I'm experimenting with an LD from a DVD burner. It puts out 100mW at about 140 mA. At this power, the beam is showing no signs of being visible.. which surprised me.
For comparison, I have a green pointer from Atlas Nova. When I first switch it on, Mr. Lasercheck says it's doing 20 mW. That beam is clearly visible, and the spot is frankly dazzling.. can't look at it for any length of time. If I keep it turned on, the power drops pretty quickly, but the beam remains visible.
How much red power would I need to get the experience of similar brightness? I have 5 times as much power as the green, but clearly it needs still more.
Also, how much is the beam visibility affected by the collimation? I think my greenie has better beam quality than what I get from the red LD. I'm using one of those brass collimators from meredith instruments for the red.