Optical-field-induced current in dielectrics

摘要

本期Nature上发表的两项研究突显了利用光场rn来在电介质中进行超快信号操纵的潜力。在电rn信号处理方面，半导体是首选材料。然而，电rn介质等绝缘体可能会成为有吸引力的替代品：rn它们原则上反应速度快，但通常在低电场中电rn导性极低，在大电场中会被击穿。电介质的电rn子性质可以用超短激光脉冲来控制，这种激光rn脉冲允许将电介质无损伤地暴露于高电场。rnAgustin Schiffrin等人演示，具有受控超短波形rn的强激光场能在光周期内(短于-飞秒)可逆地rn将一种介电绝缘体转变成一种导体。MartinrnSchultze等人研究了超快可逆性这个关键问rn题，发现电介质可以用光场反复打开和关闭，rn而不会发生降解。%The time it takes to switch on and off electric current determines the rate at which signals can be processed and sampled in modern information technology. Field-effect transistors are able to control currents at frequencies of the order of or higher than 100 gigahertz, but electric interconnects may hamper progress towards reaching the terahertz (10~(12) hertz) range. All-optical injection of currents through interfering photoexcitation pathways or photoconductive switching of terahertz transients has made it possible to control electric current on a subpicosecond time-scale in semiconductors. Insulators have been deemed unsuitable for both methods, because of the need for either ultraviolet light or strong fields, which induce slow damage or ultrafast breakdown, respectively. Here we report the feasibility of electric signal manipulation in a dielectric. A few-cycle optical waveform reversibly increases-free from breakdown-the a.c. conductivity of amorphous silicon dioxide (fused silica) by more than 18 orders of magnitude within 1 femtosecond, allowing electric currents to be driven, directed and switched by the instantaneous light field. Our work opens the way to extending electronic signal processing and high-speed metrology into the petahertz (10~(15) hertz) domain.