Spintronic terahertz emitters with integrated metallic terahertz cavities

Area of Science:

• Solid State Physics
• Terahertz (THz) Photonics
• Spintronics

Background:

• Spintronic terahertz emitters (STEs) are crucial for generating THz pulses via optical excitation of ferromagnetic/heavy metal (FM/HM) heterojunctions.
• Current optical-to-THz conversion efficiency in STEs is limited, despite advancements in optical absorption enhancement techniques.
• The application of THz cavities for enhancing STE efficiency has not been previously investigated.

Purpose of the Study:

• To enhance the terahertz (THz) emission efficiency of spintronic terahertz emitters (STEs) within a specific THz spectral range.
• To explore the use of THz resonant cavities for improving THz generation from FM/HM heterostructures.

Main Methods:

• Fabrication of FM/HM structures on ultra-thin sapphire layers capped with metallic mirrors to form lambda/4 THz resonant cavities.
• Utilized THz emission time-domain spectroscopy on STE/sapphire/mirror heterostructures with varying sapphire thicknesses (110 µm to 25 µm).
• Performed temporal simulations to model the emitted THz pulse and validate experimental results.

Main Results:

• Observed significant enhancement of the emitted THz field, consistent with lambda/4 cavity resonance.
• Achieved up to a doubling of the THz field strength within the targeted spectral range.
• Demonstrated control over the polarization state of the emitted THz pulse using birefringent materials.

Conclusions:

• The integration of THz cavities offers a viable strategy for enhancing and engineering THz emission from STEs.
• The developed cavity-based approach allows for spectral control over a broad range and can be combined with optical cavities.
• This work paves the way for more efficient and tunable THz sources based on spintronic principles.