We present a grating imaging scanning lithography system for the fabrication of large-sized gratings.In this technology,±1-order diffractive beams are generated by a phase grating and selected by a spatial filter.Meanwhile,a 4f system enables the±1-order diffractive beams to form a grating image with a clear jagged-edge boundary on the substrate.A high-precision two-dimensional(2D)mobile stage is used for complementary cyclical scanning,thereby effectively eliminating image stitching errors.The absence of such errors results in a seamless and uniform large-sized grating.Characterized by a simple structure,high energy use,and good stability,this lithography system is highly relevant to the high-speed and costeffective production of large-sized gratings.
This paper investigates the entanglement dynamics of a Heisenberg XY model for a two-spin system in the presence of a nonuniform magnetic field.The master equations and the concurrence evolution equations for the initial α state are derived and analysed.It is shown that for the symmetric initial α state,only the nonuniform field can play a role in entanglement dynamics while the uniform field and the bath will not play such a role.For the asymmetric α state,the nonuniform field leads to the beat pattern oscillation of the concurrence evolution.The inhomogeneity of the field can enhance the entanglement by suppressing the decoherence effects of both the spin-orbit interaction and the spin bath.
A semi-classical model is utilized to explain the dissociation control of the hydrogen molecular ion(H+2). By analyzing the curve of the dissociation asymmetry parameter as a function of the time delay between the exciting and steering pulses, we find that the dissociation control is dependent not only on the peak intensity and direction of the electric field of the steering pulse, but also on the peak intensity of the exciting pulse.
We experimentally investigate the high-order harmonic generation in argon gas cell driven by a multi-cycle broadband infrared laser pulse from a tunable optical-parametric-amplifier(OPA)source.The generation of high-order harmonic continuum with the cut-off photon energy up to 110 eV is observed by tuning the chirp of the 800-nm laser pulse which pumps OPA source.The generation of harmonic continuum is understood in terms of the two-hump structure of the OPA output spectrum and the optimal relative phase of the two humps.The demonstrated scheme is of importance for the generation of extreme ultraviolet(XUV)continuum at higher photon energy region.
The molecular dissociation with a two-laser-pulse scheme is theoretically investigated for the hydrogen molecular ion(H+2)and its isotopes(HD+and HT+).The terahertz pulse is used to steer the electron motion after it has been excited by an ultrashort ultraviolet laser pulse and an unprecedented electron localization ratio can be achieved.With the coupled equations,the mass effect of the nuclei on the effective time of the electron localization control is discussed.
The phase conjugation between the deformable mirror and the wavefront sensor in the aberration correction of a terawatt Ti:sapphire laser is studied experimentally and theoretically in this paper.At varying values of phaseconjugation precision,we focus the corresponding beams into spots of the same size of 5.1 μm× 5.3 μm with a f/4 parabola in the 32 TW/36 fs Ti:sapphire laser system.The results show that the precision of conjugation can induce an intensity modulation but does not significantly affect the wavefront correction.
The effects of ion motion on the generation of short-cycle relativistic laser pulses during radiation pressure acceleration are investigated by analytical modeling and particle-in-cell simulations. Studies show that the rear part of the transmitted pulse modulated by ion motion is sharper compared with the case of the electron shutter only. In this study, the ions further modulate the short-cycle pulses transmitted. A 3.9 fs laser pulse with an intensity of 1.33×1021W cm-2is generated by properly controlling the motions of the electron and ion in the simulations. The short-cycle laser pulse source proposed can be applied in the generation of single attosecond pulses and electron acceleration in a small bubble regime.
A simplified modal method to explain the resonance phenomenon in guided mode resonance(GMR) gratings with asymmetric coatings is presented.The resonance observed is due to the interaction of two propagation modes inside the grating.The reflectivity spectra and electric field distributions calculated from the simplified modal method are compared using rigorous coupled-wave analysis(RCWA).The influences of high-order evanescent modes on the resonance peak are analyzed.A matrix Fabry-Perot(FP) resonance condition is developed to evaluate the resonance wavelength.An explanation for the resonance phenomenon observed based on the FP resonance phase condition is also proposed and demonstrated.The simplified method provides clear physical insights into GMR gratings that are useful for the analysis of a variety of other resonance gratings.
We report the recent improvement on the petawatt (PW) femtosecond Ti:sapphire chirped pulse amplification (CPA) laser system at Shanghai Institute of Optics and Fine Mechanics (SIOM), Chinese Academy of Sciences. By enlarging the sizes of the pump and signal beams in the large aperture Ti:sapphire amplifiers and optimizing the whole laser system, the output laser energy before the pulse compressor is upgraded to 42.6 J. Accordingly, the peak power of the laser system exceeds 1 PW. The shot-to-shot instability of the output laser energy at about 40 J is less than ±5%.
K-shell X-ray emission from a Cu nanowire target irradiated by an ultraintense femtosecond laser pulse is studied using an elliptically bent quartz crystal and imaging plate. The designed bent crystal spectrometer has better spectral resolution, which is higher than 1 000. The absolute Kα radiation photon yields are obtained from the experimental results and the Monte-Carlo model. The conversion efficiency of the Cu Kα line is estimated to be 0.019% from the interaction of 4 J, 50-fs laser pulse irradiated on a Cu nanowire target. The high yield of K shell X-ray has important applications in X-ray emission source.
