LiDAR (Light Detection and Ranging) uses laser technology to map the contours of surfaces. LiDAR basically involves shooting millions of laser beams at a surface (for example, the surface of the ground or the vertical face of an excavated wall) and calculating how long it takes for the laser beam to "bounce back." FYI: This same technology is used in police speed guns.
Airborne LiDAR technology is used to map topography and detect cultural features concealed beneath vegetation, providing archaeologists with detailed aerial overviews of entire sites. Ground-based LiDAR can be used on a smaller scale to create very precise three-dimensional reconstructions of ancient structures.
Ground-based LiDAR was used to create the following video of the interior of a kiva test-excavated by Crow Canyon at Goodman Point Pueblo (courtesy James Holmlund, Western Mapping Co.)
Why LiDar? on the Time Team America (PBS) website includes an example from the Dillard site, excavated by Crow Canyon.
Lidar: A basic explanation of the technology and its different applications, including archaeological (Wikipedia).