An Ultrafast, Ultralarge Change In Reflectivity.

An ultrafast, ultralarge change in reflectivity can be brought about with femtosecond lasers. In a recent experiment short laser pulses, falling on an organic salt target, momentarily changed the material from an insulator (a bad reflector of light) to a semi-metal (good reflector of light). The change in reflectivity this large---more than 100%-has never been achieved before in a photonic material; photo-induced changes are usually more like a few percent. The laser pulse required doesn’t even have to be particularly intense to cause the change.

Thus gigantic photo-response work began as a Tokyo-Kyoto collaboration but now includes also LBL and Oxford. The new advance is that the change in reflectivity can be brought about in tens of femtoseconds rather than 150 ns. The new results are being reported this week at the Frontiers in Optics meeting in San Jose by Jiro Itatani, who has a joint appointment at LBL (jitatani@lbl.gov) and the Japan Science and Technology Agency. He says that dramatic reflectivity changes will be useful in bringing about direct ultrafast optical-to-optical switching. (Meeting website: http://www.osa.org/meetings/annual/default.aspx)