A Dual-wavelength Mie Polarization Raman Lidar has been developed for cloud and aerosol optical properties measurement. This idar system has built in Hefei and passed the performance assessment in 2012, and then moved to Jinhua city to carry out the long-term continuous measurements of vertical distribution of regional cloud and aerosol. A double wavelengths (532 and 1064 nm) Nd-YAG laser is employed as emitting source and four channels are used for detecting back-scattering signals from atmosphere aerosol and cloud including 1064 nm Mie, 607 nm N2 Raman, two 532 nm Orthogonal Polarization channels. The temporal and spatial resolutions for this system, which is operating with a continuing mode (24/7) automatically, are 30s and 7.5m, respectively. The measured data are used for investigating the aerosol and cloud vertical structure and cloud phase from combining of cloud signal intensity, polarization ratio and color ratio.
This paper is about cavity enhanced absorption spectroscopy (CEAS) experiment with a tunable narrow line width continuous wave DFB diode laser and it was used to measure the weak absorption band of carbon dioxide in the near infrared region. The absorption spectrum was extracted from the measurement of light intensity that leaks out of an optical cavity which was consisted of two high reflectivity mirrors separated at a distance about 34cm. In the experiment the optical cavity was scanned continuously and the laser radiation was coupled into the optical cavity via accidental coincidences of laser frequency with one of the multitude modes of the optical cavity. A wavemeter was used simultaneously to record the accurate wavelength of the DFB diode laser radiation. Absorption spectrum of vibrational combination band of carbon dioxide near 6358.65cm<sup>-1</sup> has been obtained. An absorption sensivity of about 3.6 x 10<sup>-7</sup> cm<sup>-1</sup> has been achieved. The experimental results indicate that cavity enhanced absorption spectroscopy can be used as a high sensitive direct absorption spectroscopy technology.
We measured the high resolution absorption spectroscopy of water vapor between 7599cm<sup>-1</sup> and 7615cm<sup>-1</sup> by narrow linewidth DFB diode laser and kilometers order long path White cell. We observed the minimum detectable absorption of the 10<sup>-26</sup> cm/molecular line strength. The measured line parameters show excellent agreements with the values from HITRAN2000 database. The 7600.133 cm<sup>-1</sup> line of water vapor listed in HITRAN2000 database was not observed we think the line is inexistent. Seven new weak lines unlisted in HITRAN2000 database were observed which may belong to the isotope H<sub>2</sub><sup>18</sup>0 molecular.
The absorption spectra of CH<sub>4</sub> around 1.31 μm have been observed by wavelength modulation absorption spectroscopy technique employed with a tunable diode laser at different pressure. The overtone spectra of CH<sub>4</sub> around 1.31 μm and the corresponding spectral parameters (i.e. positions intensities self-broadening coefficients) are presented. The intensity of the weakest line detected is 1.306x10<sup>-26</sup> cm<sup>-1</sup>/(molecule-cm<sup>-2</sup>) at the pressure of 0.077 Torr with a corresponding absorption of l.174x10<sup>-7</sup>.
A portable sensor based on tunable diode laser for remote sensing of methane (CH<sub>4</sub>) leakage at a wavelength of 1.65 μm was developed. Wavelength modulated spectroscopy technology is also applied. It was found that the sensor can detect a 10 cm<sup>3</sup> min<sup>-1</sup> city-gas leak with a sensor output equivalent to the range-integrated concentration over 100 ppm-mn.