Laser-controlled superconducting switch for low-field NMR applications

In the case of a low-field nuclear magnetic resonance (NMR) system, the sensible magnetic sensor can be screened or even damaged by the large magnetic field produced during the polarisation phase. A switch is then necessary to preserve this sophisticated sensor. A simple and efficient switch is described here. It is made of a twisted and wound wire heated by a laser beam, in which the alignment is simple by construction. The switch can be used without any additional contact in sensing coils, has a low inductance and flips within milliseconds. It is shown that the switch resistance in open conditions is sufficient for low-field NMR applications and that a memory behaviour can be exhibited.