Increased amplitudes of electron spin echoes by phase shifted excitation

Excitation by two 90° pulses in phase quadrature lengthens the phase memory time of electron spin echoes. This prolongation enhances the accuracy with which modulations arising from hyperfine interactions can be measured in relatively concentrated spin systems. Comparison of these echoes with ones produced normally (without the phase shift) allow one to measure selectively the electron–electron spin coupling tensor.