Development of new gas analytical technique for infrared spectroscopy combined with differential pressure measurements

A new gas analytical technique for infrared laser spectroscopy combined with differential pressure measurement (IR-DP) is developed. The basic idea of this technique is that the absorption process of molecules by laser irradiation is monitored as the pressure enhancement in a gas cell by use of a differential pressure gauge. The system is composed of a tunable IR laser system, sample cell, differential pressure gauge, and data accumulation system. Using this system, the measurements of the IR absorption spectra for cyclohexane (50 ppm) and ammonia (100 ppm) are demonstrated. By comparison of the current IR-DP spectra with conventional Fourier-transform infrared spectra, the spectral resolution is found to be about 3 cm-1, reflecting the laser resolution. Furthermore, the estimated pressure enhancement based on a simple model is consistent with the experimental results. These results suggest that the newly developed IR-DP technique is one of a powerful tool for trace gas detection.