Method and apparatus for wavefront sensing
A method of measuring characteristics of a wavefront of an incident beam includes obtaining an interferogram associated with the incident beam passing through a transmission mask and Fourier transforming the interferogram to provide a frequency domain interferogram. The method also includes selecting a subset of harmonics from the frequency domain interferogram, individually inverse Fourier transforming each of the subset of harmonics to provide a set of spatial domain harmonics, and extracting a phase profile from each of the set of spatial domain harmonics. The method further includes removing phase discontinuities in the phase profile, rotating the phase profile, and reconstructing a phase front of the wavefront of the incident beam.
1. A method of measuring characteristics of a wavefront of an incident beam having a phase front, the method comprising:
providing a transmission mask;
providing an imaging device having a detector plane;
passing a portion of the incident beam through the transmission mask;
propagating the portion of the incident beam passing through the transmission mask over a predetermined distance;
forming an interferogram at the detector plane of the imaging device;
detecting the interferogram using the imaging device;
Fourier transforming the interferogram to provide a frequency domain interferogram;
selecting a subset of harmonics from the frequency domain interferogram;
individually inverse Fourier transforming each of the subset of harmonics to provide a set of spatial domain harmonics;
extracting a phase profile from the set of spatial domain harmonics;
removing phase discontinuities in the phase profile;
rotating the phase profile; and
reconstructing the phase front of the wavefront of the incident beam.
2. The method of claim 1 further comprising:
measuring an amplitude associated with the spatial domain harmonics; and
computing an intensity profile associated with the wavefront of the incident beam.
3. The method of claim 1 wherein the transmission mask comprises a checkerboard pattern transmission mask.
4. The method of claim 3 wherein the checkerboard pattern transmission mask comprises an amplitude-only transmission mask.
5. The method of claim 1 wherein the subset of harmonics comprises a harmonic closest to an origin in each quadrant.
6. The method of claim 5 wherein the subset of harmonics comprises four harmonics closest to the origin.
7. The method of claim 1 wherein the subset of harmonics comprises a harmonic closest to an origin in two adjacent quadrants.
8. The method of claim 7 wherein the subset of harmonics comprises four harmonics closest to the origin.
9. The method of claim 1 wherein the phase profile characterizes a slope of the phase front.
10. The method of claim 1 wherein reconstructing the phase front comprises performing a two dimensional integration of the phase profile associated with each of the set of spatial domain harmonics.