Reference signal filter for interferometric system

Abstract

The invention provides a method and apparatus for applying spatial filtering the optical beam of a free space optical coherence tomography (OCT) system substantially without problematic reflections back to the optical source. The invention teaches spatially filtering the reference beam of the OCT system which is typically designed to provide isolation of the optical source from undesirable optical feed-back, thereby achieving spatial filtering without generating undesirable reflections back to the optical source. Various embodiments are taught.

We claim: 
     
         1 .- 10 . (canceled) 
     
     
         11 . An improved free space optical coherence tomography system, said system including a radiation source producing reference and probe radiation, a detector, a pathway for reference radiation, a reference mirror, a pathway for probe radiation, a processor for processing interferometric signals formed by reference and probe radiation and received at the detector, said improvement comprising:
 at least one pinhole in the path of the reference radiation, wherein said pinhole has a diameter in the range of approximately 20 to 60 microns, and wherein said pinhole spatially filters the reference radiation.   
     
     
         12 . An improved free space optical coherence tomography system, said system including a radiation source producing reference and probe radiation, at least one focusing lens, a detector, a pathway for reference radiation, a reference mirror, a pathway for probe radiation, a processor to process interferometric signals formed by reference and probe radiation and received at the detector, said improvement comprising:
 a pinhole in the path of said reference radiation such that said pinhole transmits a portion of the waist of the focused reference beam thereby spatially filtering the reference radiation   
     
     
         13 . The system of  claim 12 , wherein substantially the entire area of said reference mirror surface is reflective. 
     
     
         14 . The system of  claim 12 , wherein said pinhole is comprised of a coating on the surface of a partial mirror, said partial mirror surface facing said reflective surface of said reference mirror.