Near-field diffraction of fs and sub-fs pulses: super-resolutions of NSOM in space and time

The near-field diffraction of fs and sub-fs light pulses by nm-size slit-type apertures and its implication for near-field scanning optical microscopy (NSOM) is analyzed. The amplitude distributions of the diffracted wave-packets having the central wavelengths in the visible spectral region are found by using the Neerhoff and Mur coupled integral equations, which are solved numerically for each Fourier's component of the wave-packet. In the case of fs pulses, the duration and transverse dimensions of the diffracted pulse remain practically the same as that of the input pulse. This demonstrates feasibility of the NSOM in which a fs pulse is used to provide the fs temporal resolution together with nm-scale spatial resolution. In the sub-fs domain, the Fourier spectrum of the transmitted pulse experiences a considerable narrowing that leads to the increase of the pulse duration in a few times. This imposes a limit on the simultaneous resolutions in time and space.Comment: 5 figure

Enhanced Transmission of Light and Particle Waves through Subwavelength Nanoapertures by Far-Field Interference

Subwavelength aperture arrays in thin metal films can enable enhanced transmission of light and matter (atom) waves. The phenomenon relies on resonant excitation and interference of the plasmon or matter waves on the metal surface. We show a new mechanism that could provide a great resonant and nonresonant transmission enhancement of the light or de Broglie particle waves passed through the apertures not by the surface waves, but by the constructive interference of diffracted waves (beams generated by the apertures) at the detector placed in the far-field zone. In contrast to other models, the mechanism depends neither on the nature (light or matter) of the beams (continuous waves or pulses) nor on material and shape of the multiple-beam source (arrays of 1-D and 2-D subwavelength apertures, fibers, dipoles or atoms). The Wood anomalies in transmission spectra of gratings, a long standing problem in optics, follow naturally from the interference properties of our model. The new point is the prediction of the Wood anomaly in a classical Young-type two-source system. The new mechanism could be interpreted as a non-quantum analog of the superradiance emission of a subwavelength ensemble of atoms (the light power and energy scales as the number of light-sources squared, regardless of periodicity) predicted by the well-known Dicke quantum model.Comment: Revised version of MS presented at the Nanoelectronic Devices for Defense and Security (NANO-DDS) Conference, 18-21 June, 2007, Washington, US

Diffraction-free subwavelength-beam optics

Diffraction is a fundamental property of light propagation. Owing to this phenomenon,light diffracts out in all directions when it passes through a subwavelength slit.This imposes a fundamental limit on the transverse size of a light beam at a given distance from the aperture. We show that a subwavelength-sized beam propagating without diffractive broadening can be produced in free space by the constructive interference of multiple beams of a Fresnel source of the respective high-refraction-index waveguide. Moreover, it is shown that such a source can be constructed not only for continuous waves, but also for ultra-short (near single-cycle) pulses. The results theoretically demonstrate the feasibility of completely diffraction-free subwavelength-beam optics, for both continuous waves and ultra-short pulses. The approach extends operation of the near-field subwavelength-beam optics, such as near-field scanning optical microscopy and spectroscopy,to the "not-too-distant" field regime (0.5 to about 10 wavelengths).Comment: 4 figure