The Improved Suppression and Analysis of Stray Light in the Miniature Raman Spectrometer.

Stray light analysis has great benefits in designing Raman spectrometry system, which is the sensitive detection system of weak optical signal. In this paper, optical design software and Solidworks are utilized to optimize the optical and mechanical structure. The system resolution is 0.7 nm, and the volume is 110 mm×95 mm, which belongs to portable and miniature Raman spectrometer. Based on the stray light simulation model, we made an analysis of ray tracing simulation for this system. First, the stray light come with the incident ray were suppressed by the aperture stop. Then the receiver of stray light was introduced and improved in the design progress to suppress internal stray light, especially for zero-order diffraction light of plane grating. The improved receiver of stray light is more effectively using the internal space of the spectrometer and analysis results show that a 50% reduction in the number of stray light and stray light normalized irradiance intensity from 10-5 down to 10-7. The analysis shows that the improved receiver of stray light can effectively suppress stray light, which is beneficial to weak signal detection, and provide reference for design and adjustment of the miniature Raman spectrometer.

[Rapid recognition of common machine oils based on laser induced fluorescence].

A rapid recognition method of common engine oils, based on the principle of laser induced fluorescence (LIF), is proposed in the present paper. A 355 nm ultraviolet laser is used to induce fluorescence emission of 9 kinds of common machine oil samples. In total 450 groups of fluorescence spectral data are collected, of which 360 groups of data are used for classification training and 90 sets of data for identification. It was found that the fluorescence spectra of engine oils are distinct from each other visibly. The rapid identification of 90 groups of data is realized by using clustering analysis combined with principal component analysis. The recognition rate could reach up to 97.8%. Experiment demonstrated that the fast identification of diverse engine oils could be realized by using LIF combined with multivariate analysis method.

[Laser induced fluorescence spectrum characteristics of common edible oil and fried cooking oil].

In order to detect the trench oil the authors built a trench oil rapid detection system based on laser induced fluorescence detection technology. This system used 355 nm laser as excitation light source. The authors collected the fluorescence spectrum of a variety of edible oil and fried cooking oil (a kind of trench oil) and then set up a fluorescence spectrum database by taking advantage of the trench oil detection system It was found that the fluorescence characteristics of fried cooking oil and common edible oil were obviously different. Then it could easily realize the oil recognition and trench oil rapid detection by using principal component analysis and BP neural network, and the overall recognition rate could reach as high as 97.5%. Experiments showed that laser induced fluorescence spectrum technology was fast, non-contact, and highly sensitive. Combined with BP neural network, it would become a new technique to detect the trench oil.

[The echelle grating monochromator's design of pure rotational Raman Lidar].

The pure rotization oal Raman Lidar temperature measurement system usually retrieve atmospheric temperature according to the echo signal of high and low-level quantum numbers of N2 moleules. An effective method to detect the rotational Raman spectrum is taking a grating monochromator. In the present paper the detection principle and the structure of the echelle grating monochromator are described, the high order and lower order quantum number of the probe spectrum is resolved. The focal length of the collimating-focusing optical system is calculated by analyzing echelle grating's spectroscopic principle and dispersion ability. Subsequently spectral effect is simulated with Zemax software. The simulation result indicates that under the condition of the probe laser wavelength of 532 nm and using echelle grating monochromator, Rarnan spectrums of 529.05, 530.40, 533.77, 535.13 mn can be separated well, at the same time, the SNR of the system is enhanced by summing the spectral signals of symmetric quantum number. The echelle grating monochromator is small in size, and can easily meet the requirements of the miniaturization of Raman Lidar temperature measurement system.

[Obtaining aerosol backscattering coefficient using pure rotational Raman-Mie scattering spectrum].

Both the traditional Klett and Fernald methods used to obtain atmospheric aerosol backscattering coefficient require the hypothesis of relationship between the extinction coefficient and backscattering coefficient, and this will bring error. According to the theory that the pure rotational Raman backscattering coefficient is only related to atmospheric temperature and pressure, a new method is presented for inverting aerosol backscattering coefficient, which needed the intensity of elastic scattering and rotational Raman combined with atmospheric temperature and pressure obtained with the sounding balloons in this article. This method can not only eliminate the errors of the traditional Klett and Fernald methods caused by the hypothesis, but also avoid the error caused by the correction of the overlap. Finally, the aerosol backscattering coefficient was acquired by using this method and the data obtained via the Raman-Mie scattering Lidar of our lab. And the result was compared with that of Klett and Fernald.

[Raman Lidar measuring tropospheric temperature profiles with many rotational Raman lines].

Due to lower tropospheric aerosols, the Rayleigh and vibrational Raman methods can't measure lower tropospheric temperature profiles accurately. By using N2 and O2 molecular pure rotational Raman scattering signals, lower tropospheric temperature profiles can be gained without influence of lower tropospheric aerosols. So we decide to use a pure rotational Raman Lidar to get lower tropospheric temperature profiles. At present, because the most light-splitting systems of pure rotational Raman Lidar measure temperature by gaining a single rotational Raman line, the signal to noise ratio (SNR) of these Lidar systems are very low. So we design a new kind of Lidar light-splitting system which can sum different rotational Raman lines and it can improve SNR And we can find the sensitivity of the temperature of the ratios of multi rotational Raman lines is as same as single rotational Raman line's through theoretical analysis. Moreover, we can obtain the temperature profiles with good SNR fromthis new the system with a normal laser and a small telescope up to several kilometers. At last, with the new light-splitting system, the lower tropospheric temperature profiles are measured from 0.3 km to 5 km altitude. They agree well with radiosonde observations, which demonstrate the results of our rotational Raman lidar are reasonable.

[Inversion results of the atmospheric environment detecting airborne lidar in Qingdao, Bohai and Yellow Sea area].

Without the hypothesis of atmospheric parameters and auxiliary equipment, it is proven the slope method is capable of deriving extinction coefficients profiles and atmosphere optical depth through the analysis of the atmospheric environment detecting airborne lidar (AEDAL) data collected during November 7 to 11, 2005. The spatial and temporal variations of the planet boundary layer (PBL), aerosol optical depth (AOD) of the PBL and aerosol distribution along flight lines are exhibited from the AEDAL inversion results. Firstly, the sinking of aerosol was found in Yellow Sea area, moreover, the PBL altitude also dropped while the multi-layer aerosol presented after a cold front passage; secondly, the AOD of the PBL is the highest over Qingdao city, the lowest over foothill area and in between them over sea area, Meanwhile, it is relatively stable over sea area but slightly increases nearby upslope. The AOD values of the PBL were determined to be 0.15-0.35 in clear day and 0.3-0.45 in foggy day over the area from Qingdao to Bohai, but they are higher and reach around 0.55 in Yellow Sea area. It is evidenced that the aerosol in the PBL mainly comes from city and also is contributed by salt sea over Qingdao area, and ridge and surface wind play an important role in the aerosol transport while the monsoon affects the aerosol distribution.

[Obtaining aerosol backscattering coefficient using pure rotational Raman spectrum].

Atmospheric aerosol backscattering coefficient ratio can be obtained with the ratio of elastic signal to the total rotational Raman backscattering signal without assuming the ratio of aerosol extinction to backscatter. Generally, the intensity ofpartial rotational Raman spectrum lines instead of the total rotational Raman spectrum lines is measured. The intensity of the total rotational Raman spectrum lines is not dependent on the temperature, but the intensity of the partialrotational Raman spectrumlines is dependent on the temperature. So calculating aerosol backscattering coefficient ratio with the intensity of the partial rotational Raman spectrum lines would lead to an error. In the present paper, the change in the intensity sums of different rotational Raman spectrum lines with temperature was simulated and the errors of aerosol backscattering coefficient ratio derived from them were discussed. A new method was presented for measuring aerosol backscattering coefficient ratio, which needed not to measure the intensity of the total rotational Raman spectrum lines. Aerosol backscattering coefficient ratio could be obtained with the atmospheric temperature and a single rotational Raman spectrum line. Finally, a erosol backscattering coefficient ratio profiles of the atmosphere were acquired with the combined Raman lidar of our lab. The results show that there is no need to assume any relation between aerosol backscattering and extinction or to consider any wavelength calibration to determine the aerosol scattering coefficient.

[Method for retrieving pollution gas concentration from Raman lidar return].

Raman lidar is an important tool for the detection of atmosphere pollution, and inversion for lidar returns is an important process. The key for inversion is to get transmission exponential function exp [integral of 0 (R) [alpha(lambda1, z) - alpha(lambda2, z)]]. Three methods with extinction coefficient as the center are presented. First, 532 nm atmospheric extinction coefficient was used to indirectly obtain alpha(lambda1, z) and alpha(lambda2, z). This method has been used generally by people. Two new methods were proposed: 1, reference gas with approximate Raman wavelength is used so that alpha(lambda1, z) = alpha(lambda2, z). 2, Mie-Rayleigh scattered return with wavelength lambda1 or lambda2 is used to compute exp [integral of 0 (R) [alpha(lambda1, z) - alpha(lambda2, z)]].

[Study on the nonlinear Raman lidar monitoring the CO2 gas].

It is a new skill to use SRS rays as emitting waves for the lidar monitoring CO2 gas, and the nonlinear Raman lidar based on the SRS process was devised. The third harmonic Nd: YAG laser wave (354.7 nm) was injected into the Raman cells filled with higher pressure gases, CO2 and N2. The first Stokes (S1) line 371.66 nm (CO2) and 386.7 nm (N2) were generated by stimulated Raman scattering. The variable S1 energy was measured by changing the gas pressure in the Raman cell andthe Nd:YAG laser system output energy. The optimum pressures of the CO2 and N2 in the Raman cell were achieved. Moreover, the principles of this physical process were put forward. This skill has been applied to the lidar for monitoring the CO2 gas.