In response to the imperative requirement of the Background Oriented Schlieren (BOS) imaging system to produce exceptionally realistic target schlieren images, this paper proposes a method for generating realistic background schlieren images based on physical optical tracing. This method, grounded in real-world scene images, couples atmospheric turbulence field information with target information to establish a physics-based background schlieren imaging system ray tracing full-link simulation model. It simulates the propagation of light rays in complex refractive index fields of three-dimensional scenes and calculates the intersection points of light rays with objects based on physical principles. By using diffraction imaging principles, it accomplishes forward mapping of background images, thereby generating background schlieren images with higher realism and credibility. Experimental results demonstrate that this method offers high simulation flexibility and generates background schlieren images that are realistic and reliable, effectively showcasing schlieren characteristics. This method provides essential support for the pre-design and evaluation of background schlieren imaging system systems.
In order to study the polarization imaging characteristics of sea targets in the long-wave infrared spectrum, a set of real-time polarization imaging experimental devices were built using the focal plane long-wave infrared polarization detectors, and experiments were carried out on typical laboratory targets, and the device was used to carry out ship-borne sea surfaces. Long-wave infrared polarization imaging of typical targets. Separate 0°, 45°, 90° and unbiased infrared intensity images from the directly obtained micro-polarization array images, and use the stokes vector method to calculate the polarization degree and polarization angle of the image. The image quality is evaluated through image clarity. The clarity of polarized images is more than 20 times higher than that of infrared images, and the clarity of polarization angle images is 8~10 times higher than that of infrared images. The experimental results show that after the polarization dimension is increased, both intuitive observation and quantitative analysis can find that the clarity of the long-wave infrared polarization image is significantly improved, and the target detection ability is improved.
This paper introduces radial multi-sub-mirror (MSM) synthetic aperture system structure and imaging characteristics of the liquid lens based, and the MSM array for the simulate imaging and image restoration. In order to obtain the scaling invariance of MSM system imaging, the dimensionless method is used to reduce the structural parameters. Baseline statistical distribution diagram and modulation transfer function (MTF) are used to analyze the structural characteristics and intermediate frequency(IF) characteristics. The MSM optical characteristics are calculated and the raw image is simulated under different filling factors. For the reduction of the IF characteristics of the synthetic aperture system, the raw image is restored by Wiener filtering. Using the standard deviation and peak signal-to-noise ratio between the synthetic aperture imaging system and the filled aperture imaging system, these two indicators evaluate the image quality with different fill factors. A comparative analysis of the restored images yields a relationship between filling factor and image quality. Since the large number of sub-mirrors in the MSM array, resulting in a larger number of different baselines. Because the baseline corresponds to the distribution characteristics of spatial frequency, the baseline of the MSM has a large number of repeats in the IF region, so the structure has a good response of IF. The results showed that as the sub-aperture diameter increases, the imaging quality of the MSM structure becomes better. The image restoration effect enhance with the increase of the filling factor. After wiener filtering, the image quality is improved.
Diffractive optical imaging is a new method to realize high-resolution imaging from geostationary orbit(GEO). Technical advantages of diffractive optical imaging is analyzed in the field of space optics. For application of super large diameter space optical system, the system scheme and a new achromatic method is proposed. An imaging system is developed and tested, the result of optical system wavefront is 0.169λ(RMS), optical system MTF is 0.85, and the imaging system MTF is 0.19. Test results show the new achromatic method is feasible. The above conclusions have reference significance for the development of super large diameter diffractive optical imaging system.
Diffractive membrane imaging can be widely used in infrared band due to its longer minimum linewidth and loose requirement of RMS to fabricate more easily and reduce production period and manufacturing cost than used in visible band. A deployable infrared diffractive membrane imaging system was designed, consisting of Φ200mm imaging aperture (actual aperture is Φ500mm) and deployable structure that supports the infrared membrane under tension. Its spectral band width is >1.2μm, field of view is >1°, and diffractive efficiency can be >60%. Stowed size is 150mm×150mm×400mm. Research result of this project can promote the application of diffractive membrane imaging in infrared band and provide an effective and feasible means for achieving extremely large optical primary mirror from compact, lightweight payload.
Transmissive diffractive membrane optic can be used in space optical telescope to reduce the size and mass of imaging system. Based on the international research results about transmissive diffractive membrane, a 4-level diffractive substrate with 100mm apertures was designed and transmissive diffractive membrane was fabricated by spin coating. High-precision support structure for diffractive membrane with surface precision 0.12λ RMS (λ=632.8nm) was introduced, and that can meet the diffractive imaging requirements. Diffraction efficiency of the diffractive membrane supported by support structure was tested, and the test results showed that diffraction efficiency was >50%. The step figure test results illustrated the etched deep precision was less the 10nm. The imaging wavefront test result demonstrated a wavefront error of about 38 nm RMS. The transmissive diffractive membrane optic can be very useful for large aperture imaging system to realize low mass and low cost.
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