A. J. Sievers

Study of intrinsic localized vibrational modes in micromechanical oscillator arrays

Intrinsic localized modes (ILMs) have been observed in micromechanical cantilever arrays, and their creation, locking, interaction, and relaxation dynamics in the presence of a driver have been studied. The micromechanical array is fabricated in a 300 nm thick silicon-nitride film on a silicon substrate, and consists of up to 248 cantilevers of two alternating lengths. To observe the ILMs in this experimental system a line-shaped laser beam is focused on the 1D cantilever array, and the reflected beam is captured with a fast charge coupled device camera. The array is driven near its highest frequency mode with a piezoelectric transducer. Numerical simulations of the nonlinear Klein-Gordon lattice have been carried out to assist with the detailed interpretation of the experimental results. These include pinning and locking of the ILMs when the driver is on, collisions between ILMs, low frequency excitation modes of the locked ILMs and their relaxation behavior after the driver is turned off.

Attenuation and coupling of far infrared surface plasmos

Abstract Far infrared surface plasmon propagation has been studied on Ge coated Au and Pb surfaces. Attenuation coefficients in reasonable agreement with Drude theory are found. Anomalously large surface plasmon attenuation coefficients for bare metal surfaces reported by earlier investigators are reinterpreted in terms of bulk wave packet spreading near the surface.

IR surface plasmon attenuation coefficients for Ag and Au films

Abstract We have remeasured the surface plasmon attenuation coefficients of Ag and Au films in the 10 μ wavelength region using a different coupling geometry than earlier investigators and find much smaller values. Good agreement with the Drude model is obtained when the optical relaxation time includes both the measured d.c. contribution and diffuse scattering of the electrons at the metal surface.

Far‐infrared properties of C60 and C70 compacts

The far‐infrared transmission of polycrystalline C60 and C70 compacts has been measured from 3 to 330 cm−1 as a function of temperature. Both intrinsic and impurity‐induced absorption bands are identified in these samples. The low temperature phase of C60 is observed to have two infrared active translational modes at 40.9 and 54.7 cm−1. Samples of C60 exposed to air before cooling to low temperatures contain several additional infrared bands which have been identified with adsorbed H2O vapor. A large isotope shift is observed for some of the bands when H2O is replaced by D2O, consistent with rotational or librational behavior. For C70 one strong intrinsic band is centered at 21 cm−1 and four much weaker bands occur at 28, 32, 52, and 64 cm−1. When doped with H2O vapor, C70 also produces several strong H2O impurity bands, some of which show isotopic shifts. The temperature dependence of five intramolecular C70 modes in the frequency range from 200 to 330 cm−1 is also reported.

Experimental Observation of the Bifurcation Dynamics of an Intrinsic Localized Mode in a Driven 1D Nonlinear Lattice

Linear response spectra of a driven intrinsic localized mode in a micromechanical array are measured as it approaches two fundamentally different kinds of bifurcation points. A linear phase mode associated with this autoresonant state softens in frequency and its amplitude grows as the upper frequency bifurcation point is approached, similar to the soft-mode kinetic transition for a single driven Duffing resonator. A lower frequency bifurcation point occurs when the four-wave-mixing partner of this same phase mode intercepts the top of the extended wave branch, initiating a second kinetic transition process.

Persistent infrared spectral hole burning of NO−2 ions in potassium halide crystals. I. Principle and satellite hole generation

New features are resolved within the internal vibrational mode spectra of NO−2 defects in KCl, KBr, and KI crystals at low temperatures using high‐resolution Fourier transform spectroscopy and persistent infrared spectral hole (PIRSH) burning separately and together. With interferometry it has been discovered that the vibrational linewidths of the different modes range over a factor of 300—from 0.01 cm−1 to ∼3 cm−1 and, with PIRSH burning, it has been demonstrated that the narrowest lines are inhomogeneously broadened while the broadest ones are homogeneously broadened. PIRSH’s have been found in some internal modes and combination bands of the NO−2 molecule when pumped with low‐intensity single‐mode lead salt diode lasers; however, detectable persistent holes are not produced in all of the modes because of a competition between hole production and relaxation by tunneling at low temperatures. This competition results in a hole burning intensity, below which hole relaxation overwhelms hole production and o...

High temperature vibrational fluorescence of CN- ions in alkali halides

Abstract Infrared fluorescence from vibrational levels of matrix isolated CN - ions has been studied in the temperature range of 300 K to 600 K. At 300 K the variation in the fluorescence lifetime from host to host is compatible with a multiphonon decay mechanism, but the measured temperature dependence does not agree with thermally induced multiphonon decay.

Far-infrared absorption spectrum of NaI:NaCl☆

Abstract Our identification of three infrared active modes associated with the Cl- impurity in NaI now permits a test of the small defect-space assumption currently used in lattice dynamics calculations.

Manipulation of Autoresonant Intrinsic Localized Modes in MEMs Arrays

The smallness of MEMS oscillators makes them an important platform for studying nonlinear phenomena. A unique feature, not shared by a harmonic system, is the dynamical steady state localization of some vibrations in driven nonlinear micromechanical lattices. Such an Intrinsic Localized Mode (ILM) is stable at any lattice site, and its position can be controlled by it interacting with an external field, a defect or another ILM. Both experiments and numerical simulations are used to explore the ILM‐impurity attractive and repulsive interactions in micro‐cantilever arrays in autoresonant states. The various findings reported here have a direct bearing on the application of nonlinear energy localization to implement smart functions in large‐scale MEMS arrays.

Vibrational relaxation dynamics of matrix‐isolated BH2D−2

Infrared spectroscopy, fluorescence, and incoherent saturation experiments have been performed on matrix‐isolated BH2D−2. We find that the 942 cm−1 vibrational mode of this molecule in KBr is unsaturable up to laser pump intensities of 1 MW/cm2 in marked contrast with the earlier measurements on ReO−4, which give a saturation intensity of 55 W/cm2. The different behavior for the light molecule is a result of one‐phonon decay to a nearby lower‐lying internal vibrational mode. Because of the small moment of inertia of the molecule high frequency librational modes provide a third‐order decay channel between this lowest frequency internal vibrational mode and the ground state.