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The second harmonic generation microscope (SHGM) constructs images of intensity distributions of SH waves produced by the interaction of fundamental waves with a polar material. We have developed this nonlinear optical microscope in order to make possible nondestructive, three-dimensional (3D) observations of various kinds of inorganic and organic...
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... Concerning materials science, SHM has shown exceptionally good performance for analyzing different features of non-linear crystals [5,10], and it is particularly useful for 3D imaging of non-linear photonic devices. On the one hand, the boundaries between ferroelectric domains can be detected [11], thus allowing the mapping of complex non-linear structures [12] in materials such as in LiNbO 3 or LiTaO 3 . ...
In this work we apply second harmonic microscopy to the analysis of damage tracks inscribed by femtosecond laser irradiation in a Nd:YAG crystal. While second harmonic generation is not expected in the bulk of this centrosymmetric material, the 2D and 3D images obtained via second harmonic microscopy show that the induced micro-modification of the crystal structure leads to a localized generation of the nonlinear signal. The nature of this modification and its dependence on irradiation and detection parameters is discussed. These findings demonstrate the capability of second harmonic microscopy for the morphological analysis of written structures in Nd:YAG and open the door for the design and fabrication of new nonlinear structures to be integrated in novel photonic devices.
... Early developments of SHG microscopy sought to demonstrate the utility of the technique.[91,92, 21] Since then, SHG microscopy has been extensively developed and employed in the studies of biological and inorganic materials.[93,94] Modern SHG microscopes are continually trying to push the boundaries of conventional SHG imaging by implement unique optical geometries and illumination schemes. ...
This dissertation details the development of second-order nonlinear optical techniques for the elucidation
of crystallographic structure by second harmonic generation. Two main goals were achieved
during the research study. Firstly, a model of the second harmonic response from cubic media was
developed by extracting the signal contributions from a variety of polarization sensitive measurements
with two different excitation geometries. This was performed for the first time for a series
of crystallographic orientations for materials with both bulk and surface dipole polarizations. It
was found that second harmonic generation is capable of of crystallographic orientation determination
due to its inherent structure sensitivity. Further studies are necessary to determine the
extent at which surface and bulk dipole contributions interfere at the surface. The contribution
from higher order multipole terms need to be examined for developing a more robust model. In order
to utilize second harmonic orientation analysis for heterogeneous samples a single-pixel second
harmonic generation microscope was developed. The new microscope utilized an advanced computation
algorithm for reconstructing undersampled images based on compressive sensing theory.
The single-pixel second harmonic generation microscope was found to outperform traditional measurement
modes and enhance data acquisition times and sensitivity down to single photon counting
levels. Current limitations of the microscope implementation are due to data acquisition speeds
which can be remedied by hardware and laser power improvements
... For the intrinsic ferroelectric materials possessing a remnant polarization, SHG is one of the most powerful techniques to analyze their polar states. [100] Because the SHG only probes the polar distortions projected on the plane perpendicular to 088106-6 the incident light, [101][102][103] it is, therefore, accessible to disentangle the SH component of in-plane oriented a-domains and out-of-plane pointed c-domains by changing the orientation of the polar axis with respect to the incident light. [100] Uniaxial tetragonal ferroelectric PbZr 0.2 Ti 0.8 O 3 shows a thicknessdependent domain distribution upon its complex domain variations. ...
Photons with variable energy, high coherency, and switchable polarization provide an ideal tool-kits for exploring the cutting-edge scientific questions in the condensed matter physics and materials sciences. Over decades, extensive researches in the sample fabrication and excitations have employed the photon as one of the important means to synthesize and explore the low-dimensional quantum materials. In this review, we firstly summarize the recent progresses of the state-of-the-art thin-film deposition methods using excimer pulsed laser, by which syntactic oxides with atomic-unit-cell-thick layers and extremely high crystalline quality can be programmatically fabricated. We demonstrate the artificially engineered oxide quantum heterostructures exhibit the unexpected physical properties which are absence in their parent forms. Secondly, we highlight the recent work on probing the symmetry breaking at the surface/interface and weak couplings among nanoscale ferroelectric domains using optical second harmonic generation. We clarify the current challenges in the in-situ characterizations under the external fields and large-scale imaging using optical second harmonic generation. The improvements in the sample quality and the non-contact detection technique further promote the understanding of the mechanism of the novel properties emerged at the interface and inspire the potential applications, such as the ferroelectric resistive memory and ultrahigh energy storage capacitors.
... 80 When the non-linear optical signal is collected by means of near field, wide field, or far field microscopes, spatial distribution of the SHG can be accessed. This provides the possibility to probe ferroic domains in magnetic, 81,82 ferroelectric, 83,84 and complex multiferroic systems. [85][86][87] Recent advances on SHG studies in oxide thin films 88 involve operando measurements of functioning devices 89 as well as in situ experiments in which the domain structure can be precisely controlled during the film growth. ...
Polar domain walls are currently at the focus of intensive research owing to their unusual and highly localized functional properties, which bear great potential for technological applications. They can present unusual topological features, like swirling polar structures or defect lines. The prediction of possible non-Ising and chiral internal structures of polar domain walls has been a particularly important development in this topic over the past years. This Tutorial highlights the capabilities of non-linear optics to probe these newly discovered aspects in polar non-Ising type domain walls through the second-harmonic generation (SHG) process. Fundamental symmetry properties of domain walls are presented in the context of recent advances on chiral and abnormal polar structures. We introduce the basics of the SHG and its ability to probe the symmetry down to the nanoscale, and we explain how to obtain insight into the non-Ising character of polar domain walls by combining the SHG polarimetry analysis with modeling.
... However, RUS and RPS are macroscopic techniques and it is dif cult to separate the contributions from domains and DBs. Alternative way to examine the polar nature is the second harmonic generation (SHG) microscopy [45][46][47][48]. ...
The effect of doping metal ions in ferroelastic Pb3(PO4)2 (PPO) on the polar nature of domain boundaries (DBs) was investigated using a second harmonic generation (SHG) microscope. It has been already reported that DBs of non-doped PPO is SH active and polar. The present study reveals that DBs of Ca-doped and Mg-doped PPO show greatly enhanced SH activity. This indicates that doping by metal ions enhances the polar nature of the DBs of PPO. This is important for future applications of DB nanotechnology. The enhancement of SH intensity is explained by a larger displacement of Ca2+ and Mg2+ ions in DBs due to smaller ionic radii. Analyses of the SH anisotropy experiments reveal that the symmetry-adapted W-wall belongs to monoclinic m and the non-adapted W'-wall to monoclinic 2. Both point groups are classified as the polar classes, which coincides with the case of pure PPO.
... To characterize the BTO domain distribution in just the area where the electric field had been applied, i.e., within the gap between the electrode pairs, we used spatially resolved SHG imaging of the sample as described in Figs the case in thin films, the SHG light from different domain states interferes. SHG waves from domain states with parallel polarization interfere constructively, while antiparallel polarization leads to a 180 • phase difference between the corresponding SHG contributions so that destructive interference occurs [22,29]. Note that although the domains in our BTO | Si heterostructure are below this resolution limit, we nevertheless obtain information on the overall domain architecture through the characteristic SHG anisotropy yielded by this domain-state interference. ...
We investigate the ferroelectric domain architecture and its operando response to an external electric field in BaTiO3-based electro-optic heterostructures integrated on silicon. By noninvasive optical second-harmonic generation, we identify the preexistence of in-plane (a-) domains dispersed within a predominantly out-of-plane- (c-) oriented matrix. Monitoring the poling behavior of the respective domain populations, we show that the spontaneous polarization of these a-domains lack a predominant orientation in the pristine state, yet can be selectively aligned with an in-plane electric field, leaving the c-domain population intact. Hence, domain reorientation of a ferroelastic c-to-a type was directly excluded. Such independent electrical control of ferroelectric a-domains in a c-oriented BaTiO3 film on silicon is a valuable platform for engineering multidirectional electro-optic functionality in integrated photonic devices.
... Therefore, the determination of the point group and crystallographic axes makes it possible to uniquely determine the polarization orientation. See Ref. [45] for the precise description of the analyses. ...
Domain boundaries in lead phosphate, Pb3(PO4)2, are investigated by using second harmonic generation (SHG) microscopy. It is revealed that they are polar while the bulk is a purely ferroelastic, centrosymmetric material. Pb3(PO4)2 contains W and W′ walls with different orientations. The SHG microscopy shows that both W and W′ walls are polar, in striking contrast to the bulk, where the macroscopic polarity is forbidden by symmetry. The strongest polarity is observed in the W walls with a local symmetry of monoclinic m. The W′ walls are also monoclinic but with symmetry 2. This material is hence a new candidate for domain-boundary-induced ferroelectricity while the bulk remains fully inactive. An application of small stress to a W wall easily changes the boundary configuration without changing the type of domain boundary; i.e., the W-wall nature is conserved. While Pb3(PO4)2 was so far suggested as a device material for acousto-optic switchers, the present study adds the possibility that light scattering can be modified also by electric fields.
... Furthermore, SHG microscopy is able to visualize the 180°domains of the ferroelectric (Uesu et al. 1995;Kurimura and Uesu 1997;Flörsheimer et al. 1998) and antiferromagnetic (Fiebig and Fröhlich 1995) crystals in a nondestructive way. With the aid of the interference of SH waves generated from the sample and the reference crystal, the three-dimensional structure of the periodically inverted ferroelectric domain, which is essential for optimal design for nonlinear optical frequency conversion devices, can also be obtained by the SHG microscope (Kurimura and Uesu 1997;Flörsheimer et al. 1998;Uesu et al. 2007;Yokota et al. 2012). ...
... As the SHG microscope is able to selectively observe the region in a sample where the spatial inversion symmetry is broken, it is a valuable tool for investigating the molecular ordering and structural organization in biological samples (Campagnola et al. 2002;Mohler et al. 2003). The main sources of endogenous SHG in biological samples are collagen (Campagnola 2013;Mansfield et al. 2019), myosin (Yokota et al. 2012;Vanzi et al. 2013), and microtubule (Kwan 2013), since their polar structures are organized by non-centrosymmetric structural proteins. SHG microscope has also been used for various medical applications such as the diagnosis of collagen-related diseases and the detection of tumor-associated collagen as a cancer biomarker (Pavone and Campagnola 2013; König 2018; Kirby et al. 2018). ...
Optical second harmonic generation (SHG) is a nonlinear optical process which is sensitive to the symmetry of media. SHG microscopy allows for selective probing of a non-centrosymmetric area of sample. This type of nonlinear optical microscope was first used to observe ferroelectric domains and has been applied to various specimens including the biological samples to date. Imaging of the endogenous SHG of biological tissue has been utilized for the selective observation of filament systems in tissues such as collagen, myosin, and microtubules, which exhibit a polar structure. The cellular membrane can be selectively observed by the SHG microscope through membrane staining with amphiphilic polar dye molecules. It has been reported that, by imaging exogenous SHG of the membrane, sensitive detection of membrane damage could be realized using the SHG microscope. Because the staining dye is fluorescent, both SHG and two-photon excited fluorescence (TPF) images can be obtained simultaneously. How the SHG intensity depends on the molecular alignment of the polar dye molecules that reflects the ordering of lipid molecules in the plasma membrane and the necessity of the normalization of the SHG intensity by the TPF intensity is discussed. Furthermore, the assessment of the membrane damage induced by exposing polycation to HeLa cells has been compared with the conventional cytotoxicity and cell viability tests to demonstrate the higher sensitivity of the present SHG-based assay.
... The second harmonic generation (SHG) has long been one of the main techniques for studying the properties of the ferroelectric crystals and thin films [14][15][16][17] . Nonlinear optical measurements are sensitive to the local symmetry, crystallographic orientation, and polarization. ...
The ability to switch ferroics (magnets, ferroelectrics, multiferroics) between two stable bit states is the main principle of modern data storage technology. Due to many new ideas, originating from fundamental research during the last 50 years, this technology has developed in a breath-taking fashion. Ever increasing demands for faster and more energy efficient data storage strongly motivate fundamental studies of dynamics in ferroics triggered by ultrashort stimuli. It has been recently realized that nearly single cycle intense THz pulses and the phenomenon of the second harmonic generation are appealing tools for excitation and detection of poorly understood ultrafast dynamics of electric polarization in ferroelectrics at the picosecond timescale. Here we investigate picosecond dynamics of second harmonic from near-infrared pulse in ferroelectric heterostructure Ba0.8Sr0.2TiO3/MgO triggered by the electric field of a nearly single cycle intense THz pulse. The dynamics of the nonlinear optical signal is characterized by a step and oscillations at the frequency of about 1.67 THz. Although the observations can be mistakenly interpreted as oscillations of the electric polarization at the frequency of the soft mode and switching of the order parameter to another metastable state, here we show that the THz modulation of second harmonic generation in Ba0.8Sr0.2TiO3/MgO has a purely optical origin. The observation can be explained assuming that the THz pulse is a relativistically propagating inhomogeneity which induces center of symmetry breaking and linear birefringence. Our work reveals the role of propagation effects in interpretation of time-resolved non-linear optical experiments and thus it has important implications for experimental studies of ultrafast dynamics in ferroics.
... ) 28 , where n laser is the refractive index of the nonlinear material. For thin samples, the depth resolution is the minimum among Z R and the crystal thickness. ...
We record a sub-wavelength terahertz image of a caster sugar grain thanks to optical rectification in
the sample excited with a femtosecond laser beam. The lateral spatial resolution of this technique is
given by the laser spot size at the sample and here its measured value is 50 μm, i.e. ~λ/12. We give an
estimation of the ultimate resolution that could be achieved with this method.
