Laser damage is becoming more and more important part to consider in design of laser systems among these decade years, for high-power lasers are widely used in industry production, medicine, signal detection, and any other departments. There are two research directions of laser damage: one is the damage caused by ultra-short pulse, the other is that caused by ultraviolet beams. These two types of laser are usually combined to irradiate materials. Laser Induced Periodic Surface Structures (LIPPS) are special phenomena which can change many physical characters of materials, for example, surface absorptivity. LIPPS are usually caused by ultra-short pulse, as a step of laser processing. This paper will reveal the damage caused by ultra-short and ultraviolet beams, especially when they lead to LIPPS.
The common generation methods of two-dimensional airy beams were introduced briefly. The disadvantage of generation method by utilizing traditional two-dimensional digital phase masks was analyzed as well. Based on this, the digital blazed grating was introduced, as well as its corresponding theories. It was proposed that the traditional two-dimensional digital phase mask and the alterable digital blazed grating could be combined to generate a comprehensive phase mask. Thus, the diffraction orders of the airy beams could be controlled by changing the periods of improved comprehensive phase masks. Compared to the traditional two-dimensional digital phase masks, the airy beams generated by the proposed comprehensive phase mask had the advantage of controllable distances between different diffraction orders. At the same time, the specific order of the Airy beams could be strengthened, and the others could be weakened, which was useful to the subsequent study on the propagation and control of two-dimensional airy beams. The experimental results showed that: the proposed comprehensive phase masks could distinguish between the different diffraction orders of generated Airy beams. As a result, the mutual interference between different diffraction orders could be avoided effectively.
The universal liquid crystal spatial light modulator (LC-SLM) was widely used in many aspects of optical study. The working principles and application of LC-SLM were introduced briefly. The traditional Twyman-Green interference method which was used to measure the phase modulation characteristics of universal liquid spatial light modulator had some obvious disadvantages in the practical use, such as high environmental requirement and difficult interference fringes acquisition. The disadvantages of traditional Twyman-Green interference method gained the difficulty of carrying out corresponding optical measurement experiments. To avoid this, the traditional Twyman-Green interference method was improved in the paper. The experimental light path was designed anew. Distinct and stable interference fringes could be acquired by controlling the optical path difference (OPD) dynamically. To verify the validity of the newly proposed measurement method, the phase modulation characteristics of P512-1064 LC-SLM produced by Meadowlark Company were measured by utilizing the improved Twyman-Green interference method at the wavelength of 632.8 nm which was beyond the working wavelengths of the LC-SLM. A series of gray images covering the gray degree from 1 to 256 which were generated by computer were used in the experiment. An extra lens was added in front of a reflector in the optical path to control the OPD dynamically. 256 interference images were acquired after loading the gray image into the LC-SLM in order. After that, the acquired interference images should be pre-processed by several digital image processing methods for easier measurement later. Specifically, the method of gray filtering and morphological processing were adopted to make the interference fringes clearer and thinner in the corresponding processing. Then, the phase modulation curve of the LC-SLM was acquired through numerical computation of the cycles of the interference fringes. In general, the phase modulation curve we acquired was not so accurate in the practical use, as the LC-SLM was required to work from zero to 2pi in the linear interval. So, the nonlinear interval among the phase modulation curve should be compensated and corrected. Here, the method of inverse interpolation which was regarded as one of the most common phase correcting methods was utilized. The corrected phase modulation curve was acquired after numerical computation. The results shows that the improved Twyman-Green interference method could realize the dynamic control of the interference fringes. As a result, the method's requirement for external experiment environment was reduced and its feasibility was improved. Also, the Root Mean Squared Error (RMSE) between the calibrated phase modulation curve and the ideal phase modulation curve was reduced.
The situation of researches on laser jamming to imaging detectors is analyzed and saturation effect of CCD under laser
illumination is introduced. Combined with characteristics of CCD, diffraction limited point spread function (PSF) is
applied to analyze the laser dazzled image and process of simulation is shown. Then simulated dazzled image is obtained
and it is compared with actual image. With different laser powers, imaging performance parameters of simulated images
are analyzed, such as Peak signal to noise ratio (PSNR), gray variation, definition, uniformity and so on. Experimental
results show the feasibility and validity of laser jamming simulation. Moreover, changes of imaging performance
parameters can provide useful references for further evaluation of laser jamming effect.
The advantages and disadvantages of traditional evaluation methods for laser jamming effect are analyzed. Process of
fuzzy evaluation is presented. Combined with different parameters of CCD imaging performance, fuzzy synthetic
evaluation method is applied. In the method, several performance evaluation parameters are calculated. Then single
factor evaluation result is obtained and evaluation parameters are normalized respectively. Through fuzzy relation matrix,
single factor evaluation results are synthesized and analyzed. Under different jamming conditions, the fuzzy synthetic
evaluation results are obtained. Experimental results show that this method considers different parameters of laser
dazzled images and can reflect the effect of laser jamming to CCD imaging performance effectively.
In order to protect optical system from being discovered by the active laser reconnaissance, the unsymmetrical
covering method is proposed to realize the optical system's laser stealth. The theoretical model of the method was
established. The laser stealth effect was analyzed and the results indicate that covering a part of optical system's aperture
could obscure the echo in both the covered area and its centrosymmetric area. Therefore, the absolute laser stealth could
be achieved by covering half of the optical system's aperture, while the optical system still has good performance. An
experiment was designed to validate the theoretical analysis results. The experimental results are shown to be in good
agreement with the theoretical results. The unsymmetrical covering method is effective to the laser stealth of optical
Proc. SPIE. 7658, 5th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optoelectronic Materials and Devices for Detector, Imager, Display, and Energy Conversion Technology
KEYWORDS: Wavelet transforms, Visualization, Spatial frequencies, Image processing, Wavelets, Laser applications, Image analysis, Image quality, Human vision and color perception, Charge-coupled devices
The advantages and disadvantages of conventional image quality evaluation methods are analyzed and according to the
characteristics of laser disturbing image, an image quality evaluation method which is based on wavelet weight and
correlation is established. In the method, both the original and disturbed images are processed by wavelet decomposition,
replacement and reconstruction. Then different sub-band images are obtained and their correlations are calculated.
Combined with band-pass characteristic of human vision, visual weighted coefficients are obtained and objective
calculation results are output finally. Experimental results show that this method not only can overcome the influences of
different conditions on evaluation of laser disturbing effect, but it is also in good agreement with the subjective method.
In light of the difficulties to directly measure plume gas concentration by existing methods, the paper proposed an
inversion algorithm based on multivariate regression analysis. We first of all built up a multivariate regression model of
plume gas concentration by dividing the plume into several homogeneous layers along the observation direction. Then a
group of discrete spectral data was sampled out from plume infrared radiation curve at the intervals of certain wave
numbers. Thus the spectroscopic data without atmospheric attenuation could be obtained when the discrete spectral data
was divided by the atmospheric transmittances at corresponding wave numbers. After that, we worked on the
temperature profile of the plume, figuring out the average temperature of each layer of plume through integration
according to the outcomes of plume layering. At the same time, supported by the High Resolution Temperature Gas
Spectral Database (HITEMP), we also computed out the average absorption coefficient of each layer of plume. Thereby,
the triplicity of the spectroscopic data without atmospheric attenuation, the average temperature of each layer of plume
and the average absorption coefficient of each layer of plume, as the input parameters for the multivariate regression
model of plume gas concentration, could finally enable us to work out the concentration distribution of the plume gas
along the observation direction by least squares method which, however, only took into consideration the effect of vapor
and carbon dioxide. The comparison with the concentration distribution acquired through numerical computation of
plume flow field proves the feasibility of the inversion algorithm.
This paper is to introduce the principle and the experimental operation of Q-switching and tuning of flashlamp pumped Ti:Sapphire laser with electro-optic crystal. A LiNbO3 (LN) crystal (13.8 X 14.7 X 46.5 mm3), a quartz quarter wave plate (204 micrometer in thickness), and a Glan prism were inserted in the cavity. Before a Q-switching voltage was applied to the LN crystal, the loss corresponding to quite wide wavelength band was high, the oscillation of the laser was prevented. The Q switching was achieved with the voltage on, different voltage corresponding to different wavelength at which the laser had the highest Q figure. The Q- switching and the tuning of the laser was achieved at the same time in this way.