Time response of optical switching properties of Sb thin films under focused laser pulses

The time response of optical switching properties of Sb thin films under focused laser pulses is investigated. The results show that the response course can be divided into onset, opening, and closing stages. Formulas for their lengths are given. The onset and opening times decrease with increasing pumping light power density. The closing time is about 150 ns. For optical memory, if the power density of the readout and recording lasers changes from 5 x 10(9) to 15 x 10(9) W/m(2), the onset time changes from 2.5 to 0.30 mus, and the opening time is on the nanosecond scale. (C) 2003 Society of Photo-Optical Instrumentation Engineers.

Nonlinear response and optical limiting in SrBi2Ta2O9 thin films

SrBi2Ta2O9 (SBT) thin films on quartz substrates were prepared by use of the pulsed-laser deposition technique. The nonlinear refractive indices, n(2), Of the SBT films were measured by use of z-scan techniques with picosecond pulses. Large negative nonlinear refractive indices of 3.84 and 3.58 cm(2)/GW were obtained for the wavelengths 532 nm and 1.064 mum, respectively. The two-photon absorption coefficient was determined to be 7.3 cm/GW for 532 nm. The limiting behavior of SBT thin film on a quartz substrate was investigated in an f/5 defocusing geometry by use of 38-ps-duration, 532-nm, 1.064-mum. laser excitation. (C) 2001 Optical Society of America.

Narrativas médicas do medo: do coração ao cérebro

Desde a síndrome do coração irritável, passando pelas diversas síndromes do fin de siècle e chegando ao triunfo das teorias neurocientíficas sobre a hipersensibilidade dos centros cerebrais de resposta ao alarme e sufocação, a Medicina buscou teorias para explicar a experiência de pavor. Investiga-se o modo como ocorreram, ao longo da história, as transformações da atenção médica sobre o medo e os estados mórbidos que o acompanham. Ao se buscar na literatura médica vestígios de análises científicas sobre o mal-estar intenso, do meio do século XIX ao fim do XX, não se pretendeu construir uma história triunfalista, de modo que as teorias atuais pudessem ganhar status de superioridade em relação às do passado. Evidenciou-se, sim, a importância cultural e a força histórica de cada uma delas, salientando as possíveis continuidades e rupturas de sentido que elas assumiram.