Nuclear magnetic resonance on room temperature samples in nanotesla fields using a two-stage dc superconducting quantum interference device sensor

摘要

We describe a compact system for pulsed nuclear magnetic resonance at ultralow magnetic fields on small liquid samples ( ∼ 0.14 ml) at room temperature. The broadband spectrometer employs an integrated two-stage superconducting quantum interference device current sensor with a coupled energy sensitivity of 50h, in the white noise limit. Environmental noise is screened using a compact arrangement of mu-metal and a superconducting shield. Proton signals in water have been observed down to 93 nT (a Larmor frequency of 4.0 Hz), with a minimum linewidth of 0.16 Hz measured at ∼ 40 Hz. Two-component free induction decays were observed from oil/water mixtures between 275 and 300 K.