Kumar Sandeep, Nivedan Anand, Singh Arvind, Kumar Yogesh, Malhotra Purnima, Tondusson Marc, Freysz Eric, Kumar Sunil
Femtosecond Spectroscopy and Nonlinear Photonics Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India.
Laser Science and Technology Center, Metcalfe House, Civil Lines, New Delhi 110054, India.
iScience. 2021 Sep 21;24(10):103152. doi: 10.1016/j.isci.2021.103152. eCollection 2021 Oct 22.
THz pulses are generated from femtosecond pulse-excited ferromagnetic/nonmagnetic spintronic heterostructures via inverse spin Hall effect. The highest possible THz signal strength from spintronic THz emitters is limited by the optical damage threshold of the corresponding heterostructures at the excitation wavelength. For the thickness-optimized spintronic heterostructure, the THz generation efficiency does not saturate with the excitation fluence even up till the damage threshold. Bilayer (Fe, CoFeB)/(Pt, Ta)-based ferromagnetic/nonmagnetic (FM/NM) spintronic heterostructures have been studied for an optimized performance for THz generation when pumped by sub-50 fs amplified laser pulses at 800 nm. Among them, CoFeB/Pt is the best combination for an efficient THz source. The optimized FM/NM spintronic heterostructure having α-phase Ta as the nonmagnetic layer shows the highest damage threshold as compared to those with Pt, irrespective of their generation efficiency. The damage threshold of the Fe/Ta heterostructure on a quartz substrate is ∼85 GW/cm.
太赫兹脉冲通过逆自旋霍尔效应从飞秒脉冲激发的铁磁/非磁自旋电子异质结构中产生。自旋电子太赫兹发射器可能达到的最高太赫兹信号强度受到相应异质结构在激发波长处的光学损伤阈值的限制。对于厚度优化的自旋电子异质结构，即使直到损伤阈值，太赫兹产生效率也不会随着激发通量而饱和。基于双层(Fe, CoFeB)/(Pt, Ta)的铁磁/非磁(FM/NM)自旋电子异质结构，在由800nm的亚50飞秒放大激光脉冲泵浦时，已针对太赫兹产生的优化性能进行了研究。其中，CoFeB/Pt是高效太赫兹源的最佳组合。与具有Pt的异质结构相比，具有α相Ta作为非磁层的优化FM/NM自旋电子异质结构显示出最高的损伤阈值，无论其产生效率如何。石英衬底上Fe/Ta异质结构的损伤阈值约为85 GW/cm² 。
