Sun glint is a serious obstacle to passive optical remote sensing images. As is the specular reflection of sunlight from the facets of the water surface, sun glint has great linear polarization characteristics, and it is usually suppressed by adding polarizers. Therefore, a spaceborne sun glint polarization parameter measurement system is developed to calculate the on-orbit sun glint parameters in real time. Firstly, we analyzed the polarizing radiation distribution model of sun glint and developed a real time detection system for polarization angle of sun glint according to the principle of spaceborne polarization imager. The system is using Xilinx V5 FPGA as the on-the-satellite processing platform, and we use high-level synthesis (HLS) tools for algorithm hardware description development. By using dataflow, pipeline and other optimization methods in HLS, we greatly reducing computing time and reducing the FPGA resource use. Finally, we use it to calculate the sun glint polarization angle through a three-channel data with a granularity of 25×25 in 670nm, the simulation results show that under the 100M clock, 54% of the slice and DSP48 FPGA resources are consumed, and the sun glint polarization angle can be calculated in 8ms time, which meets the design requirements of rapid sun glint detection.
Laser-induced breakdown spectroscopy (LIBS) is an effective technology to analyze the content of the target elements. The surface morphology of the target will affect the coupling between the laser and the target, which will change the plasma spectrum and lead to inaccurate results. The surface relief and surface roughness are taken as the research parameters of the target surface morphology, the influence of which on LIBS spectrum are researched. The LIBS spectra are acquired on a set of ferroalloy targets, whose included angles θ with horizontal direction changed from -10° to 10°, or surface roughness are different. On the basis of theoretical derivation, we explore the variation trends of line intensity, line integral area, line intensity ratio of different main elements, and line intensity ratio of the same main element with surface morphology parameters. The experimental results have an increasing trend with the increase of θ and a decreasing trend with the decrease of surface roughness. The line intensity ratios are closely related to the change of surface morphology. The line integral area of Cr Ⅰ 429.3438nm has a large variation amplitude and higher correlation coefficient R, which is suitable for characterizing the change of LIBS spectrum with the target surface morphology. The results can provide a valuable reference for reducing the influence of target surface morphology on LIBS detection.
The surface laser speckle image is obtained by the reflected and scattered light beams from a rough surface illuminated by laser. Based on the fractal theory, Double Blanket Model (DBM) is proposed to analyze laser speckle images. The dimension of the space surface is regarded as the characteristic parameter in DBM method. Laser speckle images are preprocessed to remove interference and noise from the environment at first. The size and direction of optimum window are researched. The DBM characteristic parameter is calculated under the optimum window. The relationships are researched between DBM characteristic parameter and surface roughness Ra. The results show that the surface roughness contained in the surface speckle images has a good monotonic relationship with DBM characteristic parameter. To obtain roughness value through a laser speckle image, the fitting function relationship between Ra and DBM characteristic parameter is established, and the fitting function stability is analyzed by experiments. The experiment results show that surface roughness measurement based on DBM method of laser speckle is feasible and applicable to on-line high-precision roughness detection, which has some advantages such as non-contact, high accuracy, fast, remote measurement and simple equipment.
The course of “Applied Optics” is professional and foundational for the specialty of photo-electric information and engineering. According to the characteristics of the specialty, the teaching contents, teaching means, innovations and appraisal methods are mainly discussed in this paper. Firstly, one of the most difficult part to comprehend, the Fermat principle is taken as an example in the teaching content. By using the development history of optics and interesting natural phenomenon, students' understanding of the optical knowledge can be enhanced. Secondly, in various means of teaching art, ZEMAX provides students with a platform of training innovative consciousness and engineering capacity, and it make high cohesion in teaching and scientific research. Thirdly, in the teaching innovation, photoelectric contest can stimulate students' innovative thinking, innovation awareness, and cultivate undergraduate students’ optics, mechanics, electricity, numerology integrated design capabilities. Lastly, the reform in the appraisal methods guide students from focusing on the examination results to pay attention to the learning process. Eventually, students' study interest has improved, demand of the engineering practice has adapted, and the well teaching effect has realized.
The cloud in the high altitude is usually in the gas-liquid mixed state, this paper simulates the environment of the cloud particle using bubble field in the liquid. The paper research the gas-liquid mixture via measuring the size and 3D position of the bubble using a digital in-line holographic imaging system. The design of the optical system and the algorithm of reconstruction, recognition and extraction about the digital hologram is presented. The digital holography deserves to be selected as the projection to measure the bubble field because of advantages such as being able to record and reconstruct the three-dimensional position information, avoiding disturbing the object and insuring the instantaneity during the measurement. The optical system and the algorithm about the digital program have been completed, the hologram of bubbles in the liquids recorded by CCD, the hologram reconstruction using the digital hologram after denoising processing is accomplished. The character of cloud particles can be measured by using holography after analyzing the parameter of the bubbles.
In terms of climate science, getting the accurate cloud particle sizes, shape and number distributions is necessary for searching the influence of cloud on the environment, radiative transfer, remote sensing measurements and understanding precipitation formation. Many methods and instruments have been developed to measure cloud particles, yet there is still restricted to one-dimensional or two-dimensional projections of particle positions, unable to get the three-dimensional information of the spatial distribution of particles. In-line holography is particularly useful for particles field measurements, because it can directly get the three-dimensional information of the particles and quickly access and storage holographic image. In this paper, the main work is using digital in-line holographic system to measure simulated cloud particles in the laboratory. For digital recording hologram reconstructing, we consider the image intensity in conjunction with the edge sharpness of the particles, to obtain an automatically selected threshold of each particle. Using the threshold, we can get a binary image to identify the particles and separate the particles from background, and then get the information such as the location, shape, particle size of particles. The experimental results show that the in-line digital holography can be used to detect the cloud particles, which can gain many parameters of the simulated cloud particles in the plane perpendicular to the optical axis, and can estimate volume parameters of the simulated cloud particles. This experiment is a basis for the further in situ detection of atmospheric cloud particles.
In this paper, for the first time we have demonstrated a continuous wave single-pass extracavity frequency doubling by use of MgO doped stoichiometric lithium tantalite (PP-MgO: SLT). The maximum output of the second harmonic green light is 905mW with the pumping power of 7.69W. The second harmonic conversion efficiency is 11.77%. We have theoretically calculated the tolerance of the temperature of SLT SHG which is about 1.5°C. The experimental tolerance of the temperature is consistent with the calculated value.
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