Wavefront coding interference contrast imaging systems

• US 20020195548A1
• Filed: 06/06/2001
• Published: 12/26/2002
• Est. Priority Date: 06/06/2001
• Status: Abandoned Application

• Current Assignee: The Board of Regents of the University of Colorado (University of Colorado System), CDM Optics, Inc. (Will Semiconductor Co., Ltd. Shanghai)
• Original Assignee: The Board of Regents of the University of Colorado (University of Colorado System)
• Inventors: Dowski, Edward Raymond Jr., Cogswell, Carol Jean
• Application Number:
  US09/875,766
• Publication Number:
  US 20020195548A1
• Time in Patent Office: Days
• US Class Current: 250/216
• CPC Class Codes: G01J 9/0215 by shearing interferometric methods
• CPC Class Codes: G01S 3/7835 using coding masks
• CPC Class Codes: G02B 27/0025 for optical correction, e.g. distorsion, aberration
• CPC Class Codes: G02B 27/46 Systems using spatial filters
• CPC Class Codes: G02B 27/52 Phase contrast optics in microscopes G02B21/14
• CPC Class Codes: G02B 5/00 Optical elements other than lenses light guides G02B6/00; optical logic elements G02F3/00

Abstract

Contrast Imaging apparatus and methods with Wavefront Coding aspheric optics and post processing increase depth of field and reduce misfocus effects in imaging Phase Objects. The general Interference Contrast imaging system is modified with a special purpose optical element and image processing of the detected image to form the final image. The Wavefront Coding optical element can be fabricated as a separate component, can be constructed as an integral component of the imaging objective, tube lens, beam splitter, polarizer or any combination of such.

Claims

1. Apparatus for increasing depth of field and controlling focus related aberrations in an Interference Contrast Imaging system having an illumination source, optical elements for dividing light polarizations, and illumination optics placed before a Phase Object to be imaged, and elements for recombining light polarizations and objective optics after the Phase Object to form an image at a detector, the improvement comprising:

an optical Wavefront Coding mask having an aperture and placed between the Phase Object and the detector,

said coding mask being constructed and arranged to alter the optical transfer function of the Interference Contrast Imaging system in such a way that the altered optical transfer function is substantially insensitive to the distance between the Phase Object and the objective optics over a greater range of object distances than was provided by the unaltered optical transfer function,

wherein the coding mask affects the alteration to the optical transfer function substantially by affecting the phase of light transmitted by the mask; and

a post processing element for processing the image captured by the detector by reversing the alteration of the optical transfer function accomplished by the coding mask.

2. The apparatus of claim 1 wherein the detector is a charge coupled device (CCD).

3. The apparatus of claim 1, wherein the phase of light transmitted by the coding mask is relatively flat near the center of the aperture with increasing and decreasing phase near respective ends of the aperture.

4. The apparatus of claim 1, wherein the phase of light transmitted by the coding mask substantially follows a cubic function.

5. The apparatus of claim 4, wherein the phase of light transmitted by the coding mask substantially follows a function of the form:

Phase (x,y)=12[x³+y³]

where |x|≦

1, |y|≦

1.

6. The apparatus of claim 1, wherein the phase of light transmitted by the coding mask substantially follows a rectangularly separable sum of powers function of the form:

phase(x,y)=[Σ

a_isign(x)|x|^b_i+c_isign(y)|y|^d_i]

where the sum is over the index i,

sign(x)=−

1 for x<

0, sign(x)=+1 for x≧

0.

7. The apparatus of claim 1, wherein the phase of light transmitted by the coding mask substantially follows a non-separable function of the form:

phase(r,θ

)=[Σ

r^a_i cos (b_iθ

+φ

_i)]

where the sum is again over the index i.

8. The apparatus of claim 1, wherein the phase of light transmitted by the coding mask substantially follows a function of the form:

9. The apparatus of claim 1, wherein the coding mask further comprises a lens element for focussing the light.

10. The apparatus of claim 1, wherein the coding mask is integrally formed with the illumination optics.

11. The apparatus of claim 1, wherein the coding mask comprises an optical material having varying thickness.

12. The apparatus of claim 1, wherein the coding mask comprises an optical material having varying index of refraction.

13. The apparatus of claim 1, wherein the coding mask comprises spatial light modulators.

14. The apparatus of claim 1, wherein the coding mask comprises micro-mechanical mirrors.

16. The method of claim 15, wherein the modifying step modifies the phase of light transmitted according to a profile which is relatively flat near the center of the aperture with increasing and decreasing phase near respective ends of the aperture.

17. The method of claim 15, wherein the phase of light transmitted by the mask substantially follows a cubic function.

wherein the phase of light transmitted by the coding mask substantially follows a function of the form:

Phase (x,y)=12 [x³+y³]

where |x|≦

1, |y|≦

1.

18. The method of claim 15, wherein the phase of light transmitted by the coding mask substantially follows a rectangularly separable sum of powers function of the form:

phase(x,y)=[Σ

a_isign(x)|x|^b_i+c_isign(y)|y|^d_i]

where the sum is over the index i,

sign(x)=−

1 for x<

0, sign(x)=+1 for x≧

0.

19. The apparatus of claim 15, wherein the phase of light transmitted by the coding mask substantially follows a non-separable function of the form:

phase(r,θ

)=[Σ

r^a_i cos (b_iθ

+φ

_i)]

where the sum is again over the index i.

20. The method of claim 15, wherein the phase of light transmitted by the coding mask substantially follows a function of the form:

15. The method for increasing depth of field and controlling focus related aberrations in a conventional Interference Contrast Imaging system having an illumination source, optical elements for dividing light polarizations, and illumination optics placed before a Phase Object to be imaged, and elements for recombining light polarizations and objective optics after the Phase Object to form an image at a detector, the method comprising the steps of:

between the Phase Object and the detector, modifying the wavefront of transmitted light;

the wavefront modification step selected to alter the optical transfer function of the Interference Contrast Imaging system in such a way that the altered optical transfer function is substantially insensitive to the distance between the Phase Object and the objective optics over a greater range of object distances than was provided by the unaltered optical transfer function; and

post processing the image captured by the detector by reversing the alteration of the optical transfer function accomplished by the mask.

21. An Wavefront Coding Interference Contrast Imaging system for imaging a Phase Object comprising:

an illumination source for providing illumination;

polarizing optics for splitting the illumination into distinct juxtaposed polarizations;

illumination optics placed between the illumination source and the Phase Object;

polarizing optics for recombining the illumination polarizations;

a detector;

objective optics placed between the Phase Object and the detector to form an image at the detector;

an optical Wavefront Coding mask having an aperture and placed between the Phase Object and the detector,

said mask being constructed and arranged to alter the optical transfer function of the Imaging system in such a way that the altered optical transfer function is substantially insensitive to the distance between the Phase Object and the objective optics over a greater range of object distances than was provided by the unaltered Imaging system optical transfer function,

wherein the mask affects the alteration to the optical transfer function substantially by affecting the phase of light transmitted by the mask; and

a post processing element for processing the image captured by the detector by reversing the alteration of the optical transfer function accomplished by the mask.

22. The apparatus of claim 21, wherein the phase of light transmitted by the coding mask is relatively flat near the center of the aperture with increasing and decreasing phase near respective ends of the aperture.