System and method for controlling a light source for cavity ring-down spectroscopy

Abstract

An apparatus and method for controlling a light source used in Cavity Ring-Down Spectroscopy. The apparatus comprises a controller that generates a control signal to activate and deactivate the light source based on a comparison of an energy signal from a resonant cavity and a threshold. The light source is activated for a predetermined period based on the stabilization time of the light source and the time necessary to provide sufficient energy to the resonant cavity. Thereafter the controller deactivates the light source for a predetermined time period by interrupting its current source so that the light energy in the cavity ring downs and so that the presence of analyte can be measured. The light energy from the light source is directly coupled to the resonant cavity from the light source.

What is claimed is:  
     
         1 . An apparatus for controlling a light source for use with a resonant cavity, the apparatus comprising: 
 a controller for receiving a comparison of a detection signal and a predetermined threshold, the comparator generating a control signal to at least one of activate and deactivate the light source based on the comparison;    a first delay circuit coupled to the controller for generating a first delay signal to the controller; and    a second delay circuit coupled to the comparator and the controller for generating a second delay signal to the controller based on the comparison of the detection signal and the predetermined threshold.    
     
     
         2 . The apparatus according to  claim 1 , wherein the first delay circuit is initialized by an initialization signal.  
     
     
         3 . The apparatus according to  claim 1 , wherein the light source provides light as an input to the resonant cavity used to measure the presence of an analyte in the resonant cavity.  
     
     
         4 . The apparatus according to  claim 1 , wherein light from the source is coupled to the resonant cavity by an optical fiber.  
     
     
         5 . The apparatus according to  claim 4 , further comprising a fiber collimator coupled between the optical fiber and an input of the resonant cavity.  
     
     
         6 . The apparatus according to  claim 1 , further comprising a comparator to generate an output signal to the controller based on the comparison of the detection signal and the predetermined threshold.  
     
     
         7 . The apparatus according to  claim 6 , further comprising a detector coupled between an output of the resonant cavity and the comparator, the detector generating the detector signal.  
     
     
         8 . The apparatus according to  claim 1 , wherein the light source is deactivated based on a time period of the first delay circuit.  
     
     
         9 . The apparatus according to  claim 8 , wherein the first delay period is based on a ring down time period of the resonant cavity.  
     
     
         10 . The apparatus according to  claim 9 , wherein the first delay period is about 10 times the ring down period.  
     
     
         11 . The apparatus according to  claim 8 , wherein the light source is activated after an end of the first delay period.  
     
     
         12 . The apparatus according to  claim 8 , wherein an analyte level present in the resonant cavity is measured during the first delay period.  
     
     
         13 . The apparatus according to  claim 1 , wherein a period of the second delay circuit is based on a stabilization time of the light source.  
     
     
         14 . The apparatus according to  claim 13 , wherein the second delay period is about 100 msec.  
     
     
         15 . The apparatus according to  claim 1 , wherein the first delay signal is generated after a third delay period.  
     
     
         16 . The apparatus according to  claim 15 , wherein the third delay period is based on a modulation frequency of the light source.  
     
     
         17 . The apparatus according to  claim 16 , wherein the third delay period is an inverse of the modulation frequency.  
     
     
         18 . The apparatus according to  claim 15 , wherein the third delay period follows the second delay period.  
     
     
         19 . The apparatus according to  claim 15 , wherein light energy builds up within the resonant cavity during the third delay period.  
     
     
         20 . The system according to  claim 1 , wherein the light source is a laser.  
     
     
         21 . A system for use with a light source to measure the presence of an analyte in a resonant cavity, the system comprising: 
 a detector coupled to an output of the resonant cavity to generate a detection signal based on a light output from the resonant cavity;    a controller coupled to the light source, the controller activating and deactivating the light source based on the detection signal; and    a processor coupled to the controller to process the detection signal and determine a level of the analyte present in the resonant cavity.    
     
     
         22 . The system according to  claim 21 , wherein the controller deactivates the light source by shunting a supply of current for the light source.  
     
     
         23 . The system according to  claim 21 , further comprising an optical fiber coupling light energy from the light source to the resonant cavity.  
     
     
         24 . The system according to  claim 23 , further comprising a fiber collimator coupled between an end of the optical fiber and the resonant cavity.  
     
     
         25 . The system according to  claim 21 , wherein the controller activates the light source for a first predetermined time period and deactivates the light source for a second predetermined time period.  
     
     
         26 . The system according to  claim 25 , wherein the first predetermined period is about based on a stabilization time of the light source.  
     
     
         27 . The system according to  claim 26 , wherein the first predetermined period is further based on a modulation frequency of the light source.  
     
     
         28 . The system according to  claim 21 , wherein the light source is a laser.  
     
     
         29 . The system according to  claim 21 , wherein the energy is light energy.  
     
     
         30 . A method for measuring the presence of an analyte in a resonant cavity, the method comprising the steps of: 
 detecting a light energy signal output from the resonant cavity;    comparing the detected signal with a predetermined threshold;    generating a control signal to control the light source based on the comparison;    generating a first delay signal to the controller;    generating a second delay signal after an end of a first delay period; and    measuring a level of the analyte after an end of a second delay period.    
     
     
         31 . The method according to  claim 30 , further comprising the steps of: 
 activating the light source following generation of the second delay signal; and    deactivating the light source during at least said first delay period.    
     
     
         32 . The method according to  claim 30 , further comprising the step of providing an initialization signal to initialize the first delay signal.  
     
     
         33 . A system for measuring the presence of an analyte in a resonant cavity, the system comprising of: 
 detecting means for detecting a light energy signal output from the resonant cavity;    comparison means for comparing the detected signal with a predetermined threshold;    control means for generating a control signal to control the light source based on the comparison;    first delay means for generating a first delay signal to the controller and initiating a first delay period;    second delay means for generating a second delay signal and initiating a second delay period after an end of the first delay period; and    processing means for measuring a level of the analyte after an end of the second delay period.    
     
     
         34 . The system according to  claim 33 , wherein said processing means measures the level of analyte during said first delay period.  
     
     
         35 . An apparatus for controlling a light source for use in cavity ring-down spectroscopy, the apparatus comprising: 
 a controller for receiving a comparison of a detection signal and a predetermined threshold, the comparator generating a control signal to at least one of activate and deactivate the light source based on the comparison;    a first delay circuit coupled to the controller for generating a first delay signal to the controller; and    a second delay circuit coupled to the comparator and the controller for generating a second delay signal to the controller based on the comparison of the detection signal and the predetermined threshold.