Xuewei Deng

Domain wall characterization in ferroelectrics by using localized nonlinearities

In this paper, a method of domain wall characterization in ferroelectrics through Cherenkov second harmonic generation by localized nonlinearities is proposed. By this method, domain wall width is estimated to be less than 10nm. High spatial angular resolution of about 10 mrad in the experiment reveals the fine structures of the domain walls. Combined with scanning techniques, this method can reconstruct domain wall patterns with high resolution. This method has advantages of being nondestructive, noncontact, in situ as well as of high resolution.

Cherenkov high-order harmonic generation by multistep cascading in χ(2) nonlinear photonic crystal

We propose a scheme for efficient Cherenkov high-order harmonic generation. Second to fifth order harmonic wave are observed in a single periodically poled ferroelectric crystal in our experiment. The noncollinear high-order harmonic generation is produced via enhanced Cherenkov second harmonic cascaded with successive multistep sum-frequency generation with simultaneously longitudinal phase-matching. The emission angle and power dependencies are analyzed in detail experimentally, which coincide with theoretical predictions.

Research on Cherenkov second-harmonic generation in periodically poled lithium niobate by femtosecond pulses

We systematically study the characteristics of the Cherenkov second-harmonic generation in periodically poled lithium niobate by femtosecond pulses. A relatively high conversion efficiency is obtained and what we believe to be a new different explanation is proposed that nonlinearities in the domain wall region have been enhanced significantly, which is a new feature of the domain wall that has not been studied previously.

Enhanced nonlinear Cherenkov radiation on the crystal boundary

We demonstrate a method to generate enhanced nonlinear Cherenkov radiation (NCR) in the bulk medium by utilizing the total reflection on the physical boundaries inside the crystal. This is the experimental demonstration of enhanced NCR by a sharp χ(2) modulation from 0 to 1, and a new way for generating enhanced NCR in addition to using the waveguide structures and the ferroelectric domain walls, which also possesses a better beam quality for applications.

Research and construction progress of the SG-III laser facility

The under-construction SG-III laser facility is a huge high power solid laser driver, which contains 48 beams and is designed to deliver 180kJ energy at 3ns pulse duration. The testing ending up at September 2012 validated that the first bundle lasers of SG-III facility had achieved all the designed requirements. And shortly later in December 2012, the first round of running-in physics experiment provided a preliminary X-ray diagnostic result. In the testing experiment, detailed analysis of the laser energy, the temporal characteristics, the spatial distribution and the focusing performance was made by using the Beam Integrated Diagnostic System. The 25kJ 3ω energy produced by the first bundle lasers created the new domestic record in China. These great progresses in the laser performance and the physics experiment have already demonstrated that the facility is in excellent accordance with the designs, which establish a solid foundation for completing all the construction goals.

Conical second harmonic generation in one-dimension nonlinear photonic crystal

We observed conical second-harmonic generation in a one-dimension anomalous-dispersion-like medium, which manifests itself as scattering-assisted nonlinear interaction via quasi-phase-matching sum frequency process. The parameters for the ring-shaped second harmonic beam are analyzed experimentally and theoretically, which disclose the structure information of the nonlinear photonic crystal and imply potential applications as characterization methods. Furthermore, by varying the angles of incident beam, the conical beam can be significantly enhanced owing to collinear nonlinear coupling between the input beam and the scattering light.

Normal, degenerated, and anomalous-dispersion-like Cerenkov sum-frequency generation in one nonlinear medium

We report on the experimental realization of Cerenkov sum-frequency generation across the material dispersion in a one-dimensional, periodically poled ferroelectric crystal. Three schemes of sum-frequency generation, confined only in the vicinity of domain walls and in the form of nonlinear Cerenkov radiation, are demonstrated in normal, degenerated, and anomalous-dispersion-like configurations. We exploit their phase-matching geometries, which exhibit a whole scenario of the evolution of Cerenkov radiation varying with the dispersion relationship among the interaction waves. In addition, two sets of conical sum-frequency generation with different radius and center are demonstrated, which result from scattering assistant phase-matching processes.

Surface phase-matched harmonic enhancement in a bulk anomalous dispersion medium

Scattering second harmonic ring could be observed in a bulk nonlinear medium with anomalous dispersion, whose generation is derived from complete phase matching of the incident light and the scattering light. By this specific phase matching under anomalous dispersion condition, we took advantage of total internal reflection, and realized high efficiency second harmonic output to gain a single pass conversion efficiency of up to 14.8% by only once reflection. It may suggest potential applications in micro-structures, such as micro cavities and waveguides.

Spatial modulation of second-harmonic generation via nonlinear Raman-Nath diffraction in an aperiodically poled lithium tantalite.

We propose and experimentally demonstrate a colorful nonlinear Raman-Nath second-harmonic generation by engineering the quadratic nonlinearity χ((2)) in an aperiodically poled lithium tantalite. The engineered nonlinear structure allows multicolored Raman-Nath second-harmonic signal outputs along a uniform direction, which cannot be achieved in a uniform nonlinear grating. The diffraction angles are independent of the beam waist and the position of incidence. This verifies that nonlinear Raman-Nath diffraction does not depend on the local superlattice structure where the fundamental frequency beam locates, but on the whole nonlinear χ((2)) crystal.

Sum-frequency nonlinear Cherenkov radiation generated on the boundary of bulk medium crystal.

We demonstrated experimentally a method to generate the sum-frequency Nonlinear Cherenkov radiation (NCR) on the boundary of bulk medium by using two synchronized laser beam with wavelength of 1300 nm and 800 nm. It is also an evidence that the polarization wave is always confined to the boundary. Critical conditions of surface sum-frequency NCR under normal and anomalous dispersion condition is discussed.