A couple of years ago, I was looking to shield my car head lights and license plate from laser (yet still keep them 100% clear in the visible spectrum). I did a lot of research and found lots of clear materials that would block IR laser from passing through them, but they accomplished that feat by REFLECTING the laser. I only found a very few materials that would ABSORB IR laser while letting visible light pass through. In particular there was a certain kind of glass that would do the trick, but it was relatively expensive.
Interestingly enough, this particular type of glass is used in good quality photo copiers and optical scanners (it is the glass you lay your paper on that you wish to have copied). Unfortuantly, I have yet to run across any broken copiers I could salavage the glass from.
I think if any one here had such a source it would make an interesting experiment to place that glass over a license plate and run a test.
The one cavet about visibily clear IR laser absorbing materials is that they often work by converting the IR Laser into a different part of the IR spectrum, ie the glass warms up. So then question becomes, at what ambient temperature does the laser absorbency start to drop off. Would the heat from a head light make it ineffective? Would it still be effective on a 104 degree day in Oklahoma?
In anycase, it would be an interesting series of tests, and might make for an inexpensive way to shield your license plate from laser (provided you can scrounge up the glass from a good quality copier).