Will green laser light penetrate glass?
This is an important question when operating an indoor telescope observing through window glass with a green laser finderscope. Will glass stop or significantly modify the beam rendering it useless as a nighttime finderscope to find celestial objects.
Introduction
There are many heated and optical physics, optronics, and electro dynamic technical discussions that reach varying conclusions. The indoor observatory at HSO decided to test the laser beam at night and the results would speak for themselves and elicit the final say, conclusion and response. To the right of the telescope, the green gemstone laser was activated and a series of photos were take with the handheld iphone Xs Max. Would the light beam make it through the window glass and if it did, would it remain a coherent straight line? Would the laser light be significantly diminished and become unusable? Will powerful laser light reflect backwards and blind the observer?
Results
In the photo, the green line represent the laser pulse of light. At the bottom of the photo, the line begins inside the observatory room. About half way, a bright large circle of diffusion results where the beam strikes the single window glass pane first surface and enters the glass, and light scattering appears to take place. Then the beam penetrates the glass back side to exit to the outdoors and the straight line reaches skyward on the same straight and true intended path. The light is not noticeably dimmed in the process. There was no dangerous visible backtracking of the laser light and the safety of the observer was maintained by laser light continually moving in the forward direction.
Conclusion
Therefore an indoor laser can shine through window glass and be used as a finder to point to the location of celestial objects and to show where the telescope is pointing, safely by following the basic precautions. The light appears to continue moving in the forward direction. The only noticed different between the indoor and outdoor use is that indoors results in a large circle of diffusion appearing embedded in the glass or at the point of lasering entrance/exit - a bright green scattering of light - a round area of light where the laser beam enters the glass. As the laser is on only momentarily to locate an object, it won't interfere with astro imaging.
