Monday, October 31, 2011

FiO 2011 - part 6 (final)

Hey everybody..  this is going to be the last post with my notes on Frontiers in Optics 2011.

Sergio Carbajo and Ying Geng won the Hilbert Grant award in
 optical engineering, lens design and illumination. Pic courtesy OSA.

Sergio Carbajo, from Colorado State University, who won the Hilbert Grant (in pic above) showed some amazing movies taken for nanoscale moving objects at near wavelength resolution. They have built an EUV tabletop laser and use repetitive nanosecond pulses from the laser with a zone plate objective to image the nanoscale moving object.

Ying Geng from Rochester, who also won the Hilbert Grant (in pic above), showed clear and sharp images of the mouse retina obtained using an adaptive optics scanning laser ophthalmoscope. The mouse imaging is very important for disease detection, diagnosis and cure because it is easier to find transgenic and knockout models of various eye-diseases in mice. But mice have notoriously poor vision. One would assume this should make for terrible images. But Ying managed to modify the beacon used for wavefront sensing to adapt to the unusually thick retina of the mouse (compared to humans). The beacon is now an annular shape instead of the conventional full uniform beam at the pupil and gives a tight sharp wavefront sensing spot allowing her to do adaptive optics sensing and correction. She showed images of the photoreceptor mosaic, blood capillaries, nerve fiber bundles. She also showed fluorescence labeled ganglion cells and even some results of classifying the ganglion cells into bi-stratified and mono-stratified classes which have dendrites (like roots) in two layers or one layer respectively. Very cool!

In the animal optics session.. 
Ronald Kroger gave a very nice talk about multifocal optics of fish lens. He followed animal eyes over evolution and showed how a single photoreceptor evolved into a directional light sensor, then incorporating multiple sensor and even compound eyes. Fish have almost spherical eye-lens and very good color vision. Apparently many fish have excellent correction for spherical and chromatic aberration. Their multi-focal, gradient index lens, with different zones, caters to different wavelengths and focuses them all at the same plane. Apparently there are also fish with multiple layers in their retina, so that different wavelengths which naturally focus at different axial planes may be sensed by different photopigments at those respective depth planes. 

Jakub Svoboda from the Czech Technical University in Prague, showed a method of using waveguides for document security and inspection. Traditionally document security such as for credit cards and currency notes has used technologies like holograms, watermarks, etc. Jakub proposed using diffraction gratings in the material of the document to accept and guide light into waveguides hidden inside the material. These waveguides direct the in-coupled light to other areas of the document where it is coupled out. You can mix and match in-coupling areas to guide light to form letters and patterns in the document when light is incident. Very neat! 

Michael Kudenov from the Optical Detection Lab at Arizona gave a great talk on spectrometric and polarization imaging. He spoke about a compact snapshot imaging spectrometer, which works like a Michelson interferometer (FT spectrometer). But to avoid the axial/OPD scanning of a mirror they use a Wollaston prism combined with a polarizer and analyzer combination. They used this with a multi-lenslet array to obtain an imaging spectrometer. They showed a nice compact device and were able to capture multispectral images of a moving car, people etc.  He also spoke about their channeled white light polarimeter  and IR hyperspectral Imaging Polarimeter.  

Ng, Poon and Gehm used a rapid polymer jet prototyping machine to additively print layers and fabricate computer generated holograms for terahertz bands. They showed results with multiple gratings in the computer generated volume hologram. 

The wavefront sensing and adaptive optics sessions had several good talks. Martin Booth from Oxford spoke about using image based sensorless wavefront sensing for microscopes using a deformable mirror and quality metrics in the output image such as total image intensity, etc. They choose an appropriate basis to influence the aberrations in an image. Traditionally Zernike modes are used for aberration description (sensing as well as correction). Here they proposed using the natural deformation modes of the mirror as the bases to derive optimum modes. This allows them to take into consideration experimental issues such as system misalignment, etc.

This year FiO had a great Math session toward the end of the conference. Eric Clarkson from Arizona showed that it is possible to reduce the dimensions of an SVD computation for rotationally symmetric imaging systems like CT scanners by the number of angles in which the data is collected. 

Michael Gehm spoke about adaptive spectral classification without collecting a complete data cube of spectral data. If you don’t want to get an image, just classify the object or material, they propose there is no need to acquire the complete hyperspectral image data. They use adaptive feature specific spectroscopy which measures spectral features or sums of spectral channels which increase the probability of classification. They use this with a task-specific information metric so that each measurement contains the optimal amount of information for the given task. They extend the spectrometer to an imager by combining this with snapshot spectral imaging substituting the conventional aperture mask with a DMD or an SLM.

Jorge Ojeda-Castaneda gave a spectacular closing talk in the very last session at FiO, where he spoke about using tunable phase masks to obtain tunable Gaussian apodizing filters and extended depth of field. He used two optical phase arrays placed in close proximity to each other, but slightly displaced. The complex amplitude transmittance of one array was the complex conjugate of the other array. He chose the complex conjugated phases in such a way that their concatenation, combined with the displacement of one mask with respect to the other, produced a tunable cubic phase mask and allowed extended depth of field imaging. A slightly different choice of the conjugate phase allowed him to use this combination as a tunable Gaussian apodizer. He used the apodizer to reduce oscillations in the defocused MTF of an extended depth of field system. Very nice and flexible concept. 

There were several other great talks I saw, and some I still need to see on the recorded videos! But it would be endless if I wrote about them all. So this is where I will end my posts on Frontiers in Optics 2011! 

Dance party at the reception! Pic courtesy OSA.
Thanks and three cheers to the organizers and all the attendees..!! We sure make an awesome community!

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