We study the distribution of the emitted power between the free-space modes and guided modes in a semiconductor nanowire. We analyze all possible dipole orientations and nanowire radii in the range from very small to comparable to the wavelength. Our theoretical approach is based on the Fourier transform technique and equivalent to the construction of Green’s function for a dipole at an arbitrary location inside the nanowire. We show that the total emitted power can exhibit rather pronounced oscillations as a function of the frequency and radius. The far-field pattern is also very sensitive to the frequency and radius, especially in the regime when leaky (or whispering gallery) modes with finite axial wave numbers are excited. We discuss the enhancement of emission into guided modes due to formation of Fabry-Pérot cavity in a finite length nanowire. Our results yield directly the extraction efficiencies and angular distribution of radiation of light-emitting diodes made of nanowires.

A theory that describes the optical-to-terahertz conversion of femtosecond laser pulses via optical rectification in a slab of an electro-optic material is developed. Two typical experimental situations—phase-matched regime (ZnTe excited with $780\mathrm{nm}$ optical pump) and non-phase-matched regime ($\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_3$ excited with $800\mathrm{nm}$ optical pump and GaAs excited with $1.56\mu \mathrm{m}$ optical pump)—are considered. The theory accounts for the transverse size of the laser beam and allows us to explore the dependence of the conversion efficiency on laser focusing. We trace the temporal dynamics of the optical-to-terahertz conversion inside the slab and study the angular distribution of the terahertz emission from the slab. The optimal parameters (such as laser transverse size and crystal thickness) maximizing the terahertz yield for ZnTe and GaAs are calculated.

A scheme for efficient generation of broadband terahertz radiation by a femtosecond laser pulse propagating in a planar sandwichlike structure is proposed. The structure consists of a thin nonlinear core cladded with prisms made of a material with low terahertz absorption. The focused into a line laser pulse propagates in the core as a leaky or waveguide mode and emits Cherenkov wedge of terahertz waves in the cladding. We developed a theory that describes terahertz generation in such a structure and calculated spatial distribution of the generated terahertz field, its energy spectrum and optical-to-terahertz conversion efficiency. The developed theory predicts the conversion efficiency of up to several percent in a 1 cm long and 1 cm wide Si–LiNbO3–Si sandwich structure with a 20 μm thick nonlinear layer pumped by 8.5 μJ Ti:sapphire laser with pulse duration of 100 fs.

We investigate the electromagnetic force experienced by a microparticle supporting high-quality whispering gallery modes that are excited by a surface wave. Our theoretical approach is based on an analytical representation of the solution of the scattering problem with a subsequent numerical treatment. It accounts rigorously for the interaction of the microparticle with the waveguiding surface and allows us to establish the balances of electromagnetic power and momentum flow for the system. We show that the resonant excitation of the whispering gallery modes and suppression of the transmitted surface wave lead to an almost complete transformation of the momentum flow of the initial surface wave into the propelling force on the microparticle. The validation of the momentum balance justifies the definition of the momentum flow of the surface wave as the ratio of carried power and phase velocity. A simple approximate relation between the propelling force and the power of the transmitted surface wave is also introduced. The transverse force can be either attractive or repulsive depending on the particle-to-surface distance, particle size, and operating frequencies, and it can significantly exceed the value of the propelling force. A comparison with a microparticle excited by a plane wave is also included.

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We experimentally demonstrate an efficient electro-optic sampling scheme based on Cherenkov phase matching of broadband terahertz radiation with 800-nm femtosecond probe beam in a 0.5 mm-thick LiNbO₃ crystal coupled to a Si prism. The electro-optic signal from a Cherenkov-phase-matched LiNbO₃ crystal is found to be comparable to that with a 4 mm-thick ZnTe crystal using a collinear phase matching. The Cherenkov phase matching technique can be achieved with any probe wavelength and hence has an advantage over the collinear phase matching method.