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Misha Ivanov

Bio: Misha Ivanov is an academic researcher from Imperial College London. The author has contributed to research in topics: Attosecond & Ionization. The author has an hindex of 51, co-authored 234 publications receiving 12737 citations. Previous affiliations of Misha Ivanov include Humboldt University of Berlin & Vienna University of Technology.


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Journal ArticleDOI
TL;DR: A simple, analytic, and fully quantum theory of high-harmonic generation by low-frequency laser fields is presented and the exact quantum-mechanical formula for the harmonic cutoff that differs from the phenomenological law Ip+3.17Up is presented.
Abstract: We present a simple, analytic, and fully quantum theory of high-harmonic generation by low-frequency laser fields. The theory recovers the classical interpretation of Kulander et al. in Proceedings of the SILAP III Works hop, edited by B. Piraux (Plenum, New York, 1993) and Corkum [Phys. Rev. Lett. 71, 1994 (1993)] and clearly explains why the single-atom harmonic-generation spectra fall off at an energy approximately equal to the ionization energy plus about three times the oscillation energy of a free electron in the field. The theory is valid for arbitrary atomic potentials and can be generalized to describe laser fields of arbitrary ellipticity and spectrum. We discuss the role of atomic dipole matrix elements, electron rescattering processes, and of depletion of the ground state. We present the exact quantum-mechanical formula for the harmonic cutoff that differs from the phenomenological law Ip+3.17Up, where Ip is the atomic ionization potential and Up is the ponderomotive energy, due to the account for quantum tunneling and diffusion effects.

3,007 citations

Journal ArticleDOI
20 Aug 2009-Nature
TL;DR: These findings establish high harmonic interferometry as an effective approach to resolving multi-electron dynamics with sub-Ångström spatial resolution arising from the de Broglie wavelength of the recombining electron, and attosecond temporal resolution arisen from the timescale ofThe recombination event.
Abstract: High harmonic emission occurs when an electron, liberated from a molecule by an incident intense laser field, gains energy from the field and recombines with the parent molecular ion. The emission provides a snapshot of the structure and dynamics of the recombining system, encoded in the amplitudes, phases and polarization of the harmonic light. Here we show with CO2 molecules that high harmonic interferometry can retrieve this structural and dynamic information: by measuring the phases and amplitudes of the harmonic emission, we reveal ‘fingerprints’ of multiple molecular orbitals participating in the process and decode the underlying attosecond multi-electron dynamics, including the dynamics of electron rearrangement upon ionization. These findings establish high harmonic interferometry as an effective approach to resolving multi-electron dynamics with sub-Angstrom spatial resolution arising from the de Broglie wavelength of the recombining electron, and attosecond temporal resolution arising from the timescale of the recombination event. The high harmonic emission that accompanies the recombination of an electron with its parent molecular ion in an intense laser field provides a snapshot of the structure and dynamics of the recombining system. Experiments with CO2 molecules now show that high harmonic interferometry can retrieve this structural and dynamic information by measuring the phases and amplitudes of the harmonic emission. The resulting 'fingerprints' of the multiple molecular orbitals participating in the process can be used to decode the underlying attosecond multi-electron dynamics, including the dynamics of electron rearrangement upon ionization. The light emitted from the system contains images of moving electrons that can be processed into a movie. These findings establish high harmonic interferometry as an effective approach to resolving multi-electron dynamics with sub-Angstrom spatial resolution arising from the de-Broglie wavelength of the recombining electron, and attosecond temporal resolution arising from the timescale of the recombination event. The high harmonic emission that accompanies the recombination of an electron with its parent molecular ion in an intense laser field provides a snapshot of the structure and dynamics of the recombining system. Experiments on CO2 molecules now show how to extract information from the properties of the emitted light about the underlying multi-electron dynamics with sub-Angstrom spatial resolution and attosecond temporal resolution

840 citations

Journal ArticleDOI
27 Jun 2002-Nature
TL;DR: This work proposes that the electrons themselves can be exploited for ultrafast measurements, and uses a ‘molecular clock’, based on a vibrational wave packet in H2+, 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).
Abstract: 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 H2+ 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

481 citations

Journal ArticleDOI
17 May 2012-Nature
TL;DR: This approach provides a general tool for time-resolving multi-electron rearrangements in atoms and molecules—one of the key challenges in ultrafast science.
Abstract: A method of laser-induced recollision permits measurement with attosecond resolution of the times at which the electron leaves the tunnelling barrier and discriminates between the ionization times of two carbon dioxide orbitals. Tunnelling of a particle through a barrier is one of the most fundamental and ubiquitous quantum processes. One issue much debated since the early days of quantum mechanics is the link between tunnelling and the dynamics of the particle outside the barrier. Shafir et al. explore this topic by inducing electron tunnelling from atoms and molecules with a strong laser field and then using a weaker probe field to steer the tunnelled electrons in the lateral direction. The liberated electrons emit an attosecond light burst when they re-encounter their parent ions; the effect of the steering on this light burst provides a measure of the time at which the electrons first exited from the tunnelling barrier, with a sensitivity that is sufficient to resolve subtle differences. This work provides a general approach to the direct resolution of multi-electron rearrangements in atoms and molecules in both space and time. The tunnelling of a particle through a barrier is one of the most fundamental and ubiquitous quantum processes. When induced by an intense laser field, electron tunnelling from atoms and molecules initiates a broad range of phenomena such as the generation of attosecond pulses1, laser-induced electron diffraction2,3 and holography2,4. These processes evolve on the attosecond timescale (1 attosecond ≡ 1 as = 10−18 seconds) and are well suited to the investigation of a general issue much debated since the early days of quantum mechanics5,6,7—the link between the tunnelling of an electron through a barrier and its dynamics outside the barrier. Previous experiments have measured tunnelling rates with attosecond time resolution8 and tunnelling delay times9. Here we study laser-induced tunnelling by using a weak probe field to steer the tunnelled electron in the lateral direction and then monitor the effect on the attosecond light bursts emitted when the liberated electron re-encounters the parent ion10. We show that this approach allows us to measure the time at which the electron exits from the tunnelling barrier. We demonstrate the high sensitivity of the measurement by detecting subtle delays in ionization times from two orbitals of a carbon dioxide molecule. Measurement of the tunnelling process is essential for all attosecond experiments where strong-field ionization initiates ultrafast dynamics10. Our approach provides a general tool for time-resolving multi-electron rearrangements in atoms and molecules11,12,13—one of the key challenges in ultrafast science.

414 citations

Journal ArticleDOI
TL;DR: In this paper, a simple closed-form analytical expression for ionization rate as a function of instantaneous laser phase was obtained for arbitrary values of the Keldysh parameter within the usual strong-field approximation.
Abstract: We obtain a simple closed-form analytical expression for ionization rate as a function of instantaneous laser phase $\ensuremath{\varphi}(t),$ for arbitrary values of the Keldysh parameter $\ensuremath{\gamma},$ within the usual strong-field approximation. Our analysis allows us to explicitly distinguish multiphoton and tunneling contributions to the total ionization probability. The range of intermediate $\ensuremath{\gamma}\ensuremath{\sim}1,$ which is typical for most current intense field experiments, is the regime of nonadiabatic tunneling. In this regime, the instantaneous laser phase dependence differs dramatically from both quasistatic tunneling and multiphoton limits. For cycle-averaged rates, our results reproduce standard Keldysh-like expressions.

388 citations


Cited by
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[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

Journal ArticleDOI
TL;DR: In this article, the authors present the landmarks of the 30-odd-year evolution of ultrashort-pulse laser physics and technology culminating in the generation of intense few-cycle light pulses and discuss the impact of these pulses on high-field physics.
Abstract: The rise time of intense radiation determines the maximum field strength atoms can be exposed to before their polarizability dramatically drops due to the detachment of an outer electron. Recent progress in ultrafast optics has allowed the generation of ultraintense light pulses comprising merely a few field oscillation cycles. The arising intensity gradient allows electrons to survive in their bound atomic state up to external field strengths many times higher than the binding Coulomb field and gives rise to ionization rates comparable to the light frequency, resulting in a significant extension of the frontiers of nonlinear optics and (nonrelativistic) high-field physics. Implications include the generation of coherent harmonic radiation up to kiloelectronvolt photon energies and control of the atomic dipole moment on a subfemtosecond $(1{\mathrm{f}\mathrm{s}=10}^{\mathrm{\ensuremath{-}}15}\mathrm{}\mathrm{s})$ time scale. This review presents the landmarks of the 30-odd-year evolution of ultrashort-pulse laser physics and technology culminating in the generation of intense few-cycle light pulses and discusses the impact of these pulses on high-field physics. Particular emphasis is placed on high-order harmonic emission and single subfemtosecond extreme ultraviolet/x-ray pulse generation. These as well as other strong-field processes are governed directly by the electric-field evolution, and hence their full control requires access to the (absolute) phase of the light carrier. We shall discuss routes to its determination and control, which will, for the first time, allow access to the electromagnetic fields in light waves and control of high-field interactions with never-before-achieved precision.

2,547 citations

Journal ArticleDOI
TL;DR: The exciting successes in taming molecular-level movement thus far are outlined, the underlying principles that all experimental designs must follow, and the early progress made towards utilizing synthetic molecular structures to perform tasks using mechanical motion are highlighted.
Abstract: The widespread use of controlled molecular-level motion in key natural processes suggests that great rewards could come from bridging the gap between the present generation of synthetic molecular systems, which by and large rely upon electronic and chemical effects to carry out their functions, and the machines of the macroscopic world, which utilize the synchronized movements of smaller parts to perform specific tasks. This is a scientific area of great contemporary interest and extraordinary recent growth, yet the notion of molecular-level machines dates back to a time when the ideas surrounding the statistical nature of matter and the laws of thermodynamics were first being formulated. Here we outline the exciting successes in taming molecular-level movement thus far, the underlying principles that all experimental designs must follow, and the early progress made towards utilizing synthetic molecular structures to perform tasks using mechanical motion. We also highlight some of the issues and challenges that still need to be overcome.

2,301 citations

Journal ArticleDOI
TL;DR: In this paper, the main aspects of ultrashort laser pulse filamentation in various transparent media such as air (gases), transparent solids and liquids are introduced and discussed.

2,282 citations