The ultrafast coherent manipulation of electrons using waveform-controlled laser pulses 1-9 is a key issue in the development of modern electronics 10,11. Developing such an approach for a tunnel junction will provide a new platform for governing ultrafast currents on an ever smaller scale, which will be indispensable for the advancement of next-generation quantum nanocircuits 12-15 and plasmonic devices 16-18. Here, we demonstrate that carrier-envelope phase controlled single-cycle terahertz electric fields can coherently drive electron tunnelling either from a nanotip to a sample or vice versa. Spatially confined electric fields of more than 10 V/nm strongly modulate the potential barrier at a nanogap in a scanning tunnelling microscope (STM) within a sub-picosecond time scale and can steer a huge number of electrons in an extremely nonlinear regime, which is not possible using a conventional STM. Our results are expected to pave the way for the future development of nanoscale science and technologies.
Terahertz time domain spectroscopy was performed on orthoferrite ErFeO3. Through the emission from the two magnetic resonance modes, we succeeded in observing the spin reorientation transition. Depending on the orientation of the single crystal, the reorientation can be detected as either mode switching between the two modes or polarization change of the emission. This method enables picosecond resolved observation of the reorientation without disturbances such as electronic excitation and heating, and it is expected to open the doorway to observe ultrafast reorientation with the terahertz pulse.
We have observed an irreversible ultrafast crystalline-to-amorphous phase transition in Ge2Sb2Te5 chalcogenide alloy thin film using broadband single-shot imaging spectroscopy. The absorbance change that accompanied the ultrafast amorphization was measured via single-shot detection even for laser fluences above the critical value, where a permanent amorphized mark was formed. The observed rise time to reach the amorphization was found to be ∼130–200 fs, which was in good agreement with the half period of the A1 phonon frequency in the octahedral GeTe6 structure. This result strongly suggests that the ultrafast amorphization can be attributed to the rearrangement of Ge atoms from an octahedral structure to a tetrahedral structure. Finally, based on the dependence of the absorbance change on the laser fluence, the stability of the photoinduced amorphous phase is discussed.
Single-shot measurements of terahertz (THz) electric-field waveforms are demonstrated using a reflective echelon mirror, which produces multiple probe pulses with different time-delays. The polarization rotation of the probe pulses, due to the electro-optic effect induced by the THz electric field generated from grating-coupled LiNbO 3 , was imaged onto a two-dimensional complementary metal-oxide-semiconductor camera. A waveform with a weak peak field strength of 0.6 kV/cm was obtained with a good signal-to-noise ratio, demonstrating precise single-shot detection of the THz electric field waveform. V
Improved control over the electromagnetic properties of metal nanostructures is indispensable for the development of next-generation integrated nanocircuits and plasmonic devices. The use of terahertz (THz)-field-induced nonlinearity is a promising approach to controlling local electromagnetic properties. Here, we demonstrate how intense THz electric fields can be used to modulate electron delocalization in percolated gold (Au) nanostructures on a picosecond time scale. We prepared both isolated and percolated Au nanostructures deposited on high resistivity Si(100) substrates. With increasing the applied THz electric fields, large opacity in the THz transmission spectra takes place in the percolated nanostructures; the maximum THz-field-induced transmittance difference, 50% more, is reached just above the percolation threshold thickness. Fitting the experimental data to a Drude-Smith model, we found furthermore that the localization parameter and the damping constant strongly depend on the applied THz-field strength. These results show that ultrafast nonlinear electron delocalization proceeds via strong electric field of THz pulses; the intense THz electric field modulates the backscattering rate of localized electrons and induces electron tunneling between Au nanostructures across the narrow insulating bridges without any material breakdown.
We introduce a simple and efficient method of enhancing the terahertz field in an air plasma produced by two-color laser pulses, by inserting a specially designed dual-wavelength wave plate between the non-linear optical crystal and the plasma. Adjusting the polarization of the two laser pulses yielded an electric field of 1.4 MV/cm, which was 1.7 times as intense as that obtained from the unmodified system. Additionally, taking a dispersion of the group velocities of the two-color laser pulses into account, we discussed the validity of the enhancement factor.
We demonstrate the real-time observation of phonon-polariton propagation in ferroelectric LiNbO 3 using a single-shot spectroscopic setup that employs an echelon mirror. The echelon mirror provides a spatially encoded time delay for the probe pulse; therefore, the ultrafast transient behavior of materials can be detected on a single-shot basis. Using optical Kerr gate apparatus, forward and backward propagating E-mode phonon-polaritons were simultaneously induced via an impulsive stimulated Raman scattering process, and subsequently, their dynamics were readily mapped in time-frequency space using heterodyne detection. The two phonon-polaritons appeared on opposite sides of the central probe wavelength and were symmetrically imaged against the ordinary and extraordinary probe lights. By taking into account coupling of the lowest E-mode phonon-polariton to a low-frequency relaxational mode, not only the phonon-polariton dispersion but also the wavevector dependence of the damping rate was unveiled and quantitatively evaluated. V
We have generated and detected a longitudinally polarized (Z-polarized) terahertz (THz) wave by focusing a conically propagating THz beam generated from a plasma filament induced by a femtosecond laser pulse. In the experiment, we observed a radially polarized field in a collimated region and Z-polarized field at focus in the time domain. The maximum value of the Z-polarized THz electric field reached 1.0 kV/cm. It was also quantitatively discussed about the Z-polarized field and the radial field at the focal point. We expect this technique to find application in THz time domain spectroscopy.
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