Sharif Digital Repository

Interactions of two distinct shapes of the pulses namely positive/negative chirped pulse and fast/slow rising-edge pulse with plasma are studied using particle-in-cell simulation. It is found that, for a pulse duration of 34 fs and intensity a0 = 12, proton acceleration could be enhanced by asymmetric pulses with either pulse envelope or pulse frequency modification. The number of accelerated protons, as well as the proton energy cut-off, is increased by asymmetric pulses. In this work, for positive chirped pulse, electrostatic field at the rear side of the target is improved by about 30%, which in turns leads to an increase in the proton energy cut-off more than 40%. Moreover, in contrary... 

This paper will design non-linear frequency modulation (NLFM) signal for Chebyshev, Kaiser, Taylor, and raised-cosine power spectral densities (PSDs). Then, the variation of peak sidelobe level with regard to mainlobe width for these four different window functions are analyzed. It has been demonstrated that reduction of sidelobe level in NLFM signal can lead to increase in mainlobe width of autocorrelation function. Furthermore, the results of power spectral density obtained from the simulation and the desired PSD are compared. Finally, error percentage between simulated PSD and desired PSD for different peak sidelobe level are illustrated. The stationary phase concept is the possible... 

Interaction of the chirped circularly polarized laser pulse with ramped density plasma is presented by particle-in-cell simulation. The obtained results indicate that the laser penetration depth into the plasma target and hot-electron generation can be improved by chirped induced transparency (CIT). Positive chirped pulses penetrate more deeply in the plasma leading to the hot electron enhancement and improvement of the maximum separation accelerating fields at the rear side of the target. For laser pulse with 150 fs time duration, there is 40% increase in the laser penetration depth in the target and the maximum amount of the electrostatic field is improved by a factor of 5 in the present... 

The effect of pulse shaping on the intense laser-driven proton beam produced through radiation pressure acceleration as a highly efficient mechanism is investigated. In this regard, the interaction of pulses with modified frequencies, including positive and negative chirped pulses with plasma, is simulated using particle-in-cell code. The simulation results indicate that the proton acceleration could be significantly enhanced for both negative and positive chirped pulses. As a consequence of the acceleration time extension as well as the electron heating suppression, a sharper and narrower proton beam could be achieved for negative chirped pulses. The same trend is observed for all negative... 

This paper introduces the concept of on-chip temporal optical computing, based on dispersive Fourier transform and suitably designed modulation module, to perform mathematical operations of interest, such as differentiation, integration, or convolution in time domain. The desired mathematical operation is performed as signal propagates through a fully reconfigurable on-chip photonic signal processor. Although a few numbers of photonic temporal signal processors have been introduced recently, they are usually bulky or they suffer from limited reconfigurability which is of great importance to implement large-scale general-purpose photonic signal processors. To address these limitations, this...