Editorial

Abstract

The special feature in this issue is a response torecent breakthroughs in the technology of sources of ultra-shortelectromagnetic pulses; such pulses can now be delivered at the limits of coherence over a wide frequency range. Studies of ultra-short electromagnetic pulses and their interaction withmatter are attracting increasing interest in many areas ofscience and technology because of the inherent potential of suchpulses to reveal transient features of physical phenomena andprobe peculiar electromagnetic and physical properties of allkinds of matter. The laser is widely involved in generating ordetecting ultra-short electromagnetic pulses. These developmentshave consequences for the instrumentation of measurements,as scientists endeavour to implement new methods andanalytical approaches in the difficult challenge of modelling the dynamics of ultra-fast physical phenomena.The aim of this feature is to provide the reader with a comprehensive overview of the current state of research and to stimulate interest in implementing new ultra-short pulse generators and device technologies in order to study more deeplythe rich field of ultra-short wideband electromagnetic pulsetechnology. This issue includes articles exploring a `newfrontier in physics' and contributed articles on broadbandaspects of the field.Thus, we report new developments and trends in the following areas: ultra-wideband short pulse electromagnetic waves in the microwave range of frequency, developed in Section I; ultra-short laser pulse technology and coherent beam interaction with matter, developed in Section II; ultra-short high-intensity laser and plasma interactions and transient x-ray laser pulses, developed in Section III; ultra-short laser pulses inducing the emission of coherent soft x-ray beams as a result of high order harmonic generation or high contrast energy modulation, developed in Section IV; the temporal aspect in synchrotron radiation sources and applications, developed in Section V; methods of time-resolved spectroscopy applied to measurements of ultra-short electromagnetic pulses and diagnostics of dynamical phenomena, developed in Section VI.The techniques for generating, manipulating and detecting picosecond and sub-picosecond electromagnetic pulses have been documented extensively in the literature [1-6]. To measure an ultra-short electromagnetic pulse in the picosecond (or sub-picosecond) time-scale, anelectromagnetic source with a high repetition rate is required (such as a laser source or eventually a synchrotron radiation source). When this condition is fulfilled, a pump-probe optoelectronic sampling measurement method can be applied. The relatively fast detectors used for infrared and visible ultra-short pulses of radiation generally have a weak sensitivity for x-ray detection. This is because of the fast response of the photocarrier generation and the weak x-ray absorption of semiconductors. In the VUV and x-ray domain, the main system for detecting picosecond to femtosecond signals is generally a streak camera [7, 8] photoswitched by a synchronized femtosecond laser pulse (see Section VI).These researches and experiments on pulsed electromagnetic radiation interacting with matter open new domains to theoretical research and technological development [9], promising previously unsuspected knowledge about the universe. The generation, detection and measurement of transient electromagnetic waves, i.e. short pulses, are of considerable interest to experimental studies of interaction with various media and modern information and communications technologies. Numerous applications are found in the field of wideband radar echoes, measurements of electromagnetic properties of materials and time-resolved spectroscopy (e.g. x-ray diffraction, reflection and absorption, etc). New measuring techniques and data processing methods have been and are being developed and are, in fact, indispensable for analysing the detailed features of the real-time results delivered by high power lasers, wideband impulse radar and x-ray beamlines. The propagation of a transient wave packet through plasmas, for instance the ionosphere, condensed matter (obtained by inertial compression) and biological aerosol streams, is nowof widespread interest.