Biomedical subjects

Misha Yu Ivanov

Publications and source records attributed to Misha Yu Ivanov.

8 recordsLinked to original sources

PubMed2006

Dynamic stark control of photochemical processes.

A method is presented for controlling the outcome of photochemical reactions by using the dynamic Stark effect due to a strong, nonresonant infrared field. The application of a precisely timed infrared laser pulse reversibly modifies potential energy barriers during a chemical reaction without inducing any real electronic transitions. Dynamic Stark control (DSC) is experimentally demonstrated for a nonadiabatic photochemical reaction, showing substantial modification of reaction channel probabilities in the dissociation of IBr. The DSC process is nonperturbative and insensitive to laser frequency and affects all polarizable molecules, suggesting broad applicability.

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PubMed2004

Coarse-grained controllability of wavepackets by free evolution and phase shifts.

We describe an approach to controlling wavepacket dynamics and a criterion of wavepacket controllability based on discretized properties of the wavepacket's localization on the orbit. The notion of "coarse-grained control" and the coarse-grained description of the controllability in infinite-dimensional Hilbert spaces are introduced and studied using the mathematical apparatus of loop groups. We prove that 2D rotational wavepackets are controllable by only free evolution and phase kicks by AC Stark shift implemented at fractional revivals. This scheme works even if the AC Stark shifts can have only a smooth coordinate dependence, correspondent to the action of a linearly polarized laser field.

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PubMed2003

Quantum logic approach to wave packet control.

We study control of wave packets with a finite accuracy, approaching it as quantum information processing. For a given control resolution, we define the analogs of several quantum bits within the shape of a single wave packet. These bits are based on wave packet symmetries. Analogs of one- and two-bit gates can be implemented using only free wave packet evolution and coordinate-dependent ac Stark shifts applied at the moments of fractional revivals. As in quantum computation, the gates form a logarithmically small set of basis operations which can be used to approximate any unitary transformation desired for quantum control of the wave packet dynamics. Numerical examples show the application of this approach to control vibrational wave packet revivals.

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PubMed2003

Switched wave packets: a route to nonperturbative quantum control.

The dynamic Stark effect due to a strong nonresonant but nonionizing laser field provides a route to quantum control via the creation of novel superposition states. We consider the creation of a field-free "switched" wave packet through adiabatic turn-on and sudden turn-off of a strong dynamic Stark interaction. There are two limiting cases for such wave packets. The first is a Raman-type coupling, illustrated by the creation of field-free molecular axis alignment. An experimental demonstration is given. The second case is that of dipole-type coupling, illustrated by the creation of charge localization in an array of quantum wells.

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PubMed2003

Tunable optimal compression of ultrabroadband pulses by cross-phase modulation.

We show how cross-phase modulation between two pulses, combined with optimal pulse shaping at the input of a dielectric medium, can be used to generate nearly single-cycle pulses that are tunable from the ultraviolet to the mid-infrared at the output of the medium, precompensating for dispersion to all orders.

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PubMed2003

Optimal generation of single-dispersion precompensated 1-fs pulses by molecular phase modulation.

We show how an optimal control approach can be combined with the pump-probe technique for pulse compression by molecular phase modulation in hollow-core fibers to generate single 1-fs pulses in the visible. Varying the intensity and duration of the Gaussian-shaped pump pulse at the input induces optimal rotational response of the molecules. The probe pulse, which scatters off of the resulting time variation of the refractive index, is shaped at the input for optimal compression at the output, including dispersion to all orders.

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PubMed2003

Probing molecular dynamics with attosecond resolution using correlated wave packet pairs.

Spectroscopic measurements with increasingly higher time resolution are generally thought to require increasingly shorter laser pulses, as illustrated by the recent monitoring of the decay of core-excited krypton using attosecond photon pulses. However, an alternative approach to probing ultrafast dynamic processes might be provided by entanglement, which has improved the precision of quantum optical measurements. Here we use this approach to observe the motion of a D2+ vibrational wave packet formed during the multiphoton ionization of D2 over several femtoseconds with a precision of about 200 attoseconds and 0.05 ångströms, by exploiting the correlation between the electronic and nuclear wave packets formed during the ionization event. An intense infrared laser field drives the electron wave packet, and electron recollision probes the nuclear motion. Our results show that laser pulse duration need not limit the time resolution of a spectroscopic measurement, provided the process studied involves the formation of correlated wave packets, one of which can be controlled; spatial resolution is likewise not limited to the focal spot size or laser wavelength.

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PubMed2002

Sub-laser-cycle electron pulses for probing molecular dynamics.

Experience shows that the ability to make measurements in any new time regime opens new areas of science. Currently, experimental probes for the attosecond time regime (10(-18) 10(-15) s) are being established. The leading approach is the generation of attosecond optical pulses by ionizing atoms with intense laser pulses. This nonlinear process leads to the production of high harmonics during collisions between electrons and the ionized atoms. The underlying mechanism implies control of energetic electrons with attosecond precision. We propose that the electrons themselves can be exploited for ultrafast measurements. We use a 'molecular clock', based on a vibrational wave packet in H(2)(+) to show that distinct bunches of electrons appear during electron ion collisions with high current densities, and durations of about 1 femtosecond (10(-15) s). Furthermore, we use the molecular clock to study the dynamics of non-sequential double ionization.

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