A simultaneous measurement method was developed to permit the multiple detection of the first-and second-order harmonic displays of electron paramagnetic resonance (EPR) spectra. Application of integration and differentiation of amplitude and phase simultaneously, i.e., vector operations on the various displays, enables identification of signals expressed by the various harmonics. By using simultaneous detection, we found for the first time that signals indicated by the different displays are not always identical. The transformation from the first to the second harmonic displays (or vice versa) by vector operations indicated that the displays were not interchangeable when nonlinear response was involved. Simultaneous detection proved to be useful for measurements of the electron spin relaxation where multiple signals coexist. The present detection system provides a means for multivector EPR spectroscopy.
Yuhei Shimoyama and Hiroshi Watari, "Multiple Harmonic Electron Paramagnetic Resonance Spectroscopy by Simultaneous Detection," Appl. Spectrosc. 43, 1021-1026 (1989)