An absolute distance measuring device based on laser interferometry may
combine coarse, intermediate, and highest resolution measurement
techniques to find the absolute distance to a sample surface with high
resolution. The device may provide at least two laser wavelengths
simultaneously, to allow reduction or elimination of certain common-mode
error components, including dynamic error components. The device may scan
at least one of the laser wavelengths over a relatively narrow range and
may use quadrature detectors to provide enough signal data to allow
certain self-corrections to be performed on the resulting scanned signals
and measurements. A novel tunable laser and/or quadrature detector may
provide advantages in combination with the device.