Harmonic Generation Circular Dichroism Research Articles

Magneto-chiral Nonlinear Optical Effect with Large Anisotropic Response in Two-Dimensional Halide Perovskite.

The chiral organic-inorganic halide perovskites (OIHPs) are vital candidates for superior nonlinear optical (NLO) effects associated with circularly polarized (CP) light. NLO in chiral materials often couples with magnetic dipole (MD) transition, as well as the conventional electric dipole (ED) transition. However, the importance of MD transition in NLO process of chiral OIHPs has not yet been well recognized. Here, the circular polarized probe analysis of second harmonic generation circular dichroism (SHG-CD) provides the direct evidence that the contribution of MD leads to a large anisotropic response to CP lights in chiral OIHPs, (R-/S-MBACl)2PbI4. The thin films exhibit great sensitivity to CP lights over a wide wavelength range, and the g-value reaches up to 1.57 at the wavelength where the contribution of MD is maximized. Furthermore, it is also effective as CP light generator, outputting CP-SHG with maximum g-factor of 1.76 upon the stimulation of linearly polarized light. This study deepens the understanding of relation between chirality and magneto-optical effect, and such an efficient discrimination and generation of CP light signal is highly applicable for chirality-based sensor and optical communication devices.

Chirality‐Dependent Second‐Order Nonlinear Optical Effect in 1D Organic–Inorganic Hybrid Perovskite Bulk Single Crystal

AbstractThe introduction of chirality into organic–inorganic hybrid perovskites (OIHPs) is expected to achieve excellent photoelectric and nonlinear materials related to circular dichroism. Owing to the existence of asymmetric center and intrinsic chirality in the chiral OIHPs, the different efficiencies of second harmonic generation (SHG) signal occurs when the circularly polarized light (CPL) with different phases passes through the chiral crystal, which is defined as second harmonic generation circular dichroism (SHG‐CD). Here, the SHG‐CD effect is developed in bulk single crystals of chiral one‐dimensional (1D) [(R/S)‐3‐aminopiperidine]PbI4. It is the first time that CPL is distinguished using chirality‐dependent SHG‐CD effect in OIHPs bulk single crystals. Such SHG‐CD technology extends the detection range to near infrared region (NIR). In this way, the anisotropy factor (gSHG‐CD) through SHG‐CD signal is as high as 0.21.

Chirality-Dependent Second-Order Nonlinear Optical Effect in 1D Organic-Inorganic Hybrid Perovskite Bulk Single Crystal.

The introduction of chirality into organic-inorganic hybrid perovskites (OIHPs) is expected to achieve excellent photoelectric and nonlinear materials related to circular dichroism. Owing to the existence of asymmetric center and intrinsic chirality in the chiral OIHPs, the different efficiencies of second harmonic generation (SHG) signal occurs when the circularly polarized light (CPL) with different phases passes through the chiral crystal, which is defined as second harmonic generation circular dichroism (SHG-CD). Here, the SHG-CD effect is developed in bulk single crystals of chiral one-dimensional (1D) [(R/S)-3-aminopiperidine]PbI4 . It is the first time that CPL is distinguished using chirality-dependent SHG-CD effect in OIHPs bulk single crystals. Such SHG-CD technology extends the detection range to near infrared region (NIR). In this way, the anisotropy factor (gSHG-CD ) through SHG-CD signal is as high as 0.21.

Understanding laser desorption with circularly polarized light.

We present aspects of emerging optical activity in thin racemic 1,1'-Bi-2-naphthol films upon irradiation with circularly polarized light and subsequent resonant two-photon absorption in the sample. Thorough analysis of the sample morphology is conducted by means of (polarization-resolved) optical microscopy and scanning electron microscopy (SEM). The influence of crystallization on the nonlinear probing technique (second harmonic generation circular dichroism [SHG-CD]) is investigated. Optical activity and crystallization are brought together by a systematic investigation in different crystallization regimes. We find crystallization to be responsible for two counter-acting effects, which arise for different states of crystallization. Measuring crystallized samples offers the best signal-to-noise ratio, but it limits generation of optical activity due to self-assembly effects. For suppression of crystallization on the other hand, there is a clear indication that enantiomeric selective desorption is responsible for the generation of optical activity in the sample. We reach the current resolution limit of probing with SHG-CD, as we suppress the crystallization in the racemic sample during desorption. In addition, intensity-dependent measurements on the induced optical activity reveal an onset threshold (≈0.7 TW cm-2), above which higher order nonlinear processes impair the generation of optical activity by desorption with CPL.

Circular Dichroism in the Second Harmonic Field Evidenced by Asymmetric Au Coated GaAs Nanowires.

Optical circular dichroism (CD) is an important phenomenon in nanophotonics, that addresses top level applications such as circular polarized photon generation in optics, enantiomeric recognition in biophotonics and so on. Chiral nanostructures can lead to high CD, but the fabrication process usually requires a large effort, and extrinsic chiral samples can be produced by simpler techniques. Glancing angle deposition of gold on GaAs nanowires can (NWs) induces a symmetry breaking that leads to an optical CD response that mimics chiral behavior. The GaAs NWs have been fabricated by a self-catalyzed, bottom-up approach, leading to large surfaces and high-quality samples at a relatively low cost. Here, we investigate the second harmonic generation circular dichroism (SHG-CD) signal on GaAs nanowires partially covered with Au. SHG is a nonlinear process of even order, and thus extremely sensitive to symmetry breaking. Therefore, the visibility of the signal is very high when the fabricated samples present resonances at first and second harmonic frequencies (i.e., 800 and 400 nm, in our case).

Wavelength-Dependent Second Harmonic Generation Circular Dichroism for Differentiation of Col I and Col III Isoforms in Stromal Models of Ovarian Cancer Based on Intrinsic Chirality Differences.

Extensive remodeling of the extracellular matrix (ECM) occurs in many epithelial cancers. For example, in ovarian cancer, upregulation of collagen isoform type III has been linked to invasive forms of the disease, and this change may be a potential biomarker. To examine this possibility, we implemented wavelength-dependent second harmonic generation circular dichroism (SHG-CD) imaging microscopy to quantitatively determine changes in chirality in ECM models comprised of different Col I/Col III composition. In these models, Col III was varied between 0 and 40%, and we found increasing Col III results in reduced net chirality, consistent with structural biology studies of Col I and III in tissues where the isoforms comingle in the same fibrils. We further examined the wavelength dependence of the SHG-CD to both optimize the response and gain insight into the underlying mechanism. We found using shorter SHG excitation wavelengths resulted in increased SHG-CD sensitivity, where this is consistent with the electric-dipole-coupled oscillator model suggested previously for the nonlinear chirality response from thin films. Moreover, the sensitivity is further consistent with the wavelength dependency of SHG intensity fit to a two-state model of the two-photon absorption in collagen. We also provide experimental calibration protocols to implement the SHG-CD modality on a laser scanning microscope. We last suggest that the technique has broad applicability in probing a wide range of diseased states with changes in collagen molecular structure.

Chiral light intrinsically couples to extrinsic/pseudo-chiral metasurfaces made of tilted gold nanowires.

Extrinsic or pseudo-chiral (meta)surfaces have an achiral structure, yet they can give rise to circular dichroism when the experiment itself becomes chiral. Although these surfaces are known to yield differences in reflected and transmitted circularly polarized light, the exact mechanism of the interaction has never been directly demonstrated. Here we present a comprehensive linear and nonlinear optical investigation of a metasurface composed of tilted gold nanowires. In the linear regime, we directly demonstrate the selective absorption of circularly polarised light depending on the orientation of the metasurface. In the nonlinear regime, we demonstrate for the first time how second harmonic generation circular dichroism in such extrinsic/pseudo-chiral materials can be understood in terms of effective nonlinear susceptibility tensor elements that switch sign depending on the orientation of the metasurface. By providing fundamental understanding of the chiroptical interactions in achiral metasurfaces, our work opens up new perspectives for the optimisation of their properties.

Second harmonic circular dichroism by self-assembled metasurfaces [Invited

It is possible to obtain an optical response from metasurfaces that exhibit second-order circular dichroism, thanks to the recent successes in nanotechnology, opening the way to new functionalities on a spatial scale of a few hundred nanometers. The second-order nonlinear response of this kind of nanostructured material is an interesting and fascinating issue, as becomes clear from an overview of second harmonic generation and, in particular, the nonlinear circular dichroism raised by metasurfaces of different morphologies and material components, realized by means of self-assembling methods. In this article, we show that the second harmonic generation circular dichroism is very sensitive and useful in the field of nanotechnology characterization.

Second Harmonic Generation: Second Harmonic Generation Circular Dichroism from Self‐Ordered Hybrid Plasmonic–Photonic Nanosurfaces (Advanced Optical Materials 3/2014)

Second Harmonic Generation: Second Harmonic Generation Circular Dichroism from Self‐Ordered Hybrid Plasmonic–Photonic Nanosurfaces (Advanced Optical Materials 3/2014)

Second Harmonic Generation Circular Dichroism from Self‐Ordered Hybrid Plasmonic–Photonic Nanosurfaces

Hybrid structures composed by self-ordered dielectric nanospheres and partially covered by gold nanocrescents, produce efficient second harmonic generation signals due to the cooperative effect of localized plasmon excitation and 2D Bragg gratings. Asymmetries in the geometric shape of the gold nanocrescents induce a circularly polarized optical response.

Studying the chirality of polymerized 10,12-tricosadynoic acid LB films using SHG polarized angle dependence and SHG-CD method

Using optical second harmonic generation (SHG) measurements, polymerized 10,12-tricosadynoic acid (PTDA) monolayer on quartz substrate were investigated. SHG polarized angle dependence measurements and optical second harmonic generation circular dichroism (SHG-CD) measurements were carried out to reveal the chirality of PTDA monolayer. It was revealed that the chiral PTDA films were formed when subphase solution contains Cu(II) ions, while the chirality for PTDA LB films were not formed when subphase solution is pure water or contains Cd(II) ions. The conformational change of the polydiacetylene chain due to metal ions was found the most probable origin.

Twist-Grain-Boundary Structure in theB4Phase of a Bent-Core Molecular System Identified by Second Harmonic Generation Circular Dichroism Measurement

Second harmonic generation circular dichroism (SHG CD) measurements are performed on the B4 phase of a bent-core molecular system. Numerical analysis of SHG CD incorporating magnetic-dipole as well as electric-dipole interaction shows that the B4 phase is in a twist-grain-boundary structure with the helical axis along the bent direction of the molecules. The result is extremely important in the sense that achiral molecules are spontaneously optically resolved, i.e., deracemization, the chiral domains of which give rise to huge chiral nonlinear optical effect.

Cytochrome c at Model Membrane Surfaces: Exploration via Second Harmonic Generation-Circular Dichroism and Surface-Enhanced Resonance Raman Spectroscopy

The novel nonlinear optical method of second harmonic generation-circular dichroism (SHG-CD) has been used to follow the adsorption and redox properties of a peripheral membrane protein, horse heart cytochrome c, adsorbed at several model membrane surfaces. The SHG-CD response is shown to be affected by the oxidation state of the heme within surface-adsorbed cytochrome c, as is consistent with the sensitivity of SHG to the chirality of the heme. SHG-CD measurements show that adsorbed cytochrome c is reducible by ascorbate at alkanethiol surfaces, but not at phospholipid/alkanethiol hybrid bilayer membranes (HBMs). The adsorption of cytochrome c at the model membrane surfaces was verified by surface plasmon resonance. Surface-enhanced resonance Raman measurements show that cytochrome c adsorbed on a hybrid bilayer membrane retains the Fe-heme conformation associated with solution-phase cytochrome c and is reducible by applying potential to the supporting electrode. The inability of ascorbic acid to reduce ...