Virtual lens

The Phase Focus Virtual Lens^® is a novel method for high fidelity quantitative imaging and microscopy.  It is known in the scientific literature as “ptychography”[1].  It works equally well in transmitted light and reflected light applications and, given suitable illumination sources and detectors, it can operate using any wavelength in the electromagnetic spectrum, as well electron and other particle waves and even sound waves.

No focussing devices are required, so the Phase Focus Virtual Lens is an inherently ‘lensless’ imaging method.  There are therefore no associated lens-related aberrations or limitations.  However, the method can also be integrated with conventional microscopes that already possess a variety of lenses, and these can be used to provide optical or geometric flexibility, or for conventional imaging.[2]

 

Imaging Process

 

1.  A specimen is illuminated by a patch of illumination referred to as the ‘probe.’  The probe area is typically much larger than the desired resolution.  Its phase and amplitude distribution are automatically computed, and deleterious effects of any non-uniformities in the illumination can therefore be eliminated.[3] Indeed, by ‘spreading out’ the probe in an essentially random fashion, spatial resolution can be substantially increased[4].

2.  The probe is shifted to a number of approximately known overlapping positions on the specimen.   Alternatively, the specimen can be shifted with respect to a stationary probe.

3.  At each position, the transmitted or reflected diffraction pattern is recorded on a standard two-dimensional array detector (e.g. a CCD).

4.  A proprietary phase retrieval algorithm processes the diffraction patterns to create an image pair from the specimen: an amplitude image and a phase image.  The amplitude image is similar to a conventional brightfield microscope image, and is a quantitative map of the specimen’s transmittance or reflectance.   The specimen’s phase function is a quantitative measure of the phase delay introduced as the wavefront travels through, or is reflected by, the specimen.

Depending upon the specimen and the wavelength, the phase data may be used to measure thickness, refractive index, dielectric constant, surface topography, the local magnetic field environment, and other parameters of interest.