Diode Laser Spectrometer for Diagnostic Assessment of Exhaled Air Components.

The main requirements for a screening test are simplicity, non-invasiveness, safety of testing procedures, high processing speed, and ability to detect diseases at an early stage. A multichannel gas analyzer for assessment of exhaled air composition (diode laser spectrometer), non-invasive screening, and biomedical testing was developed on the basis of near-infrared diode lasers with fiber output. The device measures the following exhaled air components: 12CO2, 13CO2, CH4, NH3, H2O, and H2S. The concentration of molecules was measured in a multi-pass Herriot cell with a reference length of 40 cm, 1.8 L volume, and a total optical path length of 26 m. Three diode lasers manufactured by NTT Electronics (Japan) were used in the work. Detection of CH4 was carried out in the 1.65 µm wavelength range, 12CO2, 13CO2, and H2S levels were measured in the 1.60 µm range, NH3 and H2O in the 1.51 µm range. All measurements were taken in real time. Clinical testing of the spectrometer was carried out at V.M. Buyanov City Clinical Hospital of Moscow Department of Health. More than 150 patients were examined. The tests included analysis and measurement of these molecular components in the exhaled air of patients with various diseases. The content of these components was studied in conditions of various changes in the human physiological state (dosed physical activity, relaxation, psychoemotional stress, etc.). The studies have demonstrated efficacy of using the developed hardware system for assessment of exhaled air components in order to reveal functional disorders in various diseases of the digestive system, cardiorespiratory system, diseases caused by impaired nitrogen-excreting function of the kidneys, etc.

Diode ring-down spectroscopy without intensity modulation in an off-axis multipass cavity.

Cavity ring-down spectroscopy with an off-axis multipass cell and space separated detectors is proposed to record absorption spectra without modulation of the diode laser intensity. The spectral resolution is approximately 0.0003 cm-1. The whole spectrum is obtained for one continuous tuning of the laser frequency for approximately 20 ms. When comparing this method to conventional CRDS the required rise time is 1000 times slower. The recording of the whole spectrum for one measurement gives additional possibilities of signal extraction at relatively high noise. The technique is applied to absorption measurement of NO2 in atmosphere.