Broadband terahertz wave generation from an epsilon-near-zero material

Area of Science:

• Optics and Photonics
• Materials Science

Background:

• Broadband terahertz (THz) light sources are crucial for applications like noninvasive imaging and spectroscopy.
• Conventional THz generation methods using bulk nonlinear crystals are limited by phase-matching conditions, restricting bandwidth.

Purpose of the Study:

• To demonstrate broadband THz emission using surface optical rectification from a thin indium tin oxide (ITO) film.
• To investigate the enhancement of THz signal generation by tuning the pump laser to the epsilon-near-zero (ENZ) region of ITO.

Main Methods:

• Surface optical rectification was employed using a 19 nm-thick ITO thin film.
• The pump laser wavelength was tuned to the ENZ region of ITO to leverage field enhancement.
• The bandwidth of the generated THz signal was measured.

Main Results:

• Broadband THz emission with a bandwidth exceeding 3 THz was achieved from the ITO thin film.
• A significant enhancement in the THz signal was observed when the pump laser was tuned to the ENZ region of ITO.
• The THz generation was not limited by the phase-matching condition.

Conclusions:

• Subwavelength thin films of epsilon-near-zero (ENZ) materials offer a novel pathway for broadband THz generation.
• Surface optical rectification in ITO thin films provides a method for THz emission unrestricted by phase-matching conditions.
• This technique presents emerging physics distinct from conventional nonlinear crystals for THz applications.