- 标题
- 摘要
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- 实验方案
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Estimation of the Rashba Strength from Second Harmonic Generation in 2D and 3D Hybrid Organic-Inorganic Perovskites
摘要： The Rashba e?ect (RE), caused by concurrent spin-orbit coupling and structural inversion asymmetry (SIA), has been invoked to explain outstanding optoelectronic properties of hybrid organic inorganic perovskites (HOIPs). The SIA in HOIPs also manifests itself in second harmonic generation (SHG). Here we establish a quantitative relation between the RE strength and the low-frequency SHG value in 2D and 3D HOIPs using a newly developed e?ective-mass model. The calculated SHG, which exhibits one- and two-photon resonances between the valence and conduction bands, approaches a ?nite value at low frequencies. Using the measured SHG values in literature, the estimated RE strength is 10?3 eV?A for 3D CH3NH3PbI3 and 4 × 10?2 eV?A for 2D (C4H9NH3)2PbI4. Our results facilitate a simple and reliable determination of the RE strength of 2D and 3D HOIPs and help quantify the impact of RE on various properties in HOIPs.
关键词： second harmonic generation,Rashba effect,hybrid organic-inorganic perovskites,structural inversion asymmetry,spin-orbit coupling
更新于2025-09-23 15:21:01
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Direct mineralogical imaging of economic ore and rock samples with multi-modal nonlinear optical microscopy
摘要： Multi-modal nonlinear optical (NLO) microscopy, including stimulated Raman scattering (SRS) and second harmonic generation (SHG), was used to directly image mineralogical features of economic ore and rock samples. In SRS/SHG imaging, ore samples generally require minimal preparation and may be rapidly imaged, even in their wet state. 3D structural details, at submicron resolution, are revealed tens of microns deep within samples. Standard mineral imaging based on scanning electron microscopy (SEM), with elemental analysis via energy dispersive X-Ray spectroscopy, was used to independently validate the mineral composition of the samples. Spatially-resolved SRS from dominant Raman-resonant bands precisely maps the locations of specific minerals contained within the samples. SHG imaging reveals locally non-centrosymmetric structures, such as quartz grains. Competing absorption and nonlinear scattering processes, however, can reduce contrast in SRS imaging. Importantly, the correlation between standard electron microscopy and multi-modal NLO optical microscopy shows that the latter offers rapid image contrast based on the mineral content of the sample.
关键词： mineralogical imaging,second harmonic generation,stimulated Raman scattering,rock samples,nonlinear optical microscopy,economic ore
更新于2025-09-23 15:21:01
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IN SITU SECOND-HARMONIC GENERATION CIRCULAR DICHROISM WITH SUBMONOLAYER SENSITIVTIY
摘要： In this work, we present an experimental setup for the in situ and ex situ study of the optical activity of samples, which can be prepared under ultra-high vacuum (UHV) conditions by second-harmonic generation circular dichroism (SHG-CD) over a broad spectral range. The use of a racemic mixture as a qualified reference for the anisotropy factor is described and, as an example, the chiroptical properties of 1.5 μm thick (multilayers) as well as sub-monolayer thin films of the R- and S-enantiomer of 1,1'-Bi-2-naphthol (BINOL) evaporated onto BK7 substrates were investigated.
关键词： Submonolayer sensitivity,Second-harmonic generation circular dichroism,Circular-linear dichroism
更新于2025-09-23 15:21:01
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Photo-induced meta-stable polar conformations in polystyrene microspheres revealed by time-resolved SHG microscopy
摘要： Photo-induced second harmonic generation (SHG) was observed in centrosymmetric polystyrene (PS) microspheres using 1064 nm, sub-nanosecond laser-pulse irradiation. The SHG signal gradually increased upon stationary laser-pulse irradiation. After stopping the irradiation, the increased SHG signal disappeared in approximately 30 min. When the PS bead was irradiated by laser pulses again, the SHG signal reappeared with similar temporal behavior, which was attributed to the probable growth and contraction of meta-stable polar conformations of PS chain segments under periodic photo-thermal stimuli.
关键词： second harmonic generation,photo-induced,polystyrene microspheres,time-resolved SHG microscopy
更新于2025-09-23 15:19:57
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Structural, spectral and nonlinear optical analysis of Bis(2-methyllactato)borate tetrahydrate: a new nonlinear optical crystal for laser applications
摘要： A new nonlinear optical crystal, ‘Bis(2-methyllactato)borate tetrahydrate’ (BMBT) has been crystallized by slowly evaporating the solvent. It crystallizes in the space group P21212. Sharp peaks present in powder XRD profile reveals the good crystallinity. Its transmission bandwidth (220 nm – 1100 nm) suggest that it can be used to generate UV radiation upto 220 nm and also in optoelectronic applications. Vibrations of functional groups (B-O, CH3, CO) associated with the crystal structure have been identified through FTIR and FT-Raman spectral studies. OH stretching vibrations have been observed near 3000 cm-1 clearly endorses the existence of water molecule in the BMBT structure. The chemical shifts observed in 1H and 13C NMR spectral results establishes the molecular structure of BMBT crystal. Second harmonic generation (SHG) efficiency is obtained as 0.9 times of KDP. The third order nonlinear susceptibility (χ3), nonlinear refractive index (n2) and nonlinear absorption co-efficient (β) were found using Z-scan technique. χ3 of title crystal is found to be 4.16 X10-5 esu. The existence of SHG efficiency and the enhanced χ3 value are due to the hydrogen bonded intermolecular interactions present in the BMBT crystal structure. The observed results suggest that BMBT can be used in Q-switching, mode locking and optical sensors like night vision devices.
关键词： Crystal structure,Z-scan analysis,crystal growth,NMR spectroscopy,second harmonic generation
更新于2025-09-23 15:19:57
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Periodically Poled MgO:LiNbO <sub/>3</sub> , MgO:LiTaO <sub/>3</sub> and KTiOPO <sub/>4</sub> Crystals for Laser Light Frequency Conversion
摘要： We present the recent achievements in periodical poling in MgO doped single crystals of lithium niobate (LN), lithium tantalate (LT) and potassium titanyl phosphate (KTP) based on the experimental study of the domain structure evolution by the complementary high-resolution domain visualization methods [1]. The crystals with tailored periodically poled domain structures (PPLN and PPLT) produced with nano-scale period reproducibility have been used for Second Harmonic Generation (SHG) and Optical Parametric Oscillation (OPO) based on quasi-phase-matched nonlinear optical wavelength conversion. The periodical poling techniques were based on the deep experimental and theoretical study of the mechanisms of domain growth and domain wall motion in these crystals. The wide range of wall velocities with two orders of magnitude difference was observed for switching in a uniform electric field [2,3]. The kinetic maps allowed analyzing the spatial distribution of the wall motion velocities and classifying the walls by velocity ranges. The distinguished slow, fast, and superfast types of domain walls in KTP differed by their orientation. The revealed increase in the wall velocity with deviation from low-index crystallographic planes for slow and fast walls was considered in terms of determined step generation and anisotropic kink motion. It was shown that the polarization reversal in KTP with artificial surface dielectric layer leads to formation and growth of the large number of narrow domain streamers oriented strictly along [010] direction with about ten times higher velocity (6-60 mm/s) than the domain walls (2-5.5 mm/s). Study of the static domain structures demonstrated that the streamers are formed by [100] and [010]-oriented domain walls. The streamer width was about 500 nm and the distance between the neighboring streamers – about 100 nm. The global domain kinetics during the poling process at elevated temperatures has been studied by in situ optical observation which allowed us to reveal the main characteristics of the poling process at elevated temperatures. It has been shown that the periodically poled area propagates from the edges to the middle of the electrode pattern. The interfering effect of essential increasing of the bulk conductivity during poling has been studied and several ways to overcome this problem have been proposed. The static domain images revealed by chemical etching were visualized by optical and scanning probe microscopy. The influence of the spatially nonuniform electric field on the domain kinetics has been studied for finite-size electrodes of various shapes. The key role of the field anomalies at the electrode corners, ends, and edges in the nucleation process has been revealed by computer simulations and confirmed experimentally. Essential acceleration of the switching at the boundaries of the electrode patterns (so called “pattern effect”) has been explained. The optimized design of the electrode pattern was based on experimental results and computer simulation. The fan-out periodical domain structures created in 3-mm-thick MgO:LN wafers allowed us to realize the widely tunable OPO generation with the signal wave from 2.5 to 4.5 μm using the 1.053 μm pump. The possibility of producing the elements with thickness up to 10 mm for high-power application has been discussed. The peridical domain struture with period of 40 μm was created in KTP single crystals for OPO generation at 2.4 μm using the 1.053 μm pump. The abilities and perspectives of producing the elements with submicron periods has been discussed. The optimized periodical poling techniques have been used for creation of ridge waveguides in periodically poled MgOLN single crystals. The high-index contrast of obtained multi-mode waveguides allowed tuning of the SHG wavelength from 510 to 570 nm using the 1.064 μm pump. The deep knowledge of the domain structure evolution at elevated temperatures and relaxation of the high bulk conductivity along the charged domain walls MgO:LN and MgO:LT allowed us to optimize the periodical poling technique and to produce high-fidelity domain patterns.
关键词： domain structure evolution,MgO:LiTaO3,KTiOPO4,Second Harmonic Generation,Optical Parametric Oscillation,MgO:LiNbO3,Periodically Poled
更新于2025-09-23 15:19:57
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Editorial: Advances in Label Free Tissue Imaging With Laser Scanning Microscopy Techniques
摘要： Significant efforts are being spent at the time being for transferring various laser scanning microscopy (LSM) techniques to the realm of tissue characterization, because of their potential to circumvent some of the most important disadvantages of traditional histopathology approaches based on excisional biopsy and tissue staining. Although conventional histopathology is currently regarded as a golden standard for the diagnosing pathologies that reflect in tissular modification (e.g., cancers), limitations such as long diagnosis time, invasiveness, artifacts, sampling error, time consumption, high costs, and interpretive variability make such approaches to be impractical in many scenarios, while also placing considerable pressure on the sustainability of healthcare systems around the world. The potential of LSM techniques to contribute to overcoming these aspects derives from their “non-invasive” character. They can exploit various endogenous optical signals generated by tissues upon interaction with a laser beam and are able to provide optical sections (virtual biopsies) that reflect the tissular architecture at controlled depths. Many studies reported to date showed that LSM techniques can provide label-free information of similar pathologic relevance to the information collected for characterization/confirmation purposes with traditional histopathology approaches. These techniques are thus capable of probing optical properties of tissues with deep implications for resolving important anatomical and physiological aspects which represent hallmarks for disease predisposition and progression. To date techniques such as Confocal Laser Scanning Microscopy (CLSM) [1], Fluorescence Lifetime Imaging (FLIM) [2], Two-Photon Excited Fluorescence Microscopy (TPEF) [2–6], Second Harmonic Generation Microscopy (SHG) [5, 6], Third Harmonic Generation Microscopy (THG) [4], Coherent Anti-Stokes Raman Scattering Microscopy (CARS) [3, 7], as well as other LSM variants such as the Brillouin Microscopy [8] have already been demonstrated to be powerful tools for investigating tissue morphology, functionality, and biochemical composition with high spatial and temporal resolution. In the opinion of many, these techniques, together with investigations approaches based on their combined use, will soon become the central element of the default tissue characterization frameworks for both ex vivo and in vivo assays. Furthermore, emerging LSM techniques exploiting various ingenious strategies to achieve superresolved images in a label-free manner [9–12] are also likely to be transferred soon toward applications addressing tissue imaging.
关键词： tissue imaging,two photon excitation fluorescence microscopy,Brillouin microspectroscopy,laser scanning microscopy,second harmonic generation microscopy
更新于2025-09-23 15:19:57
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Enhancement of the second harmonic signal of nonlinear crystals by self-assembled gold nanoparticles
摘要： In second harmonic generation (SHG), the energy of two incoming photons, e.g., from a femtosecond laser, can be combined in one outgoing photon of twice the energy, e.g., by means of a nonlinear crystal. The SHG efficiency, however, is limited. In this work, the harvested signal is maximized by composing a hybrid system consisting of a nonlinear crystal with a dense coverage of plasmonic nanostructures separated by narrow gaps. The method of self-assembled diblock-copolymer-based micellar lithography with subsequent electroless deposition is employed to cover the whole surface of a lithium niobate (LiNbO3) crystal. The interaction of plasmonic nanostructures with light leads to a strong electric near-field in the adjacent crystal. This near-field is harnessed to enhance the near-surface SHG signal from the nonlinear crystal. At the plasmon resonance of the gold nanoparticles, a pronounced enhancement of about 60-fold SHG is observed compared to the bare crystal within the confocal volume of a laser spot.
关键词： gold nanoparticles,nonlinear crystal,second harmonic generation,lithium niobate,plasmonic nanostructures,electroless deposition,self-assembled diblock-copolymer-based micellar lithography,LiNbO3,SHG
更新于2025-09-23 15:19:57
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Polar coupling enabled nonlinear optical filtering at MoS2/ferroelectric heterointerfaces
摘要： Complex oxide heterointerfaces and van der Waals heterostructures present two versatile intrinsically different platforms for exploring emergent quantum phenomena and designing new functionalities. The rich opportunity offered by the synergy between these two classes of materials, however, is yet to be charted. Here, we report an unconventional nonlinear optical filtering effect resulting from the interfacial polar alignment between monolayer MoS2 and a neighboring ferroelectric oxide thin film. The second harmonic generation response at the heterointerface is either substantially enhanced or almost entirely quenched by an underlying ferroelectric domain wall depending on its chirality, and can be further tailored by the polar domains. Unlike the extensively studied coupling mechanisms driven by charge, spin, and lattice, the interfacial tailoring effect is solely mediated by the polar symmetry, as well explained via our density functional theory calculations, pointing to a new material strategy for the functional design of nanoscale reconfigurable optical applications.
关键词： nonlinear optical filtering,second harmonic generation,MoS2/ferroelectric heterointerfaces,density functional theory,polar symmetry
更新于2025-09-23 15:19:57
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Off-Resonance Control and All-Optical Switching: Expanded Dimensions in Nonlinear Optics
摘要： The theory of non-resonant optical processes with intrinsic optical nonlinearity, such as harmonic generation, has been widely understood since the advent of the laser. In general, such effects involve multiphoton interactions that change the population of each input optical mode or modes. However, nonlinear effects can also arise through the input of an off-resonant laser beam that itself emerges unchanged. Many such effects have been largely overlooked. Using a quantum electrodynamical framework, this review provides detail on such optically nonlinear mechanisms that allow for a controlled increase or decrease in the intensity of linear absorption and fluorescence and in the efficiency of resonance energy transfer. The rate modifications responsible for these effects were achieved by the simultaneous application of an off-resonant beam with a moderate intensity, acting in a sense as an optical catalyst, conferring a new dimension of optical nonlinearity upon photoactive materials. It is shown that, in certain configurations, these mechanisms provide the basis for all-optical switching, i.e., the control of light-by-light, including an optical transistor scheme. The conclusion outlines other recently proposed all-optical switching systems.
关键词： absorption,nonlinear optics,all-optical switch,resonance energy transfer,fluorescence,FRET,optical transistor,multiphoton process,laser action,second harmonic generation
更新于2025-09-23 15:19:57