Generation of unipolar half-cycle pulse via unusual reflection of a single-cycle pulse from an optically thin metallic or dielectric layer

We present a significantly different reflection process from an optically thin flat metallic or dielectric layer and propose a strikingly simple method to form approximately unipolar half-cycle optical pulses via reflection of a single-cycle optical pulse. Unipolar pulses in reflection arise due to specifics of effectively one-dimensional pulse propagation. Namely, we show that in considered system the field emitted by a flat medium layer is proportional to the velocity of oscillating medium charges instead of their acceleration as it is usually the case. When the single-cycle pulse interacts with linear optical medium, the oscillation velocity of medium charges can be then forced to keep constant sign throughout the pulse duration. Our results essentially differ from the direct mirror reflection and suggest a possibility of unusual transformations of the few-cycle light pulses in linear optical systems

Passive and hybrid mode locking in multi-section terahertz quantum cascade lasers

It is believed that passive mode locking is virtually impossible in quantum cascade lasers (QCLs) because of too fast carrier relaxation time. Here, we revisit this possibility and theoretically show that stable mode locking and pulse durations in the few cycle regime at terahertz (THz) frequencies are possible in suitably engineered bound-to-continuum QCLs. We achieve this by utilizing a multi-section cavity geometry with alternating gain and absorber sections. The critical ingredients are the very strong coupling of the absorber to both field and environment as well as a fast absorber carrier recovery dynamics. Under these conditions, even if the gain relaxation time is several times faster than the cavity round trip time, generation of few-cycle pulses is feasible. We investigate three different approaches for ultrashort pulse generation via THz quantum cascade lasers, namely passive, hybrid and colliding pulse mode locking

COMPRESSION OF FEW-CYCLE OPTICAL PULSES AND UNIPOLAR PULSE GENERATION DUE TO COHERENT INTERACTION WITH NONLINEAR RESONANT MEDIUM

We study theoretically the possibility of few-cycle short bipolar optical pulse compression and their transformation to unipolar pulses due to coherent interaction with resonance absorbing medium. It is shown that single-cycle pulse compression occurs when each half-wave starts to behave as an independent unipolar soliton. These solitons are attracted to each other under certain conditions, that leads to the emergence of single-cycle pulse of shorter duration. Numerical simulations revealed 3-5 times reduction of the pulse duration. The substantial absence of light loss in this scheme gives the possibility to create a multistage passive system of three resonance absorbers and results in a 125-time reduction of the pulse duration. Generation of unipolar pulses occurs when two powerful extremely short bipolar pulses propagate and collide in a dense resonant medium. In this case, as shown by numerical calculations, the mutual influence of oncoming solitons leads to the fact that some part of them is destroyed and another part is not. A high power unipolar soliton and low intensity bipolar optical ringing are observed in the medium output

Non-Ohmic variable-range hopping transport in one-dimensional conductors

We investigate theoretically the effect of a finite electric field on the resistivity of a disordered one-dimensional system in the variable-range hopping regime. We find that at low fields the transport is inhibited by rare fluctuations in the random distribution of localized states that create high-resistance ``breaks'' in the hopping network. As the field increases, the breaks become less resistive. In strong fields the breaks are overrun and the electron distribution function is driven far from equilibrum. The logarithm of the resistance initially shows a simple exponential drop with the field, followed by a logarithmic dependence, and finally, by an inverse square-root law.Comment: Version accepted to Phys. Rev. Let

Automated Information Systems as a New Approach to Risk Management of Pharmacotherapy in the Treatment of Epilepsy

Epilepsy is a fairly common disease which challenges social life, therefore the use of information systems and software to support patients with epilepsy is a promising trend in electronic and mobile medicine. The aim of the study was to analyse data on the existing information systems, devices, and mobile applications used to support patients with epilepsy and control risks associated with pharmacotherapy, and to assess the prospects for the development of information systems to support patients with epilepsy. The results of an advanced search and systematisation of literature and Internet data suggest a high demand for mobile and e-health. Mobile applications for patients with epilepsy have a large share of e-health tools. The applications help to monitor seizures, record the frequency of taking medications, receive advice on emergency treatment of seizures, adjust the dosage regimen, and, in general, help to reduce the risks of anticonvulsant therapy, increase patient compliance and the competence of the participants in the treatment process. The analysis of the convenience and functionality of the foreign-produced mobile applications: Epilepsy Journal, Seizure Tracker, Helpilepsy, Seizure First Aide, did not reveal any significant differences between them. The following shortcomings of the mobile applications were identified: lack of Russian language support (except Epilepsy Journal), lack of advertisement blocking options in free applications, incomplete use of video recording capabilities and location-based systems. Global trends in the development of mobile medicine suggest the need for Russian-produced software that would address the identified shortcomings of the existing foreign applications and help support patients with epilepsy

Fifty years of the Glauber diffraction theory

In this minireview a historical excursus in theoretical studies related to the Glauber diffraction theory has been presented with an accent on the recent developments in this subject.Comment: 22 pages, 4 figures, in russian;v2: an atempt to improve hyphenatio