What is claimed is:
1. A system for determining the shape of an electromagnetic wavefront, comprising:
at least one reticle positioned in a path of the wavefront to be analyzed;
at least one detector positioned to detect the wavefront passing through the reticle, the detector being substantially located at a diffraction pattern self-imaging plane relative to the reticle; and
at least one processor receiving an output signal from the light detector and calculating the shape of the wavefront based thereon.
2. The system of claim 1, wherein the location of the self-imaging plane is a function of the wavelength of the wavefront and the spatial periodicity of the reticle.
3. The system of claim 1, wherein said reticle comprises a grating having a grating spacing, p.
4. The system of claim 2, wherein said diffraction pattern self-imaging plane is located in the near field a longitudinal distance of approximately
7
d
=
(
np
2
)
from said reticle, wherein p is the grating spacing of the grating, is the spectral wavelength of the wavefront, and n is an integer.
5. The system of claim 1, wherein said reticle comprises a grating having a grid-like pattern.
6. The system of claim 1, wherein the processor executes logic to undertake method acts comprising:
determining directional derivatives of the electromagnetic wavefront.
7. The system of claim 6, wherein the method acts further include transforming a diffraction pattern of the wavefront at the detector from a spatial image domain into a spatial frequency domain, prior to the act of determining coefficients.
8. The system of claim 7, wherein selected portions in the spatial frequency domain are used to determine said coefficients.
9. The system of claim 6, wherein the method acts include determining coefficients of polynomials based on at least one gradient of a phase-front of the wavefront, the coefficients being representative of the shape of the wavefront.
10. The system of claim 9, wherein the coefficients are determined by fitting derivative functions of a set of known polynomials to the derivatives obtained during the determining act.
11. The system of claim 6, wherein directional derivatives are determined in at least two directions.
12. The system of claim 6, wherein said method acts further comprise implementing a computational matte screen for filtering out noise.
13. A method for determining aberrations in an optical system comprising at least one optical element, said method comprising:
propagating a test beam along a path with said optical system in said path of said test beam so as to be illuminated by said test beam,
inserting a reticle in said path of said test beam at a location with respect to said optical system so as to receive light from said optical system, said light propagating through said reticle;
determining directional derivatives associated with said light subsequent to passing through the reticle; and
using the derivatives to output a measure of said aberrations.
14. The method of claim 13, further comprising transforming a diffraction pattern produced by said light passing through said reticle from a spatial image into a spatial frequency distribution.
15. The method of claim 13, further comprising determining coefficients of polynomials based on the directional derivatives.
16. The method of claim 15, wherein the coefficients are determined by fitting derivatives of a set of known polynomials to data obtained during the determining act.
17. The method of claim 13, comprising determining directional derivatives in at least two directions.
18. The method of claim 13, comprising locating a light detector at a position in said path so at to receive a self-image of the reticle.
19. The method of claim 13, further comprising implementing a computational matte screen as a filter.
20. A computer program product, comprising:
a computer readable medium having a program of instructions stored thereon for causing a digital processing apparatus to execute method steps for determining aberrations in a wavefront, comprising:
representing at least a portion of an image produced by said wavefront;
determining directional derivatives of the representation;
fitting the directional derivatives to known polynomials or derivatives thereof to obtain coefficients of polynomials; and
providing a wavefront characterization based at least in part on the coefficients, the wavefront characterization representing aberrations in the wavefront.
21. The program product of claim 20, further comprising:
generating a frequency domain representation of the wavefront.
22. The program product of claim 21, wherein the directional derivatives are determined in two directions.
23. An apparatus for characterizing an object with a wavefront from the object, comprising:
at least one reticle positioned in a path of the wavefront;
at least one light detector positioned relative to the reticle to receive a self-image diffraction pattern of the reticle produced by the wavefront; and
at least one processor receiving signals from the light detector representative of the self-image diffraction pattern and deriving derivatives associated therewith, the processor using the derivatives to characterize said object.
24. The apparatus of claim 23, wherein the object is an eye.
25. The apparatus of claim 23, wherein the location of the reticle is related to the wavelength of the wavefront and spatial frequency of the reticle.
26. The apparatus of claim 23, wherein the processor produces frequency transformation of the wavefront to produce a distribution in frequency space and derives derivatives of phases of the wavefront from the distribution in frequency space.
27. The apparatus of claim 23, wherein the processor determines derivatives of phases in two directions.
28. The apparatus of claim 23, wherein the processor fits a set of known derivatives to the derivatives determined by the processor to obtain coefficients of polynomials representative of the aberrations.
29. A method for determining aberrations in a reflective or internally reflective object system, comprising:
passing a light beam from the object system through a reticle, said light beam producing a near field diffraction pattern at said Talbot plane;
imaging said near field diffraction pattern at said Talbot plane;
using said near field diffraction pattern to output a measure of aberrations in the light beam.
30. The method of claim 29, wherein the object system is an eye and said method is for determining aberration in said eye.
31. The method of claim 29, further comprising transforming a wavefront associated with the light beam from a spatial image domain into a spatial frequency domain.
32. The method of claim 31, wherein only selected portions in said spatial frequency domain are used to determine coefficients.
33. The method of claim 29, comprising locating a light detector at said Talbot plane to detect the near field diffraction pattern.
34. The method of claim 29, further comprising designing corrective optics based on said measure of aberrations in said light beam so as to reduce said aberrations.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. In a fuel cell, an electrode comprising:
a fluorinated carbon based gas diffusion layer having a built in hydrophobicity; and
an active material layer adjacent to said gas diffusion layer wherein said active material layer comprises a carbon matrix including a redox couple selected from the group consisting of a Co+2\u2014Co+3 couple, a Co+2\u2014Co+4 couple, a Ni+2\u2014Ni+3 couple, a Ni+2\u2014Ni+4 couple, a Ag\u2014Ag+ couple, a Ag\u2014Ag+2 couple, a Cu\u2014Cu+2 couple, a (NiAg)+2\u2014(NiAg) couple, a (NiFe) oxide+2\u2014(NiFe) oxide+3 couple, a Mn+2\u2014Mn+3 \u2014Mn+7 couple, a Sn+2\u2014Sn couple, and combinations thereof.
2. The electrode according to claim 1, wherein said gas diffusion layer comprises a plurality of fluorinated carbon particles.
3. The electrode according to claim 2, wherein said fluorinated carbon particles are 19 to 68 weight percent fluorinated.
4. The electrode according to claim 3, wherein said plurality of fluorinated carbon particles are at least partially coated with a hydrophobic component.
5. The fuel cell oxygen electrode of claim 4, wherein said hydrophobic component comprises polytetrafluoroethylene (PTFE).
6. The electrode according to claim 4, wherein said gas diffusion layer includes 10 to 25 percent by weight of said hydrophobic component.
7. The electrode according to claim 4, wherein said gas diffusion layer has a gas contacting surface and an electrolyte contacting surface.
8. The electrode according to claim 7, wherein said hydrophobic component is continually graded from a high concentration at said electrolyte contacting surface of said gas diffusion layer to a low concentration at said gas contacting surface of said gas diffusion layer.
9. The electrode according to claim 7, wherein said fluorinated carbon particles are continually graded throughout said gas diffusion layer from a high fluorine concentration at said electrolyte contacting surface of said gas diffusion layer to a low fluorine concentration at said gas contacting surface of said gas diffusion layer.
10. The electrode according to claim 1, wherein said carbon matrix comprises a plurality of carbon particles.
11. The electrode according to claim 10, wherein said plurality of carbon particles are at least partially coated with polytetrafluoroethylene.
12. The electrode according to claim 11, wherein said plurality of polytetrafluoroethylene coated carbon particles contains 15 to 25 percent polytetrafluoroethylene by weight.
13. The electrode according to claim 10, wherein said carbon matrix further comprises 0 to 30 percent by weight of a peroxide decomposer.
14. The electrode according to claim 13, wherein said peroxide decomposer is selected from a group consisting of MnO2, MnO, cobalt oxides, nickel oxides, iron oxides, and mixtures thereof.
15. The electrode according to claim 1, wherein said carbon matrix comprises a plurality of fluorinated carbon particles.
16. The electrode according to claim 15, wherein said plurality of carbon particles are at least partially coated with polytetrafluoroethylene.
17. The electrode according to claim 16, wherein said plurality of polytetrafluoroethylene coated carbon particles contains 15 to 25 percent polytetrafluoroethylene by weight.
18. The electrode according to claim 15, wherein said carbon matrix further comprises 0 to 30 percent by weight of a peroxide decomposer.
19. The electrode according to claim 18, wherein said peroxide decomposer is selected from a group consisting of MnO2, MnO, cobalt oxides, nickel oxides, iron oxides, and mixtures thereof.
20. The electrode according to claim 1, further comprising:
a first current collector grid disposed adjacent to said gas diffusion layer opposite said active material layer; and
a second current collector grid disposed adjacent to said active material layer opposite said gas diffusion layer.
21. The electrode according to claim 20, wherein said first current collector grid and said second current collector grid each comprise at least one selected from the group consisting of mesh, grid, matte, expanded metal, foil, foam, plate, and combinations thereof.