NSOM the fourth dimension: Integrating nanometric spatial and femtosecond time resolution

Photonic devices are becoming the cornerstone of next generation systems for computing and information processing. This paper reports on the first steps in the development of methods to understand these devices with nanometric (10⁻⁷ cm) spatial and femtosecond (10⁻¹⁵ s) time resolution. The basis of this achievement is the dramatic developments that have occurred in the past few years in a new area of optics called near‐field optics. Near‐field optics is a form of lensless optics with a resolution that is subwavelength and which is independent of the wavelength of the light being employed. We report in this paper the transmission of pulses with tens of femtosecond duration through subwavelength, near‐field optical elements. We also report on a femtosecond near‐field optical light source with cross‐correlating capabilities and on the growth of GaAs in the tip of micropipettes for use as an ultra‐fast electro‐optical switch which can cross‐correlate optical, electrical, and electro‐optical effects. These developments are especially relevant in the investigation of photonic devices since such devices can alter their characteristics as a function of size in the mesoscopic regime from just below lens‐based optical resolutions to dimensions that approach atomic scales of ∼1 nm (10⁻⁷ cm). In view of the fact that these devices and the processes that govern them also exhibit ultrafast speeds, the combination of state of the art femtosecond laser spectroscopy with the unique features of near‐field optics is a critical step in advancing our next generation understandings of such materials and structures so that their full potential in information processing can be achieved.