A visually meaningful double-image encryption scheme using 2D compressive sensing and multi-rule DNA encoding is presented. First, scrambling, diffusing and 2D compressive sensing are performed on the two plain images, and two privacy images are obtained, respectively. Then, the two privacy images are re-encrypted using DNA encoding theory to obtain two secret images. Finally, integer wavelet transform (IWT) is performed on the carrier image to obtain the wavelet coefficients, then the two secret images are embedded into the wavelet coefficients and 2k correction is performed, and the obtained result is processed by inverse IWT to obtain a visually meaningful encrypted image. DNA encoding rules selected for the pixel values of different positions in the two privacy images, and DNA operations performed between the two privacy images and the key streams at different positions are controlled by the chaotic system. The application of 2D compressive sensing reduces the amount of data, thus increasing the encryption capacity of the system. The introduction of DNA encoding theory and the double-image embedding process increases the security of the system. The simulation results demonstrate the feasibility of the scheme, and it has high data security and visual security.
In this paper, we numerically study the influence of material and laser parameters on laser spatial beam uniformity improvement based on stimulated Brillouin scattering (SBS). Owing to the intensity dependent property of SBS, the higher intensity parts of the laser beam experience a deep reflection, while the other parts transmit through the medium with weak reflection. Then, the uniformity of the input laser beam is improved. A single frequency laser with a 20th order super-Gaussian shaped output pulse was used as the pump. Five typical liquid materials were adopted as the Brillouin medium for comparison. The laser wavelength was set to 527 nm and 1053 nm; and the pulse duration was set to 3 ns and 5 ns, respectively. The numerically calculated results indicate that low gain coefficient and short phonon lifetime mediums (such as FC-70) are more suitable for the above-mentioned laser beam smoothing scheme. Meanwhile, short wavelength and pulse duration would be helpful for laser beam uniformity improvement. The energy efficiency is above 90% when the laser beam uniformity is greatly improved with an optimized input laser intensity. The calculated results are quite useful for high-power laser applications.
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