Holographic reconstruction apparatus and method

Abstract

Provided are an improved holographic reconstruction apparatus and method. A holographic reconstruction method includes: obtaining an object hologram of a measurement target object; extracting reference light information from the obtained object hologram; calculating a wavenumber vector constant of the extracted reference light information, and generating digital reference light by calculating a compensation term of the reference light information by using the calculated wavenumber vector constant; extracting curvature aberration information from the object hologram, and then generating digital curvature in which a curvature aberration is compensated for; calculating a compensated object hologram by multiplying the compensation term of the reference light information by the obtained object hologram; extracting phase information of the compensated object hologram; and reconstructing 3-dimensional (3D) shape information and quantitative thickness information of the measurement target object by calculating the quantitative thickness information of the measurement target object by using the extracted phase information of the compensated object hologram.

1 . A holographic reconstruction method comprising:
 obtaining an object hologram of a measurement target object;   extracting reference light information from the obtained object hologram;   calculating a wavenumber vector constant of the extracted reference light information, and generating digital reference light by calculating a compensation term of the reference light information by using the calculated wavenumber vector constant;   extracting curvature aberration information from the object hologram, and then generating digital curvature in which a curvature aberration is compensated for;   calculating a compensated object hologram by multiplying the compensation term of the reference light information by the obtained object hologram;   extracting phase information of the compensated object hologram; and   reconstructing 3-dimensional (3D) shape information and quantitative thickness information of the measurement target object by calculating the quantitative thickness information of the measurement target object by using the extracted phase information of the compensated object hologram.   
     
     
         2 . The holographic reconstruction method of  claim 1 , wherein the obtaining of the object hologram comprises:
 splitting, by a first beam splitter, single-wavelength light emitted from a light source into object light and reference light;   reflecting the object light from a surface of the measurement target object through an object light objective lens, and reflecting the reference light from an optic mirror after passing the reference light through a reference light objective lens;   recording, on a recording medium, an interference pattern formed when the reflected object light and the reflected reference light are transmitted to the first beam splitter, and transmitting, to a processor, an image file generated by converting the interference pattern; and   obtaining, by the processor, the object hologram from the image file.   
     
     
         3 . The holographic reconstruction method of  claim 1 , wherein the obtaining of the object hologram comprises:
 splitting, by a first beam splitter, single-wavelength light emitted from a light source into object light and reference light;   reflecting the reference light from a first optic mirror after passing the reference light through a reference light objective lens, and reflecting object penetration light, which is obtained by passing the object light through the measurement target object from a second optic mirror after passing the object penetration light through an object light objective lens;   recording, on a recording medium, an interference pattern formed by transmitting the reflected object penetration light and the reflected reference light to a second beam splitter, and transmitting, to a processor, an image file generated by converting the interference pattern; and   obtaining, by the processor, the object hologram from the image file.   
     
     
         4 . The holographic reconstruction method of  claim 1 , wherein the extracting of the reference light information comprises:
 performing inverse 2D Fourier transform on the obtained object hologram;   extracting, by using an automatic real image spot-position extraction algorithm, only a real image spot-position from a frequency spectrum that is obtained via the 2D Fourier transform and comprises spectrum information including the real image spot-position of the object hologram, spectrum information including an imaginary image spot-position, and spectrum information including direct current (DC) information; and   extracting the reference light information of the obtained object hologram by using the extracted real image spot-position.   
     
     
         5 . The holographic reconstruction method of  claim 1 , wherein the compensation term calculated in the generating of the digital reference light is a conjugate of the obtained object hologram and is the digital reference light, and is represented by R C (x,y)=conj[R(x,y)], wherein R c (x,y) denotes the digital reference light, R(x,y) denotes the reference light information of the obtained object hologram, and conj denotes a function for obtaining a conjugate complex number. 
     
     
         6 . The holographic reconstruction method of  claim 1 , wherein, in the calculating of the compensated object hologram, the calculated compensated object hologram is represented by U C (x,y,0)=O(x,y)R*(x,y)R C (x,y)R CA (x,y), wherein U C (x,y,0) denotes the compensated object hologram, O(x,y) and R*(x,y) respectively denote the object light and the reference light of the obtained object hologram, R C (x,y) denotes the digital reference light, and R CA (x,y) denotes the digital curvature. 
     
     
         7 . The holographic reconstruction method of  claim 1 , wherein, in the extracting of the phase information, the phase information of the compensated object hologram is extracted via inverse 2D Fourier transform, wherein the extracted phase information comprises only phase information of the measurement target object because light information and curvature aberration information of an objective lens are removed from the obtained object hologram. 
     
     
         8 . The holographic reconstruction method of  claim 7 , wherein the extracting of the phase information further comprises, when the phase information of the compensated object hologram comprises fine noise and a wrapped phase phenomenon, removing the fine noise and the wrapped phase phenomenon by using a 2D phase unwrapping algorithm. 
     
     
         9 . The holographic reconstruction method of  claim 1 , wherein the quantitative thickness information calculated in the reconstructing of the 3D shape information and the quantitative thickness information is represented by ΔL=λΔφ(x,y)/2πΔn(x,y), wherein ΔL denotes the quantitative thickness information, λ denotes a wavelength of the light source, Δφ(x,y) denotes the phase information of the compensated object hologram, and Δn(x,y) denotes a difference in refractive index between air and the measurement target object.