T. V. Dolgova

Giant microcavity enhancement of second-harmonic generation in all-silicon photonic crystals

Second-harmonic generation (SHG) spectra of single and coupled porous silicon-based photonic crystal microcavities are studied in both frequency and wave vector domains. For the fundamental field resonant to the microcavity mode the second-harmonic intensity is enhanced by 102 times in comparison with that outside the photonic band gap. SHG spectroscopy in identical microcavities coupled through the intermediate Bragg reflector reveals two SHG peaks if the fundamental field is in resonance with the splitted mode of coupled microcavities. The spatial confinement of the resonant fundamental radiation is directly probed at the microcavity cleavage by scanning near-field optical microscopy.

Ultrafast all-optical tuning of direct-gap semiconductor metasurfaces

Optical metasurfaces are regular quasi-planar nanopatterns that can apply diverse spatial and spectral transformations to light waves. However, metasurfaces are no longer adjustable after fabrication, and a critical challenge is to realise a technique of tuning their optical properties that is both fast and efficient. We experimentally realise an ultrafast tunable metasurface consisting of subwavelength gallium arsenide nanoparticles supporting Mie-type resonances in the near infrared. Using transient reflectance spectroscopy, we demonstrate a picosecond-scale absolute reflectance modulation of up to 0.35 at the magnetic dipole resonance of the metasurfaces and a spectral shift of the resonance by 30 nm, both achieved at unprecedentedly low pump fluences of less than 400 μJ cm–2. Our findings thereby enable a versatile tool for ultrafast and efficient control of light using light.Metasurfaces are not adjustable after fabrication, and a critical challenge is to realise a technique of tuning their optical properties that is both fast and efficient. Here, Shcherbakov et al. realise an ultrafast tunable metasurface with picosecond-scale large absolute reflectance modulation at low pump fluences.

Giant optical second-harmonic generation in single and coupled microcavities formed from one-dimensional photonic crystals

The nonlinear optical properties of one-dimensional all-solid-state photonic-crystal microcavities (MCs) are experimentally studied by second-harmonic generation (SHG) spectroscopy in both the frequency and the wave-vector domains. The studied single and coupled MCs are formed by the alternating of mesoporous silicon layers of different porosities. When the fundamental radiation is in resonance with the MC mode the second-harmonic intensity is enhanced by a factor of approximately 102. The resonant SHG response is compared with the off-resonance response, as the fundamental wavelength is outside the photonic bandgap. The splitting of the modes of two identical coupled MCs is observed in the wave-vector domain spectrum of enhanced SHG. The SHG enhancement is attributed to the combined effects of the spatial localization of the fundamental field in the MC spacer and the fulfillment of the phase-matching conditions. The confinement of the resonant fundamental field is probed directly at the MC cleavage by a scanning near-field optical microscope. The role of the phase matching that is associated with the giant effective dispersion in the spectral vicinity of the MC mode is deduced from a comparison with the SHG peaks at both edges of the photonic bandgap.

Giant Third-Harmonic in Porous Silicon Photonic Crystals and Microcavities

A giant enhancement (no less than by 103) of the optical third-harmonic generation in one-dimensional porous silicon microcavities and photonic crystals was observed experimentally. The enhancement is due to the resonant enhancement of the fundamental field in the cavity mode and the fulfillment of the phase matching condition at the photonic band gap edges of the photonic crystal and in the vicinity of the microcavity mode.

Nonlinear magneto-optical Kerr effect in garnet magnetophotonic crystals

Magnetization-induced second-harmonic (SH) generation is studied in magnetophotonic crystals formed from a magnetic garnet spacer located between two dielectric Bragg reflectors, at the resonance of the fundamental radiation with the cavity mode. Longitudinal nonlinear magneto-optical Kerr effect manifests itself in the rotation of the polarization plane of a reflected SH wave which reaches a value up to 250°/μm. A magnetization-induced variation of the SH intensity is observed in transversal configuration with magnetic contrast up to 0.3.

Magnetization-induced second- and third- harmonic generation in magnetophotonic crystals

The results of our recent studies of magnetization-induced nonlinear-optical second- and third-order effects in magnetophotonic crystals and magnetophotonic microcavities are surveyed. Magnetophotonic crystals (MPCs) are fabricated from a stack of four repetitions of lambda/4-thick layers of Bi-substituted yttrium iron garnet (Bi:YIG) and lambda/4-thick SiO2 layers. Magnetophotonic microcavities (MMCs) are formed from two dielectric (nonmagnetic) Bragg reflectors and ferromagnetic cavity spacers that are lambda/2-thick Bi:YIG layers. The nonlinear magneto-optical Kerr effect (NOMOKE), both in magnetization-induced second-harmonic generation (MSHG) and magnetization-induced third-harmonic generation (MTHG), is observed in MMCs at wavelengths of the resonant microcavity modes. Magnetization-induced variations of MSHG and MTHG intensities, as well as magnetization-induced shift of phase and rotation of polarization of second and third-harmonic waves, are observed in proper - transversal, longitudinal, or polar - NOMOKE configurations. Manyfold enhancement of the absolute values of both the MSHG and MTHG intensities are attributed to the localization of the resonant fundamental radiation in Bi:YIG microcavity spacers. The NOMOKE in MSHG intensity is observed in MPCs in the spectral range of photonic bandgap (PBG) edges. The MSHG intensity reveals enhancement by a factor of more than 10^2 if the fundamental wavelength is tuned in the vicinity of the PBG edge. This enhancement is attributed to the fulfillment of the phase-matching conditions for MSHG effect in layered structures with periodic modulation of both optical (magneto-optical) and nonlinear optical parameters.

Ultrafast polarization shaping with Fano plasmonic crystals.

Femtosecond-scale polarization state shaping is experimentally found in optical response of a plasmonic nanograting by means of time-resolved Stokes polarimetry. Simultaneous measurements of the Stokes parameters as a function of time reveal a remarkable alteration of the polarization state inside a single femtosecond pulse reflected from a plasmonic crystal due to the excitation of time-delayed polarization-sensitive surface plasmons with a highly birefringent Fano-type spectral profile. Time-dependent depolarization, indicating the sub-130-femtosecond polarization change inside the pulse, is experimentally found and described within an analytical model which predicts the fivefold enhancement of the polarization conversion effect with the use of a narrower time gate.

Femtosecond relaxation dynamics of surface plasmon-polaritons in the vicinity of fano-type resonance

Temporal modification of femtosecond laser pulses reflected from planar periodic metal nanostructures with resonant excitation of surface plasmon-polaritons is experimentally studied. Spectral time-resolved measurements of the second-order cross-correlation function performed with the pulse duration comparable with the surface plasmon-polariton relaxation time (about 100 fs) show the strong spectral dependence of the envelope of the reflected femtosecond pulse described by Fano-resonance parameters.

Plasmonic enhancement of linear birefringence and linear dichroism in anisotropic optical metamaterials

The resonant behavior of linear birefringence and linear dichroism spectra is found in anisotropic optical metamaterials made of noble metal thin films with stripes and rectangular hole nanoapertures forming one- or two-dimensional subwavelength gratings. Differences in effective refractive index and extinction coefficient for linearly polarized eigenstates are increased in spectral range of resonances of local and surface plasmon-polaritons at the normal incidence and reach the values of Δn ≃ 2.5 and Δκ ≃ 2.75, respectively.

Anisotropic Photonic Crystals and Microcavities Based on Mesoporous Silicon

A technique to prepare one-dimensional anisotropic photonic crystals and microcavities based on anisotropic porous silicon exhibiting optical birefringence has been developed. Reflectance spectra demonstrate the existence of a photonic band gap and of an allowed microcavity mode at the photonic band gap center. The spectral position of these bands changes under rotation of the sample about its normal and/or under rotation of the plane of polarization of the incident radiation. The dependence of the shift of the spectral position of the photonic band gap edges and of the microcavity mode on the orientation of the polarization vector of incident electromagnetic wave with respect to the optical axis of the photonic crystals and microcavities was studied.