I was just following along with this experiment for measuring the ripples in float glass:
Here is my setup:
I noticed that the laser (one of the cheapest available from aliexpres) was not particularly stable. The fringes sometimes went away entirely, and the diffraction pattern drifted over a period of seconds. Adjusting the power supply you could get the laser back into a good operating regime which is not surprising. I wondered if the temperature of the laser was important so gave it a hit of the ol freezer spray, and noticed that the air current coming out of it was clearly visible.
Turns out the mach diamonds that come out the end of the compressed air is also visible.
So that’s interesting. I was not able to see air currents from a blowtorch or a hot soldering iron though.