Ultrashort energetic terahertz(THz)pulses have created an exciting new area of research on light interactions with matter.For material studies in small laboratories,widely tunable femtosecond THz pulses with peak fiel...Ultrashort energetic terahertz(THz)pulses have created an exciting new area of research on light interactions with matter.For material studies in small laboratories,widely tunable femtosecond THz pulses with peak field strength close to MV cm-1 are desired.Currently,they can be largely acquired by optical rectification and difference frequency generation in crystals without inversion symmetry.We describe in this paper a novel scheme of THz pulse generation with no frequency tuning gap based on Raman-resonance-enhanced four-wave mixing in centrosymmetric media,particularly diamond.We show that we could generate highly stable,few-cycle pulses with near-Gaussian spatial and temporal profiles and carrier frequency tunable from 5 to>2o THz.They had a stable and controllable carrier-envelop phase and carried~15 nJ energy per pulse at 10 THz(with a peak field strength of~1 MV cm^(-1)at focus)from a O.5-mm-thick diamond.The measured THz pulse characteristics agreed well with theoretical predictions.Other merits of the scheme are discussed,including the possibility of improving the THz output energy to a much higher level.展开更多
A high-sensitivity DC magneto-optical Kerr effect(MOKE)apparatus is described in this Letter.Via detailed analysis on several dominatingnoise sources,we have proposed solutions that significantly lower the MOKE noise,...A high-sensitivity DC magneto-optical Kerr effect(MOKE)apparatus is described in this Letter.Via detailed analysis on several dominatingnoise sources,we have proposed solutions that significantly lower the MOKE noise,and a sensitivity of 1.5×10^(-7)rad/√Hz is achieved with long-term stability.The sensitivity of the apparatus is tested by measuring a wedgeshaped Ni thin film on SiO_(2)with Ni thickness varying from 0 to 3 nm.A noise floor of 1.5×10^(-8)rad is demonstrated.The possibility of further improving sensitivity to 10^(-9)rad via applying AC modulation is also discussed.展开更多
The surface/interface species in perovskite oxides play essential roles in many novel emergent physical phenomena and chemical processes.With low eigen-energies in the terahertz region,such species at buried interface...The surface/interface species in perovskite oxides play essential roles in many novel emergent physical phenomena and chemical processes.With low eigen-energies in the terahertz region,such species at buried interfaces remain poorly understood due to the lack of feasible surface-specific spectroscopic probes to resolve the resonances.Here,we show that polarized phonons and two-dimensional electron gas at the interface can be characterized using surface-specific nonlinear optical spectroscopy in the terahertz range.This technique uses intra-pulse difference frequency mixing process,which is allowed only at the surface/interface of a centrosymmetric medium.Submonolayer sensitivity can be achieved using the state-of-the-art detection scheme for the terahertz emission from the surface/interface.Through symmetry analysis and proper polarization selection,background-free Drude-like nonlinear response from the two-dimensional electron gas emerging at the LaAlO3/SrTiO3 or Al2O3/SrTiO3 interface was successfully observed.The surface/interface potential,which is a key parameter for SrTiO3-based interface superconductivity and photocatalysis,can now be determined optically in a nonvacuum environment via quantitative analysis on the phonon spectrum that was polarized by the surface field in the interfacial region.The interfacial species with resonant frequencies in the THz region revealed by our method provide more insights into the understanding of physical properties of complex oxides.展开更多
基金This work was supported by the National Natural Science Foundation of China Grants(No.12125403 and No.11874123)the National Key Research and Development Program of China(No.2021YFA1400503 and No.2021YFA1400202).
文摘Ultrashort energetic terahertz(THz)pulses have created an exciting new area of research on light interactions with matter.For material studies in small laboratories,widely tunable femtosecond THz pulses with peak field strength close to MV cm-1 are desired.Currently,they can be largely acquired by optical rectification and difference frequency generation in crystals without inversion symmetry.We describe in this paper a novel scheme of THz pulse generation with no frequency tuning gap based on Raman-resonance-enhanced four-wave mixing in centrosymmetric media,particularly diamond.We show that we could generate highly stable,few-cycle pulses with near-Gaussian spatial and temporal profiles and carrier frequency tunable from 5 to>2o THz.They had a stable and controllable carrier-envelop phase and carried~15 nJ energy per pulse at 10 THz(with a peak field strength of~1 MV cm^(-1)at focus)from a O.5-mm-thick diamond.The measured THz pulse characteristics agreed well with theoretical predictions.Other merits of the scheme are discussed,including the possibility of improving the THz output energy to a much higher level.
基金support from the National Natural Science Foundation of China(Nos.12125403 and 11874123)the Shanghai Science and Technology Committee(No.20ZR1406000)。
文摘A high-sensitivity DC magneto-optical Kerr effect(MOKE)apparatus is described in this Letter.Via detailed analysis on several dominatingnoise sources,we have proposed solutions that significantly lower the MOKE noise,and a sensitivity of 1.5×10^(-7)rad/√Hz is achieved with long-term stability.The sensitivity of the apparatus is tested by measuring a wedgeshaped Ni thin film on SiO_(2)with Ni thickness varying from 0 to 3 nm.A noise floor of 1.5×10^(-8)rad is demonstrated.The possibility of further improving sensitivity to 10^(-9)rad via applying AC modulation is also discussed.
基金C.T.acknowledges the funding support from the National Key Research and Development Program of China(nos.2021YFA1400503 and 2021YFA1400202)National Natural Science Foundation of China(nos.12125403,11874123,and 12221004)+2 种基金Shanghai Science and Technology Committee(no.20ZR1406000)L.C.acknowledges the support from the National Natural Science Foundation of China(no.12104305)X.Z.acknowledges the support from the Science and Technology Commission of Shanghai Municipality(no.21JC1405000).
文摘The surface/interface species in perovskite oxides play essential roles in many novel emergent physical phenomena and chemical processes.With low eigen-energies in the terahertz region,such species at buried interfaces remain poorly understood due to the lack of feasible surface-specific spectroscopic probes to resolve the resonances.Here,we show that polarized phonons and two-dimensional electron gas at the interface can be characterized using surface-specific nonlinear optical spectroscopy in the terahertz range.This technique uses intra-pulse difference frequency mixing process,which is allowed only at the surface/interface of a centrosymmetric medium.Submonolayer sensitivity can be achieved using the state-of-the-art detection scheme for the terahertz emission from the surface/interface.Through symmetry analysis and proper polarization selection,background-free Drude-like nonlinear response from the two-dimensional electron gas emerging at the LaAlO3/SrTiO3 or Al2O3/SrTiO3 interface was successfully observed.The surface/interface potential,which is a key parameter for SrTiO3-based interface superconductivity and photocatalysis,can now be determined optically in a nonvacuum environment via quantitative analysis on the phonon spectrum that was polarized by the surface field in the interfacial region.The interfacial species with resonant frequencies in the THz region revealed by our method provide more insights into the understanding of physical properties of complex oxides.
