Majority of the people are familiar with handheld laser pointers which are used for presentations. They are about 5 milliWatts. You can also create superpowered handheld lasers ranging over 50 Watts. Gazing at the beam or reflection of the laser over 0.5 W has the capability of making you blind or causing irreparable damage. Although they are not for playing, it is fun watching them. On YouTube, a Geek has combined four 50W blue lasers in order to build an enormous 200W laser bazooka that can easily melt through anything. Take a look at this crazy dangerous machine.
Lasers of up to 0.5 W are permitted by FDA in America, however, a little expertise about electronics can help you in making more powerful lasers, not that we are recommending it. You must be very vigilant with high-powered lasers as they have the ability to make you blind in case you are not wearing any eye protection. Also, shining it at an aeroplane is considered a federal crime.
Parts from old DLP projectors all assembled with a lens aperture to focus the beam are used in this laser cannon. This focused beam is able to melt through plastic, instantaneously catch wood on fire, and of course, pop balloons. Taking this devise out in public would most probably get you arrested. Also, there is no practical use of this device.
In case you resolve to play with powerful lasers, ensure that you are doing so legally and safely. After all, becoming blind or landing in jail is not something anyone would want.