Y. Beaudoin

High harmonic generation in atomic and diatomic molecular gases using intense picosecond laser pulses-a comparison

High harmonic generation has been investigated in the atomic gases Ar and Xe as well as in the diatomic molecular gases H2, D2, N2 and O2 using a linearly polarized picosecond dye laser (594 nm) and a linearly polarized subpicosecond Ti:sapphire/Nd:glass laser (1053 nm). The harmonic conversion efficiencies are compared by choosing different gas pairs as a function of three parameters: (1) field-free ionization potential (2) mass and (3) static average polarizability. It is shown that the ionization potential and mass are not sensitive parameters for harmonic efficiency, but the polarizability is an important factor.

Nonlinear refraction in CS 2 at 10.6 μm

The nonlinear refractive index n(2) of CS(2) at 10.6 microm, the value of which is a subject of a recent controversy, is measured by an external self-focusing method. We found that n(2) = (2.1 +/- 0.7) x 10(-11) esu, similar to the accepted value of n(2) in the visible. Self-bending of spatially asymmetric CO(2) laser beam in CS(2) due to an ultrafast Kerr effect is observed, and the deduced value of n(2) is in agreement with our results.

Self-bending of a spatially asymmetric carbon dioxide laser beam in a nonlinear medium

Self-bending of a transversely nonuniform CO2 laser beam owing to the Kerr effect in CS2 is studied. The effect is used to measure the nonlinear refractive index n2 of CS2 at 10.6 μm. Self-bending can be used for ultrafast all- optical light-beam manipulation such as light-by-light deflection and nonlinear-optical switching/power limiting and for an optical streak camera.

Investigation of photon emission spectra of hydrogen using intense subpicosecond Ti:sapphire/Nd:glass laser pulses

High-harmonic generation processes have been experimentally investigated in molecular hydrogen gas as both molecular dissociation and ionization occur in the gas. The high harmonics observed in our experiment can be mainly attributed to neutral hydrogen molecules. Besides the harmonic spectra, two strong Lyman lines from the dissociated hydrogen atoms and the emission from the neutral hydrogen molecules are observed. Several possible excitation and dissociation channels of hydrogen molecules are proposed. It is found that resonance effects are important for both high-harmonic generation and molecular dissociation. Theoretical calculations using the time-dependent Hartree-Fock (TDHF) method for H2 reproduce some of the resonance effects.

Measurement of the nonlinear refractive index of SF6 with a hollow prism

We measure the nonlinear refractive index of SF6 at three different CO2 laser lines. Higher terms than the cubic nonlinearity are found and the behavior of the refractive index as a function of the laser intensity depends strongly on the frequency used, reflecting the characteristic SF6 absorption dynamics.

High harmonics generation in atoms and molecules using ultrashort laser pulses in the multiphoton regime

Summary form only given. We studied high harmonic generation in jets of atomic gases Ar and Xe as well as diatomic molecular gases H/sub 2/, D/sub 2/, N/sub 2/, and O/sub 2/ using a linearly polarized picosecond dye laser (594nm) and a linearly polarized subpicosecond Ti:sapphire/Nd:glass laser (1053nm). The harmonic conversion efficiencies are compared by choosing different gas pairs as a function of three parameters: (1) field-free ionization potential (2) mass and (3) static average polarizability.

Frequency Tuning and Chirping of a Pulsed CO2 Laser by an Intracavity Prism

Abstract Based on results of TEA-CO2 laser-frequency tuning by an intracavity dispersive prism, the feasibility of CO2 laser-frequency chirping by a nonlinear intracavity prism or due to self-bending effects is discussed. The proposed scheme is shown to be superior to other nonlinear optics methods for CO2 laser-frequency chirping.

Direct Measurement Of The Nonlinear Refractive Index Of Sf 6 Around 10 µm

For many applications related to high power laser propagation such as laser isotope separation or parametric wave mixing, knowledge of the refractive index n in the infrared (IR) is very important to obtain maximum efficiency in these processes. We present here a simple technique to measure directly the nonlinear refractive index n2 of a molecular gas in the IR. We use CO2 laser propagation in SF6 as an example. SPE, is a well-studied molecule exhibiting nonlinear properties such as self-focusing (S.F.), self-defocusing (S.D.) and four-wave mixing of a CO2 laser radiation around 10.6 pm. However, n2 and the related nonlinear susceptibility x(3) of SF6 were derived from indirect experiments by measuring the reflectivity of phase-conjugated signall or from the self-focused beam diameter dependence on laser intensity2. In our case the technique allows to measure directly n2 and to tell the occurence of S.D. or S.F. without having to take into account intensity dependent absorption.