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Tuesday, 26 May 2015

Peter: JC: Effect of multiple conduction bands on high-harmonic emission from dielectrics

We find that, for sufficiently strong mid-IR fields, transitions between different conduction bands play an important role in the generation of high-order harmonics in a dielectric. The transitions make a significant contribution to the harmonic signal, and they can create a single effective band for the motion of an electron wave packet. We show how high harmonic spectra produced during the interaction of ultrashort laser pulses with periodic solids provide a spectroscopic tool for understanding the effective band structure that controls electron dynamics in these media.
Figure 3

Tuesday, 12 May 2015

No JC, but OSA/SPIE student chapter seminar

No Jc today, but please go to Blackett 630 for 15:00 for this seminar organised by the local OSA/SPIE student chapter!

Microcirculation imaging with light and sound

Martin J. Leahy, Haroon Zafar, Sean O’Gorman, Aed├ín Breathnach,  and Hrebesh M. Subhash

Tissue Optics & Microcirculation Imaging Facility, National University of Ireland, Galway, Ireland and National Biophotonics & Imaging Platform, Ireland.

Structural and functional imaging of the microcirculation is necessary to understand many diseases such as diabetes mellitus, heart disease, peripheral vascular disease and arteriosclerosis. We have developed several methods for assessment of both the structural and dynamic properties of the capillaries in the upper dermis and the vessels which supply them.

We have developed 2D devices based on polarisation spectroscopy which output colour-coded maps which are sensitive to the concentration of red blood cells in the skin tissue. The hardware design consists of two orthogonally placed polarisation filters over the light source and sensor of a standard digital camera and utilises the video mode to provide 15/30 frames per second at a resolution of ~ 200 mm. We have also developed correlation mapping optical coherence tomography (cmOCT) to render the 3D microcirculation. To obtain microvascular maps without motion artefact, we used the full-field technique and applied the cmOCT algorithm to the data. We are developing miniature low cost OCT. and nanosensitive OCT [3&4]. Since the depth is limited to one or two millimetres with OCT and much less with full-field OCT, we have recently begun to work with photoacoustic tomography where we find a backscatter type probe, similar to existing clinical ultrasound, has advantages of ease of use, speed and familiarity for radiographers.

1. Microcirculation Imaging. (Wiley-VCH), Leahy, M.J. editor, 2012.
2. Enfield, J., Jonathan, E. and Leahy, M.J., 2011. In vivo imaging of the microcirculation of the volar forearm using correlation mapping optical coherence tomography (OCT). Biomedical Optics Express 2 (5) 1184-1193.
3. Dsouza, R., Subhash, H.M., Neuhaus, K., Hogan, J., Wilson, C., and Leahy, M.J. 2014, Dermascope guided multiple reference optical coherence tomography, Biomedical Optics Express, 5(9) 2870-2882.
4. Alexandrov, S., Subhash, H.M., Zam, A. and Leahy M.J. 2014, Nano-sensitive optical coherence tomography, Nanoscale, 6, 3545-3549, DOI: 10.1039/C3NR06132A