Compressive imaging（CI）can offer a versatile improvements for imaging systems, such as smaller compressed data volume and super-resolution. Among various methods to realize Compressive imaging, pushing encoding mask has attracted the most attention with its compatibility to the space remote sensing. However, complex pre- calibrations are usually needed for calibrating the encoding mask to achieve the measurement matrix for the image reconstruction. Herein, we design a pushing compressive imaging system which fixed with the function of situ calibration of the encoding mask. The pushing compressive imaging system was constructed, and the experimental results confirmed that the system had the ability for data compression and super-resolution. And above all, the system can avoid the complex pre-calibration, which makes the on-orbit calibration feasible. In the simulations, twice, three times and four times resolutions higher than the captured image’s resolution are performed respectively, which confirm that the method can improve the target image resolution based on the relative low resolution raw captured target images. Furthermore, by pushing the mask precisely which can be considered equivalent to the real pushing imaging, we have reconstructed the true super-resolution target image accurately based on the mask calibration and 6 captured pushing imaging frames.
Streak tube imaging lidar, as a novel flash lidar, due to its advantages of higher resolution for low contrast conditions, compact and rugged physical configurations, small image distortions owing to its scannerless design, and higher image update rates, has immense potential to provide 3D single-laser-pulse scannerless imaging, 3D multispectral imaging, 3D multispectral fluorescence imaging, and 3D polarimetry. In order to further reduce the size and enlarge the field of view (FOV) of the lidar system, we designed a super small-size, large photocathode area and meshless streak tube with spherical cathode and screen. With the aid of Computer Simulation Technology Software package (CST), a model of the streak tube was built, and its predominant performances were illustrated via tracking electron trajectories. Spatial resolution of the streak tube reaches 20lp/mm over the entire ∅28mm photocathode working area, and its temporal resolution is better than 30ps. Most importantly, the external dimensions of the streak tube are only ∅50mmx100mm. And several prototypes are already manufactured on the basis of the computer design.
When radially polarized light beams focus through high numerical-aperture lens, there will be a very strong longitudinal component of the light field near the focus. And, under the condition of certain system parameters, they can shape a spot which is over the focusing spot of the diffraction limit, which are the superiorities that linearly polarized light and circularly polarized light do not have. Besides, what we have found in the experiment is that radially polarized femtosecond laser pulses own the same superiorities, which provides the basis for using the focusing characteristics of radially polarized light beams under the condition of shorter and more powerful laser pulses. So far, although people have studied a lot on radially polarized light beams, this kind of light beams’ focusing characters are rarely researched. What is worse, most research of its focusing characters still stays in the stage of theoretical simulation，and it seems that none of people have really studied it by the way of experiments. This article is precisely based on this. On the basis of predecessors' a lot of theoretical research, the article pays more attention on analyzing radially polarized light beams’ focusing character through experiments. What’s more, the article, based on femtosecond laser pulses, compares the differences of the focusing nature among linearly polarized light, circularly polarized light and radially polarized light. And it gets the conclusion that radially polarized femtosecond laser pulses have better focusing character in longitudinal light field, confirming the feasibility that radially polarized light beams can be used in the fields of pulling, catching, and accelerating particles, metal cutting and high-density storage.
The generation of femtosecond optical vortex beam based on direct wave-front modulation with phase-only liquid crystal spatial light modulator is demonstrated. The spatial and temporal properties of the generated femtosecond vortices are investigated in detail. The experimental results show remarkable agreement with the results of the theoretical analysis and simulations, and indicate that the method we utilized can efficiently generate femtosecond optical vortex beam of arbitrary topological charge. The temporal and spectral properties of the femtosecond pulsed beam are hardly affected by the phase dislocation imposed on the wave-front.
We present a superresolution imaging method based on the dynamic single-pixel compressive sensing (CS) system. Different from the traditional static CS, this system is slowly moving in parallel with the scene during the compressive sampling, implying that the measurements are possible to contain the information about the scene with the subpixel resolution. Here we first build the dynamic compressive sampling model and give the recovery method via traditional CS scheme, and then we propose the image superresolution recovery method in the CS framework, where a subdivision scheme is used. The proposed method not only has remarkable superresolution performance, but also has low requirements on the imaging system, since it is associated with the single-pixel imager, which is one of the simplest systems in the existing CS imaging architectures. The feasibility of the proposed method is demonstrated by the numerical simulations as well as the optical experiments.
Both in-phase and out-phase radially polarized femtosecond-pulse (RPFP) beams have been generated with one phase-only liquid crystal spatial light modulator, which effectively modulates the phase retardation distributions of a pulse beam wavefront by two reflections. The intensity distributions and polarizing properties of both in-phase and out-phase RPFP beams are detected, and the temporal properties of in-phase RPFP beams are investigated in detail. Experimental results indicate that we effectively produce an RPFP beam. And the temporal duration of the output in-phase RPFP beam is 183 fs about 14 fs shorter than the input Gaussian femtosecond-pulse beam. The temporal durations of arbitrary polarized components of an in-phase RPFP beam vary less than 3.5%.