This paper numerically simulates the process of ablation of an aluminum target by an intense femtosecond laser with a fluence of 40 J/cm 2 based on the two-temperature equation,and obtains the evolution of the free el...This paper numerically simulates the process of ablation of an aluminum target by an intense femtosecond laser with a fluence of 40 J/cm 2 based on the two-temperature equation,and obtains the evolution of the free electron temperature and lattice temperature over a large temporal and depth range,for the first time. By investigating the temporal evolution curves of the free electron temperature and lattice temperature at three representative depths of 0,100 nm and 500 nm,it reveals different characteristics and mechanisms of the free electron temperature evolution at different depths. The results show that,in the intense femtosecond laser ablation of aluminum,the material ablation is mainly induced by the thermal conduction of free electrons,instead of the direct absorption of the laser energy; in addition,the thermal conduction of free electrons and the coupling effect between electrons and lattice will induce the temperature of free electrons deep inside the target to experience a process from increase to decrease and finally to increase again.展开更多
A method of color image single-channel encryption is proposed. The proposed method uses tricolor grating to encode a color image into a gray level image, then the gray level image is encrypted by double random phase e...A method of color image single-channel encryption is proposed. The proposed method uses tricolor grating to encode a color image into a gray level image, then the gray level image is encrypted by double random phase encryption, so a color image is encrypted in a single-channel and its security is ensured. Computer simulations and the chromatic aberration analysis are given to prove the possibility of the proposed idea.The optical system is simpler and is easy to be applied into practice. The simulation resu...展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10904079 and (60338001), the Speclanzed Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20090031120041), and the Natural Science Foundation of Tianjin (Grant No. 10JCYBJC01300).
文摘This paper numerically simulates the process of ablation of an aluminum target by an intense femtosecond laser with a fluence of 40 J/cm 2 based on the two-temperature equation,and obtains the evolution of the free electron temperature and lattice temperature over a large temporal and depth range,for the first time. By investigating the temporal evolution curves of the free electron temperature and lattice temperature at three representative depths of 0,100 nm and 500 nm,it reveals different characteristics and mechanisms of the free electron temperature evolution at different depths. The results show that,in the intense femtosecond laser ablation of aluminum,the material ablation is mainly induced by the thermal conduction of free electrons,instead of the direct absorption of the laser energy; in addition,the thermal conduction of free electrons and the coupling effect between electrons and lattice will induce the temperature of free electrons deep inside the target to experience a process from increase to decrease and finally to increase again.
基金supported by the Opening Subject of KeyLaboratory of Opoelectronic Information Science & Technology,Ministry of Education of China(Grant No. 2005-141)
文摘A method of color image single-channel encryption is proposed. The proposed method uses tricolor grating to encode a color image into a gray level image, then the gray level image is encrypted by double random phase encryption, so a color image is encrypted in a single-channel and its security is ensured. Computer simulations and the chromatic aberration analysis are given to prove the possibility of the proposed idea.The optical system is simpler and is easy to be applied into practice. The simulation resu...