In which application is a laser rangefinder primarily used?

A laser rangefinder is primarily used in applications that require precise distance measurements, which is most notably seen in surveying, robotics, and military applications. In surveying, laser rangefinders provide accurate measurements over long distances, enabling professionals to create topographic maps and assess land features effectively. In robotics, these devices help navigate environments by measuring distances to avoid obstacles and build spatial awareness. In military applications, laser rangefinders are employed for targeting, reconnaissance, and mapping terrain with high precision.

While the other applications listed, such as laser engraving and marking, medical imaging and diagnostics, and optical data storage, involve lasers, they do not utilize the specific measuring capabilities of laser rangefinders. Therefore, option A accurately reflects the primary use of laser rangefinders in these critical fields.