Z-scan method for nonlinear saturation intensity determination, using focused intense laser beams

Abstract

We describe a method for determining saturation peak intensities of nonlinear intense field processes. The Z-scan method takes advantage of the balance between nonlinear response and interaction volume change as an intense laser pulse is focused onto a sample. We derive a robust geometric factor, directly relating the peak intensity at optimal target displacement from the focal plane and the corresponding saturation intensity. The Z-scan method allows obtaining saturation intensities with no need of a priori assumptions about the nonlinear process; surprisingly even for unfavorable finite depth samples. The method is demonstrated experimentally for an intense laser pulse interaction with molecular anions.

Intense-Field Multiple-Detachment of F2¯: Competition with Photodissociation

“…Due to the decreasing interaction volume with increasing intensity, non-linear processes exhibit maximal yields at specific "zmax" positions. 37 The peak laser intensity at the zmax position can be directly focal displacements beyond 14mm. Double-detachment of the atomic F¯ anion to produce F + is represented by empty circles and exhibits maximal yield at zmax ~ 4mm.…”

“…The experimental apparatus was previously described in detail. 5,[19][20][21]37 Briefly, cold anions are produced by a 200 eV pulsed electron gun in a supersonic expansion of argon carrier gas, seeded with 2% NF3 precursor gas sample at a total pressure of 14 atm. Atomic F¯ and molecular F2¯ species are produced by dissociative electron attachment to the NF3 precursor.…”

“…The two colors are collinearly combined with a dichroic mirror at a computer controlled relative time delay. The dependence of different processes on the laser peak intensity is examined using only the intense 800 nm pulse and systematic displacement of a 250 mm focal length lens, 37 reaching up to ~10 16 W/cm 2 at the focal spot. The response of the F2¯ anion to the increasing peak intensity is directly compared to the previously studied atomic F¯ species, 19 by continuously alternating between the two species that are formed in the ion source, while maintaining the same laser conditions.…”

Simultaneous 3D coincidence imaging of cationic, anionic, and neutral photo-fragments

“…In our experimental setup, [28][29][30][31][32] anions are produced in a cold ion source, equipped with a pulsed electron gun and an Even-Lavie pulsed valve. 34 by dissociative electron attachment to the NF precursor sample, 35,36 supersonically expanded with Ar carrier gas.…”

“…[25][26][27] Using a fast anion beam target and a similar concept of an electrostatic spectrometer, we are able to investigate different competing dissociation and electron detachment channels in intense field interaction with atomic, molecular, and cluster anions. [28][29][30][31][32][33] The photofragment spectrometer design allows coincidence detection of all the possible dissociation products on the same detector, including the anionic, cationic, and neutral fragments. In the present study, we describe the design, calibration, and optimization of the photofragment spectrometer as well as an analytic model for extracting channel specific KER spectra from 3D coincidence imaging data.…”