Optical damage limit of efficient spintronic THz emitters

Area of Science:

• Terahertz (THz) science and technology
• Spintronics
• Optoelectronics

Background:

• Terahertz (THz) pulses are generated using femtosecond laser excitation of ferromagnetic/nonmagnetic spintronic heterostructures via the inverse spin Hall effect.
• The THz signal strength is fundamentally limited by the optical damage threshold of these heterostructures.

Purpose of the Study:

• To optimize spintronic heterostructures for efficient THz generation.
• To investigate the relationship between material composition, optical damage threshold, and THz generation efficiency.

Main Methods:

• Fabrication and characterization of various bilayer (Fe, CoFeB)/(Pt, Ta) spintronic heterostructures.
• Optical pumping experiments using sub-50 fs amplified laser pulses at 800 nm.
• Measurement of THz signal strength and determination of optical damage thresholds.

Main Results:

• CoFeB/Pt demonstrated the highest THz generation efficiency among the studied combinations.
• Optimized heterostructures with an alpha-phase Ta nonmagnetic layer exhibited the highest optical damage threshold compared to Pt.
• The Fe/Ta heterostructure showed a damage threshold of approximately 85 GW/cm^2 on a quartz substrate.
• THz generation efficiency did not saturate with excitation fluence up to the damage threshold for thickness-optimized structures.

Conclusions:

• Spintronic heterostructures, particularly CoFeB/Pt, are promising for efficient THz sources.
• Incorporating alpha-phase Ta enhances the optical damage threshold of spintronic THz emitters, enabling higher THz output.
• Further optimization of spintronic heterostructures is key to overcoming current limitations in THz generation.