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Lecture Dmitry Mazurenko

Rooster

WanneerWaar
12 maart 2004 FWN-Building 5113.0202, Nijenborgh 4, 9747 AG, Groningen
Speaker: Dr. Dmitry Mazurenko
Affiliation: University of Utrecht
Title: Ultrafast optical switching in three-dimensional photonic crystals
Date: Fri Mar 12, 2004
Start: 14.00
Location: FWN-Building 5113.0202
Host: P.H.M. van Loosdrecht
Telephone: +31 50 363 8149

Abstract

Photonic crystals are materials with a periodic refractive index on the scale of the wavelength of light. The big issue is to create a sufficient contrast, in order to form a photonic band gap within which the electromagnetic field cannot propagate. Much less studied is the non-linear optical behaviour of photonic crystals, which are relevant not only from a fundamental point of view but also for applications, e.g., fast optical switchers, all-optical transistors, and low threshold microlasers. In my talk I will present the experimental results that demonstrate non-linear all-optical switching in a three-dimensional photonic crystal on a femtosecond time scale. Our sample are synthetic opals filled with silicon (Si) or vanadium dioxide (VO2). The ultrafast dynamics of the Bragg reflection was monitored by a white-light pump-probe setup. An optical pump pulse is absorbed in the material in the voids and the second probe pulse at a variable time-delay monitors the Bragg reflection spectrum in a direction near to the normal of the (111) surface of the sample. We observe in the reflection spectra an ultrafast shift of the stop band for the VO2-opal and a drop for the Si-opal. This can be explained by a change of the imaginary and/or the real part of the dielectric constant of the sample, because of laser-induced phase transitions (VO2) or by photo-excited hot carriers(Si). As a result, the band structure of the photonic crystal is modified. We show that the switching time of the Bragg reflectivity can be as short as 30 fs and the relative changes in the Bragg reflection can reach as much as 50%. The recovery time is determined by the material properties in the voids and the heat conductivity of the opal structure. The results are compared with two-band mixing theory.
Laatst gewijzigd:22 oktober 2012 14:30