capabilities empirically determined by others. Our model requires parameters that can be taken from the data sheet of the scanner or approximated using a simple experiment. We describe this experiment herein and provide the required software on GitHub. Our approach is thus easily accessible, enables the prediction of the resolution capability with little effort and supports assessing the suitability of a specific scanner or of specific scanning parameters for a given application. [ABSTRACT FROM AUTHOR]