Please explain the difference between the spot size and the crater diameter and how to find them? the ablation threshold range of steels machined by femtosecond laser?
Dear Rajashekar, you can use the method used in this paper,
Appl. Phys. A 74, 729–739 (2002)/ (DOI) 10.1007/s003390101183
It is possible to calculate the ablation treshold by measuring the radius of the ablated craters, it is possible to calculate the fluence of the focused beam by directly correlating the measured radius of the craters with the radius of calculated profile fluence. In order to carry out this procedure, a simulation of the propagation of a Gaussian beam through a lens must be made by using Fresnel diffraction.
Most popular method being D-square method (https://www.osapublishing.org/ol/abstract.cfm?URI=ol-7-5-196). You plot the square of the crater diameter against laser power/pulse fluence/fluence(if you know w0). This method allows you deduce ablation threshold, w0 and incubation coefficient of any given material.