This image shows the laser radiation pattern applied to the main Advanced LIGO optics and used to control their thermal lenses. The image is constructed from the product of the intensity distribution from a CO2 laser multiplied by a binary mask. The leaves on the mask provide radial pulse width modulation and, hence, the average radial intensity distribution is as desired to achieve optimum lens control. This particular mask design was custom tailored to match the specific intensity distribution from one of our CO2 lasers - if you look closely, you can see small variations by comparing leaves at the same radii but different angles. For reference, the actual diameter of the mask is just under an inch - but it is projected up to a final image approximately 13" in diameter. For the color scale, bright yellow/white represents most intense, orange, medium intensity and dark brown represents zero intensity.