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

We present a method for controlling the bulk permeability via spin polariza tion generated by light excitation. This process involves the magnetic inte raction of photoexcited triplets with stable radicals in liquid solution. T he resulting non-Boltzmann spin population of the stable radical is reflect ed by a significant change in the permeability of the chemical system. We d emonstrate how these light-driven changes result in conspicuous changes in the reflection coefficient (amplitude and phase) of a microwave cavity in w hich 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). More over, the nonlinear character of the phenomenon can be utilized for devices , which protect sensitive instrumentation from a strong destructive microwa ve pulse. (C) 2001 American Institute of Physics.