EXPERIMENTAL TRIAL OF A HOLLOW-CORE WAVE-GUIDE USED AS AN ABSORPTION CELL FOR CONCENTRATION MEASUREMENT OF NH3 GAS WITH A CO2-LASER

The basic idea of using a hollow-core waveguide as an absorption cell in a spectroscopic gas measurement system is proposed. Measurements of NH3 gas concentration were made with different absorption methods at an absorption wavelength of 10.719 mum and a nonabsorption wavelength of 10.697 mum and by using a 1-m hollow-core waveguide whose transmission loss was approximately 1 dB/m in a CO2 laser with wavelengths ranging from 10.261 to 10.719 mum. The hollow-core part of the waveguide was filled with NH3 gas to form an absorption cell through which the two wavelengths were transmitted. The minimum detectable concentration level of the measurement system was limited to 5 parts in 10(6) because of the limitations of the manometers used in the gas-concentration monitor.