Lasers and microwaves both would work. This paper from 30 years ago shows 50%+ efficiency with microwaves. https://ui.adsabs.harvard.edu/abs/1992ITMTT..40.1239

Lasers and microwaves both would work. This paper from 30 years ago shows 50%+ efficiency with microwaves. https://ui.adsabs.harvard.edu/abs/1992ITMTT..40.1239B/abstract https://ui.adsabs.harvard.edu/abs/1992ITMTT..40.1239B/abstra...