Observing ultrafast pulse-to-pulse dynamics of highly photoexcited materials could foster a compr... more Observing ultrafast pulse-to-pulse dynamics of highly photoexcited materials could foster a comprehensive understanding of the initial stage of irreversible photoinduced events, such as phase change, structural deformation, and laser ablation. In this study, using high-repetition-rate single-shot spectroscopy and a laser microscope, the pulse-to-pulse ultrafast dynamics of energy relaxation in Ge2Sb2Te5 thin films are revealed under high-density photoexcitation that induces sequential events involving the crystalline-to-amorphous phase transition, melt and quench processes, and formation of laser-induced periodic surface structures (LIPSSs). Above the threshold excitation density for LIPSS formation, the first excitation pulse induces the transient transmittance change of the crystalline phase in a picosecond timescale, and subsequent pulses provoke the amorphous phase energy relaxation with a long decay time of hundreds of picoseconds. We observed that the subsequent pulses gradual...
We demonstrate supercontinuum spectral phase interferometry with an isolated attosecond pulse (IA... more We demonstrate supercontinuum spectral phase interferometry with an isolated attosecond pulse (IAP). The interferogram indicates a high degree of temporal coherence over the full IAP continuous spectrum, which will contribute to exploring dispersive electron dynamics. 1. Introduction Combining spatial and temporal detection by means of self-referencing interferometry with high-order harmonics has a variety of applications in, for instance, molecular orbital tomography [1], nanoscale sample imaging [2], and the characterization of complex electron dynamics [3]. Meanwhile, an isolated attosecond pulse (IAP) with short duration and broadband supercontinuum spectrum have contributed to observing ultrafast electronic motions in various targets [4]. The self-referencing interferometry with two IAPs will be an important tool for observing electron dynamics through the phase-based spectroscopy. Here, we demonstrated the supercontinuum spectral phase interferometry with IAP [5]. The coherence over broadband spectral region will contribute to studying the dispersive electron dynamics through Fourier spectroscopy.
We demonstrated a new method of measuring Kerr-ultrafast waveforms using chirped femtosecond puls... more We demonstrated a new method of measuring Kerr-ultrafast waveforms using chirped femtosecond pulses, a single photodiode and an oscilloscope. This allowed thee full pump intensity dependence to bewas obtained recorded within one second.
The combination of terahertz (THz) pulses with scanning tunneling microscopy (STM) enables us to ... more The combination of terahertz (THz) pulses with scanning tunneling microscopy (STM) enables us to investigate ultrafast dynamics at material surfaces with high spatial (nanoscale) and temporal (femtosecond) resolution. In this Perspective, we review the basic principles of THz-STM, outline the related literature, and discuss its future outlook capable of advancing nanoscience, especially by introducing further combination of THz-STM with scanning tunneling luminescence spectroscopy, which can extract more fruitful information about nanoscale materials via obtaining luminescence spectra compared to just observing the net tunneling current induced by THz pulses in THz-STM. By shining THz pulses onto an STM tip, we can observe plasmon luminescence locally confined between the tip and the surface, whose spectrum changes with tip conditions. The combined approach is a stepping stone toward investigating the ultrafast excited-state dynamics of nanoscale materials with high spatiotemporal resolution.
The main objective of this research is to study the effect on gold nanostructures (~10 nm diamete... more The main objective of this research is to study the effect on gold nanostructures (~10 nm diameter size) deposited in highly ordered pyrolytic graphite (HOPG), by measuring coherent phonon spectroscopy with ultrashort (7.5 fs) laser pulses. The gold average thickness d was varied from 2 to 40 Å. We focused on the influence of gold nanoparticles in the interlayer shearing mode E2g, whose energy is about 1.3 THz. We found a destructive interference of the phonon oscillations to decrease the intensity spectral peak which was critical for d=1.8 nm.
Observing ultrafast pulse-to-pulse dynamics of highly photoexcited materials could foster a compr... more Observing ultrafast pulse-to-pulse dynamics of highly photoexcited materials could foster a comprehensive understanding of the initial stage of irreversible photoinduced events, such as phase change, structural deformation, and laser ablation. In this study, using high-repetition-rate single-shot spectroscopy and a laser microscope, the pulse-to-pulse ultrafast dynamics of energy relaxation in Ge2Sb2Te5 thin films are revealed under high-density photoexcitation that induces sequential events involving the crystalline-to-amorphous phase transition, melt and quench processes, and formation of laser-induced periodic surface structures (LIPSSs). Above the threshold excitation density for LIPSS formation, the first excitation pulse induces the transient transmittance change of the crystalline phase in a picosecond timescale, and subsequent pulses provoke the amorphous phase energy relaxation with a long decay time of hundreds of picoseconds. We observed that the subsequent pulses gradual...
We demonstrate supercontinuum spectral phase interferometry with an isolated attosecond pulse (IA... more We demonstrate supercontinuum spectral phase interferometry with an isolated attosecond pulse (IAP). The interferogram indicates a high degree of temporal coherence over the full IAP continuous spectrum, which will contribute to exploring dispersive electron dynamics. 1. Introduction Combining spatial and temporal detection by means of self-referencing interferometry with high-order harmonics has a variety of applications in, for instance, molecular orbital tomography [1], nanoscale sample imaging [2], and the characterization of complex electron dynamics [3]. Meanwhile, an isolated attosecond pulse (IAP) with short duration and broadband supercontinuum spectrum have contributed to observing ultrafast electronic motions in various targets [4]. The self-referencing interferometry with two IAPs will be an important tool for observing electron dynamics through the phase-based spectroscopy. Here, we demonstrated the supercontinuum spectral phase interferometry with IAP [5]. The coherence over broadband spectral region will contribute to studying the dispersive electron dynamics through Fourier spectroscopy.
We demonstrated a new method of measuring Kerr-ultrafast waveforms using chirped femtosecond puls... more We demonstrated a new method of measuring Kerr-ultrafast waveforms using chirped femtosecond pulses, a single photodiode and an oscilloscope. This allowed thee full pump intensity dependence to bewas obtained recorded within one second.
The combination of terahertz (THz) pulses with scanning tunneling microscopy (STM) enables us to ... more The combination of terahertz (THz) pulses with scanning tunneling microscopy (STM) enables us to investigate ultrafast dynamics at material surfaces with high spatial (nanoscale) and temporal (femtosecond) resolution. In this Perspective, we review the basic principles of THz-STM, outline the related literature, and discuss its future outlook capable of advancing nanoscience, especially by introducing further combination of THz-STM with scanning tunneling luminescence spectroscopy, which can extract more fruitful information about nanoscale materials via obtaining luminescence spectra compared to just observing the net tunneling current induced by THz pulses in THz-STM. By shining THz pulses onto an STM tip, we can observe plasmon luminescence locally confined between the tip and the surface, whose spectrum changes with tip conditions. The combined approach is a stepping stone toward investigating the ultrafast excited-state dynamics of nanoscale materials with high spatiotemporal resolution.
The main objective of this research is to study the effect on gold nanostructures (~10 nm diamete... more The main objective of this research is to study the effect on gold nanostructures (~10 nm diameter size) deposited in highly ordered pyrolytic graphite (HOPG), by measuring coherent phonon spectroscopy with ultrashort (7.5 fs) laser pulses. The gold average thickness d was varied from 2 to 40 Å. We focused on the influence of gold nanoparticles in the interlayer shearing mode E2g, whose energy is about 1.3 THz. We found a destructive interference of the phonon oscillations to decrease the intensity spectral peak which was critical for d=1.8 nm.
Uploads
Papers by Ikufumi Katayama