An optical remote sensing system by molecular absorption spectroscopy

Abstract

Recent developments in laser technology have led to new prospects for remote sensing with the use of laser spectroscopic methods. The recent progress in optical electronics technology, particularly, the realization of ultralow-loss silica optical fibers, has opened brighter possibilities for remote sensing. This paper presents the basic features of an optical fiber remote sensing system by near-infrared molecular absorption spectroscopy. The experimental arrangement and procedure for operation are described. This remote sensing scheme, using ultralow-loss optical fiber network and compact absorption cells in conjunction with high-radiant InGaAsP light-emitting diodes, has been demonstrated to be feasible with the measurement of the absorption spectra of a number of molecular species found in the atmosphere. Based on these spectroscopic studies in the near-infrared, the optical fiber based remote sensing of these substances has been carried out. Experimental results of these spectral and remote measurements, some of which are to be described in this paper, demonstrate the practical feasibility of this method. It is to be noted that most of these substances are inflammable and toxic and may be present in the environment in initially minute quantities. This system has been shown to be sensitive and capable of remote monitoring and detection of environmental pollution and spilled dispersals of inflammable, explosive and toxic gases/vapors down to levels of nearly 1 Torr.