Photovoltage Detector

Abstract

A method and system for detecting and monitoring a temporal and spatial distribution of a light beam are provided. A semiconductor substrate ( 120 ) having a given doping concentration range is partially exposed to an incident laser beam ( 150 ). Each part of the semiconductor structure ( 120 ) which is exposed to the laser beam is provided with an electrical contact ( 145 ), which outputs a voltage which is directly related to the optical power or energy incident on the exposed area. The thermo-voltage is produced by the laser induced thermal gradients. The sensitivity and inter-pixel cross-talk is determined by pixel pitch, doping concentration and window opening ( 110 ). Depending of the design, each pixel might be sensitive to the temporal variation of the laser beam.

1 - 24 . (canceled)  
   
   
       25 . A detector for characterising a high power light beam, said detector comprising at least one pixel, wherein each of said at least one pixel comprises 
 a doped semiconductor substrate adapted to substantially absorb an incident light beam, being at least a fraction of said high power light beam, over an absorption distance L, said semiconductor substrate having thermoelectric properties, said doped semiconductor substrate being doped over at least part of the thickness of the semiconductor substrate;    means for partly covering the doped semiconductor substrate such that a window opening is provided at a first side of the doped semiconductor substrate for receipt of said incident light beam in said doped semiconductor substrate; and    means for measuring an electrical signal induced by a thermoelectric effect in said doped semiconductor substrate comprising a first electrode at said first side of said doped semiconductor substrate and a reference electrode, said reference electrode positioned outside an absorption volume determined by said window opening and said absorption distance L.    
   
   
       26 . A detector according to  claim 25 , the detector operating according to an absorption principle, wherein the absorption principle is a free carrier absorption process.  
   
   
       27 . A detector according to  claim 25 , the detector comprising a means for reducing cross-talk.  
   
   
       28 . A detector according to  claim 27 , wherein said means for reducing the cross-talk is a means for reducing the cross-talk between neighboring pixels of said plurality of pixels adapted for reducing the cross-talk at least below a 5% acceptance level.  
   
   
       29 . A detector according to  claim 27 , wherein said means for reducing the cross-talk is a means for reducing the cross-talk between any pixel electrode of said plurality of pixels and the reference electrode, adapted for reducing the cross-talk at least below a 5% acceptance level.  
   
   
       30 . A detector according to  claim 27 , wherein said means for reducing the cross-talk comprises a cooling channel between at least two pixels.  
   
   
       31 . A detector according to  claim 27 , wherein the means for reducing cross-talk are positioned outside a plane determined by said semiconductor substrate.  
   
   
       32 . A detector according to  claim 27 , wherein the means for reducing cross-talk comprises a heat sink provided in thermal contact with said semiconductor substrate.  
   
   
       33 . A detector according to  claim 27 , the means for reducing cross-talk comprising a reflector material positioned around the window opening.  
   
   
       34 . The detector according to  claim 25 , wherein the means for partly covering the doped semiconductor substrate and said absorption distance L are adjusted so that  
     
       
         
           
             
               
                 P 
                 pixel 
               
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               L 
             
             
               
                 S 
                 pixel 
               
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     is in the range 0.1 to 100 wherein P pixel  is the perimeter of the pixel window and S pixel  is the surface area of the pixel window.  
   
   
       35 . A detector according to  claim 25 , said characterising being detecting a profile selected from the group consisting of at least one of a spatial and temporal intensity profile, a spatial energy profile, a spatial energy density profile and at least one of a spatial and temporal power profile of the beam.  
   
   
       36 . A detector according to  claim 25  wherein said first electrode defines at least the perimeter of the window opening.  
   
   
       37 . A detector according to  claim 25 , wherein said first electrode furthermore comprises at least one elongate electrode extending over the window opening.  
   
   
       38 . A detector according to  claim 25  wherein said first electrode is separated at least partly from said doped semiconductor substrate by means of an insulating layer.  
   
   
       39 . A detector according to  claim 34 , wherein the adjustment of the absorption distance L is performed by adjusting the doping level of said doped semiconductor substrate.  
   
   
       40 . A detector according to  claim 25 , comprising a plurality of pixels, each pixel having a pixel window with an average pixel window width w, the pixels being separated by at least an interpixel pitch P, wherein said interpixel pitch P is between 1 and 10 times the average pixel window width w.  
   
   
       41 . A detector according to  claim 25 , wherein at each first electrode a switch and a storage means is provided, for temporary storing the pixel information.  
   
   
       42 . A detector according to  claim 25 , wherein said detector system furthermore comprises a read-out electronic circuitry adjusted to sample at regular moments the time evolution of the electrical detector outputs and convert the sampled analog voltages into digital signals.  
   
   
       43 . A detector according to  claim 25 , wherein said second electrode is positioned at a second side of the completely doped semiconductor substrate, the first and second side being opposite with respect to each other.  
   
   
       44 . A system for monitoring the output of a light beam producing means comprising a light beam sampling means and a detector, wherein said light beam sampling means is adjusted to split the light beam in a first small fraction and a second large fraction, and wherein said first small fraction of said light beam is directed towards a detector according to  claim 25 .  
   
   
       45 . A system for monitoring according to  claim 44 , wherein said beam sampling means is a mirror, said mirror being rotatably mounted as to split the light beam at regular periods.  
   
   
       46 . A method for measuring the optical power of a high power incident radiation beam, the method comprising: 
 receiving an incident light beam, being at least a fraction of the high power incident radiation beam, in a doped semiconductor substrate through a window opening provided at a first side of the doped semiconductor substrate;    absorbing the incident light beam in the doped semiconductor substrate being doped over at least part of the thickness of the semiconductor substrate; and    measuring at least one electrical signal induced by a thermoelectric effect in the doped semiconductor substrate using a first electrode at a first side of the doped semiconductor substrate and a reference electrode outside an absorption volume determined by the window opening and an absorption distance of the incident light beam in the doped semiconductor substrate, wherein the absorption length L abs  for the light beam in said doped semiconductor substrate may furthermore be adjusted to keep the temperature of the surface of said doped semiconductor substrate in said window opening below a maximum temperature.    
   
   
       47 . A method according to  claim 46 , wherein said measuring comprises measuring at several points in the cross section of the fraction of the incident light beam by subsequently shifting a single or multiple pixel detector, as described in  claim 25 , to another point in the cross-section of the fraction of the light beam and recording a measurement.  
   
   
       48 . A method according to  claim 46 , said incident light beam having a pulse width and said detector being capable of measuring in intensity measuring mode, in energy measuring mode, in energy density mode or in power measuring mode, the method comprising setting a pulse width of said light beam for measuring in a mode selected from the group consisting of intensity measuring mode, energy measuring mode, energy density mode and power measuring mode.  
   
   
       49 . A detector according to  claim 25 , comprising a plurality of pixels, each pixel having a pixel window with an average pixel window width w, the pixels being separated by at least an interpixel pitch P, wherein said interpixel pitch P is between 1.5 and 4 times the average pixel window width w.