Big-data-accelerated aperiodic Si/Ge superlattice prediction for quenching thermal conduction via pattern analysis

Thermal conductivity of material is one of the basic physical properties and plays an important role in manipu-lating thermal energy.In order to accelerate the prediction of material structure with desired thermal property,machine learning algorithm has been widely adopted.However,in the optimization of multivariable material structure such as different lengths or proportions,the machine learning algorithm may be required to be recon-ducted again and again for each variable,which will consume a lot of computing resources.Recently,it has been found that the thermal conductivity of aperiodic superlattices is closely related to the degree of the structural ran-domness,which can also be reflected in their local pattern structures.Inspired by these,we propose a new pattern analysis method,in which machine learning only needs to be carried out for one time,and through which the optimal structure of different variables with low thermal conductivity can be obtained.To verify the method,we compare the thermal conductivities of the structure obtained by pattern analysis,conventional machine learning,and previous literature,respectively.The pattern analysis method is validated to greatly reduce the prediction time of multivariable structure with high enough accuracy and may promote further development of material informatics.

Nonlinear distortion and spatial dispersion of intense terahertz generation in lithium niobate via the tilted pulse front technique

We systematically investigate the influences of the input infrared spectrum, chirp, and polarization on the emitted intense terahertz spectrum and spatial dispersion in lithium niobate via optical rectification. The terahertz yield and emission spectrum depend on both the chirp and spectrum of the input pump laser pulses. We also observe slight non-uniform spatial dispersion using a knife-edge measurement, which agrees well with the original predictions. The possible mechanism is the nonlinear distortion effect caused by high-energy laser pumping.Our study is very important and useful for developing intense terahertz systems with applications in extreme terahertz sciences and nonlinear phenomena.

Double-slit diffraction of terahertz wave generated by tilted-pulse-front pumping

We propose a spatial diffraction diagnostic method via inserting a millimeter-gap double slit into the collimated terahertz beam to monitor the minute variation of the terahertz beam in strong-field terahertz sources,which is difficult to be resolved in conventional terahertz imaging systems.To verify the method,we intentionally fabricate tiny variations of the terahertz beam through tuning the iris for the infrared pumping beam before the tilted-pulse-front pumping setups.The phenomena can be well explained by the theory based on the tilted-pulse-front technique and terahertz diffraction.

Optimization of highly efficient terahertz generation in lithium niobate driven by Ti:sapphire laser pulses with 30 fs pulse duration

We systematically study the optimization of highly efficient terahertz（THz） generation in lithium niobate（LN）crystal pumped by 800 nm laser pulses with 30 fs pulse duration. At room temperature, we obtain a record optical-to-THz energy conversion efficiency of 0.43% by chirping the pump laser pulses. Our method provides a new technique for producing millijoule THz radiation in LN via optical rectification driven by joule-level Ti：sapphire laser systems, which deliver sub-50-fs pulse durations.