As a calibrated laser pulse propagates through the atmosphere, the intensity
of the Rayleigh scattered light arriving at the VERITAS telescopes can be
calculated precisely. This allows for absolute calibration of imaging
atmospheric Cherenkov telescopes (IACT) to be simple and straightforward. In
these proceedings, we present the comparison between laser data and simulation
to estimate the light collection efficiencies of the VERITAS telescopes, and
the analysis of multiple laser data sets taken in different months for
atmospheric monitoring purpose.Comment: Submitted to Proceedings of "4th Heidelberg International Symposium
on High Energy Gamma-Ray Astronomy 2008
