Yehuda Braiman

Disorder-enhanced synchronization

Abstract We find that an increase in the disorder of an array of Josephson junctions can lead to significant improvement in the synchronization of the array. Both this effect and the opposite, more expected behavior are seen over a broad parameter range.

Microwave‐induced ’’Devil’s Staircase’’ structure and ’’chaotic’’ behavior in current‐fed Josephson junctions

We have obtained the various types of I‐V characteristics measured experimentally and in analog simulations, by merely changing the junction and the microwave parameters within the same resistively shunted junction model with purely sinusoidal current‐phase relation. It was found that the subharmonic steps do exist in the limit βc→0, though they can have finite rounding without thermal noise. The statistical properties of the ’’chaotic’’ solutions wer e discussed and their effective temperature was defined and calculated.

Effect of normal vibration on friction in the atomic force microscopy experiment

We studied the effect of periodic normal (out-of-plane) surface vibrations on friction in an atomic force microscope experiment. Vibration frequency was varied in the range of 1–100kHz, and vibration amplitude was varied in the range of a few nanometers. We observed a reduction of a few orders of magnitude in friction coefficient due to the periodic vibrations. Friction reduction is over a wide range of vibration frequencies and amplitudes. Very low values (of the order of 0.01) of friction coefficient were measured. Our numerical simulation based on a minimalist modeling qualitatively agrees with the experimental results. Based on numerical simulations, a mechanism of friction reduction and/or increase with normal vibrations is proposed.

Injection locking of individual broad-area lasers in an integrated high-power diode array

We report experimental results on the injection locking of individual multimode broad-area high-power laser (one-in-a-time) in a linear array bar consisting of 19 lasers driven by a common current source. Each broad-area laser, capable of generating a beam with a power of 1 W, is injection locked to a single-longitudinal and transverse mode with less than 0.5 mW of injection power. The injection-locked broad-area laser shows very narrow linewidth close to the injection laser regardless of the output power. Our research suggests that the matching of the injection wavelength to one of the free-running modes of lasers in the array is the essential condition for achieving coherent operation of the array via injection locking.

Coherent beam combining of high power broad-area laser diode array with a closed-V-shape external Talbot cavity

We have coherently combined a high-power broad-area laser diode array by using a feedback loop closed off-axis external Talbot cavity. The off-axis feedback from two gratings provides transverse-mode control of broad-area lasers. The Talbot configuration of the external cavity implements diffractive coupling among laser diodes. Feedback from two gratings increases external cavity quality factor and spectrum selection capability. As a result, spatial coherence was improved and spectral linewidth was narrowed down. The high visibility of the far-field profile indicates that high spatial coherence was achieved. We also observed symmetric far-field profiles indicating that laser array was phase locked to in-phase and out-of-phase super-modes, respectively. Transition between these super-modes was observed by tuning one gratings tilted angle.

Torsional spring constant obtained for an atomic force microscope cantilever

In this letter, a method to measure the torsional spring constant of a microcantilever is described. The cantilever was twisted laterally without any normal load by inducing the Lorentz force. An electrical current was applied to the cantilever in a magnetic field, and the torsional resonance frequency of the cantilever was obtained. Based on the observation that the torsional resonance frequency is the same as the second resonance peak of the thermally vibrating cantilever, the ratio of deflection spring constant to torsional spring constant is easily obtained from a simple relationship. For the cantilever used here, the torsional spring constant is 11.24 N/m, 28 times greater than the deflection spring constant.

Coherent addition of high power laser diode array with a V-shape external Talbot cavity.

We designed a V-shape external Talbot cavity for a broad-area laser diode array and demonstrated coherent laser beam combining at high power with narrow spectral linewidth. The V-shape external Talbot cavity provides good mode-discrimination and does not require a spatial filter. A multi-lobe far-field profile generated by a low filling-factor phase-locked array is confirmed by our numerical simulation.

Phase model analysis of two laser with injected field

Abstract We study the dynamics of two coupled solid state lasers subject to an injected field. A singular perturbation technique is used to reduce the full set of rate equations; we present a comprehensive bifurcation analysis of the resulting phase model. We find four distinct routes to full entrainment as the injected field amplitude increases; bifurcation diagram predicts that the entrainment (reflected in the total intensity) does not monotonically improve with the injected field strength. Our numerical simulations suggest that the reduced phase model captures the relevant dynamics well beyond the asymptotic regime in which it is derived.

Simultaneous injection locking of couples of high-power broad-area lasers driven by a common current source

We experimentally demonstrate the simultaneous injection locking of pairs of high-power broad-area laser diodes in a 19-laser array driven by a common current source. Each pair is injection locked by use of a single-mode low-power semiconductor laser. The frequency and phase locking are verified bythe optical spectrum and the interference pattern between the injection-locked lasers. The influence of frequency detuning on the (simultaneous) injection behavior has been experimentally clarified. We validate a necessary condition for the injection locking of a broad-area laser array.

Nanotribology and nanoscale friction

Tribology is the science and technology of contacting solid surfaces in relative motion, including the study of lubricants, lubrication, friction, wear, and bearings. It is estimated that friction and wear cost the U.S. economy 6% of the gross national product (Persson, 2000). For example, 5% of the total energy generated in an automobile engine is lost to frictional resistance. The study of nanoscale friction has a technological impact in reducing energy loss in machines, in microelectromechanical systems (MEMS), and in the development of durable, low-friction surfaces and ultra-thin lubrication films.