César L. Ordóñez-Romero

Null Ronchi-Hartmann test for a lens

A method to design Ronchi-Hartmann screens for improved alignment in the testing of fast plano-convex spherical lenses is presented. We design null screens that produce aligned straight fringes for observed patterns. The designs of these null screens are based on knowledge of the caustic by refraction. A qualitative test for a lens is presented.

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.

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.

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.

Bragg diffraction of guided optical waves by spin dipole waves in a ferrimagnetic heterostructure

The peculiarities of the Bragg diffraction of guided optical waves (GOWs) by spin-dipole waves (SDWs) in a ferrite heterostructure, based on Bi3Fe5O12 (BIG) thin film deposited on a standard YIG/GGG sample, is presented. It is shown that the efficiency of waveguide magneto-optic interaction between GOWs and SDWs in BIG/YIG/GGG can be 4–14 times large compared to the standard YIG/GGG waveguide, even in the case when the interacting waves are localized in YIG waveguide layer.