O. Kolokoltsev

Hot spin-wave resonators and scatterers

A method used to achieve efficient optical control of a spin wave system in yttrium iron garnet is described. Using a focused laser beam, spin wave resonators and reflectors are induced by controlled local thermal demagnetization of a thin film. We report on the formation of an optically induced potential well for magnetostatic surface spin waves (MSSWs) leading to the formation of a high-Q MSSW resonator, and a high potential barrier that efficiently reflects magnetostatic backward volume waves.

Optimization of MO Bragg diffraction of guided optical waves by MSW in YIG films by using inclined magnetic bias field

Abstract We describe a new scheme of noncollinear interaction geometry for magneto-optical (MO) Bragg cells based on inelastic scattering of guided optical wave beams by magnetostatic waves in yttrium–iron–garnet (YIG) films. A great increase of the diffracted light intensity was obtained when using an inclined magnetization of the film, in the case when static in-plane magnetization component is directed along the light propagation direction. It is shown that the diffraction efficiency can be increased more than two times, at a specific value of the angle (≈35°) between the saturation magnetization vector and the normal to the film surface. The effect can be explained through a four-wave model of the diffraction process, which can take place in optical waveguides with MO gyrotropy. The results obtained by a simple analytical solution of the diffraction problem are found to be in good qualitative agreement with the experimental observations.

Synthesis and processing of pseudo noise signals by spin precession in Y3 Fe5O12 films

A simple method for synthesis of phase shift keying (PSK) signals in the microwave frequency range is presented. It is shown that the signal coding and processing can be efficiently realized by spin excitations in thin ferrite films. PSK signals are constructed through control of magnetization precession in a magnetic material by a pulsed magnetic field, and their compression is performed by a spin-wave based correlator, eliminating the need for semiconductor circuitry.

Mapping of spin wave propagation in a one-dimensional magnonic crystal

The formation and evolution of spin wave band gaps in the transmission spectrum of a magnonic crystal have been studied. A time and space resolved magneto inductive probing system has been used to map the spin wave propagation and evolution in a geometrically structured yttrium iron garnet film. Experiments have been carried out using (1) a chemically etched magnonic crystal supporting the propagation of magnetostatic surface spin waves, (2) a short microwave pulsed excitation of the spin waves, and (3) direct spin wave detection using a movable magneto inductive probe connected to a synchronized fast oscilloscope. The results show that the periodic structure not only modifies the spectra of the transmitted spin waves but also influences the distribution of the spin wave energy inside the magnonic crystal as a function of the position and the transmitted frequency. These results comprise an experimental confirmation of Bloch′s theorem in a spin wave system and demonstrate good agreement with theoretical o...

An active resonator based on magnetic films for near field microwave microscopy

An active resonator perturbation method is introduced as a sensitive and versatile way to probe material properties in near field microwave microscopy. An active ring microwave oscillator based on magnetostatic excitations in a yittrium iron garnet thin film has been developed with a coaxial near field probe connected directly to the resonator ring. The probe tunes the resonator’s emission frequency, and the high Q-factor of the magnetostatic oscillations allows for a very sensitive spatially resolved probe of surface impedance and material properties with a much larger dynamic range than conventional resonant probes for microwave microscopy.

Phase-reversal broad-band traveling-wave LiNbO/sub 3/ electrooptic modulator optimized for time-domain applications by a genetic algorithm

Several new nonperiodic spatial codes for phase-reversal coplanar waveguides (CPWs) used in the framework of the quasi-phase match technique (QPM) for broadening the optical response of z-cut LiNbO/sub 3/ electrooptic modulators (EOMs) are presented. The peculiarity of the codes is that they open the possibility for time-domain applications of EOMs based on nonperiodic QPM structures. They were obtained by using a specialized version of the genetic algorithm that generates an optimal length and number of the phase-reversal sections. The codes provide both flat amplitude and nearly linear phase frequency responses of the EOM within several frequency ranges important for fiber-optical/radio systems: from dc to 25, 40, and 90 GHz. The phase-reversal structures described here were optimized taking into account the CPW electrode losses and under the matching condition with 50 /spl Omega/-sources. They possess as low value of the drive voltage (V/sub /spl pi//, required for realization of 100% EO modulation efficiency) as possible for EOMs based on QPM, under the above conditions.

Acoustic Sensors Based on Amino-Functionalized Nanoparticles to Detect Volatile Organic Solvents

Love-wave gas sensors based on surface functionalized iron oxide nanoparticles has been developed in this research. Amino-terminated iron oxide nanoparticles were deposited, by a spin coating technique, onto the surface of Love-wave sensors, as a very reproducible gas-sensing layer. The gases tested were organic solvents, such as butanol, isopropanol, toluene and xylene, for a wide and low concentration range, obtaining great responses, fast response times of a few minutes (the time at which the device produced a signal change equal to 90%), good reproducibilities, and different responses for each detected solvent. The estimated limits of detection obtained have been very low for each detected compound, about 1 ppm for butanol, 12 ppm for isopropanol, 3 ppm for toluene and 0.5 ppm for xylene. Therefore, it is demonstrated that this type of acoustic wave sensor, with surface amino-functionalized nanoparticles, is a good alternative to those ones functionalized with metal nanoparticles, which result very expensive sensors to achieve worse results.

Analysis of near field microwave and conventional optical images

In this work we present near field microwave images of microelectronic circuits and their interpretation to complement the conventional optical analysis. We show a highly simplified design of a resonant probe with dynamically tunable capacitive coupling and with high sensitivity. Images were obtained by measuring the microwave reflection coefficient operating a 7 GHz. This design represents a simplified and highly effective approach to implementing near field microwave microscopy.

Swept Source OCT Beyond the Coherence Length Limit

We present a simple modification to a swept source optical system that overcomes the limitations in the depth range associated with the short coherence length of fast swept lasers. It is based on a wavelength dependent delay induced by a diffraction grating pair with negative dispersion incorporated in a reference arm of a Mach-Zehnder optical coherence tomography interferometer. The experimental depth range in air obtained was as large as 1.6 cm for a source coherence length of 4 mm.

Propagation of centimeter and millimeter spin-dipolar waves in nonuniform magnetic fields

Propagation of exchangeless spin-dipolar waves (SDW) of centimeter (f ∼ 3-20 GHz) and millimeter (f ∼ 30–60 GHz) wavelength ranges in ferrite films into nonuniform magnetic fields was researched analytically and numerically. Applied magnetic field is directed along film plane and it is slightly nonuniform in this plane. Proposed SDW propagation in magnetic fields was researched with complex geometric optics. We have shown a possibility of SDW type transformation from superficial SDW into backward volume SDW along propagation trajectory in both centimeter and millimeter wavelength range. An influence of electromagnetic delay on SDW propagation in nonuniform magnetic fields is essential in millimeter wavelength range and it can modify wave trajectories.