Polarization-induced size control and ablation dynamics of Ge nanostructures formed by a femtosecond laser

We report a method for controlling the size of a Ge (germanium) nanostructure by changing the angle between the ultrafast laser polarization and the crystal axis of Ge. The nanostructure size dependence on the laser polarization with respect to the Ge crystal axis exhibits a sinusoidal function with a minimum size at (100) axis. Moreover, the measurement of transient reflection reveals the presence of large anisotropies in both its amplitude and its relaxation dynamics with a minimum at (100) crystal axis. This implies that the observed anisotropic dependence of nanostructure size of Ge is followed by a different carrier density as well as its relaxation process, depending on the orientation of the Ge crystal axis only at near and above threshold fluence

Optical absorption and photoluminescence properties of the PPV nanotubes and nanowires

We measured optical absorption and time resolved photoluminescence decay properties of the PPV nanotubes and nanowires which were prepared by CVD polymerization using templates. When compared with bulk PPV films, their nano objects showed different optical properties, long photoluminescence decay time and higher photoluminescence efficiencies.X1110sci

Fabry-Perot effects in THz time-domain spectroscopy of plasmonic band-gap structures

Using terahertz time-domain spectroscopy, we study transmission in one-dimensional arrays of slits fabricated on metal plates by laser machining. The enhanced peaks of zero-order transmission spectra are attributed to the combined effects of Fabry-Perot and surface plasmon resonances. Angle dependence of transmission spectra shows that the strongly surface plasmon-enhanced peaks appear when the Fabry-Perot-type resonance is located nearby in energy. This means that surface waves traveling in the horizontal direction couple with nearest Fabry-Perot resonance to generate enhanced peaks. These results are in excellent agreement with theoretical calculations

Impedance matching plasmonic metamaterials to vacuum

We report on a 100% transmission in one- and two-dimensional plasmonic metamaterials in the terahertz frequency range. At a specific frequency at which the plasmonic meta material is perfectly impedance matched to vacuum, the metal material becomes essentially invisible. In the case of a two-dimensional array of square holes, perfect impedance matching occurs when the effective dielectric constant becomes -2 for samples with hole coverages larger than 0.19. In a one-dimensional array of slits, transmission becomes 100% when a symmetric eigenmode is excited and therefore the system becomes effectively impedance-matched

Shape resonance omni-directional terahertz filters with near-unity transmittance

Terahertz transmission filters have been manufactured by perforating metal films with various geometric shapes using femtosecond laser machining. Two dimensional arrays of square, circular, rectangular, c-shaped, and epsilon-shaped holes all support over 99% transmission at specific frequencies determined by geometric shape, symmetry, polarization, and lattice constant. Our results show that plasmonic structures with different geometric shaped holes are extremely versatile, dependable, easy to control and easy to make terahertz filters

Invisible plasmonic meta-materials through impedance matching to vacuum

We report on perfect transmission in two-dimensional plasmonic matamaterials in the terahertz frequency range, in which zeroth order transmittance becomes essentially unity near specific resonance frequencies. Perfect transmission may occur when the plasmonic metamaterials are perfectly impedance matched to vacuum, which is equivalent to designing an effective dielectric constant around epsilon(r) = -2. When the effective dielectric constant of the metamaterial is tuned towards epsilon(r) and the hole coverage is larger than 0.2, strong evanescent field builds up in the near field, making perfect transmission possible. (c) 2005 Optical Society of America