A High Power ESR Spectrometer for Microwave Stimulated Neutron Scattering*

The physical properties of magnetic condensed matter systems are typically measured while the sample is in thermal equilibrium with its surroundings. We describe the commissioning of a high power, high frequency microwave spectrometer designed to drive magnetic phases out of equilibrium while measuring the inelastic neutron scattering spectrum. A 105 (210) GHz signal is generated at 1 (0.3) W, and directed through a compact, 3D quasi-optical bridge to the sample. By tuning to a resonance condition with a magnetic field, we are able to select our excitation of interest. Reflected microwaves are detected by a heterodyne mixer, and a Martin Puplett Interferometer on the bridge isolates the reflected signal into co-polarized and cross-polarized channels. This unique design allows for compatibility with many top loading magnet systems, the power to induce a statistically significant population inversion required for neutron scattering, and the ability to do Pulsed Electron Spin Resonance experiments as a standalone unit. Performance of the system is shown by Saturation Recovery on a single crystal of Ruby with 0.05% Cr/Al by weight.