Study of nonlinear optical phenomena in silicon nanowires

This work studies generation of second and third harmonics in arrays of vertically oriented silicon nanowires (SiNWs) encapsulated into a silicone membrane and separated from the growth substrate. The structures were produced by plasma-chemical etching of silicon substrate resulting in a formation of homogeneous arrays of SiNWs. Such SiNW-based membranes demonstrated efficient infrared-to-visible light conversion by generation of second and third harmonic signals visible by a naked eye. This study contributes to the development of technology of optical devices based on silicon and presents a new route for visualization of infrared radiation.

Study of nonlinear optical phenomena in silicone films encapsulated with SiO2 and Si/SiO2 spherical particles

Infrared converters to visible range are in demand for creation of optoelectronic devices, infrared visualizers and other non-linear optical devices. In this work we study nonlinear optical properties of monodisperse SiO2 and Si/SiO2 spheres encapsulated into silicone films. The fabricated silicone films containing SiO2 spheres demonstrated a bright third harmonic generation signal, and films with Si/SiO2 spheres demonstrated a significant second harmonic generation signal in the whole visible range. The developed materials and methods provide a platform for future infrared to visible converters based on silicon.

Spatiotemporal imaging of 2D polariton wave packet dynamics using free electrons

Coherent optical excitations in two-dimensional (2D) materials, 2D polaritons, can generate a plethora of optical phenomena that arise from the extraordinary dispersion relations that do not exist in regular materials. Probing of the dynamical phenomena of 2D polaritons requires simultaneous spatial and temporal imaging capabilities and could reveal unknown coherent optical phenomena in 2D materials. Here, we present a spatiotemporal measurement of 2D wave packet dynamics, from its formation to its decay, using an ultrafast transmission electron microscope driven by femtosecond midinfrared pulses. The ability to coherently excite phonon-polariton wave packets and probe their evolution in a nondestructive manner reveals intriguing dispersion-dependent dynamics that includes splitting of multibranch wave packets and, unexpectedly, wave packet deceleration and acceleration. Having access to the full spatiotemporal dynamics of 2D wave packets can be used to illuminate puzzles in topological polaritons and discover exotic nonlinear optical phenomena in 2D materials.

Time reversed optical waves by arbitrary vector spatiotemporal field generation

Lossless linear wave propagation is symmetric in time, a principle which can be used to create time reversed waves. Such waves are special “pre-scattered” spatiotemporal fields, which propagate through a complex medium as if observing a scattering process in reverse, entering the medium as a complicated spatiotemporal field and arriving after propagation as a desired target field, such as a spatiotemporal focus. Time reversed waves have previously been demonstrated for relatively low frequency phenomena such as acoustics, water waves and microwaves. Many attempts have been made to extend these techniques into optics. However, the much higher frequencies of optics make for very different requirements. A fully time reversed wave is a volumetric field with arbitrary amplitude, phase and polarisation at every point in space and time. The creation of such fields has not previously been possible in optics. We demonstrate time reversed optical waves with a device capable of independently controlling all of light’s classical degrees of freedom simultaneously. Such a class of ultrafast wavefront shaper is capable of generating a sequence of arbitrary 2D spatial/polarisation wavefronts at a bandwidth limited rate of 4.4 THz. This ability to manipulate the full field of an optical beam could be used to control both linear and nonlinear optical phenomena.

Multi-pulse laser-induced bubble formation and nanoparticle aggregation using MoS2 nanoparticles

Understanding of how particles and light interact in a liquid environment is vital for optical and biological applications. MoS2 has been shown to enhance nonlinear optical phenomena due to the presence of a direct excitonic resonance. Its use in biological applications is predicated on knowledge of how MoS2 interacts with ultrafast (< 1 ps) pulses. In this experiment, the interaction between two femtosecond pulses and MoS2 nanoparticles suspended in liquid is studied. We found that the laser pulses induce bubble formation on the surface of a nanoparticle and a nanoparticle aggregate then forms on the surface of the trapped bubble. The processes of formation of the bubble and the nanoparticle aggregation are intertwined.

Structural diversity of hydrogen-bonded complexes comprising phenol-based and pyridine-based components: NLO properties and crystallographic and spectroscopic studies

Synthesis of compounds with improved physicochemical properties, including nonlinear optical phenomena such as second harmonic generation, might be considered as one of the most challenging aspects of crystal engineering.

Nonlinear Optical Phenomena in a Silicon-Smectic A Liquid Crystal (SALC) Waveguide

Liquid crystals (LCs) are organic materials characterized by the intermediate properties between those of an isotropic liquid and a crystal with a long range order. The LCs possess strong anisotropy of their optical and electro-optical properties. In particular, LCs possess strong optical nonlinearity. LCs are compatible with silicon-based technologies. Due to these unique properties, LCs are promising candidates for the development of novel integrated devices for telecommunications and sensing. Nematic liquid crystals (NLCs) are mostly used and studied. Smectic A liquid crystals (SALCs) have a higher degree of long range order forming a layered structure. As a result, they have lower scattering losses, specific mechanisms of optical nonlinearity related to the smectic layer displacement without the mass density change, and they can be used in nonlinear optical applications. We theoretically studied the nonlinear optical phenomena in a silicon-SALC waveguide. We have shown theoretically that the stimulated light scattering (SLS) and cross-phase modulation (XPM) caused by SALC nonlinearity can occur in the silicon-SALC waveguide. We evaluated the smectic layer displacement, the SALC hydrodynamic velocity, and the slowly varying amplitudes (SVAs) of the interfering optical waves.