Field-free molecular orientation steered by combination of super-Gaussian and THz half-cycle laser pulses

The molecular orientation created by laser fields is important for steering chemical reactions. In this paper, we propose a theoretical scheme to manipulate field-free molecular orientation by using an intense super-Gaussian laser pulse and a time-delayed terahertz half-cycle pulse(THz HCP). It is shown that the degree of field-free orientation can be doubled by the combined pulse with respect to the super-Gaussian pulse or THz HCP alone. Moreover, different laser intensities, carrier envelop phases, shape parameters, and time delays have great influence on the positive and negative orientations, with other conditions unchanged. Furthermore, it is indicated that the maximum degree and direction of molecular orientation can be precisely controlled by half of the duration of the super-Gaussian pulse. Finally, by adjusting the laser parameters of the super-Gaussian laser pulse and THz HCP, the optimal results of negative orientation and corresponding rotational populations are obtained at different temperatures of the molecular system.

Fast Rail Defect Inspection Based on Half-Cycle Power Demodulation Method and FPGA Implementation

In this paper,a fast-speed and real-time online rail inspection method based on half-cycle orthogonal power demodulation algorithm is proposed.For this method,the power characters of de-tection signal which represent the degree of rail track can be calculated using only half-cycle detec-tion signal because of the symmetry characteristic of detected sine signal and reference signal.The theoretical analysis,simulation results and experiment results show that the demodulation preci-sion of proposed method is almost equal to fast Fourier transform(FFT)demodulation method and orthogonal demodulation method,but has high demodulation efficiency and less FPGA resources cost.A high-speed experiment system based on three coils structured sensor is built for rail inspec-tion experiment at a moving speed of 200 km/h.The experiment results show that proposed meth-od is more effective for rail inspection and the time resolution of proposed method is double of clas-sic method that based on FFT and orthogonal.