Just thought I’d post some photos which I took earlier to view the brightness of the 532nm wavelength compared with the 1064nm line on a tattoo…
Note: all photos and videos were taken using an iPhone 6.
The top photo shows the tattoo just before the laser is fired at 1064 nm. The lower photo shows a picture from a video frame-grab during irradiation. The white spot is interesting – it is not the 1064 nm since that is invisible (even with the camera’s range). So what is it?
This photo shows what the 532nm wavelength looks like during irradiation. The is taken from a frame-grab, hence the bottom section showing the previous frame.
This is the reflection and back-scattered light coming from the skin. The reflection accounts for about 4% of the incident energy. The back-scattered light accounts for a lot more. However, this light emanates in all directions from the skin into, essentially, a hemisphere (or, approximately 2π steradians, to be technical!!)
The camera only detects a tiny fraction of this light and yet, as you can see from the photo, it is insanely bright!! This is what you might see if you were not wearing the proper safety glasses.
If the incident energy density on the skin surface is, say, 5 J/cm2, and the fraction entering the camera (or your eye) is, say, 0.01%, then the total reflected/back-scattered power density from a Q-switched laser (with a 10 ns pulsewidth) which can enter your eye is 50,000 watts/cm2!!
That can do some serious damage!
Always wear the proper laser safety glasses!!!