Fluorescent fiber diagnostics

Abstract

A fluorescent fiber (13) having a doped core (16) is pumped (11) by light (18) of a relatively short wavelength to produce fluorescence at a longer wavelength that is detected by detector (24). The level of fluorescence is monitored (26) and evaluated to provide information as to the excitation of the fiber (13) or the environment thereof. In particular, the level of intensity of the detected fluorescence may be used to measure the intensity of a light beam (18) passing axially through an optical fiber system (12) (FIG. 1 ), or the intensity of a light beam (46) passing radially through a fluorescent fiber (13) (FIG. 2 ), or the level of a fluid (32) in a tank (31) (FIG. 3 ), or a scintillation event (37) in a fluorescent fiber (13) pumped to produce amplification of the scintillation event (FIG. 4 ).

It is claimed: 
     
       1. A method of using a fluorescing optical fiber having a doped core that will fluoresce at a relatively long wavelength when pumped by light of a shorter wavelength, comprising: a) pumping said doped core with light of said shorter wavelength to cause fluorescence in said core at said relatively long wavelength   b) detecting light of said relatively long wavelength exiting from one end of said fiber   c) monitoring the degree of intensity of said detected light of said relatively long wavelength.   
     
     
       2. The method as set forth in claim 1, wherein said doped core is pumped from one end of said fiber. 
     
     
       3. The method as set forth in claim 2, wherein said core is lightly doped so that only a small percentage of the pumping light of said shorter wavelength is absorbed by said core. 
     
     
       4. The method as set forth in claim 2 wherein said pumping light is maintained at a stable level and further including disposing said fiber in a medium that produces changes in the amount of light in said fiber that can escape through the wall of said fiber. 
     
     
       5. The method as set forth in claim 1, wherein said doped core is pumped by a stable level of light of said shorter wavelength from one end thereof, and wherein said doped core is additionally pumped through the wall of said fiber. 
     
     
       6. The method as set forth in claim 5, wherein the pumping light into said doped core from said one end maintains said core in fluorescence just below the lasing level, such that said additional pumping through the wall of said fiber will cause lasing to occur within said core. 
     
     
       7. The method as set forth in claim 1, wherein the pumping of said doped core with light of said shorter wavelength is wholly done through the wall of said fiber. 
     
     
       8. The method as set forth in claim 7, wherein said fiber is disposed in and crosswise of a light beam of said shorter wavelength. 
     
     
       9. The method as set forth in claim 8, and further including moving said fiber in a plane crosswise to said light beam to dispose said fiber in different portions of said light beam. 
     
     
       10. The method as set forth in claim 1, wherein said fluorescent fiber has a core doped with neodymium to cause fluorescence at around 950 nanometers in response to absorption of light of 510 and 578 nanometer wavelengths, and wherein the core of said fiber is pumped by a copper vapor laser beam.