But although you can make a microwave oven radiate a lot of energy as highly energetic microwaves, there is no way to make your food radiate microwaves in order to cool itself more quickly. It will only produce ordinary infrared waves. So, if you can provide a large temperature difference, your food will initially cool relatively quickly, with the rate of heat flow gradually dropping as thermal equilibrium approaches. But as it would be very expensive to keep a large cryostat in your kitchen, the largest possible temperature difference available for domestic use is that provided by your freezer. In industry such a device is known as a scraped-surface heat exchanger.
Versions are available for domestic users in the form of ice cream makers.
More rapid cooling can be achieved by liquid nitrogen or, for small quantities of food in an emergency, even a carbon dioxide fire extinguisher. A microwave oven causes heating by increasing the kinetic energy of the water molecules in the food which, at a macroscopic level, manifests itself as an increase in temperature. The radio frequency energy of the microwaves is converted into thermal energy, so the degree of disorder of the system, and hence its entropy, increases. Hence, a microwave cooler would contravene the second law of thermodynamics. While a hot object will cool until it reaches the same temperature as its surroundings, any further decrease in temperature can only be achieved by means of a refrigerator.