Distance and Displacement Measurements by Laser Technique

Abstract

This special section is devoted to recent advances in distance measurement techniques. Following the Optical Distance Measurements and Applications ~ODIMAP! Workshops we organized in Nantes, France in 1997, and in Pavia, Italy in 1999, attended by more than 120 delegates from all over the world, we believe that distance measurement is still a very fertile ground for new ideas and engineering approaches, with a solid history of achievements behind it and a bright perspective of new achievements ahead. Indeed, the story of distance measurement and interferometric techniques is studded with big discoveries and surprising results. We may trace the first ones back to the Michelson interferometer ruling out the ether hypothesis, closely followed by the Sagnac and Fizeau interferometers supplying key results to check relativity. After the invention of the laser, the laser interferometer has become the workhorse of tool-machine and mechanical metrology, while its two-beam counterpart, the laserDoppler velocimeter as it is called, has filled the need for noncontact, precision anemometry. These two instruments have sold in the thousands of units per year for at least 30 years—a big success and a record in electro-optics instrumentation. Almost contemporary, the measurement of angular velocity through a Sagnac interferometer has generated the ring-laser gyro ~RLG! and the fiber-optic gyroscope ~FOG!—the heart of the inertial navigation unit ~INU! of any modern airliner. Also, since lasers became available, the pulsed and sine-wave telemeters have flourished and provided an invaluable tool both in aerospace and civil topography. Readers may remember the first big science experiment LURE ~Lunar Ranging Experiment! in 1969, when Apollo 11 astronauts brought several corner cubes onto the moon, and five large telescopes aimed a 1-J Q-switch pulse ruby laser on them, measuring the earth–moon distance with a 30-cm resolution. Nowadays, telemetry of satellites is a basic tool in geodesy of the earth, and last year the Mars Orbiting Laser Altimeter ~MOLE! returned an amazing map of the red planet with 100-3100-m pixel resolution. Meanwhile, work is in progress to complete multikilometer arm, 10-m resolution interferometers intended to sense gravitational waves, with a capability of detecting gravitational collapse of stars megaparsec away. These developments, and their fallout in industrial applications, are very promising of an exciting prospect for interferometry, range finding, and distance measurement techniques. In this special section we have collected original papers on the different aspects of this field, and we hope this will provide a useful picture of the current state of the art as well as a stimulus for further advances.