Refractive index-based sensor for the discrimination of chlorinated hydrocarbons from groundwater

Abstract

A refractive index-based sensor uses a light source and an optical fiber to direct an optical beam towards a sensor/environment face at a specific angle. The sensor has a predetermined shape selected such that the light directed into the sensor will have a specific angle of incidence designed to detect a plurality of liquids. A second optical fiber carries the light reflected off the sensor/environment face to a photodetector. The optical beam will either be transmitted through or reflected off the sensor/environment face based upon the refractive indices of the sensor and the environment and upon the angle of incidence of the optical beam. The amount of light reflected is indicative of the refractive index of the material in a given area of the sensor/environment face and, thus, the type of material. By adjusting the angle at which the light is directed to the sensor/environment face, the photodetector response can be calibrated to identify the type of liquid present at the sensor/environment face.

What is claimed is: 
     
       1. An apparatus for detecting liquid materials, said apparatus comprising: a light source;   a sensor selected to have a shape such that light directed into said sensor has a specific angle of incidence, said angle of incidence selected for detecting a plurality of liquids;   means for collimating light from said light source and directing said light into said sensor;   means for collecting light reflected within said sensor; and   means for detecting said collected light.   
     
     
       2. The apparatus of claim 1 further including: means for introducing said sensor into the ground.   
     
     
       3. The apparatus of claim 2 wherein said introducing means is a cone penetrometer, said apparatus further including: means for polarizing light disposed between said light source and said collimating means.   
     
     
       4. The apparatus of claim 2 wherein: said collimating means is a graded index lens and   said collecting means is a graded index lens.   
     
     
       5. An apparatus for detecting liquid materials, said apparatus comprising: a light source;   a sensor;   means for collimating light from said light source, said collimating means affixed to said sensor for directing said light into said sensor at a preselected angle;   means for collecting light reflected within said sensor; and   means for detecting said collected light.   
     
     
       6. The apparatus of claim 5 further including: means for introducing said sensor into the ground.   
     
     
       7. The apparatus of claim 6 wherein said introducing means is a cone penetrometer, said apparatus further including: means disposed between said light source and said collimating means for polarizing light from said light source.   
     
     
       8. The apparatus of claim 6 wherein: said collimating means is a graded index lens; and   said collecting means is a graded index lens.