Mr Amir Hossein Shahbazi, Prof. Khosro Madanipour, Prof. Ata Koohian,
Volume 9, Issue 2 (11-2015)
Abstract
Defocusing effects in modulation transfer function (MTF) measurement of charge coupled device (CCD) cameras is the main focus of current paper. We introduce measuring Point-spread function (PSF) in order to calculate the MTF and further more we will study the shape of MTF and its cut-off frequency by adjusting the lens focusing in different locations. A collimated white light LED by broadband spectra is used as source and our results shows that the cut-off frequency is related to defocusing.
Shadi Davoudi, Somayeh Mehrabian,
Volume 16, Issue 1 (1-2022)
Abstract
In this study, the self-guiding of an ultrashort laser pulse through air is investigated. Therefore, the terms of self-focusing, plasma defocusing and the pulse energy depletion due to the ionization, are considered in the wave equation. Then the laser pulse spot size equation is obtained using the source-dependent expansion method. Our results show that the laser pulse self-guiding occurs for the first twenty Rayleigh lengths. However, the laser pulse undergoes diffraction as it propagates further along the z axis. Moreover, it is seen that the back of the laser pulse is diffracted the most owing to the fact that the plasma is formed as the laser pulse propagates through air. It is also shown that the spot size variations affect the temporal and spatial profiles of the laser intensity, the laser pulse power and the ionization process.
