N. Dimitrov, M. Zhekova, G. G. Paulus and A. Dreischuh
In this work, we present an improved technique for measuring both the magnitude and sign of the topological charge of input optical vortex beams carried by short laser pulses. Numerical simulations and experimental evidences for the interference signal obtainable at the output of an inverted field interferometer (IFI) valid for both continuous wave and femtosecond optical vortex beams and pulses with an eventual pulse front tilt are in an excellent agreement. An IFI also appears to be a valuable tool for calibrating a built-in variable delay line and for estimating an eventual pulse front tilt of the input ultrashort laser pulses without any realignments. As a trivial side effect, by blocking alternatively one of the two arms of the interferometer, one can use OV beams/pulses of opposite TCs, which are well located in the plane of a desired target, eventually — at precisely known time delays..