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Spiral phase contrast (SPC):

Using a helical phase pattern as phase filter in a Fourier plane gives rise to a doughnut-like point spread function. Convolution with an extended (amplitude- or) phase-object leads to strong isotropic edge enhancement in the image

Fig. 1: Basic idea of SPC: convolution with phase vortex kernel.

An intuitive way to understand this is looking at the convolution integrals describing image formation for a “doughnut-kernel”: in a homogeneous (region of the) sample destructive interference occurs because of the π phase shift across the doughnut (for any angle along the ring). Structure in the sample will give rise to less imperfect cancellation and thus to a local brightening in the image. Consequently the light is redistributes into edges and borderlines within the sample.

Experimental demonstrations with a spiral phase plate manufactured by photolithography:

Fig. 2: Spiral Phase contrast in transmission: fibroblasts (left brightfield, right SPC).

Fig. 3: Spiral Phase contrast in treflection: highlighting structures on a semiconductor (left brightfield, right SPC).

Publication(s):

S. Fürhapter, A. Jesacher, S. Bernet, M. Ritsch-Marte: Spiral phase contrast imaging in microscopy, Optics Express 13, 689 (2005).

A. Jesacher, S. Fürhapter, Bernet, M. Ritsch-Marte: Shadow effects in spiral phase contrast microscopy, Physical Review Letters 94, 233902 (2005).

S. Bernet, A. Jesacher, S. Fürhapter, C. Maurer, M. Ritsch-Marte: Quantitative imaging of complex samples in spiral phase contrast microscopy, Optics Express 14, 3792 (2006).

C. Maurer, A. Jesacher, S. Fürhapter, S. Bernet, and M. Ritsch-Marte: Upgrading a microscope with a spiral phase plate, J. Microscopy 230, 134-142 (2008).

For optically thick transparent objects one finds spiraled interferograms which enable one-image demodulation of optical thickness profiles:

Fig. 4: Spiral Interferogramme of an optically thick transparent object.

Publication(s):

A. Jesacher, S. Fürhapter, S. Bernet,. Ritsch-Marte: Spiral interferogram analysis, Journal of the Optical Society of America A 23, 1400 (2006).

S. Fürhapter, A. Jesacher, S. Bernet, M. Ritsch-Marte: Spiral interferometry, Optics Letters 30, 1953 (2005).