A 1 watt laser would do damage. In fact my burning lasers operate in the milliwatts. My first UV laser was pumped to 110mw and could cut through tape, start things on fire and I even lit my cigarette once, although this was difficult due to the very small focal point.
And at 110mw it most definitely required a heat sink to keep from burning itself up after prolonged use. I would encourage you to build one in the visible wavelength. Not only is it awesome to see the beam but the lasers that operate in the invisible spectrum are dangerous cause you can't see the beam and it definitely can reflect off other objects and render you blind.
Get safety glasses that are designed for the wavelength your working with.
"Energy flows where attention goes"
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