Thermal radiation from high-temperature application conditions of infrared windows can cause serious interference with infrared imaging. To suppress the thermal radiation from the window, the modulation effects of the optical properties and curvature characteristics of the two surfaces on the thermal radiation distribution from the window are investigated, respectively. The film–substrate–film radiation system is modeled. And the backward emissivity in the different cases of surface optical properties is investigated by the application of zinc sulfide (ZnS) windows and Y2O3 thin films as an example. It is shown that the backward emissivity is suppressed when the outer surface reflectivity is lower and the inner surface reflectivity is higher. A new definition of spectral directional locational emissivity is proposed to characterize the nonplate window emissivity. A model of thermal radiation propagation from the spherical substrate is developed. The emissivity distribution of the window with different curvature characteristics is investigated. It is shown that the curvature radius of the two surfaces can be matched to change the spatial distribution of the emissivity to reduce the effect of thermal radiation on the imaging of the backward optical system.
Airborne LiDAR has become a kind of indispensable measurement device in the current field of remote sensing. However, target extraction using traditional airborne LiDAR based on single-point scanning requires filtering and point cloud segmentation operations, which are complicated and time consuming. Although some researchers have studied streak tube imaging LiDAR (STIL) before, there are few reports in which it is used as an airborne LiDAR for ground measurement in large-scale field. We propose a method of ground target extraction using STIL. Taking advantage of the structural properties of the STIL, complex filtering and point cloud segmentation algorithms are avoided in the target extraction method. The purpose of this article is to verify the feasibility of airborne STIL in ground target extraction. We analyzed the raw streak signal image collected by field experiment and used morphology and intensity information to extract features. After that, we employed the decision tree classifier to classify the four kinds of targets and evaluated the extraction results. The results show that the target extraction achieved satisfactory consequences under an acceptable level. That demonstrates that ground target extraction using STIL is feasible in the field of large-scale remote sensing.
Planar laser induced fluorescence (PLIF) diagnosis technology has been widely applied in flow field study and combustion diagnosis. Due to the complexity of the experimental environment of practical PLIF applications, The PLIF diagnostic system needs a good environment adaptation. In this paper, we reported a high energy Nd:YAG MOPA laser with repetition rate of 500Hz, which was applied in PLIF diagnostic system. A diode-laser side-pumped Nd:YAG module, which was pumped from five directions and optimized for better gain distribution, was employed to build a EO Q-switched Nd:YAG oscillator. A stable structure design of oscillator resonant cavity was used to improve the environmental adaptability of Nd:YAG laser. In our environmental adaptation experimentation, the laser oscillator has an energy fluctuation of <5% in the temperature range from 5°C to 45°C. In order to scale the pulse energy to meet the PLIF system requirements, we employed three 2500W diode-laser five-direction-side-pumped Nd:YAG modules as laser amplifiers to build MOPA system. Finally, the laser pulse energy of ~18mJ was amplified to 68mJ at 1064nm. Using KTP crystal as a frequency doubling crystal, we obtained a pulse energy of 35.6mJ at 532nm. The developed Nd:YAG laser has been used in our 500Hz-PLIF diagnostic system successfully.
Classification of pork soft tissues, including skin, fat, loin, tenderloin and ham muscles, was achieved using combination of laser-induced breakdown spectroscopy, principal component analysis and k nearest neighbors classification.
Waveform sampling LiDAR is a hot topic in LiDAR technique due to its high precision geodesy and multi-layer target detection ability. Especially, the LiDAR systems applying streak tube have encouraging application due to their special properties about high-sensitivity and full waveform sampling ability. This paper describes a kind of LiDAR system applying the full waveform sampling stripe principle array. Basing on the planar fitting of square object, the elevation error of points cloud got from flight experiment is analyzed. The statistical properties of elevation error are got.
Streak tube imaging lidar (STIL) is an active imaging system that has a high depth resolution with the use of a pulsed laser transmitter and streak tube receiver to produce three-dimensional (3-D) range images. This work investigates the optimal signal width of the lidar system, which is helpful to improve the depth resolution based on the centroid algorithm. Theoretical analysis indicates that the signal width has a significant effect on the depth resolution and the optimal signal width can be determined for a given STIL system, which is verified by both the simulation and experimental results. An indoor experiment with a planar target was carried out to validate the relation that the range error decreases first and then increases with the signal width, resulting in an optimal signal width of 8.6 pixels. Finer 3-D range images of a cartoon model were acquired by using the optimal signal width and a minimum range error of 5.5 mm was achieved in a daylight environment.
Dye-doped distributed feedback (DFB) structure is an essential structure for DFB laser. This paper presents an operative method to design a kind of dye-doped distributed feedback laser based on dye-doped holographic polymer dispersed liquid crystal (HPDLC) matrix. The results show that we have processed DFB structure of 10μm period, with a relatively low period deviation of less than 1%. Furthermore, we gain output characteristics of DFB structure through experimental methods, which show good characteristics for wide tuning range, narrow linewidth laser output production.
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