Applications of photoinduced electron spin polarization at room temperature to microwave technology

We present a method for controlling the bulk permeability via spin polarization generated by light excitation. This process involves the magnetic interaction of photoexcited triplets with stable radicals in liquid solution. The resulting non-Boltzmann spin population of the stable radical is reflected by a significant change in the permeability of the chemical system. We demonstrate how these light-driven changes result in conspicuous changes in the reflection coefficient (amplitude and phase) of a microwave cavity in which the active chemical system is placed. This effect can lead the way to ultralow noise microwave amplifiers and low-loss microwave phase shifters, operating at room temperature with very low spin temperature (< 16 K). Moreover, the nonlinear character of the phenomenon can be utilized for devices, which protect sensitive instrumentation from a strong destructive microwave pulse. (C) 2001 American Institute of Physics.