Second-harmonic generation of single-mode Laguerre-Gaussian beams with an improved quasi-phase-matching method.

In the second-harmonic generation processes involving Laguerre-Gaussian (LG) beams, the generated second-harmonic wave is generally composed of multiple modes with different radial quantum numbers. To generate single-mode second-harmonic LG beams, a type of improved quasi-phase-matching method is proposed. The Gouy phase shift has been considered in the optical superlattice designing and an adjustment phase item is introduced.

Multibeam Electron Diffraction.

One of the primary uses for transmission electron microscopy (TEM) is to measure diffraction pattern images in order to determine a crystal structure and orientation. In nanobeam electron diffraction (NBED), we scan a moderately converged electron probe over the sample to acquire thousands or even millions of sequential diffraction images, a technique that is especially appropriate for polycrystalline samples. However, due to the large Ewald sphere of TEM, excitation of Bragg peaks can be extremely sensitive to sample tilt, varying strongly for even a few degrees of sample tilt for crystalline samples.

Nearly Diffraction-Free Nonlinear Imaging of Irregularly Distributed Ferroelectric Domains.

Second-harmonic generation is used experimentally for the nonlinear imaging of two-dimensional irregular domain structures. Analytical solutions and simulation results for the Fresnel distribution of domain walls are obtained. The results show that the domain wall plays an important role in the imaging process and the corresponding diffraction effect is greatly suppressed (we call it a nearly diffraction-free effect), thus providing a simple way to realize high-resolution imaging for ferroelectric domains.

Adjuvant Photothermal Therapy Inhibits Local Recurrences after Breast-Conserving Surgery with Little Skin Damage.

Adjuvant treatments following breast-conserving surgery (BCS) are essential to reduce the risk of local recurrences in patients with breast cancer. However, current adjuvant treatments are based on ionizing radiation, which brings radiation-induced damage and amplifies the risk of death. Here we explore the feasibility of using non-ionizing light to induce photothermal therapy as an adjuvant treatment to BCS.

Time-reversed and reciprocal second-harmonic generation with pump depletion.

The time-reversed second-harmonic generation in one-dimensional nonlinear photonic crystals has been theoretically studied without the undepleted pump approximation. A simple criterion has been deduced which determines the energy flow. Based on it, two kinds of structures with different symmetries are presented to realize the nonlinear time reversal effect.

Analytical investigation of nonreciprocal response in 1D nonlinear photonic crystals.

The nonreciprocal response of the SHG process in 1D periodical nonlinear photonic crystals with a defect embedded has been theoretically studied by solving the nonlinear coupled equations. The nonreciprocal response has been deduced analytically with the solution of non-reciprocity parameters obtained. The result shows that as the non-reciprocity approaches 100%, the crystal length and the input power needed increase at a logarithmic rate.

Electroplating lithium transition metal oxides.

Materials synthesis often provides opportunities for innovation. We demonstrate a general low-temperature (260°C) molten salt electrodeposition approach to directly electroplate the important lithium-ion (Li-ion) battery cathode materials LiCoO, LiMnO, and Al-doped LiCoO. The crystallinities and electrochemical capacities of the electroplated oxides are comparable to those of the powders synthesized at much higher temperatures (700° to 1000°C).

Theoretical study on the Cerenkov-type second-harmonic generation in optical superlattices without paraxial approximation.

In this paper, the Cerenkov-type second-harmonic generation in bulk optical superlattices has been studied theoretically with the non-paraxial wave equations, where the paraxial approximation is avoided. The corresponding phase-matching condition is determined strictly by solving the non-paraxial wave equations under proper boundary conditions, and the result coincides well with the traditional Cerenkov phase-matching condition. In addition, a backward Cerenkov phase-matching condition is deduced from the wave equations as well, and the physical requirement of this condition is clarified.

From Ewald sphere to Ewald shell in nonlinear optics.

Ewald sphere is a simple vector scheme to depict the X-ray Bragg diffraction in a crystal. A similar method, known as the nonlinear Ewald sphere, was employed to illustrate optical frequency conversion processes. We extend the nonlinear Ewald sphere to the Ewald shell construction.

2D wave-front shaping in optical superlattices using nonlinear volume holography.

Nonlinear volume holography is employed to realize arbitrary wave-front shaping during nonlinear processes with properly designed 2D optical superlattices. The concept of a nonlinear polarization wave in nonlinear volume holography is investigated. The holographic imaging of irregular patterns was performed using 2D LiTaO crystals with fundamental wave propagating along the spontaneous polarization direction, and the results agree well with the theoretical predictions.

Rigorous intensity and phase-shift manipulation in optical frequency conversion.

A simple method is employed to investigate the nonlinear frequency conversion in optical superlattices (OSL) with pump depletion. Four rigorous phase-matching conditions for different purposes are obtained directly from the nonlinear coupled equations, and the resulting OSL domain structures are generally aperiodic rather than periodic. With this method, not only the intensity but also the phase-shift of the harmonic waves can be manipulated at will.

Nonlinear optical Fourier transform in an optical superlattice with "x+2" structure.

We proposed a simple method to realize optical Fourier transform during the nonlinear wave shaping processes. In this method, an integrated optical superlattice is designed to realize multiple optical functions, which plays important roles in both the nonlinear harmonic generation process and the optical Fourier Transform process. We demonstrated our method by the nonlinear generation of Airy beams as an example.

Miniature spectrometer based on diffraction in a dispersive hole array.

We present an ultra-compact spectrometer that uses a 10×10 hole array as the dispersive component. Our analysis shows that the two-dimensional intensity distribution can be modeled by a system of simultaneous linear equations when the size of each hole in the dispersive component has been pre-designed appropriately. One can readily recover the spectral contents of the input radiation by solving the linear equation system with regularized procedure.

Nonlinear volume holography for wave-front engineering.

The concept of volume holography is applied to the design of an optical superlattice for the nonlinear harmonic generation. The generated harmonic wave can be considered as a holographic image caused by the incident fundamental wave. Compared with the conventional quasi-phase-matching method, this new method has significant advantages when applied to complicated nonlinear processes such as the nonlinear generation of special beams.

Controllable polarization coupled dual-focused second-harmonic generations in a two-dimensional optical superlattice.

The nonlinear Huygens-Fresnel principle has been used to design multifunctional nonlinear optical devices. Focused second-harmonic generations have been observed with strong polarization sensitivity. Numerical simulations have been performed, and the results fit well with the experiments.