Sang-Young Chung

Generation of Attosecond X-ray and gamma-ray via Compton backscattering

The generation of an isolated attosecond gamma-ray pulse utilizing Compton backscattering of a relativistic electron bunch has been investigated. The energy of the electron bunch is modulated while the electron bunch interacts with a co-propagating few-cycle CEP (carrier envelope phase)-locked laser in a single-period wiggler. The energy-modulated electron bunch interacts with a counter-propagating driver laser, producing Compton back-scattered radiation. The energy modulation of the electron bunch is duplicated to the temporal modulation of the photon energy of Compton back-scattered radiation. The spectral filtering using a crystal spectrometer allows one to obtain an isolated attosecond gamma-ray.

Effects of high-order fields of a tightly focused laser pulse on relativistic nonlinear Thomson scattered radiation by a relativistic electron

The effects of high-order fields of a tightly focused laser beam on the generation of relativistic nonlinear Thomson scattered radiations by a relativistic electron were investigated through numerical simulations. The high-order terms of the laser fields obtained by a series expansion in a diffraction angle were found to strongly affect the nonlinear Thomson scattered radiations by an increase in the transverse acceleration when electrons co-propagate with the laser pulse: the spectral range was broadened by a large factor and the angular power was enhanced by seven orders of magnitude compared to the corresponding values for a paraxial Gaussian laser beam. For electron energies higher than 200 MeV, the scaling exponent of the peak angular power with respect to the initial electron energy was also found to increase by a factor of 2.5 compared to the case of the paraxial laser beam.

Relativistic Nonlinear Thomson Scattering: Toward Intense Attosecond Pulse

Over many millennia of human history, mankind has been interested in how events change in time, namely their dynamics. However, the time resolution of recording individual steps has been limited to direct sensory perception such as the eye’s ability (0.1 sec. or so) to recognize the motion, until 1800 AD when the technical revolution occurred following the industrial revolution. A famous motion picture of a galloping horse by E. Muybridge in 1878 is a good example of the technological development in time-resolved measurement. By this time, the nanosecond time resolution has been achieved; however, it took another century to break the nanosecond barrier as shown in Fig.1. The Advent of a laser has paved ways to ever shorter time resolution: in the 1980’s, the picosecond barrier was broken and the femtosecond science and technology has rapidly progressed in the 1990’s; at the turn of the 21st century, the femtosecond barrier has been broken (Hantschel et al., 2001), opening up the era of attosecond science and technology. The current shortest duration of a pulse achieved is 80 attoseconds around 100 eV of photon energy (Goulielmakis et al., 2008). Femtosecond science and technology have allowed us to explore various ultrafast phenomena in physical (Siders et al., 1999), chemical (Zewail, 2000) and biological (Vos et al., 1999) systems. A great number of ultrafast atomic motions in biology, chemistry, and physics have been investigated with optical probes. In physics, the nature of atomic rearrangements during phase transitions and the relation between amorphous, liquid and crystalline states has been interest (Afonso et al., 1996; Huang et al., 1998). Along with much interest in spintronics during the last decade, efforts have been made to understand spin dynamics in various pure and complex magnetic systems. In chemistry, the real time observation of atomic motions in chemical reactions has been long thought for. Femtosecond optical and IR technology has served this purpose in excellent ways. Femtosecond pulses have pumped molecules to create wavepackets. The observation of the motion of the wavepackets using femtosecond pulse probe or other methods has provided rich information on chemical reactions (Zewail, 2000). The various chemical bonds such as covalent, ionic, dative, metallic, hydrogen and van der Waals bonds have been studied in the varying complexity of molecular systems from diatomics to proteins and DNA. All of

Generation of coherent attosecond pulses from a nano-tube array illuminated by a high-power femtosecond laser

A method to generate an isolated single-cycle attosecond pulse from the interaction of a high-power femtosecond laser pulse with a nano-tube array is demonstrated using a two-dimensional relativistic particle-in-cell simulation. The radiation mechanism is relativistic nonlinear Thomson scattering from the electrons in a target material. Coherent radiation is emitted in the direction of specular reflection for the incident laser pulse while the electrons make a bunch size smaller than a wavelength of the laser pulse. Maintaining the coherence of the radiation from the electrons is essential to get an intense attosecond duration, which is achieved by using a nano-tube array target and a sharply increasing laser pulse. Optimal conditions for attosecond pulse generation are investigated by parameter scanning over plasma density, target thickness and laser pulse duration.

For the extension of current attosecond pulses to multi-cycle driver regime and hard X-ray regime

For the wider application of attosecond pulses, new physical schemes are devised for the usage of a multi-cycle driver laser and for the extension of photon energy of attosecond pulse into keV range.

Generation of Single Attosecond UV/XUV pulses via the Interaction of Femtosecond High-power Laser with Electron Bunch

The study of the interaction of a fs laser co-propagating with an electron bunch reveals that an isolated single attosecond pulse can be generated. The carrier-envelop-phase and strong focus effect play a key role.