  Active photonic cooling is of significant importance to realize robust,
compact, vibration-free, all-solid-state refrigeration. Currently proposed
photonic cooling approaches are based on luminescence and impose stringent
requirements on luminescence efficiency. We propose a new photonic cooling
mechanism arising from temporal modulation of thermal emission. We show that
this mechanism has a high thermodynamic performance that can approach the
Carnot limit and yet does not rely on luminescence. Further, our work opens
exciting new avenues in active, time-modulated control of thermal emission for
cooling and energy harvesting applications.
