Since there is a paywall it will do no good to give you a link to the New York Times story that states that the Department of Homeland Security contemplated using a heat ray weapon against migrants in 2018. It was never authorized for use.

To provide a little bit of background on the impact of a "heat gun" there is this CBS video (I recalled seeing it on 60 Minutes), The Ray Gun in Action

Another story, Active Denial System Tested