Volume 98, Issue 3, 01 August 2005
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS
98(2005); http://dx.doi.org/10.1063/1.1999828View Description Hide Description
We show that a weakly focused ultrashort laser pulse with tilted intensity front can efficiently excite a terahertz surface wave via phase-matched optical rectification at the surface of a semiconductor. The surface wave is excited by a strip of nonlinear polarization moving along the semiconductor surface with subluminous velocity. The amplitude and power of the radiated surface wave are calculated. For a optical pulse with a peak intensity of , we estimate the energy conversion coefficient to be at the surface of GaAs. The direct excitation of surface waves at terahertz frequencies can be particularly attractive for terahertz spectroscopy of semiconductor surfaces.
98(2005); http://dx.doi.org/10.1063/1.1999031View Description Hide Description
Using both analytic theory and first-principles finite-difference time-domain simulations, we introduce a displacement sensing mechanism using photonic crystal slabs coupled in the near-field regime. In this regime, the operating characteristics are completely different from conventional resonant optical sensors, and high sensitivity can be obtained without the use of highly reflecting mirrors. This enables high displacement sensitivity combined with low sensitivity to wavelength and to structural disorders, thereby simplifying operation and fabrication of high-sensitivity displacement sensors.
98(2005); http://dx.doi.org/10.1063/1.2006224View Description Hide Description
In this paper, the behavior at resonance of split ring resonators (SRRs) and other related topologies, such as the nonbianisotropic SRR and the broadside-coupled SRR, are studied. It is shown that these structures exhibit a fundamental resonant mode (the quasistatic resonance) and other higher-order modes which are related to dynamic processes. The excitation of these modes by means of a properly polarized time varying magnetic and/or electric fields is discussed on the basis of resonator symmetries. To verify the electromagnetic properties of these resonators, simulations based on resonance excitation by nonuniform and uniform external fields have been performed. Inspection of the currents at resonances, inferred from particle symmetries and full-wave electromagnetic simulations, allows us to predict the first-order dipolar moments induced at the different resonators and to develop a classification of the resonances based on this concept. The experimental data, obtained in SRR-loaded waveguides, are in agreement with the theory and point out the rich phenomenology associated with these planar resonant structures.
98(2005); http://dx.doi.org/10.1063/1.1999827View Description Hide Description
We have investigated high-frequency ultrasound generated by single laser pulses in thin aluminum foils as a function of the laser fluence. Laser-pulse durations of and were used to compare the ultrasound generated in two very different regimes: thermoelastic and ablation. The measured rear-surface displacement induced by the ultrasound pulse is similar after propagation through the foils for the two laser-pulse durations in the fluence range of . For fluences greater than the ablation threshold (0.25 and for the and pulses, respectively), the ultrasound amplitude generated by the laser pulse is increased significantly due to absorption of laser energy by the ablating plasma. This is not observed for the laser pulse since ablation is produced well after the laser-pulse irradiation of the target. The measured surface displacement as a function of laser fluence is compared to the calculations of a one-dimensional fluid code for both laser-pulse durations. The model calculations agree in many ways with the experimental results, but some discrepancies are observed.