Biomedical subjects

Alan H Greenaway

Publications and source records attributed to Alan H Greenaway.

4 recordsLinked to original sources

PubMed2006

Three-dimensional particle imaging by wavefront sensing.

We present two methods for three-dimensional particle metrology from a single two-dimensional view. The techniques are based on wavefront sensing where the three-dimensional location of a particle is encoded into a single image plane. The first technique is based on multiplanar imaging, and the second produces three-dimensional location information via anamorphic distortion of the recorded images. Preliminary results show that an uncertainty of 8 microm in depth can be obtained for low-particle density over a thin plane, and an uncertainty of 30 microm for higher particle density over a 10 mm deep volume.

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PubMed2004

Generalized phase diversity for wave-front sensing.

Phase diversity is a phase-retrieval algorithm that uses a pair of intensity images taken symmetrically about the wave front to be determined. If these images are taken about the system input pupil this is equivalent to a curvature-sensing algorithm. Traditionally a defocus aberration kernel is used to produce the phase-diverse data. We present a generalization of this method to allow the use of other functions as the diversity kernel. We discuss the necessary and sufficient conditions that such a function must satisfy for use in a null wave-front sensor. Computer simulations were used to validate these results.

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PubMed2004

Compact optical system for pulse-to-pulse laser beam quality measurement and applications in laser machining.

Fluctuations in beam quality (M2) have been observed on a pulse-to-pulse basis from an industrial Nd:YAG laser. This was achieved with a compact multiplane imaging method incorporating quadratically distorted diffraction gratings, which enabled simultaneous imaging of nine planes on a single CCD array. With this system, we measured across a range of beam qualities with an associated error (in M2 variation) of the order of 0.7%. Application of the system to fiber-optic beam delivery and laser drilling is demonstrated.

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PubMed2003

Wave-front sensing by use of a Green's function solution to the intensity transport equation.

A method for reconstructing an unknown wave front from measurements of its intensity distribution on two planes along the direction of propagation is described. The method solves the intensity transport equation by use of Neumann boundary conditions, leading to a solution that requires only matrix multiplication. The method provides real-time wave-front reconstruction with high accuracy and is easily reposed to permit reconstruction of the wave front in any orthonormal basis set.

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