52 research outputs found
Laser-induced fine structures on silicon exposed to THz-FEL
We found the irradiation of focused linearly polarized terahertz (THz)-waves emitted from THz free-electron laser (THz-FEL) engraved fine periodic stripe structures on the surfaces of single-crystal Si wafers. The experiments were performed at several wavelengths ranging from 50 to 82 μm with a macro-pulse fluence up to 32 J/cm2. The engraved structures are considered equivalent to the laser-induced periodic surface structures (LIPSS) produced by the irradiation of a femtosecond (fs)-pulsed laser in the near-infrared (NIR) region. However, the minimum period of ∼1/25 of the wavelength in the present case of THz-FEL is surely much smaller than those reported so far by use of fs-lasers and no more explicable by the so far proposed mechanisms. The finer LIPSS confirmed by longer-wavelength laser excitation by means of THz-FEL motivates investigation into the universal mechanism of LIPSS formation, which has been under a hot debate for decades
Spatially Resolved Spectral Imaging by A THz-FEL
Using the unique characteristics of the free-electron-laser (FEL), we successfully
performed high-sensitivity spectral imaging of different materials in the terahertz (THz) and
far-infrared (FIR) domain. THz imaging at various wavelengths was achieved using in situ
spectroscopy by means of this wavelength tunable and monochromatic source. In particular, owing
to its large intensity and directionality, we could collect high-sensitivity transmission imaging of
extremely low-transparency materials and three-dimensional objects in the 3–6 THz range. By
accurately identifying the intrinsic absorption wavelength of organic and inorganic materials, we
succeeded in the mapping of spatial distribution of individual components. This simple imaging
technique using a focusing optics and a raster scan modality has made it possible to set up and
carry out fast spectral imaging experiments on different materials in this radiation facility
Development of a soft X-ray angle-resolved photoemission system applicable to 100 µm crystals
A soft X-ray angle-resolved photoemission system applicable to 100 µm crystals has been developed
- …