[The Development of Ammonia Sensor Based on Tunable Diode Laser Absorption Spectroscopy with Hollow Waveguide].

Hollow waveguides(HWG)have recently emerged as a novel concept serving as an efficient optical waveguide and a highly miniaturized gas cell. Compared with conventional multi-pass gas cells, HWG gas cell has the advantages of facilitating gas exchanging because of its small size and fast responding speed. In this paper, we poposed an ammonia sensor based on tunable diode laser absorption spectroscopy(TDLAS) using HWG as the gas cell.

[Absorption spectrum of Quasi-continuous laser modulation demodulation method].

A software phase-locked amplifier demodulation method is proposed in order to demodulate the second harmonic (2f) signal of quasi-continuous laser wavelength modulation spectroscopy (WMS) properly, based on the analysis of its signal characteristics. By judging the effectiveness of the measurement data, filter, phase-sensitive detection, digital filtering and other processing, the method can achieve the sensitive detection of quasi-continuous signal The method was verified by using carbon dioxide detection experiments. The WMS-2f signal obtained by the software phase-locked amplifier and the high-performance phase-locked amplifier (SR844) were compared simultaneously.

[Selection of digital filtering in the escaping ammonia monitoring with TDLAS].

Tunable diode laser absorption spectroscopy technology (TDLAS), with its advantages of high selectivity and accuracy, provides a reliable approach to the on-line detection of escaping ammonia. Firstly, the present paper introduces the TDLAS principle, experimental system and the analyses of system noise. Then with the concentration of 90 x 10(-6) and 30 x 10(-6) NH3 for example, we used TDLAS system to collect their second harmonic original spectrum with all kinds of noise interference.

[Comparison of quasi-continuous and continuous tunable diode laser absorption spectroscopy for gas detection].

The theoretical analysis of the direct absorption spectroscopy, the continuous modulation spectroscopy and the quasi-continuous modulation spectroscopy was shown and the corresponding experiments were carried out in order to choose the adequate scheme of the laser modulation spectroscopy to satisfy different requirements of the detection. CO2 gas with different concentrations was detected under the same experimental conditions by using the three different modulation techniques with the same laser. Technical characteristics, signal features and detection limits were compared respectively.

[Research on the analytical line auto-selection for quantitative analysis of materials with laser-induced breakdown spectroscopy].

To realize auto-selection of analytical lines for quantitative analysis of materials with laser-induced breakdown spectroscopy, two parameters, i. e. the relative detected-to-theory intensity ratio (RDTIR) and wavelength difference of detected and theory (WDDT) were defined.

[Multi-harmonic analysis of quasi-continuous-wave laser modulation absorption spectroscopy].

Numerous harmonic components such as multiple frequency, sum frequency and difference frequency of multiple modulation signals were found in quasi-continuous-wave (QCW) diode laser modulation absorption spectroscopy. Then, the authors analyzed these harmonic components' existence in terms of non-linear interactions of laser and gas absorption line. And the signals' characteristics were studied experimentally.

[System parameters selection and optimization of tunable diode laser absorption spectroscopy].

The system performance of tunable diode laser absorption spectroscopy (TDLAS) is affected by the modulation parameters such as modulation index, modulation frequency, scanning amplitude and scanning frequency. There is a lack of definite parameters selection basis in practical measurement. Aiming at this problem, the influence of modulation parameters on second harmonic signals was observed by experiment based on a certain theory in the present paper, and the basis and method of modulation parameters optimization for various system functions and demands were summarized by analyzing the signal characteristic including amplitude, signal to noise ratio, symmetry and peak width.

[Techniques of on-line monitoring volatile organic compounds in ambient air with optical spectroscopy].

Volatile organic compounds (VOCs) are harmful gaseous pollutants in the ambient air. The techniques of on-line monitoring VOCs are very significant for environment protection. Until now, there is no single technology that can meet all the needs of monitoring various VOCs.

[Application of NIR spectroscopy to multiple gas components identification].

Multiple gas components monitoring in situ by near infrared (NIR) spectroscopy is of great significance in the environmental monitoring. In the present paper, the apectral characteristics of the three types of the volatile organic compounds (VOCs)-propane, propylene and methylbenzene were analyzed, the linear relationship of propylene between concentration and absorbance was considered, and the NIR spectra from 1620 to 1750 nm including the characteristic absorption of the three VOCs were acquired, A linear regression model of chemical metrology was created by partial least-squares method and it predicted the concentration of propane and isobutene in the validation set. The results of the experiment indicated that NIR spectroscopy could easily, accurately and quantitatively determine the content of the multiple gas components, and can be used for monitoring the multiple components of the VOCs in situ.

[Investigation on baseline correction in pollutant monitoring on-line by NIR spectroscopy].

Spectroscopic data pre-processing is important to spectra scaling and quantitative analysis, and correction of baseline drift caused by variation of measuring condition is critical in NIR spectroscopy analysis in-situ. In the present paper, the NIR absorption spectra of propane and isobutane with different concentration were detected by BRUKER EQUINOX55 spectrometer. The "Derivative-smooth" method and the baseline correction method which is accessory of the instrument were theoretically analyzed, and the data processed by the two kinds of method were compared.

[Research on shortwave NIR spectroscopy and its application to in situ flammable liquid detection].

Fast, accurate and highly effective detection in situ was important to the control of illegal transportation and the use of liquid state dangerous goods. The present article used the strong penetrability of the shortwave near-infrared ray to the packing material and liquid and measured the absorption spectra of some flammable liquids such as the absolute ethyl alcohol, absolute methanol, ammonia, turpentine, gasoline, diesel oil, petroleum etc and the partial liquors in the short wavelength region of NIR (667-1000 nm). The primitive spectral data were standardized and compressed, and then, the characteristic wavelength of the absorption spectra was analyzed using the SPSS statistics software.

[Theoretical analysis of the single optical path spectrum detection in biological tissue].

The technology of spectrum detection with high sensitivity is of significance in clinic diagnosis and tissue optical parameter measurement. A new method of difference-modulated laser spectrum detection was developed in the present paper. The measuring light and the reference light are separated from the lasing light source in this method.

[Isolation and identification of a photosynthetic bacteria producing coenzyme Q10].

13 isolates producing Coenzyme Q10 (CoQ10) of purple non sulfur photosynthetic bacteria were enriched out of pond sludge, one isolate named 2c was selected based on its high CoQ10 content and identified systematically. The gram-negative and short-rod shaped strain 2c is 0.6microm - 0.