Laser light is of a single color, the light waves are in step with each other, and the light beam spreads only slightly as the distance from the light generator to the target increases. These characteristics make the laser useful for surveying equipment used in various types of construction layout. Although a wide variety of special-purpose laser instruments are manufactured, most of these have been designed for construction layout and are classified into two general groups as follows:

1. Single-beam laser alignment instruments. These instruments project a single beam of light that is visible on targets under all lighting conditions. Included in this group are laser equipped theodolites

2. Rotating laser levels. These are instruments in which the laser beam is rotated by rapidly spinning optics to provide a reference plane in space over open areas.

SINGLE-BEAM LASER ALIGNMENT INSTRUMENTS

A typical single-beam laser alignment instrument can be mounted on a transit-like framework with horizontal and vertical motions, a spirit level that is parallel to the axis of the laser, and both vertical and horizontal circles. A telescope is attached to the laser housing to allow the operator to sight the location of the transmitted laser spot. A separate fanning lens, when attached, allows the laser beam to be converted to a horizontal or vertical line instead of a spot.