ABSTRACT
A homemade low-temperature T shape photoacoustic system (PAS) in the range from 0 to - 100 degrees C is well established. The mode distribution, the temperature dependence of the resonant frequency, Q-factor and the sensitivity of the PAS were investigated. The measurement of the carbon dioxide in the range from 0 to -100 degrees C showed that the system can be used in trace gas detection under low-temperature. The results show that the PAS can be used to study the atmospheric molecules continuous absorption at low-temperature.
ABSTRACT
A new cryogenic cell was developed and could operate at any stabilized temperature ranging from room temperature down to 100 K with temperature fluctuation less than +/- 1 K. The structure and performance of the cryogenic cell was given in detail and the temperature stability of the sample cell was evaluated. The methane low temperature absorption spectra at 1.65 microm were recorded at 296, 248, 198 and 176 K and while the characteristic of methane low temperature absorption spectra at 6 039.70 cm(-1) was given. According to the characteristic of our cryogenic cell, we measured the temperature-dependent exponent n of self-broadening coefficient at 6 039. 657 9 cm(-1).
ABSTRACT
Stable-isotope ratio analysis of water is an important tool for geology, meteorology, and earth sciences. Measurements of water vapor isotopes are very helpful to explaining stratospheric aridity and related issues in atmospheric sciences. The absorption of water vapor near 2.7 microm is very strong so it is suitable for measuring high sensitivity spectra. Based on difference frequency generation and quasi-phase matching, by mixing an Nd : YAG laser with Ti : Sapphire tunable from 750 to 840 nm in a 50 mm long periodically poled lithium niobate (PPLN) crystal, a widely tunable CW laser source was generated for the mid-infrared spectral range from 2.5 to 4 microm. We chose lambda = 20 microm for PPLN crystal, the generated laser was around 2.7 microm. This laser is widely tunable and of inherent narrow linewidth based on difference-frequency generation. Using this idler laser and 100 m multi-pass cell, and direct absorption the water vapor isotopes were measured in the laboratory air. The authors measured isotopes ratios and delta17O, delta18O and deltaD. The values were found to be in excellent agreement with the standard value for three individual lines.
ABSTRACT
The continuously tunable laser source has been realized in a periodically poled LiNO3 crystal based on difference frequency generation and quasi-phase-matching technique. The pump laser is an 1 W tunable Ti: Sapphire laser with a tunable region from 770 to 870 nm. The signal laser is an 1 W diode-pumped monolithic Nd : YAG laser. When the grating period is 20 microm and the temperature is tuned between room temperature and 200 degrees C, the generated wavelength of idler laser is around 2. 8 microm with the general power of .1-2 microW. The direct absorption spectra of (001 <-- 000) band of water in laboratory air were measured based on the laser source. The concentration of water vapor in the laboratory air was estimated with an absorption optical path of 8. 5 cm in open air.
ABSTRACT
Fifteen new absorption lines were observed when studying CO2 absorption spectroscopy by wavelength modulation (WM) technique with a DFB laser. The line intensity we can detect is 2.251 63 x 10(-27) cm(-1) x (moleculecm(-2))(-1) at 6.67 x 10(2) Pa pressure, corresponding to an absorbance of 3. 88 x 10(-8). The overtone spectra of CO2 around 1.31 microm have been measured with a tunable diode laser and the corresponding spectral parameters (positions, intensities, and self-broadening coefficients) are presented.
