Fourier transform holography using pseudo-random phase shifting of object illuminating beams and apodization
First Claim
1. A system for forming a hologram of an array of beams of electromagnetic radiation on a Fourier transform plane, comprising:
- a pseudo-random phase mask receptive in use of a beam of electromagnetic radiation and comprised of a plurality of phase shifting areas arranged in a pattern of rows and columns, there being an approximately equal number of phase shifting areas for each of the different phase shifts, wherein the number of different phase shifts is N which is greater than three inclusive and each of the different phase shifts is one of the multiples of m360°
/N, where m ranges from 1 to N, and the phase difference between orthogonally adjacent phase shifting areas is 360°
/N, whereby the power spectrum of each of said phase-shifted beams on the Fourier transform plane distributes in orthogonal directions from the center maximum of the power spectrum;
means for apodizing the phase-shifted beams; and
means for recording a Fourier transform hologram of said phase-shifted, apodized beams.
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Abstract
A phase mask comprised of a square array of phase shifting areas arranged in pseudo-random pattern is illuminated with a beam of electromagnetic radiation, as a result of which an array of pseudo-randomly phase shifted beams emerges from the phase mask and impinges upon an object transparency to be intensity-modulated thereby and come to a focus on a Fourier transform plane. The power spectrum of the beams distributes in orthogonal directions on the Fourier transform plane from its center maxima in a distinct pattern of series of fringes. The technique of apodization is employed to suppress the fringes to thereby reduce the coherent noise of a hologram to a minimum.
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Citations
7 Claims
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1. A system for forming a hologram of an array of beams of electromagnetic radiation on a Fourier transform plane, comprising:
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a pseudo-random phase mask receptive in use of a beam of electromagnetic radiation and comprised of a plurality of phase shifting areas arranged in a pattern of rows and columns, there being an approximately equal number of phase shifting areas for each of the different phase shifts, wherein the number of different phase shifts is N which is greater than three inclusive and each of the different phase shifts is one of the multiples of m360°
/N, where m ranges from 1 to N, and the phase difference between orthogonally adjacent phase shifting areas is 360°
/N, whereby the power spectrum of each of said phase-shifted beams on the Fourier transform plane distributes in orthogonal directions from the center maximum of the power spectrum;means for apodizing the phase-shifted beams; and means for recording a Fourier transform hologram of said phase-shifted, apodized beams. - View Dependent Claims (2, 3, 4, 5)
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6. A method for reconstructing a Fourier transform hologram, wherein said hologram is prepared by a method comprising the steps of directing a beam of electromagnetic radiation to a pseudo-random phase mask comprised of a plurality of phase shifting areas arranged in a pattern of rows and columns, there being an approximately different phase shifts, wherein the number of different phase shifts is N which is greater than three inclusive and each of the different phase shifts is one of the multiples of m360°
- /N, where m ranges from 1 to N, and the phase difference between orthogonally adjacent phase shifting areas is 360°
/N, to produce a plurality of phase-shifted beams, placing an object transparency behind the phase mask in the direction of the beam to intensity-modulate the phase-shifted beams, subjecting a recording medium to the intensity-modulated, phase-shifted beams and directing a reference beam to said recording medium to produce an interference fringe pattern with said intensity-modulated, phase-shifted beams, said method comprising;directing a beam of electromagnetic radiation to said hologram, said beam having a uniform intensity distribution across the transverse cross-section thereof; and placing an apodization filter in the path of said beam to impart a substantially Gaussian intensity distribution to said beam.
- /N, where m ranges from 1 to N, and the phase difference between orthogonally adjacent phase shifting areas is 360°
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7. A method for reconstructing a Fourier transform hologram, wherein said hologram is prepared by a method comprising the steps of directing a beam of electromagnetic radiation to a pseudo-random phase mask comprised of a plurality of phase shifting areas arranged in a pattern of rows and columns, there being an approximately equal number of phase shifting areas for each of the different phase shifts, wherein the number of different phase shifts is N which is greater than three inclusive and each of the different phase shifts is one of the multiples of m360°
- /N, where m ranges from 1 to N, and the phase difference between orthogonally adjacent phase shifting areas is 360°
/N, to produce a plurality of phase-shifted beams, placing an object transparency behind the phase mask in the direction of the beam to intensity-modulate the phase-shifted beams, subjecting a recording medium to the intensity-modulated, phase-shifted beams and directing a reference beam to said recording medium to produce an interference fringe pattern with said intensity-modulated, phase-shifted beams, said method comprising,directing a beam of electromagnetic radiation to said hologram, said beam having a substantially Gaussian intensity distribution across the transverse cross-section thereof.
- /N, where m ranges from 1 to N, and the phase difference between orthogonally adjacent phase shifting areas is 360°
Specification