Probehead with interchangeable tunable bridged loop-gap resonator for pulsed zero-field optically detected magnetic resonance experiments on photoexcited triplet states

Abstract

Conventional zero-field optically detected magnetic resonance (ODMR) is normally performed by using a slow-wave helix for microwave excitation with a quality factor Q≈1. With available microwave sources this low Q factor leads to long microwave pulse lengths for coherent pulse experiments (π-pulse duration of about 300 ns for 20 W microwave excitation power). For our zero-field experiments we took advantage of the bridged loop-gap microwave resonator configuration with relatively high Q factor. Without the possibility of tuning the Zeeman energy level splitting as in electron paramagnetic resonance (EPR), in zero-field ODMR the resonator has to cover a wide range of frequencies. We are able to tune our probehead in the range of 1.9–8 GHz with a loaded Q factor of up to 800 by using interchangeable bridged loop-gap resonators of various designs. Thereby, the pulse lengths, compared to the slow-wave helix, could be reduced by nearly one order of magnitude (tresonatorπ=45 ns employing the same microwave power of 20 W). Experimental data are presented for triplet states of photoexcited acridine and benzophenone molecules at different resonance frequencies for their |Tx〉−|Tz〉 transitions (ν=2.472 GHz and ν=5.226 GHz), respectively.