Abstract: When light from a laser diode having a wavelength in the interval from 670 to 880 nm is directed through a sample containing nitrogen molecules, the nitrogen molecules do not absorb the laser light; but if the sample is energized under suitable conditions so that the nitrogen molecules are raised to the normally unpopulated ##EQU1## energy level, which differs in energy from a higher energy level .beta..sup.3 .pi.g by an energy difference corresponding to the wavelength of the laser light, then some of the laser light will be absorbed by driving the energized nitrogen molecules from the ##EQU2## energy level to the .beta..sup.3 .pi.g energy level. The amount of absorpiton is proportional to the concentration of nitrogen molecules in the sample. Thus, if the absorption by a sample having a known concentration of nitrogen molecules is determined, the unknown concentration of nitrogen molecules in a second sample can be determined by measuring the absorption in the second sample.

Abstract: An apnea detector uses an active pulsed source of radiation to monitor the respiration of a patient. Radiation from the source is formed into a collimated beam that is directed through the space into which the patient is breathing. The exhaled gases contain a smaller concentration of oxygen and a larger concentration of carbon dioxide compared with the atmosphere. Each exhalation of the patient produces a small cloud of the exhaled gases, which rapidly diffuse and disperse. Corresponding to the appearance and disappearance of these clouds of gas, the transmission of the collimated beam will vary in step with the patient's breathing. The fluctuations in the transmitted radiation are analyzed by a signal processor which generates an alarm signal when either the magnitude or the frequency of these fluctuations falls outside of preset limits. Either carbon dioxide or oxygen may be monitored as the absorbing gas.