Laser-Chirp Controlled Terahertz Wave Generation from Air Plasma

We report the laser-chirp controlled terahertz(THz) wave generation from two-color-laser-induced air plasma.Our experimental results reveal that the THz wave is affected by both the laser energy and chirp,leading to radiation minima that can be quantitatively reconstructed using the linear-dipole-array model.The phase difference between the two colors,determined by the chirp and intensity of the laser,can account for the radiation minima.Furthermore,we observe an asynchronous variation in the generated THz spectrum,which suggests a THz frequency-dependent phase matching between the laser pulse and THz wave.These results highlight the importance of laser chirp during the THz wave generation and demonstrate the possibility of modulating the THz yields and spectrum through chirping the incident laser pulse.This work can provide valuable insights into the mechanism of plasma-based THz wave generation and offer a unique means to control THz emissions.

The Mars rover subsurface penetrating radar onboard China's Mars 2020 mission

China's Mars probe,named Tianwen-1,including an orbiter and a landing rover,will be launched during the July-August 2020 Mars launch windows.Selected to be among the rover payloads is a Subsurface Penetrating Radar module(RoSPR).The main scientific objective of the RoSPR is to characterize the thickness and sub-layer distribution of the Martian soil.The RoSPR consists of two channels.The low frequency channel of the RoSPR will penetrate the Martian soil to depths of 10 to 100 m with a resolution of a few meters.The higher frequency channel will penetrate to a depth of 3 to 10 m with a resolution of a few centimeters.This paper describes the design of the instrument and some results of field experiments.

An ultra-sensitive metasurface biosensor for instant cancer detection based on terahertz spectra

Metasurface biosensors have become the core label-free and rapid-detection technology in bioanalysis.Lung cancer and brain cancer are the first leading causes of cancer death among adults and adolescents,respectively,where poor early diagnosis results from expensive detection costs and time consumption.To tackle the above problems,here,we introduce a terahertzdomain metasurface biosensor for cancer diagnosis,relying on a perfectly symmetrical periodic surface structure,which significantly exhibits polarization-insensitivity at 2.05 THz and the high-sensitivity of 504 GHz/RIU(RIU=refractive index unit).According to the frequency shifts and transmittance variations,four cell types are successfully distinguished from each other.The minimum number of cells is required for thousands of cells to display the differences of spectra,which is 1/30 of clinical methods.Furthermore,the results were consistent with pathological results(the gold standard in clinic)by Gaussian curve fitting.The proposed biosensor has really achieved the characterization of cells in normal and cancerous state.This detection strategy dramatically reduced the cost of detection by reuse and time consumption was reduced to 1/20 of the pathology testing.In addition,it is flexible to set samples and easy to realize automatic operation due to the great polarization-insensitivity of the proposed biosensor,which can further reduce labor costs in the future.It is envisioned that the proposed biosensor will present immense potential in the fields of cancer detection,distinguishing different cancers,identifying primary lesion cancer or metastatic cancer.

Lithospheric structures across the Qiman Tagh and western Qaidam Basin revealed by magnetotelluric data collected using a self-developed SEP system

Geophysics offers an important means to investigate the physical processes occurring inside the earth.In particular,since the 1960s,electromagnetic(EM)methods have played important roles in mineral exploration and engineering investigation.Such investigation requires extensive data acquisition and experimental analysis based on geophysical techniques.However,high-performance geophysical equipment,particularly EM exploration equipment,has been dominated by large geophysical companies from the United States,Canada,Germany,and other European countries for decades.This has limited the development of deep exploration technology in China.Recently,we have developed a high-resolution acquisition system with a wireless control unit and a high-power transmitting system for surface EM prospecting(SEP).The new system has been tested in the high-intensity,noisy environment in Jian-sanjiang area,Heilongjiang Province.We then conducted a field survey on the western edge of Qaidam Basin,Qinghai Province.A highly conductive anomaly was found in the upper mantle below the Qinmantage Mountains,which indicates a possible northward fluid channel that runs from below the Qinmantage Mountains to the bottom of the western crust of the Qaidam Basin.Identification of this significant feature was made possible by the new SEP for its better resolution than the previous systems.Also,geophysical analysis confirmed that the thick Cenozoic sediments of the Qaidam Basin are underlain by rigid Precambrian basement rocks and are characterized by a series of folds.The resistivity profile indicates that the Qaidam Basin was formed due to the folding structures in the northern part of the Qinghai-Tibet Plateau which provided an additional evidence for the uplifting of the Qinghai-Tibet Plateau.