A Talebpour

Re-focusing during the propagation of a focused femtosecond Ti:Sapphire laser pulse in air

Abstract The dependence of the intensity of a focused Ti:Sapphire laser pulse in air on the propagation distance was studied by measuring the photo-emission spectrum of N 2 and N 2 + . Refocusing was observed directly that agrees with the predictions put forward by Mlejnek et al. [M. Mlejnek, E.M. Wright, J.V. Moloney, Opt. Lett. 23 (1998) 382].

Semi-empirical model for the rate of tunnel ionization of N2 and O2 molecule in an intense Ti:sapphire laser pulse

Abstract A semi-empirical model capable of predicting the rate of tunnel ionization of N 2 and O 2 molecules interacting with strong Ti:sapphire laser pulses is derived.

Non-sequential multiple ionization of rare gas atoms in a Ti:Sapphire laser field

Multiple ionization of neon, argon and xenon in a high-intensity Ti:Sapphire laser field has been studied. Ion yield curves of xenon versus laser intensity have been obtained for the first six charges. Curves of charges 2+ to 6+ present obvious structures which can be attributed to the occurrence of non-sequential ionization processes. Also, comparison of the ion yields of the first three charges of Ar with previously obtained results inside a different laser field (Nd:Glass laser , ) indicates that non-sequential ionization is strongly wavelength dependent.

Multiphoton ionization of inner-valence electrons and fragmentation of ethylene in an intense Ti:sapphire laser pulse

Abstract Using linearly polarized 200 fs Ti:sapphire laser pulses the multiphoton ionization and fragmentation of ethylene was studied. A model is proposed which is able to satisfactorily predict the abundance of the different fragments, C2H4+, C2H3+ and C2H2+ as a function of laser intensity. It is shown that fragmentation of the molecule occurs as a result of multiphoton ionization of inner-valence electrons followed by radiationless transitions to various dissociation channels of the molecular ion.

The effects of dissociative recombination in multiphoton ionization of

Using stable, intense fs Ti:sapphire laser pulses, a distinct difference between the multiphoton ionization of and Xe, which have the same ionization potential, was observed. Considering electron rescattering and dissociative recombination, a new model for the dissociation of at low intensities is proposed which can explain this observation.

Fast pulsed electric field created from the self-generated filament of a femtosecond Ti:Sapphire laser pulse in air

Abstract We present an experiment demonstrating the generation of fast pulsed electric field from a plasma column created in air as a result of the interaction of N 2 and O 2 molecules with a 220 fs laser pulse. By first measuring the distribution of N 2 + and then by measuring the net charge present at different positions in the focal region, we determined that this plasma column has an intrinsic dipole moment, which generates these pulses. The origin of this dipole moment was attributed to longitudinal separation of electrons due to ponderomotive acceleration of electrons created through multiphoton ionization of N 2 and O 2 molecules.

Coulomb effect in multiphoton ionization of rare-gas atoms

Using 200 fs, 800 nm Ti:sapphire laser pulses to ionize noble atom gases, the ion versus intensity curves of these gases were obtained. By comparing the experimental curves with those obtained using different theoretical ionization rates, it was found that the inclusion of the effects on the ionization rate of the long-range Coulomb potential of the parent ion through quasi-classical perturbation theory (as proposed by Perelomov et al and Krainov) gives a rather good overlap with the experimental results.

Polarization dependence of the propagation of intense laser pulses in air

Measuring the photo-emission from a restricted section of a filament created in air as a result of propagation of a strong Ti:Sapphire laser pulse, the dependence of the propagation on the polarization (linear and circular) of the laser was studied. The results clearly indicate the dominant roles of two processes: self-focusing due to the nonlinear refractive index in the neutral gas and defocusing in the plasma as a result of multiphoton ionization. Multiple refocusing was observed in both polarizations.

Focusing limits of intense ultrafast laser pulses in a high pressure gas : road to new spectroscopic source

As a result of focusing ultrafast Ti:Sapphire laser pulses in a gas, a plasma column is created. Its density does not exceed some limiting value as a result of the defocusing by the electrons resulting from multiphoton ionization and the involvement of high order nonlinearities. The spectrum of the radiation from the excited species in the column has little contribution from the plasma continuum and the line broadening is less than that of the spectra radiated from a plasma generated by a long laser pulse. Thus, the spectroscopic source obtained using short laser pulses is an excellent source for spectroscopy.

Dissociative ionization of benzene in intense ultra-fast laser pulses

Based on the possibility of multiphoton ionization of the inner valence electrons in polyatomic molecules, a model was proposed to predict the abundance of different fragments resulting from dissociative ionization of the polyatomic molecules interacting with short laser pulses. According to this model the fragmentation of these molecules occurs through multiphoton ionization of the inner valence electrons, which results in a molecular ion in an excited state. Through radiationless transition the population is transferred to the highly excited levels of the ground electronic state. The molecular ion created in this manner is not stable and dissociates rapidly. To test the applicability of the model, the fragmentation of a benzene molecule interacting with linearly and circularly polarized Ti:sapphire laser pulses was studied. The model was tested by comparing the measured laser-intensity-dependent abundance of C4H4+ fragment ions with the calculated ones and excellent agreement was obtained with the experimental results.