What happens if you fire a laser pointer at the mirror, that is, the light returns to itself? Over the years, in many optical devices, I accomplished this accidentally. Yes, lasers usually have a resonant cavity, but if you add another mirror outside the cavity, it can change everything, just like placing a radio tower around a radio transmitter.
Usually, this completely destroys the laser, makes it unstable, emits almost no light, then turns on quickly, and then turns off irregularly. In very high gain devices like thin disk lasers, the laser can be destroyed. For very high-power military lasers, we will consider this issue very carefully to prevent problems. I have tried my best to prevent even small reflections from returning to the laser.
If you hold your laser pointer, mount it on a stable stand, and use a mirror to reflect the beam back to yourself at close range, you may make it unstable or even destroyed. Some laser gain media must extract power, otherwise the media will overheat. If the extraction is interrupted, the energy entering the beam will remain inside the laser and become heat.
Fortunately, I have never destroyed a laser in this way*, but I was asked to join one or two review committees to find out what happened when a laser was destroyed.
*However, I have destroyed many laser mirrors and laser windows. I have used a high-energy laser beam somewhere near one million watts. This is enough to soften the steel shell of the ballistic missile in a 10-square-foot area and cause the missile to explode. You can imagine how difficult such a beam would be on copper mirrors, coated glass mirrors, or sodium chloride windows.
Early high-power green laser pointer were very unstable, hot spots were generated in the beam, or a piece of dust would fall on the mirror surface. The hot spot may burn through within a few milliseconds, causing the entire mirror or window to quickly fail. One of my early tasks was to burn 5 or 6 10-inch diameter sodium chloride and potassium chloride windows. In today's U.S. dollars, this is about 5 million U.S. dollars worth of windows.
Unfortunately, I cannot keep videos or pictures, but I have many. Argon ion interferometer, mid-wave infrared, long-wave infrared, helium-neon polarization film film, and ordinary old TV camera video. Until someone in the Air Force ordered the destruction of all videos, movies, and pictures, all these things were sorted and locked in safes.