Look up "Thermoacoustic laser" on google, and then look it up
on youtube. Its one of the simplest and coolest demos I've seen!
I messed with it (using the celcor material that forms their thermal
stacks) and got it to work using a cigar tube, PC power supply, and
piece of blow-drier nichrome. Celcor is used in catalytic converters.
Its refractory, a square array of rectangular tubes, lots of surface
area, doesn't conduct heat well.

Stick it in a test tube with a heating coil on the closed side and it
self-oscillates. The temp diff across the stack provides gain.

One group uses this to make electricity from waste heat, another
to run in reverse and make a fridge!

Weird but true science/engineering.

Though its a hundred years old (glass wool, bunsen burner, metal tube).