Time-to-Space Converter


Ok, here is what my dissertation is all about.  I fabricate and study sol-gel films doped with various organic dyes and organic or nanoparticle quenchers for their potential use in an all-optical Time-to-Space converter.  Essentially we are interested in producing dye doped films in which rapid deactivation of the dye's excited state occurs.  This will form the active component in an all-optical time-to-space converter.

Essentially this device, is an optical shutter that takes a series of femtosecond signal pulses, closely spaced in time (a picosecond or less) and spatially disperses them so the distance between them corresponds to their temporal separation.  In order to accomplish this, a femtosecond gate pulse which is angled relative to the plane of the active layer, is used to excite specific regions in sequence as it propagates through this layer.  Upon excitation, the transparency of a particular region increases, but only for a duration of time slightly longer than the temporal width of the gating pulse.  This allows the area of the signal pulse that spatially overlaps this region to undergo a higher degree of transmission as it passes through.  As subsequent signal pulses arrive, different areas of them undergo this process.  The signal pulses can now be detected as distinct signals in adjacent regions of the array detector, and the spacing between time now corresponds to their separation in time.  In theory, such a device has the ability to separate pulses that are spaced in time on the order of their duration, however, the optical response of the active layer would be the limiting factor.  So the faster this response, the better the overall performance of the device.   A practical application of such a device would be in the telecommunication arena, because the faster you can switch on and off light the more data you can transmit.

Optical Switch

One dye system that has shown some promise is the cyanine dye DODC.  Upon intercalation into the hybrid film, it forms a H-type aggregate which undergoes rapid excited state deactivation due to exciton dynamics.  Below are some steady state and time-resolved results for this system.





DODC structure



absorption spectra

Chemical structure of the DODC molecule.  Several of this molecules stack to form the H-aggregate structure. Here we see the absorption bands of the monomer (590 nm) and H-type aggregate (542 nm).

Exciton levels
streak camera
The exciton levels in H- and J- aggregates.  In the case a H-aggregate, only the transitions to the uper level is allowed.
Streak camera decay profile showing the fast and slow components.  The time resolution of the system is ± 30 ps.