M. Mechler

Enhanced transmission versus localization of a light pulse by a subwavelength metal slit

Institute of Spectrochemistry and Applied Spectroscopy,Bunsen-Kirchhoff-Str. 11, D-44139 Dortmund, GermanyThe existence of resonant enhanced transmission and collimation of light waves by subwavelengthslits in metal films [for example, see T.W. Ebbesen et al., Nature (London) 391, 667 (1998) andH.J. Lezec et al., Science, 297, 820 (2002)] leads to the basic question: Can a light be enhanced andsimultaneously localized in space and time by a subwavelength slit? To address this question, thespatial distribution of the energy flux of an ultrashort (femtosecond) wave-packet diffracted by asubwavelength (nanometer-size) slit was analyzed by using the conventional approach based on theNeerhoff and Mur solution of Maxwell’s equations. The results show that a light can be enhancedby orders of magnitude and simultaneously localized in the near-field diffraction zone at the nm-and fs-scales. Possible applications in nanophotonics are discussed.

Nonlinear distortion of intense THz beams

Near- and far-field beam profiles were measured for THz pulses generated in LiNbO3 by optical rectification of 200 fs pulses with a tilted pulse front. The variation of the THz beam size and a dramatically increasing divergence angle with increasing pump fluence were observed in the (horizontal) plane of the pulse front tilt. No significant variation was observed in the vertical direction. The reason for the observed nonlinear beam distortion is the shortening of the effective interaction length for THz generation caused by the combined effect of pump spectral broadening and angular dispersion in the tilted pulse front geometry. Our results indicate that nonlinear THz beam distortion effects have to be taken into account when designing intense THz sources and related experiments.

Analytical model of the enhanced light transmission through subwavelength metal slits: Green’s function formalism versus Rayleigh’s expansion

We present an analytical model of the resonantly enhanced transmission of light through a subwavelength nm-size slit in a thick metal film. The simple formulae for the transmitted electromagnetic fields and the transmission coefficient are derived by using the narrow-slit approximation and the Green’s function formalism for the solution of Maxwell’s equations. The resonance wavelengths are in agreement with the semi-analytical model [Y. Takakura, Phys. Rev. Lett. 86, 5601 (2001)], which solves the wave equations by using the Rayleigh field expansion. Our formulae, however, show great resonant enhancement of a transmitted wave, while the Rayleigh expansion model predicts attenuation. The difference is attributed to the near-field subwavelength diffraction, which is not considered by the Rayleigh-like expansion models.

Enhanced transmission and reflection of few-cycle pulses by a single slit.

We show that a physical mechanism responsible for the enhanced transmission and reflection of ultrashort (few-cycle) pulses by a single subwavelength slit in a thick metallic film is the Fabry-Perot-like resonant excitation of stationary, quasistationary, and nonstationary waves inside the slit, which leads to the field enhancement inside and around the slit. The mechanism is universal for any pulse-scatter system, which supports the stationary resonances. We point out that there is a pulse duration limit below which the slit does not support the intraslit resonance.

Resonant backward scattering of light by a subwavelength metallic slit with two open sides

The backward scattering of TM-polarized light by a two-side-open subwavelength slit in a metal film is analyzed. We show that the reflection coefficient versus wavelength possesses a Fabry-Perot-like dependence that is similar to the anomalous behavior of transmission reported in the study [Y. Takakura, Phys. Rev. Lett. \textbf{86}, 5601 (2001)]. The open slit totally reflects the light at the near-to-resonance wavelengths. In addition, we show that the interference of incident and resonantly backward-scattered light produces in the near-field diffraction zone a spatially localized wave whose intensity is 10-10

Proposal for sub-femtosecond pulse generation with controlled carrier-envelope phase

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Anomalous backward scattering of light by a two-side-open subwavelength metallic slit

times greater than the incident wave, but one order of magnitude smaller than the intra-cavity intensity. The amplitude and phase of the resonant wave at the slit entrance and exit are different from that of a Fabry-Perot cavity.

Proposal for carrier-envelope-phase stable single-cycle attosecond pulse generation in the extreme-ultraviolet range.

A robust method for producing few-cycle pulses with controlled waveform in the EUV-VUV spectral range by coherent undulator radiation of relativistic ultrathin electron layers produced by inverse free-electron laser (IFEL) action is proposed. The realization of such exceptional pulses will enable time- and CEP-resolved measurements with less than 100 as resolution.

Efficient semiconductor source of multicycle terahertz pulses using intensity-modulated pump

The backward scattering of TM-polarized light by a two-side-open subwavelength slit in a metal film is analyzed. We show that the reflection coefficient versus wavelength possesses a Fabry-Perot-like dependence that is similar to the anomalous behavior of transmission reported in the study [Y. Takakura, Phys. Rev. Lett. 86, 5601 (2001)]. The open slit totally reflects the light at the near-to-resonance wavelengths. In addition, we show that the interference of incident and resonantly backward-scattered light produces in the near-field diffraction zone a spatially localized wave whose intensity is 10-103 times greater than the incident wave, but one order of magnitude smaller than the intra-cavity intensity. The amplitude and phase of the resonant wave at the slit entrance and exit are different from that of a Fabry-Perot cavity.