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

Abstract

Summary: 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 ultrafast 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.

The optical near-field: super-resolution imaging with structural and phase correlation

“…A recent emulation of this concept is far-field illumination of a gold wire that guides plasmons along the wire to its tapered tip where it emits photons. Consistent with what was determined for conventional apertured glass probes earlier [42] femtosecond pulses propagate while maintaining their temporal profile and pulse characteristics [43]. Many concepts in this later area of metallic nanofocusing have to be credited to the theoretical work of Stockman [44].…”

Measuring the spatiotemporal electric field of tightly focused ultrashort pulses with sub-micron spatial resolution

“…Another potential source of error in our measurements is spectral filtering of the collected light by the NSOM probe (the probe could, in principle, collect some colors more efficiently than others), but we made spectral transmission measurements, as well, and confirmed that ours did not. Previous papers have also reported that NSOM probes do not change the spectrum as long as the power is low enough to avoid nonlinear effects, which it is here [32,33].…”

Ultrahigh spatiotemporal resolved spectroscopy

“…Except for the applications on microfabrications [15,16] , ultrafast nanometric light sources and optical switches [9] , the main application of fs-SNOM system is spectroscopic measurement. It can obtain ultrahigh resolution spectroscopy in space and time, thus is very useful in the research of ultrafast process in mesoscopic systems.…”

“…A scanning near-field optical microscope (SNOM or NSOM) [7,8] can obtain an ultrahigh optical resolution below a few tens of nanometers, which uses a nanometer-scale aperture at the end of a fiber tip to scan in the near-field of a sample. Thus, combining femtosecond spectroscopy and SNOM, the femtosecond-SNOM (fs-SNOM) system can realize spectroscopy with ultrahigh resolutions in both space and time simultaneously [9] , and provides people a powerful tool for the study of ultrafast process in the mesoscopic dimension.…”