Noncolinear Second-Harmonic Generation Pairs and Their Scatterings in Nd3+:SBN Crystals with Needle-Like Ferroelectric Domains

Second-harmonic generation in Nd3＋ ：SBN crystal with needle-like ferroelectric with aperiodic domain structures is investigated. Two pairs of second harmonic （SH） waves appearing in lines are observed in unpoled Nd3＋ ：SBN crystals with aperiodic needle-like domains. A pair of SH waves emit from the exit face, whose intensities are angle-dependent. The angular dependence is corresponding to the spatial frequency spectrum of the aperiodic domain structure. Another pair of SH waves emit from both the side surfaces, which are mainly the scattered SH waves by needle-like domain walls and obey the theory of Rayleigh scattering.

Optical force-induced nonlinearity and self-guiding of light in human red blood cell suspensions

Osmotic conditions play an important role in the cell properties of human red blood cells(RBCs),which are crucial for the pathological analysis of some blood diseases such as malaria.Over the past decades,numerous efforts have mainly focused on the study of the RBC biomechanical properties that arise from the unique deformability of erythrocytes.Here,we demonstrate nonlinear optical effects from human RBCs suspended in different osmotic solutions.Specifically,we observe self-trapping and scattering-resistant nonlinear propagation of a laser beam through RBC suspensions under all three osmotic conditions,where the strength of the optical nonlinearity increases with osmotic pressure on the cells.This tunable nonlinearity is attributed to optical forces,particularly the forward-scattering and gradient forces.Interestingly,in aged blood samples(with lysed cells),a notably different nonlinear behavior is observed due to the presence of free hemoglobin.We use a theoretical model with an optical force-mediated nonlocal nonlinearity to explain the experimental observations.Our work on light self-guiding through scattering biosoft-matter may introduce new photonic tools for noninvasive biomedical imaging and medical diagnosis.

Phonon-assisted upconversion in twisted two-dimensional semiconductors

Phonon-assisted photon upconversion(UPC)is an anti-Stokes process in which incident photons achieve higher energy emission by absorbing phonons.This letter studies phonon-assisted UPC in twisted 2D semiconductors,in which an inverted contrast between UPC and conventional photoluminescence(PL)of WSe2 twisted bilayer is emergent.A 4-fold UPC enhancement is achieved in 5.5°twisted bilayer while PL weakens by half.Reduced interlayer exciton conversion efficiency driven by lattice relaxation,along with enhanced pump efficiency resulting from spectral redshift,lead to the rotation-angle-dependent UPC enhancement.The counterintuitive phenomenon provides a novel insight into a unique way that twisted angle affects UPC and light-matter interactions in 2D semiconductors.Furthermore,the UPC enhancement platform with various superimposable means offers an effective method for lighting bilayers and expanding the application prospect of 2D stacked van der Waals devices.

Giant excitonic upconverted emission from two-dimensional semiconductor in doubly resonant plasmonic nanocavity

Phonon-assisted upconverted emission is the heart of energy harvesting,bioimaging,optical cryptography,and optical refrigeration.It has been demonstrated that emerging two-dimensional(2D)semiconductors can provide an excellent platform for efficient phonon-assisted upconversion due to the enhanced optical transition strength and phonon-exciton interaction of 2D excitons.However,there is little research on the further enhancement of excitonic upconverted emission in 2D semiconductors.Here,we report the enhanced multiphoton upconverted emission of 2D excitons in doubly resonant plasmonic nanocavities.Owing to the enhanced light collection,enhanced excitation rate,and quantum efficiency enhancement arising from the Purcell effect,an upconverted emission amplification of>1000-fold and a decrease of 2~3 orders of magnitude in the saturated excitation power are achieved.These findings pave the way for the development of excitonic upconversion lasing,nanoscopic thermometry,and sensing,revealing the possibility of optical refrigeration in future 2D electronic or excitonic devices.