Alexey V. Maslov

Spectrally resolved resonant propulsion of dielectric microspheres

Use of resonant light forces opens up a unique approach to high-volume sorting of microspherical resonators with much higher uniformity of resonances compared to that in coupled-cavity structures obtained by the best semiconductor technologies. In this work, the spectral response of the propulsion forces exerted on polystyrene microspheres near tapered microfibers is directly observed. The measurements are based on the control of the detuning between the tunable laser and internal resonances in each sphere with accuracy higher than the width of the resonances. The measured spectral shape of the propulsion forces correlates well with the whispering-gallery mode resonances in the microspheres. The existence of a stable radial trap for the microspheres propelled along the taper is demonstrated. The giant force peaks observed for 20-μm spheres are found to be in a good agreement with a model calculation demonstrating an efficient use of the light momentum for propelling the microspheres.

Imaging of sub-wavelength structures radiating coherently near microspheres

Using a two-dimensional model, we show that the optical images of a sub-wavelength object depend strongly on the excitation of its electromagnetic modes. There exist modes that enable the resolution of the object features smaller than the classical diffraction limit, in particular, due to the destructive interference. We propose to use such modes for super-resolution of resonant structures such as coupled cavities, metal dimers, or bowties. A dielectric microsphere in contact with the object forms its magnified image in a wide range of the virtual image plane positions. It is also suggested that the resonances may significantly affect the resolution quantification in recent experimental studies.

Microspherical photonics: Sorting resonant photonic atoms by using light

A method of sorting microspheres by resonant light forces in vacuum, air, or liquid is proposed. Based on a two-dimensional model, it is shown that the sorting can be realized by allowing spherical particles to traverse a focused beam. Under resonance with the whispering gallery modes, the particles acquire significant velocity along the beam direction. This opens a unique way of large-volume sorting of nearly identical photonic atoms with 1/Q accuracy, where Q is the resonance quality factor. This is an enabling technology for developing super-low-loss coupled-cavity structures and devices.

Microspherical Photonics: Ultra-High Resonant Propulsion Forces

In 1977, Arthur Ashkin and Joseph M. Dziedzic demonstrated that optical forces possess narrow spectral peaks determined by the internal resonances in microdroplets. These resonant optical forces open up a unique way of high-volume sorting of nearly identical “photonic atoms,” which may be used as building blocks for coupled-cavity structures and devices. However, to date, only relatively subtle resonant effects have been observed.

Fundamental limits of super-resolution microscopy by dielectric microspheres and microfibers

In recent years, optical super-resolution by microspheres and microfibers emerged as a new paradigm in nanoscale label-free and fluorescence imaging. However, the mechanisms of such imaging are still not completely understood and the resolution values are debated. In this work, the fundamental limits of super-resolution imaging by high-index barium-titanate microspheres and silica microfibers are studied using nanoplasmonic arrays made from Au and Al. A rigorous resolution analysis is developed based on the object’s convolution with the point-spread function that has width well below the conventional (~λ/2) diffraction limit, where λ is the illumination wavelength. A resolution of ~λ/6-λ/7 is demonstrated for imaging nanoplasmonic arrays by microspheres. Similar resolution was demonstrated for microfibers in the direction perpendicular to the fiber axis with hundreds of times larger field-of-view in comparison to microspheres. Using numerical solution of Maxwell’s equations, it is shown that extraordinary close point objects can be resolved in the far field, if they oscillate out of phase. Possible super-resolution using resonant excitation of whispering gallery modes is also studied.

Giant resonant light forces in microspherical photonics

Giant optical propelling velocities of 15–20 μm polystyrene microspheres are observed in evanescent fiber-taper-to-microsphere couplers. The results demonstrate a possibility of parallel particle-sorting according to the frequency of their whispering gallery mode resonances.

Large-signal coherent control of normal modes in quantum-well semiconductor microcavity

We demonstrate coherent control of the cavity-polariton modes of a quantum-well semiconductor microcavity in a two-color scheme. The cavity enhancement of the excitonic nonlinearity gives rise to a large signal; modulating the relative phase of the excitation pulses between zero and π produces a differential reflectivity (ΔR/R) of up to 20%. The maximum nonlinear signal is obtained for cocircular pump and probe polarization. Excitation-induced dephasing is responsible for the incoherent nonlinear response, and limits the contrast ratio of the optical switching.

Frequency upshifting of electromagnetic radiation via oblique incidence on an ionization front

Frequency upshifting of electromagnetic radiation impinging on a relativistically moving ionization front is theoretically investigated. Unlike previous works in this field treating the case of normal incidence and qualitatively similar case of oblique incidence of a transverse electric polarized wave, oblique incidence of a transverse magnetic polarized wave on the front is considered. The peculiarities of the case under consideration are connected with the generation of Langmuir waves behind the front and Brewsters phenomenon. We present a complete analysis of the incident wave transformation including analysis of the frequencies and amplitudes of the waves excited ahead of and behind the front. Special emphasis is made on energy transformation in the case when a wave packet is incident on the front. In particular, we show that even for negligible angles of incidence, energy losses via transformation into Langmuir waves may be very high (up to /spl sim/60%). In general, generation of Langmuir waves may play a significant role in the plasma-based radiation sources with relativistic ionization fronts.

Extraction of the frequency-domain optical response function of a periodically modulated medium with short optical pulses

The interaction of a short optical pulse with a medium whose optical properties are periodically modulated depends on the modulation phase at the moment of the pulse arrival. A technique of extracting the linear optical response function of such a medium to the cw optical field with a judiciously chosen series of short pulses rather than with cw optical fields is presented. An example of using the technique in numerical simulations is given, and a possible experimental arrangement is discussed. In particular, this technique may be convenient for extracting the optical properties of quantum wells modulated by a terahertz field.

Scattering of a surface plasmon polariton by rapid plasma creation in a semiconductor slab

The scattering of a surface plasmon polariton in a semiconductor slab by rapid plasma creation in the slab is explored. As a result of the scattering, the initial surface wave breaks up into two frequency-upshifted surface waves propagating in opposite directions along the slab and generates a static magnetic field and a dc inside the slab and transient radiation that escapes the slab. A part of the initial energy can also be trapped inside the slab owing to total internal reflection and forms frequency-upshifted guided modes of the slab. The scattering of a surface wave by a rapidly created plasma allows the analysis of basic processes that occur in nonstationary media in the presence of boundaries. The practical applications include the control of propagation of guided radiation in integrated optics devices, coupling the radiation out of waveguides, and ultrafast transient spectroscopy of an electron–hole plasma in semiconductors.