An approach of in-situ measuring the complex response of a scene spatial light modulator which working in differential
state was presented by using an image of Ronchi grating substituted for a concrete one. Its principle and testing method
have been studied and a typical XGA2L11 spatial light modulator has been characterized. The scene image under
complicated background has been edge enhanced by mapping the measurement results, and the correlation results
showed that scene spatial modulator with the differential state can increase the SNR and PCE of correlation peak. The
way could be wholly applied in Vander Lugt Correlator and has very strong practicability and effectiveness.
For the design of DOE with rotational symmetric phase distribution, the Fourier Transform (FT) and Inverse Fourier Transform (IFT) take the form of the first order of Hankel transform. The speed of numerical calculation for Hankel transform becomes the bottleneck of phase retrieval algorithms. A new fast Hankel transform method is applied to DOE designing process, in which Hankel transform is achieved by one time's of projection integration and one time's of Fast Fourier Transform (FFT). Utilizing the merits of FFT, speed of Hankel transform is greatly improved. Therefore, rotational symmetric DOE can be designed with fast speed and good designed result can be obtained more easily. Some examples of DOE designing with the help of FHT are given.
Diffractive optical element (DOE) is used to convert inputting optical field to the outputting one on image plane with desired intensity distribution. Since DOE design is a numerical process, the definition of performance parameter of approach distance (PPAD) under continuous condition is given and methods of calculation from discrete samples are argued. Correspondingly, discrete performance parameter of approach distance (DPPAD) is defined to evaluate designed results during designing process under discrete condition. According to the PPAD calculation equation under continuous condition and DPPAD under discrete condition, a general DOE designed result shows that sometimes there are tremendous differences between PPAD value and DPPAD. By analyzing the errors of DPPAD, it is pointed out that to design a faithful DOE result, the sampling interval between 2 neighbor points on outputting plane must has extra limitation despite of sampling theory. Otherwise, the designed result just looks good but it is a bad one in fact, and the DPPAD will not be consistent with PPAD. In the end, an example of faithful designed DOE is given.
It is needed to divert the unwanted harmonic waves out of high power laser system to perform Inertial Confinement Fusion (ICF) and several color separation gratings (CSGs) have been put forward. For a general multilevel grating, the Fraunhofer diffraction patterns of harmonics in ICF laser system have been derived taking no account of optical dispersion. According to the wavelength relationship of the harmonics, the multilevel CSG adaptive for ICF must have special structure features to meet the requests. It is found that a CSG can be used in ICF when its steps number being common multiple of 3 and at the same time the optical path difference for 3ω harmonics between neighboring steps being integral multiple of its wavelength. However, the optical dispersion practically exists for actual laser system and the functions of CSG will be affected. Though by optimization method, the step width and step height of CSG can be changed slightly to compensate the influences, but its performance will be played down. For the CSGs with general structure, the influences of chromatic dispersion have been analyzed when the number of steps and phase delay difference between two neighboring steps varied. By comparison, it is found that the CSG with smaller steps and step height difference is more preferable for color separation in ICF.
A diffractive micro-optics element with hybrid functions has been designed to perform Inertial Confinement Fusion (ICF). The functions of a lens, a low efficiency beam sampler, a Color Separation Grating (CSG) and a binary optical element for target uniform illumination has been integrated to the diffractive optical element (DOE). Its phase distribution is continuous on a disk with diameter of 45mm. The focal length of element is 2400mm. Sampling efficiency for 3ω+(0.351um) light at +1 diffraction order is under 0.1% and the space between sampled beam and focal spot is more than 30mm on the target plane. Unwanted harmonic waves of fundamental wave (1ω+) at 1.053 um and second harmonic wave (2ω+) at 0.527 um are diverted out of the high power laser system and the remnant ratio of them at zero order are less than 2%. Meanwhile, the micro-optics element has excellent ability for beam uniform. The side lobe of the 3ω+ focal spot is suppressed very well and the root-mean-square percent error of its top uniformity is less than 1.5%. Although effected by focusing, beam sampling, color separating and beam smoothing, the synthetic efficiency of 3ω+ light is more than 96%. For the functions integrated diffractive micro-optics element, different designing methods have been applied to implement its corresponding aims. The compatibility, fabrication method and influences between the hybrid functions are discussed in detail.
Many phase retrieval algorithms are used for the designing process of diffractive optical element (DOE). To design a DOE, it is almost the occasions to recovery phase distribution on the micro-optics element when the amplitude distribution of inputting plane and outputting plane has been known. Generally, there are two kinds of strategies to resolve phase retrieval problems, namely iterative method and try-and error method. There are a lot of famous algorithms have been successful used in this field, such as Gerchberg and Saxton (GS), ST, Input-Output, Yang and Gu (YG) etc. In this paper, a novel algorithm is brought forward. The phase on DOE is considered as the superposition of a serial of sinusoidal curves. Randomly, a concrete sinusoidal phase disturbance with definite frequency and amplitude is selected. Correspondent disturbance complex amplitude distribution on image plane can be considered as transformation result of the disturbance phase by the optical system. Then, new complex amplitude on image plane can be calculated as the convolution of its original one and the disturbance one. By Simulated Annealing algorithm, the optimal frequency and amplitude for the sinusoidal phase disturbance are searched. Gradually, when enough sinusoidal phase disturbances are searched, the phase of DOE will approximate to its global optimum solution. At last, for the optimum phase solution, phase smoothing method is used to relieve jump discontinuity.
The design of the Shenguang system calls for a beam sampler to provide 3rd harmonic laser energy for diagnostics in the highly constrained area of the target chamber, The beam sampler should diffract 0.01%-0.5% of the 3rd harmonic light into a calorimeter at a small angle to estimate its corresponding energy. In order to achieve low efficiency beam sampling with the least energy lost, two kinds of surface-relief grating have been designed with different method. One is the rectangular phase grating with its step height and width optimized. Another one is the sinusoidal phase grating. For each kind of beam sampler, the permissible fabrication errors have been analyzed. The characteristics of them have been compared in detail.
A micro-optics element has been designed for diverting unwanted harmonic waves out of high power laser system to perform Inertial Confinement Fusion (ICF). Based on scalar diffraction theory, a basic structure of color separation gratings (CSG) has been designed, which almost meets the request of ICF target system. To increase the diffraction efficiency of third harmonic wave at 0.351 micrometers and decrease that of fundamental wave at 1.053 micrometers and second harmonic at 0.527 micrometers , the basic CSG structure has been optimized by a hybrid algorithm based on simulated annealing algorithm and hill-climbing algorithm. During the optimization procedure, the freedom variable is the step width and step height in one period and the degree of freedom is totally four. By applying several different bounds for objective function, several optimized micro- optical structures have been obtained, which all meet requirements of ICF target system. The influences of step width errors, step height errors and mould collimating errors of the optimized CSG have been analyzed respectively. Among these schemes, a most ideal structure has been selected which is most insensitive to fabrication errors. Under given error limitation, the diffraction efficiency's root-mean-square value at zero order for selected CSG have been investigated by statistical method.
This article intends to talk about the characteristics of a kind of intelligent optical measuring equipment and the technical method to realize its intellectualization. Meanwhile, in the following three aspects, this article points out the prominent difference between intelligent optical equipment and conventional optical measuring equipment. 1) Intelligent optical measuring equipment has the ability to compensate the errors from part or subassembly of system itself. 2) Intelligent optical measuring equipment has self-adaptation ability to changes of environment. 3) Intelligent optical measuring equipment has the ability to analyze and determine fault.
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