Microwave spectroscopy of the positronium fine structure

I will discuss recent measurements of the positronium fine structure performed using microwave spectroscopy. Using pulsed laser excitation, Ps atoms were produced in metastable 2S states and subsequently driven to 2P levels using radiation produced in rectangular waveguides. The transitions were detected via time-resolved gamma-ray lifetime spectroscopy. Various systematic effects related to reflected radiation have been studied, allowing for improved measurements with a modified apparatus. I will also discuss other measurements performed using similar methods such as measurements of the spin polarization of positron beams and tests of C violation. Finally, progress with some new measurements performed using Ramsey spectroscopy will be described.