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There is no unified thoracic surgery training system in China, neither in the trainee selection or evaluation, nor in the training curriculum or the graduation requirements. A literature review was performed for available publications regarding international thoracic surgical training. A brief comparison was made regarding the thoracic surgery residency programs in China, Japan, United States and United Kingdom, including training pathway, recruitments, training content, performance assessment and academic experience. In conclusion, there are four key aspects worth noting. Firstly, an effective residency programme is invaluable to specialty training, and effort should be made to create a unified training programme that allows trainee to progress from residency to specialty training smoothly. Secondly, flexibility and personalization should be allowed in higher specialty training, so that trainee can develop their subspecialty interests. Thirdly, a unified clinical curriculum, selection and standardized income should be promoted to minimalize the variation of training outcome between provinces. Fourthly, additional training and time should be allowed for trainee who wants to pursue an academic career, and academic outcomes should be evaluated alongside with the standard clinical training.我国的胸外科专科医师规范化培训在受训者筛选和考核、培训内容设置和出站要求设定等方面尚未形成统一制度。从培训模式、基地认证、对象招收、培训内容、考核标准及科研能力培训六个方面，对比我国与日本、美国、英国的胸外科专科培训制度后发现，各国培训体制存在差异，建立有效的专科培训制度需立足我国的基本国情。应建立住院医师规范化培训和专科医师规范化培训相衔接的培养模式，逐步打造一体化培训体系，并针对受训者的需求，制定不同的培训模式，提供多样化选择。通过设置全国统一的课程大纲，严格筛选培训基地，缩小各省市医院间培养的专科医师在业务能力和学术能力上的差异，保障培训的同质化。同时需注重科研教学，提升受训者的创新能力和科研素养，推动科研型临床人才的建设。建立合理且高效的培训模式，有望推动我国专科医学教育的进步。.

OBJECTIVE: To compare the retentions of different designs of cobalt-chromium (Co-Cr), pure titanium (CP Ti), and titanium alloy (Ti-6Al-4V) removable partial denture (RPD) circumferential clasps manufactured by selective laser melting (SLM) and to analyze the stress distribution of these clasps during the removal from abutment teeth. METHODS: Clasps with clasp arm size A (1.9 mm width/1.1 mm thickness at the body and 0.8-taper) or B (1.2 times A) and 0.25 mm or 0.50 mm undercut engagement were modeled on a prepared first premolar die, named as designs A1, A2, A3, and A4, respectively. The density and elastic modulus of SLM-built Co-Cr, CP Ti, and Ti-6Al-4V were measured and given to different groups of clasps. The density, elastic modulus, and Poisson ' s ratio of enamel were given to the die. The control group was the cast Co-Cr clasp with design A1, to which the density and elastic modulus of cast Co-Cr alloy were given. The Poisson's ratio of all metals was 0.33. The initial 5 N dislodging force was applied, and the maximum displacement of the clasp along the insertion path was computed. The load was reapplied with an increment of 5 N than in the last simulation until the clasp was completely dislodged. The retentive force range of different groups of clasps was obtained. The retentive forces of the SLM-built Co-Cr, CP Ti, and Ti-6Al-4V clasps with equivalent computed retentive force range to the control group were validated through the insertion/removal experiment. The von Mises stress distributions of these three groups of SLM-built clasps under 15 N loads were analyzed. RESULTS: SLM-built Co-Cr, CP Ti, and Ti-6Al-4V clasps with designs B1 or B2, and Co-Cr clasps with design A2 had higher retentive forces than those of the control group. SLM-built CP Ti and Ti-6Al-4V clasps with design A1 had lower retentive forces than those of the control group. SLM-built Co-Cr clasp with design A1 and SLM-built CP Ti and Ti-6Al-4V clasps with design A2 had equivalent retentive forces to those of the control group. The insertion/removal experiment showed that the measured retentive forces of these three groups of SLM-built clasps were (21.57±5.41) N, (19.75±4.47) N, and (19.32±2.04) N, respectively. No statistically significant measured retentive force difference was found among these three groups of SLM-built clasps (P>0.05). The maximum von Mises stress of these three groups of SLM-built clasps exceeded their responding yield strength except for the Ti-6Al-4V one. CONCLUSION: SLM-built Co-Cr circumferential clasps had higher retention than CP Ti and Ti-6Al-4V ones with the same clasp arm size and undercut engagement. The retention of SLM-built circumferential clasps could be adjusted by changing the undercut engagement and clasp arm size. If SLM-built circumferential clasps are used in clinical practice, the Ti-6Al-4V clasp with clasp arm size A and 0.50 mm undercut engagement is recommended considering the long-term use of RPD in the patient's mouth.

The basic theory of sum-frequency generation (SFG) is revisited. A rigorous derivation showing that linear optical transmission and reflection at an interface result from the interference of the incident wave and induced radiation wave in a medium is presented. The derivation is extended to SFG in a medium with a finite interface layer to see how SFG evolves. Detailed description on interface vs bulk and electric dipole (ED) vs electric quadrupole (EQ) contribution to SFG are provided with essentially no model dependence, putting the theory of SFG on a solid ground and removing possible existing confusions. Electric-quadrupole contributions to SFG from the interface and bulk are discussed. It is seen that there is a relevant bulk EQ contribution intrinsically inseparable in measurement from the interface ED contribution but plays a major role among all EQ contributions; its importance relative to the ED part can only be judged by referring to the established reference cases.

Materials with massless Dirac fermions can possess exceptionally strong and widely tunable optical nonlinearities. Experiments on graphene monolayer have indeed found very large third-order nonlinear responses, but the reported variation of the nonlinear optical coefficient by orders of magnitude is not yet understood. A large part of the difficulty is the lack of information on how doping or chemical potential affects the different nonlinear optical processes. Here we report the first experimental study, in corroboration with theory, on third harmonic generation (THG) and four-wave mixing (FWM) in graphene that has its chemical potential tuned by ion-gel gating. THG was seen to have enhanced by ~30 times when pristine graphene was heavily doped, while difference-frequency FWM appeared just the opposite. The latter was found to have a strong divergence toward degenerate FWM in undoped graphene, leading to a giant third-order nonlinearity. These truly amazing characteristics of graphene come from the possibility to gate-control the chemical potential, which selectively switches on and off one- and multi-photon resonant transitions that coherently contribute to the optical nonlinearity, and therefore can be utilized to develop graphene-based nonlinear optoelectronic devices., Comment: submitted for publication on August 14th, 2017

Surface plasmons (SPs) and phonon polaritons (PhPs) are two distinctive quasiparticles resulting from the strong coupling of photons with electrons and optical phonons, respectively. In this Letter, we investigate the interactions between one-dimensional (1D) plasmons in silver nanowires with two-dimensional (2D) surface phonon polaritons of the silicon carbide (SiC) substrate. Using near-field infrared spectroscopy of the silver nanowire-SiC heterostructure at wavelengths close to the phonon resonance of SiC, we observe that the 1D plasmon dispersion is strongly modified by the 2D phonon polaritons in SiC. In particular, we observe for the first time well-defined 1D plasmon oscillations with the plasmon wavelengths longer than the free-space photon wavelengths due to the 1D plasmon-2D phonon polariton coupling. Our work demonstrates that unusual polariton behavior can emerge from interactions between polariton excitons of different dimensionality, which can enable new ways to engineer plasmons in hybrid structures.

Layer-stacking domain walls in bilayer graphene are emerging as a fascinating one-dimensional system that features stacking solitons structurally and quantum valley Hall boundary states electronically. The interactions between electrons in the 2D graphene domains and the one-dimensional domain-wall solitons can lead to further new quantum phenomena. Domain-wall solitons of varied local structures exist along different crystallographic orientations, which can exhibit distinct electrical, mechanical and optical properties. Here we report soliton-dependent 2D graphene plasmon reflection at different 1D domain-wall solitons in bilayer graphene using near-field infrared nanoscopy. We observe various domain-wall structures in mechanically exfoliated graphene bilayers, including network-forming triangular lattices, individual straight or bent lines, and even closed circles. The near-field infrared contrast of domain-wall solitons arises from plasmon reflection at domain walls, and exhibits markedly different behaviours at the tensile- and shear-type domain-wall solitons. In addition, the plasmon reflection at domain walls exhibits a peculiar dependence on electrostatic gating. Our study demonstrates the unusual and tunable coupling between 2D graphene plasmons and domain-wall solitons.

Sum-frequency vibrational spectroscopy was employed to probe polymer contaminants on chemical vapor deposition (CVD) graphene and to study alkane and polyethylene (PE) adsorption on graphite. In comparing the spectra from the two surfaces, it was found that the contaminants on CVD graphene must be long-chain alkane or PE-like molecules. PE adsorption from solution on the honeycomb surface results in a self-assembled ordered monolayer with the C-C skeleton plane perpendicular to the surface and an adsorption free energy of ∼42 kJ/mol for PE(H(CH2CH2)nH) with n ≈ 60. Such large adsorption energy is responsible for the easy contamination of CVD graphene by impurity in the polymer during standard transfer processes. Contamination can be minimized with the use of purified polymers free of PE-like impurities.

The authors report the observation of plasmons that exhibit quantized velocities in carbon nanotubes.

Topological dislocations and stacking faults greatly affect the performance of functional crystalline materials1-3. Layer-stacking domain walls (DWs) in graphene alter its electronic properties and give rise to fascinating new physics such as quantum valley Hall edge states4-10. Extensive efforts have been dedicated to the engineering of dislocations to obtain materials with advanced properties. However, the manipulation of individual dislocations to precisely control the local structure and local properties of bulk material remains an outstanding challenge. Here we report the manipulation of individual layer-stacking DWs in bi- and trilayer graphene by means of a local mechanical force exerted by an atomic force microscope tip. We demonstrate experimentally the capability to move, erase and split individual DWs as well as annihilate or create closed-loop DWs. We further show that the DW motion is highly anisotropic, offering a simple approach to create solitons with designed atomic structures. Most artificially created DW structures are found to be stable at room temperature.

Second harmonic generation (SHG) and sum frequency spectroscopy (SFS) have provided unique opportunities to probe surfaces and interfaces. They have found broad applications in many disciplines of science and technology. In recent years, there has been significant progress in the development of SHG/SFS technology that has significantly broadened the applications of SHG and SFS. In this article, we review the recent progress of the field with emphasis on SFS.

Artificial structures made of stacked two-dimensional crystals have recently been the focus of intense research activity. As in twisted or stacked graphene layers, these structures can show unusual behaviours and new phenomena. Among the various layered compounds that can be exfoliated, transition-metal dichalcogenides exhibit interesting properties governed by their structural symmetry and interlayer coupling, which are highly susceptible to stacking. Here, we obtain-by folding exfoliated MoS2 monolayers-MoS2 bilayers with different stacking orders, as monitored by second harmonic generation and photoluminescence. Appropriate folding can break the inversion symmetry and suppress interlayer hopping, evoking strong valley and spin polarizations that are not achieved in natural MoS2 bilayers of Bernal stacking. It can also enlarge the indirect bandgap by more than 100 meV through a decrease in the interlayer coupling. Our work provides an effective and versatile means to engineer transition-metal dichalcogenide materials with desirable electronic and optical properties.

Phytosterols are intended for use as a novel food ingredient with plasma cholesterol-lowering activity. Although phytosterols are naturally present in the normal diet, daily consumption is insufficient to ensure plasma cholesterol-lowering levels. Therefore, phytosterols may be added to the diets to achieve the desired cholesterol-lowering activity. A subchronic laying hen safety study was conducted to examine if high-dose phytosterols could affect the safety of hens. Three hundred sixty 21-wk-old Hy-Line Brown laying hens were randomly assigned to 5 groups with 6 replicates of 12 birds each; after 3 wk, birds were fed diets supplemented with 0, 20, 80, 400, and 800 mg/kg of phytosterols for 12 wk. Throughout the study, clinical observations and laying performance were measured. At the end of the study, birds were subjected to a full postmortem examination: blood samples were taken for clinical pathology, selected organs were weighed, and specified tissues were taken for subsequent histological examination. No treatment-related changes that were considered to be of toxicological significance were observed. Therefore, a nominal phytosterol concentration of 800 mg/kg was considered to be the no-observed-adverse-effect level.

Nonlinear optical reflection spectroscopies for surface studies often suffer from their relatively weak signals. To enhance the signal strength, femtosecond input pulses are generally preferred, but their intensity is usually limited by supercontinuum (SC) generation in a bulk medium. We show here that the problem can be largely resolved by means of spatiotemporal focusing (STF) of the input that effectively suppresses the SC, permits much higher input intensity on a medium, and greatly enhances the nonlinear output signal. We use second-harmonic generation (SHG) on oxide as examples and demonstrate that, with STF, the input intensity for the onset of the SC can be increased by ∼30 times in comparison with conventional focusing, and the reflected SHG can be increased by about three orders of magnitude.

The SFG technique has become popular since the pioneering work conducted by Shen's group in late 1980s. Combined the advantages of other surface-detecting techniques, the SFG technique could identify both chemical species and orientations adsorbed on surfaces or inserted between surfaces. In view of the recent tremendous experimental activities of SFG in surface chemistry, biochemistry and material sciences, quantum chemical calculations of SFG spectra to analyze the experimental SFG spectra are badly needed. In this paper we presented the theoretical expressions of various SFG techniques and showed how to employ the quantum chemical calculations to simulate the corresponding SFG spectra.

In present letter the adiabatic approximation is applied to the intramolecular vibrational redistribution (IVR) of water clusters. The isotope, blocking and cluster-size effects are investigated. This letter also examines the assumption associated with the transition state theory applied to unimolecular reactions; that is, IVR is assumed to be completed before the reaction takes place. For this purpose, we choose to study (H 2 O) 2 H + → H 2 O + H 3 O + , and (H 2 O) 2 → 2H 2 O processes. In molecular clusters, the vibrational excitation energy transfer between different normal modes has been observed. This will also be investigated for the deuterated species of (HOD) 2 H + .

Surface-sensitive sum-frequency vibrational spectroscopy (SFVS) has grown into a most viable analytical tool to investigate Langmuir monolayer systems. It has been successful in deducing information on many key properties of Langmuir films not obtainable by other techniques. This review gives a survey on the current status of SFVS studies of Langmuir monolayers with emphasis on the structures of both surfactant monolayers and interfacial water under various circumstances.

Phase-sensitive sum-frequency spectroscopy (SFS) allows the complete measurement of the complex spectra of surface nonlinear response coefficients. Similar to linear spectroscopy, the spectrum of the imaginary part of a surface response coefficient directly characterizes surface resonances without complication. This newly developed technique has greatly enhanced the capability of surface SFS and provides many new research opportunities for surface science. This article describes the experimental schemes and underlying theory for the technique and briefly reviews works that have clearly demonstrated its power.

In-situ X-ray Absorption Spectroscopy (XAS), Raman Spectroscopy, AFM and XPS have been used to investigate the effect of reactions occurring in aqueous electrolytes on the structure of a single-layer graphene produced by CVD. It was found that defects are readily and irreversibly produced by application of electrode voltages. The defects and the products were identified also by new features in the XAS spectra. Our findings show the poor stability of the CVD graphene, which could be a challenge in applications

Second harmonic generation (SHG) from three-dimensional topological insulators originates from both surface and bulk, which does not allow probing of surface states unless the measurement can separate the two contributions. In this paper, we used combined measurements of transmitted and reflected SHG from epitaxially grown $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ thin films of different thickness on $\mathrm{Ba}{\mathrm{F}}_{2}$, and a bulk $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ crystal, to deduce surface and bulk nonlinear susceptibilities of $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ separately. We found that the surface contribution to SHG was comparable to that from the bulk of the crystal, but becomes dominant in ultrathin films. In the latter case, contributions from both air/$\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ and $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}/\mathrm{Ba}{\mathrm{F}}_{2}$ interfaces were significant and exhibited a strong out-of-plane polar ordering. The bulk contribution came mainly from the space charge region (SCR), which was formed by Se vacancies aggregated at the air/$\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ interface; its magnitude can provide an estimate on the field strength in the SCR. Clarification of surface and bulk contributions to SHG can help nonlinear optical techniques be used as a versatile in situ probe for topological insulators.

Vibrational signature reveals the structure around, and evolution of, active sites on anatase (101) in real ambient., Surface active sites of crystals often govern their relevant surface chemistry, yet to monitor them in situ in real atmosphere remains a challenge. Using surface-specific sum-frequency spectroscopy, we identified the surface phonon mode associated with the active sites of undercoordinated titanium ions and conjoint oxygen vacancies, and used it to monitor them on anatase (TiO2) (101) under ambient conditions. In conjunction with theory, we determined related surface structure around the active sites and tracked the evolution of oxygen vacancies under ultraviolet irradiation. We further found that unlike in vacuum, the surface oxygen vacancies, which dominate the surface reactivity, are strongly regulated by ambient gas molecules, including methanol and water, as well as weakly associated species, such as nitrogen and hydrogen. The result revealed a rich interplay between prevailing ambient species and surface reactivity, which can be omnipresent in environmental and catalytic applications of titanium dioxides.

A detailed description on the basic theory of optical sum-frequency generation from an interfacial system is presented. Both the interface and the bulk generally contribute to the sum-frequency output. Two seemingly different approaches to specify bulk nonlinearity that includes electric-quadrupole and magnetic-dipole contributions are shown to yield the same sum-frequency output if surface nonlinearity is properly taken into account. The question of whether surface and bulk nonlinearities can be uniquely defined and separately measured is discussed. It is shown that the answer is affirmative. Truly bulk and truly surface nonlinear susceptibilities can be uniquely defined and separately deduced from measurements of transmitted and reflected sum-frequency generation.

Recent molecular simulations of liquid interfaces yield surface sum-frequency vibrational spectra that can be highly sensitive to the seemingly-arbitrary choice of molecular center in the calculation method. We show that the ambiguity arises because widely-used approaches, focusing exclusively on electric-dipole contributions from the surface, neglect coordinate-dependent quadrupole-order contributions of comparable magnitude from the bulk. The correct calculation includes both surface and bulk responses. With a judicious choice of molecular center, however, it may be possible to minimize the bulk contribution, allowing the surface-only calculation to produce a reasonably accurate spectrum. We use water as an example to elucidate the problem.

We studied the insulator-metal transition (IMT) in single-domain, single crystalline vanadium dioxide (VO(2)) microbeams with infrared microspectroscopy. The unique nature of such samples allowed us to probe the intrinsic behavior of both insulating and metallic phases in the close vicinity of IMT, and investigate the IMT driven by either strain or temperature independently. We found that the VO(2) insulating band gap narrows rapidly upon heating, and the infrared response undergoes an abrupt transition at both strain- and temperature-induced IMT. The results are consistent with recent studies attributing the opening of VO(2) insulating band gap to a correlation-assisted Peierls transition.

The authors of this Article have become aware of the following recent paper that reports the electrically tunable degenerate four-wave mixing in graphene-covered SiN waveguides: “Alexander, K., Savostianova, N. A., Mikhailov, S. A., Kuyken, B. & Van Thourhout, D. Electrically tunable optical nonlinearities in graphene-covered SiN waveguides characterized by four-wave mixing. ACS Photon. 4, 3039–3044 (2017).” This reference has been added as ref. 33 in the new sentence “Very recently, degenerate four-wave mixing in graphene-covered SiN waveguides with ion-gel gating was experimentally studied33.” Accordingly, the previous sentence has been amended to read as “Few such experiments have been reported, although they have been suggested in theoretical work28–32” and all subsequent references have been renumbered. These changes have been made in the online versions.

Sum-frequency vibrational spectroscopy can be used to study photoinduced structural change at polymer surfaces. Results on rubbed and unrubbed surfaces of poly(vinyl cinnamate) (PVCi), a well-known photopolymer, show that polarized UV irradiation dimerizes rather than isomerizes the protruding cinnamoyl side chains at the surfaces and creates significant surface structural anisotropy needed in many applications. Anchoring energy measurements of a nematic liquid crystal film on PVCi irradiated by low UV dosages yield results in good correlation with the observed spectral anisotropy.

Phase-sensitive sum-frequency vibrational spectroscopy was used to obtain the OH and OD stretch spectra of the imaginary part of the nonlinear susceptibility, ImχS(2)(ωIR), for H2O/vapor, D2O/vapor, and 2:1 H2O–D2O/vapor interfaces that explicitly characterize their resonances. They all exhibit a positive and a negative resonance band in the bonded-OH region, clearly different from those deduced from fitting of the |χS(2)(ωIR)|2 spectra, and from MD simulations. The broad continuum is characteristic of inhomogeneously broadened resonances associated with interfacial water species of various hydrogen-bonding geometries and strengths. Spectral changes due to excess ions at the interfaces support the picture.

Atomic force microscopy, attenuated-total-reflection Fourier-transform infrared (FTIR) spectroscopy, and sum-frequency vibrational spectroscopy (SFVS) were employed to study effects of heat treatment in different gas atmospheres on three different alumina crystalline surfaces (a, c and r) and subsequent hydroxylation. Samples heat-treated at a higher temperature (1550 °C) exhibited more surface roughening and faceting than those heated at 1000 °C. Also, the roughening and faceting depended on the gaseous atmosphere used during heat treatment. The SFVS and FTIR spectra showed clearer spectral features of hydroxylation and higher degree of hydroxylation for heat treatment at higher temperatures. Different crystalline surfaces displayed different spectral features upon hydration. Hydration of sample surfaces in water appears to be more effective than in humid air.

Early struggles in the development of THz spectroscopy are reviewed. The field, covering an important spectral region for material characterization, suffered badly from poor lightsources and detectors in the old days, but blossomed rapidly after the arrival of femtosecond lasers. It provides another example how advances of laser technology revolutionize a field.

We measured circular dichroism (CD) of hydrated and non-hydrated powder crystals of cobaloxime complex. The CD spectrum was found to depend on the crystalline forms. Non-hydrated crystals exhibited an extra pair of exciton-split CD peaks associated with the chiral molecular arrangement in the crystals. We also made direct observation of a photo-induced chirality change or switching in the alkyl ligand of the cobaloxime complex in both crystalline forms.

Recent advances in developing sum frequency generation (SFG) as a novel spectroscopic probe for molecular chirality are reviewed. The basic principle underlying the technique is briefly described, in comparison with circular dichroism (CD). The significantly better sensitivity of the technique than CD is pointed out, and the reason is discussed. Bi-naphthol (BN) and amino acids are used as representatives for two different types of chiral molecules; the measured chirality in their electronic transitions can be understood by two different molecular models, respectively, that are extensions of models developed earlier for CD. Optically active or chiral SFG from vibrational transitions are weaker, but with the help of electronic-vibrational double resonance, the vibrational spectrum of a monolayer of BN has been obtained. Generally, optically active SFG is sufficiently sensitive to be employed to probe in-situ chirality of chiral monolayers and thin films.

A theoretical formulation for optically active sum frequency generation (OA-SFG) from isotropic chiral solutions was proposed for molecules with a chiral side chain and an intrinsically achiral chromophore. Adapting an electron correlation model first proposed by Höhn and Weigang for linear optical activity, we presented a dynamic coupling model for OA-SFG near the electronic resonance of the achiral chromophore. As a demonstration, we used this model to explain the observed OA-SFG spectra of a series of amino acids near the electronic resonance of the intrinsically achiral carboxyl group. Our model shows that the nonlinear chiroptical response comes about by the through-space correlative electronic interactions between the chiral side chain and the achiral chromophore, and its magnitude is determined by the position and orientation of the bonds that make up the chiral side chain. Using the bond polarizability values in the literature and the conformations of amino acids obtained from calculation, we were able to reproduce the relative OA-SFG strength from a series of amino acids.

Sum-frequency vibrational spectroscopy was used to probe the adsorption of C1–C4 1-alcohol molecules at both vapor/silica and liquid/silica interfaces. The observed CH stretching spectra show that alcohol molecules adsorbed on silica with methyl groups pointing away from the interface. Reduction of the symmetric modes and enhancement of the antisymmetric modes of alcohol at liquid/silica interfaces are understood from a model of oppositely oriented molecules forming a bilayer at the interfaces.

Optical second-harmonic generation and sum-frequency generation as novel spectroscopic tools to probe molecular chirality are currently being developed. The latter in particular allows studies of chirality associated with both electronic and vibrational transitions of molecules in isotropic bulk, thin films, and monolayers. We review here the recent theoretical and experimental progress in the field. It is shown theoretically and experimentally that both processes can have monolayer sensitivity to detect chirality in electronic and vibrational transitions and that the sensitivity of the sum-frequency spectroscopy of chirality in vibrational transitions can be greatly enhanced through vibrational-electronic double-resonance. Measurements with short-pulsed lasers provide opportunities for time-resolved in situ studies of chirality. Contents PAGE 1. Introduction 258 2. Basics of chiral responses in SFG and SHG 259 2.1. General considerations of SFG and SHG 259 2.2. Non-linear susceptibility for an azimutha...

In materials with negative refraction, the direction of wave propagation is opposite to the direction of the wave vector. Using an approach that characterizes the optical response of a medium totally by a generalized dielectric permittivity, e ˜ ( ω , k ⇒ ) , we discuss the possibility of seeing negative refraction for optical waves in a number of nonmagnetic media. These include bulk waves in organic materials and in gyrotropic materials where additional exciton–polariton waves can have a negative group velocity. It is known that dispersion of surface waves can be engineered by tailoring a surface transition layer. We show how this effect can be used to obtain surface waves with negative refraction.

Theoretical expressions for sum-frequency generation (SFG) signals, which can be applied to treat various SFG experiments, have been derived. We have applied the theoretical results to study the SF...

The strength of the chiral vibrational peaks in infrared-visible sum-frequency (SF) vibrational spectra from isotropic chiral liquids is proportional to the square of the corresponding antisymmetric Raman element. Under the Born-Oppenheimer adiabatic approximation with nonadiabatic corrections, the antisymmetric Raman tensor is much weaker than the symmetric counterpart, but becomes significantly stronger as the input frequency (or the sum-frequency in SF generation) approaches electronic resonance. We verify the theory with experimental results obtained from infrared-visible doubly resonant sum-frequency generation from an isotropic solution of chiral molecules.

Sum frequency vibrational spectroscopy was used to study adsorption of leucine molecules at air-water interface from solutions with different concentrations and pH values. The surface density and the orientation of the isopropyl head group of the adsorbed leucine molecules could be deduced from the measurements. It was found that the orientation depends on the surface density, but only weakly on bulk pH value at the saturated surface density. The vibrational spectra of the interfacial water molecules appeared to be strongly affected by the charge state of the adsorbed leucine molecules. Enhancement and inversion of polar orientation of interfacial water molecules by surface charges or field controllable by the bulk pH value were observed.