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We report on measurements of the anisotropy of velocities and attenuation of GHz-frequency acoustic phonons in a cubic MgO crystal at room temperature. They are used to quantify the strong anisotropy of the Grüneisen parameter and calculate the attenuation anisotropy for Rayleigh surface acoustic waves. These observations constitute important building blocks for better understanding of ultrafast laser-based magneto-acoustic and nonlinear acoustic experiments at ultrahigh frequencies. [ABSTRACT FROM AUTHOR]

Microwave magnetic impedance spectra are obtained for (x = 0.46–0.88) films in a DC magnetic field of 0‒0.7 T. The modulus of microwave impedance in films with x = 0.76 is found to fall by as much as 6% upon magnetization. The maximum negative microwave magnetic impedance of the films is established along with its shift from 2.2 to 0.4 GHz as x rises. A striped magnetic structure with oppositely directed magnetizations of neighboring stripes is observed. [ABSTRACT FROM AUTHOR]

Cycling between the crystalline and amorphous phases of 25-nm-thick GeSb films induced by single laser pulses of duration of 100 fs or 20 ps is investigated in the 400–800 nm wavelength range. The time evolution of the phase transformations has been studied with picosecond resolution real-time reflectivity measurements at a probe wavelength of 514.5 nm and also with femtosecond and picosecond pump-probe measurements. Upon picosecond irradiation, three regimes are identified: for wavelengths below ∼550 nm and above ∼750 nm, the total time to transform between the crystalline and amorphous phases is of the order of 10–24 ns while in the intermediate wavelength range of 600–750 nm, the transformation time is only ∼650 ps. Upon 100 fs irradiation, the transformation times are observed to decrease with increasing wavelength with the shortest times of ∼5 ns for crystallization and ∼10 ns for amorphization, both occurring at 800 nm. This behavior is discussed in terms of how the wavelength-dependent refractive index of the phases involved influences the initial supercooling of the molten volume and the subsequent resolidification scenario. [ABSTRACT FROM AUTHOR]

The detection of ultrashort laser-generated acoustic pulses at a metal surface and the reconstruction of the acoustic strain profile are investigated. A 2 ps-long acoustic pulse generated in an SrRuO3 layer propagates through an adjacent gold layer and is detected at its surface by a reflected probe pulse. We show that the intricate shape of the transient reflectivity waveform and the ability to resolve acoustic pulses shorter than the optical skin depth are controlled by a single parameter, which is determined by the ratio of the real and imaginary parts of the photoelastic constant of the material. We also demonstrate a Fourier transform-based algorithm that can be used to extract acoustic strain profiles from transient reflectivity measurements. [ABSTRACT FROM AUTHOR]

We discuss the implications of a frequency-dependent complex dielectric function ε( ω) of a metal for the interpretation of scanning near-field optical microscopy (SNOM) measurements in the vicinity of metallic nanoapertures. For subwavelength slits in gold films we observe distinct spatial intensity oscillations in the near-field signal for specific wavelengths in the visible spectrum. These oscillations of the SNOM signal far away from the nanoslit are ascribed to a constructive interference between the propagating surface plasmon (SP) with light scattered parallel to the gold–air interface. In these spatial SNOM-signal oscillations information about the surface plasmon dielectric function is encoded which can be extracted, for example, in surface plasmon interferometry for applications as sensors or waveguides. [ABSTRACT FROM AUTHOR]

We present experimental investigations of ultrafast phase transitions in tellurium following excitation by an intense femtosecond laser pulse. Femtosecond time-resolved polarization-sensitive microscopy is used to monitor the temporal evolution of optical anisotropy (birefringence) of the irradiated material. The decay of optical anisotropy associated with the loss of order in crystalline tellurium is fluence-dependent and occurs within 0.5–3 ps. © 2002 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Femtosecond laser-induced structural transitions in graphite were studied by time-resolved optical anisotropy measurements. The decay of the anisotropic reflectivity seems to indicate a loss of long-range order on a subpicosecond time scale, which is much faster than the electron–phonon relaxation time. This observation confirms the nonthermal nature of the structural transition. © 2002 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]