Preparation And Terahertz Radiation Characteristics Of Nanocrystal Diamond-based Composite Metasurface

With the development of ultrafast laser technology and semiconductor growth technology,more and more emerging materials have been proven to generate terahertz(THz)radiation under femtosecond laser irradiation,providing many alternative materials for finding suitable THz sources.Nanocrystal diamond(NCD),as a nanomaterial,possesses excellent properties of both diamond and nanomaterials,and its excellent optoelectronic properties make it promising for a wide range of applications in the field of THz.However,there is still a lack of research on its THz emission properties.Meanwhile,the weak light-matter interaction in NCD makes its THz emission efficiency low.Based on this,this thesis investigates the THz radiation properties of NCD using a THz emission spectroscopy system and analyzes the mechanism of its generation.On top of that,the split-ring resonator(SRR),which can introduce resonance at the desired wavelength position,is designed and combined with the NCD.Using a THz emission spectroscopy system to analyze the THz generation process in the composite metasurface.The main work of this thesis is as follows:(1)The THz radiation properties of NCD film were investigated using a THz emission spectroscopy system.The results show that the NCD film can produce broadband THz radiation with a bandwidth of about 2.5 THz under 800 nm femtosecond laser excitation.The dependence of the THz radiation generated by NCD on the sample azimuth,incident light pumping fluence,and incident light polarization angle indicates that the generation of the THz radiation in the NCD film is dominated by the photon drag effect.(2)The split-ring resonator plasmonic metasurface which can excite higher-order magnetic resonance modes under fundamental frequency light irradiation at 800 nm was designed and prepared.The THz radiation properties generated by the SRR higher-order magnetic resonance mode were investigated using THz emission spectroscopy.The results show that under femtosecond laser excitation,the SRR higher-order magnetic resonance mode can produce a broadband THz radiation comparable to that of the magnetic dipole resonance mode through the resonant optical rectification.Since the transient current in the SRR is divided into three segments in the higher-order magnetic resonance mode,it makes the generated THz radiation more sensitive to the azimuthal angle and exhibits a 3-fold rotational symmetry relationship.(3)The split-ring resonator was fabricated on the nanocrystal diamond film(SRR-NCD)using micro and nano processing techniques.The THz radiation properties of the SRR-NCD were investigated by THz emission spectroscopy.The experimental results show that the SRRNCD produces angular-dependent THz radiation under 800 nm femtosecond laser excitation,and the mechanism of the THz radiation generation is different for pump light excitation with different incidences.The THz radiation of the SRR-NCD under normal incidence mainly originates from the resonant optical rectification in SRR,and the THz radiation generation under oblique incidence is produced by the interplay between the NCD film and SRR.According to the THz radiation dependence of NCD,SRR and SRR-NCD on the incidence angle,the contribution ratio of the NCD film and SRR for the THz radiation in the SRR-NCD is calculated as 2.5:1 under the 40° incidence.