新しい青色光技術により、ナノスケール技術の解明が進む可能性がある。(New blue light technique could enable advances in understanding nanoscale technologies)

2023-04-19 ブラウン大学

＜関連情報＞

• https://www.brown.edu/news/2023-04-19/blue-light
• https://www.nature.com/articles/s41377-023-01137-y

青色光による近接場テラヘルツ非線形光学系 Near-field terahertz nonlinear optics with blue light

Angela Pizzuto,Pingchuan Ma & Daniel M. Mittleman
Light: Science & Applications  Published:19 April 2023
DOI:https://doi.org/10.1038/s41377-023-01137-y

Abstract

The coupling of terahertz optical techniques to scattering-type scanning near-field microscopy (s-SNOM) has recently emerged as a valuable new paradigm for probing the properties of semiconductors and other materials on the nanoscale. Researchers have demonstrated a family of related techniques, including terahertz nanoscopy (elastic scattering, based on linear optics), time-resolved methods, and nanoscale terahertz emission spectroscopy. However, as with nearly all examples of s-SNOM since the technique’s inception in the mid-1990s, the wavelength of the optical source coupled to the near-field tip is long, usually at energies of 2.5 eV or less. Challenges in coupling of shorter wavelengths (i.e., blue light) to the nanotip has greatly inhibited the study of nanoscale phenomena in wide bandgap materials such as Si and GaN. Here, we describe the first experimental demonstration of s-SNOM using blue light. With femtosecond pulses at 410 nm, we generate terahertz pulses directly from bulk silicon, spatially resolved with nanoscale resolution, and show that these signals provide spectroscopic information that cannot be obtained using near-infrared excitation. We develop a new theoretical framework to account for this nonlinear interaction, which enables accurate extraction of material parameters. This work establishes a new realm of possibilities for the study of technologically relevant wide-bandgap materials using s-SNOM methods.