Transient Cherenkov radiation from an inhomogeneous string excited by an ultrashort laser pulse at superluminal velocity

An optical response of one-dimensional string made of dipoles with a periodically varying density excited by a spot of light moving along the string at the superluminal (sub-luminal) velocity is theoretically studied. The Cherenkov radiation in such system is rather unusual, possessing both transient and resonant character. We show that under certain conditions, in addition to the resonant Cherenkov peak another Doppler-like frequency appears in the radiation spectrum. Both linear (small-signal) and nonlinear regimes as well as different string topologies are considered.Comment: accepted to Phys. Rev.

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

Self-starting stable coherent mode-locking in a two-section laser

Coherent mode-locking (CML) uses self-induced transparency (SIT) soliton formation to achieve, in contrast to conventional schemes based on absorption saturation, the pulse durations below the limit allowed by the gain line width. Despite of the great promise it is difficult to realize it experimentally because a complicated setup is required. In all previous theoretical considerations CML is believed to be non-self-starting. In this article we show that if the cavity length is selected properly, a very stable (CML) regime can be realized in an elementary two-section ring-cavity geometry, and this regime is self-developing from the non-lasing state. The stability of the pulsed regime is the result of a dynamical stabilization mechanism arising due to finite-cavity-size effects

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