Scissor-cross ionization injection in laser wakefield accelerators

We propose to use a frequency doubled pulse colliding with the driving pulse at an acute angle to trigger ionization injection in a laser wakefield accelerator. This scheme effectively reduces the duration that injection occurs, thus high injection quality is obtained. Three-dimensional particle-in-cell simulations show that electron beams with energy of ~500 MeV, charge of ~40 pC, energy spread of ~1% and normalized emittance of a few millimeter milliradian can be produced by ~100 TW laser pulses. By adjusting the angle between the two pulses, the intensity of the trigger pulse and the gas dope ratio, the charge and energy spread of the electron beam can be controlled.

Wavelet Spectra of a Chirped Gaussian Pulsed-Driven Harmonic Oscillator

We investigate the nature of spectral lines of emitted radiation due to of a non-dissipative single-mode quantized harmonic oscillator (HO) with train of n-chirped Gaussian pulses. Specifically, we analyze the transient emitted spectrum through two window wavelet functions of the radiation detector, namely the Haar wavelet and Morlet wavelet. Computational display of the exact analytical results shows how the driving pulse parameters (strength and number of pulses, chirping, repetition time) act as control knobs to shape the detected emitted spectrum as desired.

Time-resolved studies of low-temperature, EUV-induced plasmas: EUV emission in selected spectral ranges

Interaction of extreme ultraviolet (EUV) pulses of high intensity with gases results in the creation of non-thermalized plasmas. Energies of the driving photons and photoelectrons are sufficient for creation of excited states, followed by emission of the EUV photons. In most cases, decay times of these states are short comparing to the driving EUV pulse. It means that just after stopping of the driving pulse, the EUV emission corresponding to the excited states should also stop. From our earlier measurements in the optical range, however, it can be concluded that lifetimes of such plasmas exceed a time duration of the driving pulse even two orders of magnitude. Hence, it can be expected that the time duration of the EUV emission can be also significantly longer than the irradiation time. In this work, EUV-induced, low-temperature helium (He), krypton, and xenon plasmas were investigated. EUV emission from these plasmas was studied, using a specially prepared detection system, allowing for time-resolved measurements, in selected spectral ranges. The detection system was based on a paraboloidal collector and a semiconductor photodiode, sensitive for the EUV photons. For spectral selection, the corresponding filters or multilayer mirrors were employed. In most cases, the time duration of the EUV emission was significantly longer than the driving EUV pulse. In case of He plasmas, the emission corresponding to excited atoms was detected even hundreds of nanoseconds after the irradiation. It was also shown that the corresponding time profiles depended on densities of gases to be ionized.

Minimizing attosecond CEP jitter by carrier envelope phase tuning

Minimizing the CEP jitter of isolated attosecond pulses (IAP) will be important for future applications. This jitter is experimentally and theoretically investigated and can be minimized when the driving pulse is near its Fourier limit but with slightly negative chirp. Thus, understanding and characterization of the CEP jitter of IAPs is a first step towards exact control of the electric field of IAP pulses.

Suppressing Electromagnetic Interference in Switching Converters by Chaotic Duty Modulation

The switching converter generates serious electromagnetic interference (EMI), which impairs other devices‘ performance and harms human being’s health. As a way of chaos technique, chaotic modulation has been developed to suppress EMI of the switching converter by dispersing the energy into a wide frequency band and smoothing the peaks of the EMI spectrum. Unlike the well-studied chaotic frequency modulation, the chaotic duty modulation is concerned in this dissertation, which is just to change the duty of the transistor driving-pulse while maintains the fixed switching frequency. Chaotic duty modulation is realized by appending an external chaotic signal to the existing PWM module of the switching converter, which is practicable without the loss of the generality. It is thus verified that this proposal of using chaotic duty modulation in switching converters for EMI suppression is feasible and lays a foundation for industrial applications. ...