Attosecond physics at the nanoscale.

Recently two emerging areas of research, attosecond and nanoscale physics, have started to come together. Attosecond physics deals with phenomena occurring when ultrashort laser pulses, with duration on the femto- and sub-femtosecond time scales, interact with atoms, molecules or solids. The laser-induced electron dynamics occurs natively on a timescale down to a few hundred or even tens of attoseconds (1 attosecond = 1 as = 10-18 s), which is comparable with the optical field. For comparison, the revolution of an electron on a 1s orbital of a hydrogen atom is ∼152 as. On the other hand, the second branch involves the manipulation and engineering of mesoscopic systems, such as solids, metals and dielectrics, with nanometric precision. Although nano-engineering is a vast and well-established research field on its own, the merger with intense laser physics is relatively recent. In this report on progress we present a comprehensive experimental and theoretical overview of physics that takes place when short and intense laser pulses interact with nanosystems, such as metallic and dielectric nanostructures. In particular we elucidate how the spatially inhomogeneous laser induced fields at a nanometer scale modify the laser-driven electron dynamics. Consequently, this has important impact on pivotal processes such as above-threshold ionization and high-order harmonic generation. The deep understanding of the coupled dynamics between these spatially inhomogeneous fields and matter configures a promising way to new avenues of research and applications. Thanks to the maturity that attosecond physics has reached, together with the tremendous advance in material engineering and manipulation techniques, the age of atto-nanophysics has begun, but it is in the initial stage. We present thus some of the open questions, challenges and prospects for experimental confirmation of theoretical predictions, as well as experiments aimed at characterizing the induced fields and the unique electron dynamics initiated by them with high temporal and spatial resolution.

Discrete dispersion scanning as a simple method for broadband femtosecond pulse characterization.

A simple and easy to implement technique for femtosecond pulse characterization is proposed and experimentally verified. It is based on the introduction of a known amount of dispersion (by controlling the number of passes through dispersive material) and subsequent recording of the spectral positions of second harmonic peaks obtained in a non-linear crystal. Such dependence allows for direct retrieval of the pulse spectral phase. The presented pulse characterization method is beneficial especially for broadband pulses, where the second harmonic spectrum exceeds the detection bandwidth of a single spectrometer.

Steering Proton Migration in Hydrocarbons Using Intense Few-Cycle Laser Fields.

Proton migration is a ubiquitous process in chemical reactions related to biology, combustion, and catalysis. Thus, the ability to manipulate the movement of nuclei with tailored light within a hydrocarbon molecule holds promise for far-reaching applications. Here, we demonstrate the steering of hydrogen migration in simple hydrocarbons, namely, acetylene and allene, using waveform-controlled, few-cycle laser pulses. The rearrangement dynamics is monitored using coincident 3D momentum imaging spectroscopy and described with a widely applicable quantum-dynamical model. Our observations reveal that the underlying control mechanism is due to the manipulation of the phases in a vibrational wave packet by the intense off-resonant laser field.

Electron localization following attosecond molecular photoionization.

For the past several decades, we have been able to directly probe the motion of atoms that is associated with chemical transformations and which occurs on the femtosecond (10(-15)-s) timescale. However, studying the inner workings of atoms and molecules on the electronic timescale has become possible only with the recent development of isolated attosecond (10(-18)-s) laser pulses. Such pulses have been used to investigate atomic photoexcitation and photoionization and electron dynamics in solids, and in molecules could help explore the prompt charge redistribution and localization that accompany photoexcitation processes. In recent work, the dissociative ionization of H(2) and D(2) was monitored on femtosecond timescales and controlled using few-cycle near-infrared laser pulses. Here we report a molecular attosecond pump-probe experiment based on that work: H(2) and D(2) are dissociatively ionized by a sequence comprising an isolated attosecond ultraviolet pulse and an intense few-cycle infrared pulse, and a localization of the electronic charge distribution within the molecule is measured that depends-with attosecond time resolution-on the delay between the pump and probe pulses. The localization occurs by means of two mechanisms, where the infrared laser influences the photoionization or the dissociation of the molecular ion. In the first case, charge localization arises from quantum mechanical interference involving autoionizing states and the laser-altered wavefunction of the departing electron. In the second case, charge localization arises owing to laser-driven population transfer between different electronic states of the molecular ion. These results establish attosecond pump-probe strategies as a powerful tool for investigating the complex molecular dynamics that result from the coupling between electronic and nuclear motions beyond the usual Born-Oppenheimer approximation.

Competition of single and double rescattering in the strong-field photoemission from dielectric nanospheres.

Nanostructures exposed to ultrashort waveform-controlled laser pulses enable the generation of enhanced and highly localized near fields with adjustable local electric field evolution. Here, we study dielectric SiO2 nanospheres (d = 100-700 nm) under strong carrier-envelope phase-controlled few-cycle laser pulses and perform a systematic theoretical analysis of the resulting near-field driven photoemission. In particular, we analyze the impacts of charge interaction and local field ellipticity on the near-field driven electron acceleration. Our semiclassical transport simulations predict strong quenching of the electron emission and enhanced electron energies due to the ionization induced space charge. Though single surface backscattering remains the main emission process for the considered parameter range, we find a substantial contribution of double rescattering that increases with sphere size and becomes dominant near the cutoff energy for the largest investigated spheres. The growing importance of the double recollision process is traced back to the increasing local field ellipticity via trajectory analysis and the corresponding initial to final state correlation. Finally, we compare the carrier-envelope phase-dependent emission of single and double recollision electrons and find that both exhibit a characteristic directional switching behavior.

Coherent electronic wave packet motion in C(60) controlled by the waveform and polarization of few-cycle laser fields.

Strong laser fields can be used to trigger an ultrafast molecular response that involves electronic excitation and ionization dynamics. Here, we report on the experimental control of the spatial localization of the electronic excitation in the C_{60} fullerene exerted by an intense few-cycle (4 fs) pulse at 720 nm. The control is achieved by tailoring the carrier-envelope phase and the polarization of the laser pulse. We find that the maxima and minima of the photoemission-asymmetry parameter along the laser-polarization axis are synchronized with the localization of the coherent electronic wave packet at around the time of ionization.

[The factor analysis results of the relationship of socio-demographic, clinical and functional indicators with the likelihood of identifying age-related disorders in the population in North-Western Russia].

By using the method of factor analysis (principal component method) the determinants of disease in elderly and senile patients were searched with an estimate of their influence degree in the population of the North-West Russia. The data from medical records of 712 patients of both sexes aged 59 to 98 years were analyzed. The factor 1 proved to be associated with: marital status, living conditions, family relationships, bad habits, appearance, cough, diet, hearing and vision, laxatives, joint health, ability to move and sleep disturbances. Factor 2 combined diseases of older: cerebral stroke, myocardial infarction, cardiac arrhythmia, diabetes, kidney disease, obesity, thyroid disease, Parkinson's disease, lung disease, anemia, arthritis, osteoporosis, the number of surgeries and joint diseases. The factor 3 was found to self-association ability before and after admission to the assessment of the patients' mental state for MMSE test after admission. It is concluded that the development of age-related (especially the musculoskeletal system pathology) is associated with social characteristics and living conditions of patients, and treatment of the most age-related diseases requires consideration of comorbidity.

[Diagnostics of ataxia-telangiectasia by the express-test found on the method of indirect immunofluorescence].

Ataxia-telangiectasia (AT) is a hereditary severe neurodegenerative disease developing, when mutations take place in both alleles of the atm gene, which encodes the key protein of the cellular response to DNA damage (DDR)--ATM proteinkinase. In response to the occurrence of double-strand DNA breaks, the ATM proteinkinase pass the autophosphorylation, and its active form--the phospho-ATM (P-ATM) appears in cells. In the nuclei of cells having the atm gene, P-ATM is revealed, being absent in cells with mutated forms of this gene, by means of the application of the modified method of indirect immunofluorescence. This peculiarity may be applied in the clinic, in order to confirm the diagnosis of AT.

Subcycle controlled charge-directed reactivity with few-cycle midinfrared pulses.

The steering of electron motion in molecules is accessible with waveform-controlled few-cycle laser light and may control the outcome of light-induced chemical reactions. An optical cycle of light, however, is much shorter than the duration of the fastest dissociation reactions, severely limiting the degree of control that can be achieved. To overcome this limitation, we extended the control metrology to the midinfrared studying the prototypical dissociative ionization of D(2) at 2.1 µm. Pronounced subcycle control of the directional D(+) ion emission from the fragmentation of D(2)(+) is observed, demonstrating unprecedented charge-directed reactivity. Two reaction pathways, showing directional ion emission, could be observed and controlled simultaneously for the first time. Quantum-dynamical calculations elucidate the dissociation channels, their observed phase relation, and the control mechanisms.

Waveform control of orientation-dependent ionization of DCl in few-cycle laser fields.

Strong few-cycle light fields with stable electric field waveforms allow controlling electrons on time scales down to the attosecond domain. We have studied the dissociative ionization of randomly oriented DCl in 5 fs light fields at 720 nm in the tunneling regime. Momentum distributions of D(+) and Cl(+) fragments were recorded via velocity-map imaging. A waveform-dependent anti-correlated directional emission of D(+) and Cl(+) fragments is observed. Comparison of our results with calculations indicates that tailoring of the light field via the carrier envelope phase permits the control over the orientation of DCl(+) and in turn the directional emission of charged fragments upon the breakup of the molecular ion.

Attosecond electron spectroscopy using a novel interferometric pump-probe technique.

We present an interferometric pump-probe technique for the characterization of attosecond electron wave packets (WPs) that uses a free WP as a reference to measure a bound WP. We demonstrate our method by exciting helium atoms using an attosecond pulse (AP) with a bandwidth centered near the ionization threshold, thus creating both a bound and a free WP simultaneously. After a variable delay, the bound WP is ionized by a few-cycle infrared laser precisely synchronized to the original AP. By measuring the delay-dependent photoelectron spectrum we obtain an interferogram that contains both quantum beats as well as multipath interference. Analysis of the interferogram allows us to determine the bound WP components with a spectral resolution much better than the inverse of the AP duration.

[An atypical case of Werner syndrome: epigenetic control and DNA damage response alterations].

A case of adult progeria has been described. It has been suggested that this case is an atypical form of Werner syndrome with laminopathy--not WRN helicase-nuclease defect. During detailed studies of the patient's cells, epigenetic control and DNA damage response alterations were detected.

Attosecond nanoscale near-field sampling.

The promise of ultrafast light-field-driven electronic nanocircuits has stimulated the development of the new research field of attosecond nanophysics. An essential prerequisite for advancing this new area is the ability to characterize optical near fields from light interaction with nanostructures, with sub-cycle resolution. Here we experimentally demonstrate attosecond near-field retrieval for a tapered gold nanowire. By comparison of the results to those obtained from noble gas experiments and trajectory simulations, the spectral response of the nanotaper near field arising from laser excitation can be extracted.

Postreplication DNA repair in ultraviolet-irradiated Micrococcus luteus.

Postreplication DNA repair was studies in three strains of Micrococcus luteus having different sensitivity to ultraviolet light: a wild type ATCC 5698, a ultraviolet-sensitive mutant G7, deficient in the incision step of repair and in ultraviolet-resistant transformant obtained from G7 by treatment with DNA of wild type cells, Trf(G7). It is shown that the G7 mutant has a low capacity for repair of postreplication DNA gaps compared with the wild type or Trf(G7). It seems to be that postreplication repari capacity contributes significantly to the ultraviolet resistance of M. luteus in addition to the excision repair. In contrast with G7 the size of the DNA fragments synthesized immediately after ultraviolet irradiation in the wild type (and Trf(G7)) seems to be much higher than that expected if each dimer produces one DNA gap in the daughter strand. Since this cannot only be explained by the excision of dimers from parental DNA we have suggested that a rapid repair of postreplication DNA gap occurs in M. luteus.

An analysis of the repair processes in ultraviolet-irradiated Micrococcus luteus using purified ultraviolet-endonuclease.

The measurement of the frequency of endonucleolytic incisions in ultraviolet-irradiated DNA serves as the test for the presence of pyrimidine dimers. In accordance with this approach, the lysates of three Micrococcus luteus strains containing radioactively labeled chromosomes were treated with purified M. luteus ultraviolet-endonuclease to trace segregation of dimers amongst parental and newly synthesized DNA and their removal during postreplication and excision DNA repair. A considerable proportion of the dimers in all strains tested proved to be insensitive to the action of exogenous incising enzyme. The use of chloramphenicol as an inhibitor of postirradiation protein synthesis in combination which ultraviolet-endonuclease treatment of DNA allowed to reveal at least two alternative pathways of postreplication repair: constitutively active recombinational pathway and inducible nonrecombinational one.

The roles of different repair mechanisms in the ultraviolet resistance of Micrococcus luteus.

In ultraviolet-irradiated Micrococcus luteus wild type the replication of DNA was not interrupted at every pyrimidine dimer, in contrast to that in ultraviolet-sensitive G7 and some other mutants. The contribution of uninterrupted replication to the ultraviolet resistance of M. luteus proved to be equal to the contributions of excision repair and inducible postreplication repair. It was found that some postreplication gaps could be filled by constitutive pathways of postreplication repair when inducible pathways were suppressed by chloramphenicol. Prolonged treatment with chloramphenicol was shown to block not only inducible repair but also other processes essential for ultraviolet irradiation survival.

Field propagation-induced directionality of carrier-envelope phase-controlled photoemission from nanospheres.

Near-fields of non-resonantly laser-excited nanostructures enable strong localization of ultrashort light fields and have opened novel routes to fundamentally modify and control electronic strong-field processes. Harnessing spatiotemporally tunable near-fields for the steering of sub-cycle electron dynamics may enable ultrafast optoelectronic devices and unprecedented control in the generation of attosecond electron and photon pulses. Here we utilize unsupported sub-wavelength dielectric nanospheres to generate near-fields with adjustable structure and study the resulting strong-field dynamics via photoelectron imaging. We demonstrate field propagation-induced tunability of the emission direction of fast recollision electrons up to a regime, where nonlinear charge interaction effects become dominant in the acceleration process. Our analysis supports that the timing of the recollision process remains controllable with attosecond resolution by the carrier-envelope phase, indicating the possibility to expand near-field-mediated control far into the realm of high-field phenomena.

[Effect of thermal shock on resistance of filamentous Bacillus subtilis strain to some hazardous substances]. / Vliianie teplovogo shoka na rezistentnost filamentoobrazuiushchego shtamma Basillus subtilis k nekotorym povrezhdaiushchim agentam.

When grown at 30 degrees C and heat shocked in a liquid medium at 45 degrees C, the filamentous cells of Bacillus subtilis 168 became more sensitive to subsequent killing with N-methyl-N'-nitro-N-nitrosoguanidine and UV light but not with gamma-rays. Certain characteristics (for instance, the increased tolerance to damaging agents at 30 degrees C and the time-dependent changes in the sensitivity to MNNG induced by thermal shock) evidence against direct involvement of repair systems in this phenomenon.

[Absence of various manifestations of adaptive response in Bacillus subtilis transformants]. / Otsutstvie nekotorykh proiavlenii adaptivnogo otveta v transformantakh Bacillus subtilis.

Competent cells of Bacillus subtilis are more sensitive to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) than total population, exhibit higher level of spontaneous mutations to kanamycin resistance. However, the absolute number of mutated transformants doesn't rise with MNNG treatment in the range of 5 to 50 micrograms per ml. The adaptation to low concentrations of MNNG affects neither spontaneous nor MNNG-induced mutagenesis in the competent (transformed) cells, in contrast to their resistance which is stronger for the adapted transformants. The transformation by MNNG-treated plasmid pUB 110 doesn't reveal any difference between adapted and non-adapted cultures in transformation efficiency decline.

Some routine and novel approaches to chemical dosimetry of far-ultraviolet light emitted by bactericidal tubes.

Detailed protocols are presented of two improved chemical procedures, based upon a photochemical decomposition of uranyl oxalate or potassium ferrioxalate, enabling a reliable measurement of the far-ultraviolet light emitted by a low-pressure mercury-vapour lamp. Besides, an original semi-quantitative method of UV dosimetry is presented and discussed, employing optical detection of a chromophore formed in the photo-oxidized glutathione. In addition to exemplary computations of UV light dose rate, a simple formula is proposed for recalculating its value while varying the distance from the lamp.