US PATENT-Systems, apparatus, and methods of nonlinear terahertz (THz) magnetic resonance measurement

United States Patent 9945914
Inventors:
Hwang, Harold Young (Cambridge, MA, US) 
Lu, Jian (Medford, MA, US) 
Zhang, Yaqing (Cambridge, MA, US) 
Ofori-okai, Benjamin K. (Cambridge, MA, US) 
Nelson, Keith A. (Newton, MA, US) 
Li, Xian (Cambridge, MA, US) 

http://www.freepatentsonline.com/9945914.html

A nonlinear terahertz (THz) spectroscopy technique uses a sample illuminated by two THz pulses separately. The illumination generates two signals BA and BB, corresponding to the first and second THz pulse, respectively, after interaction with the sample. The interaction includes excitation of at least one ESR transition in the sample. The sample is also illuminated by the two THz pulses together, with an inter-pulse delay τ, generating a third signal BAB. A nonlinear signal BNL is then derived via BNL=BAB−BA−BB. This nonlinear signal BNL can be then processed (e.g., Fourier transform) to study the properties of the sample.

Abstract-Nonlinear high-temperature superconducting terahertz metamaterials

Nathaniel K Grady¹, Bradford G Perkins Jr^2,3, Harold Y Hwang², Nathaniel C Brandt², Darius Torchinsky², Ranjan Singh¹, Li Yan¹, Daniel Trugman¹, Stuart A Trugman¹, Q X Jia¹, Antoinette J Taylor¹, Keith A Nelson² and Hou-Tong Chen^1,4

http://iopscience.iop.org/1367-2630/15/10/105016

We report the observation of a nonlinear terahertz response of split-ring resonator arrays made of high-temperature superconducting films. Intensity-dependent transmission measurements indicate that the resonance strength decreases dramatically (i.e. transient bleaching) and the resonance frequency shifts as the intensity is increased. Pump–probe measurements confirm this behaviour and reveal dynamics on the few-picosecond timescale.