Circular polarization excitation and detection in (14)N NQR

Circular polarization excitation and detection of (14)N NQR signal are reported. A theoretical model is presented in terms of fictitious spin-1/2 operators and is compared to experiments performed on a powder crystalline sample of RDX. It is shown that in spin-1 systems with finite asymmetry--unlike previously reported NMR and symmetric spin-3/2 NQR systems (Chen et al., J. Magn. Reson. 54, 324--327, 1983; Weber and Hahn, Phys. Rev. 120, 365--375, 1960)-the circular polarization nature of the signal is due to powder orientation effects in polycrystalline samples. Sensitivity improvements up to a factor of the square root of 2 are reported using the same hardware and switching modes from linear polarization to circular polarization; this also is shown to result from the polycrystalline nature of the samples.