Megahertz repetition rate-based lock-in detection scheme for rapid data acquisition in terahertz time domain spectroscopy.

We report a fast pump modulation scheme in a terahertz time domain spectroscopy (THz-TDS) system by utilizing the intensity modulation from the megahertz repetition rate of the pump pulse for lock-in detection. In conventional THz-TDS, the modulation required for the high signal-to-noise ratio lock-in detection is achieved through the use of an optical chopper or an AC bias. Here, we propose the use of an electro-optic modulator (EOM), operated as a pulse picker, to vary the repetition rate of the pump pulse, relative to the probe pulse, allowing us to directly use the megahertz laser repetition rate as the reference modulation frequency for lock-in detection.

Dynamic measurement of an angular Goos-Hänchen shift at a surface plasmon resonance in liquid.

We developed a surface plasmon resonance (SPR)-enhanced angular Goos-Hänchen (GH) shift measurement system capable of tracking small refractive index changes with high sensitivity in a liquid environment. Our method can be performed in angular interrogation schemes, where we demonstrate a simple zero-finding algorithm to locate the SPR angle instead of the complicated data processing algorithms used in conventional sensors. We also propose a displacement interrogation scheme for dynamic measurement of small refractive index changes in the sample.

Monatomic Iodine Dielectric Layer for Multimodal Optical Spectroscopy of Dye Molecules on Metal Surfaces.

Fluorescence and Raman scattering spectroscopies have been used in various research fields such as chemistry, electrochemistry, and biochemistry because they can easily obtain detailed information about molecules at interfaces with visible light. In particular, multimodal fluorescence and Raman scattering spectroscopy have recently attracted significant attention, which enables us to distinguish chemical species and their electronic states that are important for expressing various functions. However, a special strategy is required to perform simultaneous measurements because the cross sections of fluorescence and Raman scattering differ by as much as ∼10.

Localized Graphitization on Diamond Surface as a Manifestation of Dopants.

Doped diamond electrodes have attracted significant attention for decades owing to their excellent physical and electrochemical properties. However, direct experimental observation of dopant effects on the diamond surface has not been available until now. Here, low-temperature scanning tunneling microscopy is utilized to investigate the atomic-scale morphology and electronic structures of (100)- and (111)-oriented boron-doped diamond (BDD) electrodes.