On the progress of ultrafast time-resolved THz scanning tunneling microscopy

Scanning tunneling microscopy combined with terahertz (THz) electromagnetic pulses and its related technologies have developed remarkably. This technology has atomic-level spatial resolution in an ultrahigh vacuum and low-temperature environment, and it measures the electrical dynamical behavior of a sample’s surface with femtosecond temporal resolution. In particular, it has been used to image the diffusion and relaxation dynamics of electrons in real time and real space and even instantaneously control molecular motions. In this Perspective, we focus on recent progress in research and development of ultrafast time-resolved THz scanning tunneling microscopy and its application to materials research

Acoustic whispering-gallery modes generated and dynamically imaged with ultrashort optical pulses

Broadband coherent surface phonon wave packets up to 1 GHz in a microscopic embedded disk are excited and dynamically imaged with ultrashort optical pulses. We isolate a whispering-gallery-like mode using a technique involving quadrature detection of the out-of-plane surface motion on modulating the optical excitation beam. The eigenmode distribution is obtained from spatiotemporal Fourier transforms and a radial-azimuthal decomposition demonstrates the selective excitation of a mode with 26-fold rotational symmetry and allows an estimate of the cavity Q factor to be made

On the progress of ultrafast time-resolved THz scanning tunneling microscopy

Scanning tunneling microscopy combined with terahertz (THz) electromagnetic pulses and its related technologies have developed remarkably. This technology has atomic-level spatial resolution in an ultrahigh vacuum and low-temperature environment, and it measures the electrical dynamical behavior of a sample’s surface with femtosecond temporal resolution. In particular, it has been used to image the diffusion and relaxation dynamics of electrons in real time and real space and even instantaneously control molecular motions. In this Perspective, we focus on recent progress in research and development of ultrafast time-resolved THz scanning tunneling microscopy and its application to materials research

A Real-Time Terahertz Time-Domain Polarization Analyzer with 80-MHz Repetition-Rate Femtosecond Laser Pulses

We have developed a real-time terahertz time-domain polarization analyzer by using 80-MHz repetition-rate femtosecond laser pulses. Our technique is based on the spinning electro-optic sensor method, which we recently proposed and demonstrated by using a regenerative amplifier laser system; here we improve the detection scheme in order to be able to use it with a femtosecond laser oscillator with laser pulses of a much higher repetition rate. This improvement brings great advantages for realizing broadband, compact and stable real-time terahertz time-domain polarization measurement systems for scientific and industrial applications

Ultrafast ellipsometric interferometry for direct detection of coherent phonon strain pulse profiles

We describe an ultrafast optical technique to quantitatively detect picosecond ultrasonic displacements of solid surfaces, thus giving access to the longitudinal strain pulse shape. Transient optical reflectance changes recorded at oblique optical incidence with a common-path interferometric configuration based on ultrafast ellipsometry monitor gigahertz coherent phonon pulses. We demonstrate for a tungsten film the quantitative extraction of the strain pulse shape free of distortions arising from the photoelastic effect, and analyze the results with the two-temperature model to obtain the value g approximate to 3 x 10(17) Wm(-3) K-1 for the electron-phonon coupling constant. Analysis of the data also reveals a thermo-optic contribution. (C) 2013 Optical Society of Americ

Terahertz ultrasonic generation and detection in GaAs/AlGaAs quantum wells

High frequency ultrasonic pulse generation and detection are investigated in a sample with three embedded GaAs/Al0.3Ga0.7As quantum wells by means of ultrashort optical pulses. The experimental results, showing that ultrasonic frequencies up to 0.5 THz are detected, are compared with numerical simulations of the ultrasonic pulse generation, propagation and attenuation, and of the optical detection process. The effective optical extinction coefficients of the embedded quantum wells and the ultrasonic attenuation coefficient of Al0.3Ga0.7As are determined from the analysis

Spectral analysis of amplitude and phase echoes in picosecond ultrasonics for strain pulse shape determination.

We introduce a spectral analysis method in picosecond ultrasonics to derive strain pulse shapes in a opaque sample with known optical properties. The method makes use of both the amplitude and phase of optical transient relative reflectance changes obtained, for example, by interferometry. We demonstrate this method through numerical simulation and by analysis of experimental results for a chromium film

Scanning ultrafast Sagnac interferometry for imaging two-dimensional surface wave propagation

We describe an improved two-dimensional optical scanning technique combined with an ultrafast Sagnac interferometer for delayed-probe imaging of surface wave propagation. We demonstrate the operation of this system, which involves the use of a single focusing objective, by monitoring surface acoustic wave propagation on opaque substrates with picosecond temporal and micron lateral resolutions. An improvement in the lateral resolution by a factor of 3 is achieved in comparison with previous setups for similar samples