Laser-induced optical nonlinearity in a Li-rich glass

The selective crystallization of a photosensibilized lithium silicate glass after a light emitting diode (280 nm) and a nanosecond laser (355 nm) UV irradiation and subsequent heat treatment was studied. Using a focused beam of the laser allows successive drawing regions in which the formation of silver nanoparticles after 500°C heat treatment of the glass co-doped with silver and cerium ions takes place. It is shown that this treatment is a necessary step for the growth of sodium metasilicate crystals under the second thermal treatment of the glass at 600 °C, while these regions demonstrate second optical harmonic generation of 1064 nm nanosecond laser radiation.

Competing processes in generation of the third optical harmonic in air under femtosecond infrared repetitively pulsed excitation

Parametric interaction of electromagnetic and gravitational waves with the radiation generation at the third harmonic wavelength is one of the ways to detect gravitational interaction in a material medium. To implement the effect in question, superstrong fields must be used, but in this case competing nonlinear processes arise, leading to the generation of the third harmonic as a result of laser radiation filamentation. This paper investigates the characteristics of the radiation recorded for femtosecond (250 fs) laser pulses with a wavelength of λ = 1032 nm focused in air. The threshold pump power made it possible to observe the formation of a filament with concomitant generation of narrow-band radiation at the focus of the lens at the third harmonic wavelength λ = 344 nm. The research presents spectral and spatial dependences of ultraviolet radiation (λ = 344 nm) at pumping power of infrared radiation (λ = 1032 nm) of 500 mW. Energy dependences of the third harmonic generation efficiency in the power range from 150 to 1750 mW are obtained.

Recent Advancements in Optical Harmonic Generation Microscopy: Applications and Perspectives

Second harmonic generation (SHG) and third harmonic generation (THG) microscopies have emerged as powerful imaging modalities to examine structural properties of a wide range of biological tissues. Although SHG and THG arise from very different contrast mechanisms, the two are complimentary and can often be collected simultaneously using a modified multiphoton microscope. In this review, we discuss the needed instrumentation for these modalities as well as the underlying theoretical principles of SHG and THG in tissue and describe how these can be leveraged to extract unique structural information. We provide an overview of recent advances showing how SHG microscopy has been used to evaluate collagen alterations in the extracellular matrix and how this has been used to advance our knowledge of cancers, fibroses, and the cornea, as well as in tissue engineering applications. Specific examples using polarization-resolved approaches and machine learning algorithms are highlighted. Similarly, we review how THG has enabled developmental biology and skin cancer studies due to its sensitivity to changes in refractive index, which are ubiquitous in all cell and tissue assemblies. Lastly, we offer perspectives and outlooks on future directions of SHG and THG microscopies and present unresolved questions, especially in terms of overall miniaturization and the development of microendoscopy instrumentation.

Second optical harmonic generation by a layered plasmon nanoparticle

The features of second harmonic generation by a spherical nanoparticle with a plasmon shell are theoretically studied. In the framework of the quasistatic perturbation theory, expressions for the oscillating at a doubled frequency induced dipole and quadrupole moments of a particle were obtained. The second harmonic radiation power was calculated, which showed the resonance nature of the dependence of power on the exciting wavelength. Moreover, the positions of the radiation power resonances significantly depend on the dielectric permittivity of the particle core and its size.