I was thinking about that too. You would need one or more sheets of something transparent to infrared 8-13 microns. Such materials apparently do exist: http://

I was thinking about that too. You would need one or more sheets of something transparent to infrared 8-13 microns. Such materials apparently do exist: http://www.infraredtraininginstitute.com/infrared-transparent-materials/ http://www.infraredtraininginstitute.com/infrared-transparen... Such a material would also have to not absorb too much sunlight.