Digital interference holographic microscope and methods

• US 7,127,109 B1
• Filed: 09/27/2000
• Issued: 10/24/2006
• Est. Priority Date: 09/27/1999
• Status: Expired due to Term

• Current Assignee: University of South Florida (State University System of Florida)
• Original Assignee: University of South Florida (State University System of Florida)
• Inventors: Kim, Myung K.
• Primary Examiner(s): Mancuso, Joseph
• Assistant Examiner(s): Tarcu, Robert
• Application Number:
  US10/089,266
• Time in Patent Office: 2,218 Days
• Field of Search: 356/457, 356/489, 356/458, 356/495, 356/512, 356/513, 356/514
• US Class Current: 382/210
• CPC Class Codes: G02B 21/0004 specially adapted for specific applications
• CPC Class Codes: G03H 1/0005 Adaptation of holography to specific applications holographic optical element G02B5/32; holographic scanner G02B26/106; recognition using holographic mask G06V10/88; holographic memories G11B7/0065, G11C13/042
• CPC Class Codes: G03H 1/0443 Digital holography, i.e. recording holograms with digital recording means holobject computation G03H1/0866
• CPC Class Codes: G03H 1/0866 Digital holographic imaging, i.e. synthesizing holobjects from holograms
• CPC Class Codes: G03H 2001/005 in microscopy, e.g. digital holographic microscope [DHM] microscopes G02B21/00; digital holography G03H1/0866
• CPC Class Codes: G03H 2210/33 3D/2D, i.e. the object is formed of stratified 2D planes, e.g. tomographic data
• CPC Class Codes: G03H 2222/13 Multi-wavelengths wave with discontinuous wavelength ranges G03H2222/18 takes precedence

Abstract

A simple digital holographic apparatus and method allow reconstruction of three-dimensional objects with a very narrow depth of focus or high axial resolution. A number of holograms are optically generated using different wavelengths spaced at regular intervals. They are recorded, such as on a digital camera, and are reconstructed numerically. Multiwavelength interference of the holograms results in contour planes of very small thickness and wide separation. Objects at different distances from the hologram plane are imaged clearly and independently with complete suppression of the out-of-focus images. The technique is uniquely available only in digital holography and has applications in holographic microscopy.

Claims

1. A method for imaging a three-dimensional object comprising the steps of:

(a) illuminating an object with radiation at a wavelength to form a reflected image beam;

(b) providing a reference beam comprising the wavelength;

(c) recording an interference pattern between the reference beam and the image beam;

repeating steps (a)–

(c) at a succession of different wavelengths separated by a predetermined wavelength step;

computing a holographic image from the interference pattern for each wavelength;

adding the holographic images together to form an intensity distribution pattern;

extracting out a series of two-dimensional cross-sectional images from the intensity distribution pattern;

correcting microscopic image distortion in the cross-sectional images; and

reassembling the cross-sectional images into a three-dimensional model of the object.

2. The method recited in claim 1, wherein the illuminating step comprises illuminating the object with coherent radiation.

3. The method recited in claim 2, further comprising the step of expanding the coherent radiation prior to the illuminating step.

4. The method recited in claim 1, wherein the predetermined wavelength step comprises a function of an axial scale of the object.

5. The method recited in claim 1, further comprising the step of subtracting a zero-order intensity from each computed holographic image prior to the adding step.

6. A method for imaging a three-dimensional object comprising the steps of:

(a) illuminating an object with radiation at a wavelength to form a reflected image beam;

(b) providing a reference beam comprising the wavelength;

(c) recording an interference pattern between the reference beam and the image beam;

(d) recording an image of the object only; and

(e) recording an image of the reference beam only;

repeating steps (a)–

(e) at a succession of different wavelengths separated by a predetermined wavelength step;

computing a holographic image from the interference pattern for each wavelength;

subtracting a zero-order intensity from each computed holographic image, wherein the subtracting step comprises subtracting the object-only and reference-beam-only images from the interference pattern; and

adding the holographic images together to form an intensity distribution pattern.

7. The method recited in claim 6, wherein the computing step comprises calculating a holographic image field at each wavelength using a Fresnel diffraction formula.

8. A method for imaging a three-dimensional object comprising the steps of:

(a) illuminating an object with radiation at a wavelength to form a reflected image beam;

(b) providing a reference beam comprising the wavelength;

(c) recording an interference pattern between the reference beam and the image beam;

repeating steps (a)–

(c) at a succession of different wavelengths separated by a predetermined wavelength step;

computing a holographic image from the interference pattern for each wavelength; and

adding the holographic images together to form an intensity distribution pattern, wherein the object comprises two two-dimensional objects positioned different distances from a source of the radiation, and further comprising the step of extracting out two two-dimensional cross-sectional images from the intensity distribution pattern, each image representative of one of the objects.

9. The method recited in claim 8, wherein the extracting step comprises encoding the Fresnel diffraction as a function of a Fourier transform with respect to radiation wavelength.