Browsing by Author "Bernhardt, J."

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Direct observation of super-excited states in methane created by a femtosecond intense laser field
(2008-11-28)
Azarm, A.
;
Xu, H. L.
;
Kamali, Y.
;
Bernhardt, J.
;
Song, D.
We report, for the first time, a direct observation of the super-excited states of CH(4) in femtosecond intense laser fields using a pump (800 nm)-probe (1338 nm) technique. An unambiguous depletion of the CH (A (2) Delta -> X (2)Pi) fluorescence signal as a function of the delay time is attributed to the de-excitation of the super-excited states by the probe laser pulse. The lifetime of the super-excited state is measured to be about 160 fs.
Population trapping and rotational revival of N(2) molecules during filamentation of a femtosecond laser pulse in air
(2010-12-14)
Azarm, A.
;
Ramakrishna, S.
;
Talebpour, A.
;
Hosseini, S.
;
Teranishi, Y.
We study the fluorescence emitted from filaments in air using a pump-probe scheme with a femtosecond Ti-sapphire laser. The fluorescence intensities from the first negative band (B(2)Sigma(+)(u) -> X(2)Sigma(+)(g)) and the second positive band (C(3)Pi(u) -> B(3)Pi(g)) show enhancement and change periodically as a function of the pump-probe time delay. We attribute this phenomenon to the universal yet probably forgotten phenomenon of population trapping of nitrogen molecules in highly excited states together with field-induced alignment of nitrogen molecules followed by revivals of the rotational wavepackets. Theoretical calculation of the alignment dynamics of nitrogen molecules is consistent with the experimental data.
Population trapping and rotational revival of N-2 molecules during filamentation of a femtosecond laser pulse in air
(2010-12-14)
Azarm, A.
;
Ramakrishna, S.
;
Talebpour, A.
;
Hosseini, S.
;
Teranishi, Y.
We study the fluorescence emitted from filaments in air using a pump-probe scheme with a femtosecond Ti-sapphire laser. The fluorescence intensities from the first negative band (B-2 Sigma(+)(u) -> X-2 Sigma(+)(g)) and the second positive band (C-3 Pi(u) -> B-3 Pi(g)) show enhancement and change periodically as a function of the pump-probe time delay. We attribute this phenomenon to the universal yet probably forgotten phenomenon of population trapping of nitrogen molecules in highly excited states together with field-induced alignment of nitrogen molecules followed by revivals of the rotational wavepackets. Theoretical calculation of the alignment dynamics of nitrogen molecules is consistent with the experimental data.
Studying the neutral dissociation of O-2 and CH4 Molecules in strong laser field
(2009)
Azarm, A.
;
Kamali, Y.
;
Bernhardt, J.
;
Xu, H. L.
;
Song, D.
We report neutral dissociation of oxygen and methane in femtosecond laser field through superexcited states. Moreover, the lifetime of the superexcited state is measured by pump and probe technique to be about few hundred femtosecond. (C)2009 Optical Society of America