In the world of lasers, those handheld laser pointers for presentations are about 5 milliWatts. On the opposite end of the spectrum, you can build superpowered handheld lasers ranging over 50 Watts. Once you get over .5 W, just looking at the beam or reflection of the laser can blind you and cause irreversible damage. They are certainly not for play, but boy to they make a lot of fun to use. One Youtuber has taken 4 50W blue lasers and combined them to create a giant 200W laser bazooka that can melt through anything. Check out the insanely dangerous machine below.
The FDA only allows the sale of up to .5 W lasers in America, but with a little electronics know-how, you can build more powerful ones, not that we are recommending it. You have to be really careful with high-powered lasers as they can blind you if you are not wearing eye protection, not to mention it is a federal crime if you happen to shine one at an airplane.
This laser cannon uses parts from old DLP projectors all assembled with a lens aperture to focus the beam. This focused beam can melt through plastic, instantly catch wood on fire, and of course, pop balloons. There are really no practical use for this device, and taking it out in public would likely get you arrested.
[Image Source: StyroPyro]
If you decide to play with powerful lasers, make sure you are doing so legally and safely. After all, you kind of become a useless engineer if you become blind and land yourself in jail, no one wants that.