Light emitting diodes (LEDs) have recently gained much interest as projection light sources. In this work, a compound parabolic concentrator (CPC) coupled to a biologically inspired compound-eye array is designed and fabricated as a light collection engine of a pico-projector. The results indicate that more than 90% light emitted by a monolithic LED array can be collected by the CPC coupled to a compound-eye array and transmitted within the designed angle. This method is advantageous in many respects compared with those available, such as compact volume, high collection efficiency, rectangular radiation pattern and controllable output divergence angle. The result validates that the system reaches a collection efficiency of 87% of micro-LED emitted light. Moreover, the beam collimation quality has been analyzed obtaining a residual divergence of less than 2º. Thus, the results achieved by the proposed optical system improve those obtained with several commercially available devices.
In the detection of atmospheric temperature profile by Rayleigh scattering, the influence of Brillouin scattering is usually ignored and the accuracy of temperature detection is reduced. Current researches on Brillouin scattering are mainly focusing on hydrodynamic and Knudsen regime, few researches has been done on the kinetic regime. In order to improve the precision of atmospheric temperature measurement, a mathematical model based on three Gussian distributions was adopted to study the Rayleigh-Brillouin scattering spectrum (RBS) in kinetic regime, the mixed Rayleigh and Brillouin signal in atmospheric echo signal is separated to obtain independent Rayleigh and Brillouin spectrum. Finally, the experimental platform was set up to control simulation of atmospheric environment system and establishes a hyperspectral splitting optical system based on Fabry-Perot interferometer. The spectrum obtained by the experiment was used to optimize the mathematical model and improve the detection accuracy of atmospheric temperature profiles.
Aim to the current situation that the haze distribution detection is limited by network of point-type instruments, a three dimension scanning micro pulse lidar is researched on the basis of the Mie scattering theory of atmospheric particles. In order to strengthen detective ability of fine particles having a significant effect on human respiratory system, we choose a diode-pumped Nd:YAG solid laser with 532-nm wavelength and wind cooled technique as excited optical source to actualize lidar miniaturization. The pulse energy of 50 μJ and pulse repetitive frequency of 1 kHz are configured to ensure the eye-safety and high temporal-spatial resolution, while the lidar operates in the horizontal scanning mode. A Cassegrain telescope with clear aperture of 254 mm is utilized to collect the backscattering signal for portable multi-location observation. The lidar echo signal is filtered through an interference filter with passed bandwidth of 0.2 nm to implement all-time efficient detection. The experimental observation of atmospheric particle distribution is carried out in horizontal scanning mode. Each plane- position-indication of atmospheric particle distribution contains approximately 300 profiles in the horizontal plane within 6-min interval. Experimental results show that this lidar prototype can probe the space distribution of atmospheric particle with the range of 6 km, and that the influence of industrial production on the atmospheric particle density is 2-3 times as much as that of human activity.
To realize the improvement of signal-to-noise ratio and rejection rate for elastic Mie-Rayleigh signals, a set of dichroic mirrors and narrow-band interference filters with high efficiency was proposed to constitute a new spectroscopy for atmospheric water vapor, aerosol, and cloud studies. Based on the curves of signal-to-noise ratio at three different channels, the actual rejection rates of elastic Mie-Rayleigh signals at the Raman channels were found to be higher than eight orders of magnitude with the cloudy conditions. Continuous nighttime observations showed that the statistical error of the water vapor mixing ratio was <10% at a height of 2.3 km with an aerosol backscatter ratio of 17. Temporal variations of water vapor and aerosols were obtained under the conditions of cloud and cloud-free, the change relevance between aerosol and water vapor was analyzed, and the growth characteristics of water vapor and aerosols showed a good agreement within the cloud layers. Obtained results indicate achievement of the continuous detection of water vapor, aerosol, and cloud with a high efficiency and stability by Raman lidar.
A portable Micro-pulsed Mie scattering lidar at the laser wavelength of 532 nm has been developed for routine observation of atmospheric optical properties of the lower troposphere, including boundary layer structure, cloud, the distribution of aerosol and horizontal visibility and so on. The configuration of lidar and its design methods including the hardware and software were described in details. The lidar system was controlled by compact computer, including self adjustment for coaxial lidar, three-dimensional scanning, real-time data processing of visualization and inversion online. The experimental results illustrate that the system can measure the atmospheric aerosols up to the range of near 5 km at daytime and up to 15 km at nighttime under the measurement conditions of laser energy of 50 μJ, signal averaging time of 40s, a receiving aperture 254 mm, range resolution of 7.5 m and analog detection model, which can provide scientific measurement data for studying the atmospheric environment change, particularly for resolving the particulate pollutant generation, transmission and diffusion characteristics.
Long-term observations of atmosphere aerosol optical properties over Xi’an area have been carried out by a Raman-Mie
lidar and a Micro-pulsed 3D Scanning Mie lidar, which were built at Xi’an University of technology with the laser
wavelength of 355nm and 532nm, respectively. The Raman-Mie lidar is used for observation of the atmospheric
temperature, water vapor and aerosol profiles simultaneously. In order to deeply discuss the temporal-spatial evolution of
the mixed-layer within the urban boundary layer (UBL), the method of combining the absolute minimum of first
derivative and second derivative of the range-squared-corrected signal (RSCS) of lidar was used to retrieve the
mixed-layer depth (MLD). By using continuous observations of 24-hour (THI display), the MLD in temporal and spatial
variation are clearly revealed. Also, the results of continuous observations from July 2006 to October 2011 have been
analyzed for revealing the seasonal cycle and the annual cycle of the MLD. By analyzing the average MLD, it is
obviously shown that the MLD of seasonal cycle is higher in summer than in winter over Xi’an area. Otherwise, by
investigating the relationship of atmospheric boundary layer height, relative humidity and temperature, and the
dependence characteristics and a general disciplinarian between them are then obtained. The achievement is of great
importance for studying the proliferation of urban pollution and obtaining a complete meteorological status of the urban