A laser beam of power around 1 watt, directly entering the eye, may cause a blood vessel in the retina to burst faster than one can react, resulting in bleeding inside the eye. This is obviously a very serious eye injury. Furthermore, a retinal nerve may get cooked within a fraction of a second, which would cause permanent serious vision loss. Please read some legal stuff on Class IIIb and IV lasers. Furthermore, even looking at the spot that is formed when a Class IV laser beam hits a white surface or other diffusely reflecting surface can be hazardous. If a narrow 1 watt laser beam hits a perfectly white surface, viewing the spot straight-on from 4.5 inches away results in eye exposure of approx. 2.5 mW per square centimeter, which is borderline between Class II and Class IIIa for laser radiation coming from a point but not in a narrow beam.
This could result in permanent eye damage in about a second if a focused image of the spot is formed on the retina and the pupil is fully dilated. Even at greater distances and with less dilated pupils, the spot is still not safe to stare at. Such a spot would expose one to 1 microwatt per square centimeter from a distance of 5.6 meters, approx. 18.5 feet. This is the borderline between Class I and Class II for laser radiation coming from a point on a diffuse surface. One thing to keep in mind is that this wavelength is often considered more dangerous to eyes than most other visible wavelengths. The danger of permanent eye damage may be even greater than I mentioned above. Without collimating optics, the beam from these laser diodes has been mentioned as approximately 7 by 16 degrees. If the beam is a uniform ellipse, then 1 watt in such a beam would have an intensity of 37 watts per steradian.
However, this 7 by 16 degree beam is not uniform and the center of the beam likely has an intensity roughly twice that, or roughly 74 watts per steradian. This works out to 12.5 mW per square centimeter at 77 centimeters away (give or take). This is the threshold of Class IIIb intensity for laser radiation coming from a point but not in a narrow beam. This is approximately (give or take) the threshold of being able to cause permanent eye damage faster than one can react if one's pupils are fully dilated. Obviously, even without collimating optics, these laser diodes are extremely dangerous to look into when they are producing laser radiation. One eBay seller of these laser diodes has mentioned that one that he was selling produces 7 milliwatts of radiation even when operated at a little less than laser threshold. One thing about laser diodes is that when operated below laser threshold, their output takes a path similar to that taken by their laser radiation when they are lasing.
UPDATE 1/2/2019: 520 nm high power laser diodes and laser "pointers" made with these are now available. The color as seen by most people is green, MedicGLP although not the perhaps very slightly yellowish green or lime green of 532 nm, 520nm has a pure green to emerald green color. Sam Goldwasser's mighty laser FAQ - Over 45 meg of laser goodies (broken into several parts) including over 600 GIFs/JPEGs from Sam Goldwasser. MUST READ! This includes lots of info on HeNe, diode, argon, CO2, dye, copper vapor, and nitrogen lasers. If you have already seen this but not in the past few years, you may want to look again since this document has continued to grow and be renewed. Links updated 9/3/2022 because the upenn ones are no longer working. Copy and paste this into a browser. Some GIFs and some other files are "cleaned up" for slightly faster download.