Efficient Cherenkov-type optical-to-terahertz converter with terahertz beam combining

Area of Science:

• Optics and Photonics
• Materials Science
• Electromagnetism

Background:

• Efficient generation of terahertz (THz) radiation is crucial for various scientific and technological applications.
• Existing methods for THz emission often face limitations in efficiency, beam quality, or spectral characteristics.
• Cherenkov-type radiation offers a promising mechanism for THz generation, but requires optimized structures.

Purpose of the Study:

• To propose, model, and experimentally demonstrate a novel nonlinear structure for efficient Cherenkov-type terahertz emission.
• To investigate the characteristics of the generated THz radiation, including beam profile, spectral flatness, and conversion efficiency.
• To explore methods for further enhancement of the THz generation process.

Main Methods:

• A nonlinear structure composed of a thin lithium niobate layer sandwiched between two silicon prisms was designed.
• Ultrashort laser pulses were focused to a line and propagated through the lithium niobate layer.
• The generated Cherenkov wedge of terahertz radiation was analyzed, including its propagation and emergence into free space.

Main Results:

• The proposed structure successfully generated a Cherenkov-type terahertz wedge, which emerged as two collinear beams.
• A centimeter-wide terahertz beam with high transverse uniformity and a flat frequency spectrum was achieved.
• An optical-to-terahertz conversion efficiency of up to 0.35% was demonstrated with 10-µJ laser pulses.

Conclusions:

• The demonstrated nonlinear structure provides an efficient method for generating high-quality terahertz radiation from ultrashort laser pulses.
• The structure's performance can be further improved by reducing the thickness of the lithium niobate layer.
• This approach holds potential for advancing THz spectroscopy, imaging, and communication technologies.