UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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Conference: Bucharest University Faculty of Physics 2009 Meeting


Section: Optics, Spectroscopy, Plasma and Lasers


Title:
Tilted front correction on the SHG pulse duration measurement for ultrashort pulse lasers


Authors:
R. Banici 1-2, D. Ursescu 1, R. Dabu 1


Affiliation:
1) National Institute for Laser Plasma and Radiation Physics - INFLPR , Atomistilor 409, 077125 Magurele, Bucharest, Romania

2) University of Bucharest, Physics Faculty, Romania


E-mail
romeo.banici@inflpr.ro


Keywords:
femtosecond laser pulses, optical aberrations,laser pulse duration measurement


Abstract:
Measurement of the pulse duration for ultrashort pulse lasers is usually performed using Second Harmonic Generation (SHG), Third Harmonic Generation, Frequency-Resolved Optical Gating or Spectral Phase Interferometry for Direct Electric-field Reconstruction. The measured pulse duration of ultrashort laser pulses in the focus of the beam is modified by optical aberrations. The tilted front of such ultrashort pulses is a typical optical aberration in Chirped Pulsed Amplification (CPA) laser systems. It appears from the non-parallel diffraction gratings in optical stretcher or compressor. Here it is analyzed the influence of the tilted front on the pulse duration measurement, both theoretically and in experiments, using Inverted Field Autocorrelator (IFA) and SHG autocorrelator. For a pulse with 2 mm diameter and pulse duration 250 fs (corresponding to 75 microns), the displacement between left and right edge of the pulse at 1.3 degree front tilt angle is about 50 microns. When we focus such a pulse to tens of microns, the focal spot distribution of the EM field intensity can look very different. We simulate the effect of the tilted front in the SHG autocorrelator and we find that in order to obtain an autocorrelation curve with FWHM of 250 *1.41 fs, the real pulse duration is 20% smaller that the one evaluated in the case of no tilt. In the case of shorter pulses, this effect can be dramatically larger. Example: for a 25 fs pulse with 1.3 degree front tilt at 2 mm diameter, focused at 10 microns,the autocorrelation curve FWHM is more then 3 times larger then in the case without tilt aberration. The results are important for experiments using CPA laser systems, such as electron acceleration experiments. This work was financially supported by the project PNCDI2-RP6/2007. References: G.Pretzler, A. Kasper, K.J.Witte; Appl. Phys. B 70,1-9 (2000)