Abstract

A pulsed laser caliper (PLC) is a device which can make noncontacting dimensional measurements on macroscopic objects using short laser pulses in a time-of-flight configuration. It can be adapted, in principle, to measure caliper dimensions of a discrete part, thickness variations across a continuous slab, or the shapes of complex contours. In operation, a laser pulse is split in two, one pulse going directly to a fast photodetector and the other reflecting off both sides of an object. The time-of-flight difference between the pulses is then measured with a counter or a sampling oscilloscope. The device is next zeroed by removing the object and again measuring the time-of-flight difference. Subtracting these two differences gives a caliper measurement of the object’s dimension. As a demonstration of the principle, a PLC consisting of a mode-locked argon laser, a high-speed photodiode, and a sampling oscilloscope was assembled and used to measure the lengths of five steel gauge blocks. The gauge blocks ranged in length from ¾ to 4 in. and were measured by the PLC to an accuracy of 0.03 in. Various sources of inaccuracy in and limitations on the PLC were determined and are discussed in the presentation.

© 1985 Optical Society of America