Xianying Ge

Classification of edible oils using 532 nm laser-induced fluorescence combined with support vector machine

In this paper, laser-induced fluorescence (LIF) is used to characterize and distinguish between different vegetable oils, including soybean, olive, grapeseed, rapeseed, corn, peanut, sunflower, canola, and walnut oils. A 532 nm laser, rather than an ultraviolet (UV) light source, is proposed and used as an excitation light source for the fluorescence analysis of edible oils. It was found that this laser is superior to UV lasers, the fluorescent characteristics become more distinct under 532 nm laser excitation. Edible oils were differentiated by LIF combined with principal component analysis which was used to reduce the dimensionality of data by finding key attributes, and support vector machine. This paper demonstrates, that for ten popular edible oils, the recognition rate can reach up to 100% when a 532 nm laser serves as an excitation light source.

Effect of laser pulse shape and duration on spectrum width of coherent LIDAR

Doppler spectrum width, which relates to wind turbulence, is one of the essential parameters of coherent LIDAR. Using the Fourier transform theorem and the definition of correlation function, the power spectrum function in the stationary condition is deduced. The effects of pulse shape, pulse duration and the windowing are included. The spectrum width resulted from the turbulence is given under Kolmogorov turbulence model. Based on the power spectrum theory, the spectrum broadening by different pulse shapes and pulse durations are calculated. To validate the accuracy of the theory and usage in the retrieval of turbulence parameters, the numerical simulations of the echo signal are carried out in turbulence conditions. The statistics characteristics of the spectrum broadening from laser pulse shapes and durations are inverted and compared. The results show that the spectrum broadening varies greatly due to the selection of pulse shapes and pulse durations, and the numerical simulation is in accordance with the theory results.

The double grating monochromator’s design for pure rotational Raman lidar

The pure rotational Raman lidar temperature measurement system is usually used for retrieval of atmospheric temperature according to the echo signal ratio of high and low-level quantum numbers of N2 molecules which are consistent with the exponential relationship. An effective method to detect the rotational Raman spectrum is taking a double grating monochromator. In this paper the detection principle and the structure of the dual-grating monochromator are described, with analysis of rotational Raman’s Stokes and anti-Stokes spectrums of N2 molecule, the high order and lower order quantum number of the probe spectrum are resolved, then the specific design parameters are presented. Subsequently spectral effect is simulated with Zemax software. The simulation result indicates that under the condition of the probe laser wavelength of 532nm and using double-grating spectrometer which is comprised by two blazed gratings, Raman spectrums of 529.05nm, 530.40nm, 533.77nm, 535.13nm can be separated well, and double-grating monochromator has high diffraction efficiency.

Analysis of optimum coupling efficiency between random light and single-mode fiber

By assuming that the light coupled into a single-mode fiber is monochromatic generated by the diffused far field , employing the lens coupling theory and van Cittert-Zernike theorem，we obtain the general expressions of the coupling efficiency of an optical fiber. This subject focuses on the analysis that the incident light is plane wave; we obtain the F number of coupling lens, which provides the theory support for the design of the coupling lens, corresponding to the optimum coupling efficiency. Fiber coupling efficiency is not only related to the mode matching of incident light and the fiber; the optical axis, the symmetrical axis of lens and the fiber center line misalignment also affect. Simulation results of misalignment errors show that the defocus alignment has little effect on the coupling efficiency, while the effect of both lateral alignment error and angle offset on the coupling efficiency is relatively large.

The influence factors and optimization methods of the local oscillator power for coherent doppler lidar

Coherent doppler lidar for wind is based on the heterodyne detection between local oscillator signal and the echo signal. Optimum optical local oscillator power is an important factor of the signal to noise ratio. The dynamic range of echo signal, the relative intensity noise and the photoelectric detector saturation effect are studied comprehensively as the local oscillator power influence factors for the first time. The expression of the local oscillator power and SNR is derived. Using the computer simulation, the conclusion that the dynamic range of the echo signal will not affect the optimum of the local oscillator is obtained. Selecting different values of the relative intensity noise, the curves of the SNR versus local oscillator are given. Comparing the SNR formula in the quantum limit with the derived SNR formula, the saturation effect of the photoelectric devices is studied.

Comparing methods for retrieving aerosol extinction coefficient with U.S. Standard Atmospheric Model and Temperature Gradient

Aerosol extinction coefficient in troposphere is retrieved from Raman-Mie lidar returns. Both the basic principle and the two retrieving methods are introduced in this paper. Calculated by U.S. Standard Atmospheric Model and Temperature Gradient, the latter of which means temperature value may decrease with the rising of the altitude, their results are compared so that the differences between the two can be clearly seen. A more suitable condition, which matches the U.S. Standard Atmospheric Model more and which matches Temperature Gradient, is presented.

Lidar data acquisition system for detecting atmospheric temperature and extinction coefficient

Digital data acquisition system is a key part of the whole lidar system, which plays an important role in ensuring detecting accuracy and is the emphasis of this paper. Lidar system could detect both Raman and Mie backscattering signal simultaneously. A digital data acquisition system is designed to capture the signal in this paper. A FPGA chip is used as an essential part in the digital data acquisition system to control time sequence and process capturing data. Then the data is transmitted into the computer through a USB interface, and displayed in the real-time by dedicated software. Three channels of the system can be programmed separately to measure Mie and Raman scattering signal simultaneously within a single measurement. Moreover, acquisition resolution can be chosen among 15m, 30m and 45m. Meanwhile, some other detecting parameters can also be specified, such as height layers and so on. In the aspect of communicating with PC, a Cypress USB CY7C68013A chip is used in this design. The interface is set to work in Slave FIFO mode in the USB firmware, by which FPGA can control USB easily, just like controlling a normal external FIFO. Usually, USB interface can transmit the data faster and more convenient than other PC interfaces. Results of experiments demonstrate that the digital data acquisition system works correctly and accurately.