In a typical rangefinder application, the line-of-sight (LOS) of a high quality visual optical path used for locating and identifying a target is aligned with the LOS of a second optical path associated with an eye-safe laser. The eye-safe laser beam reflects off the target and becomes a return optical signal that is received along a path that is aligned with the transmitted eye-safe laser. A receiver detector senses the received beam to acquire information that can be used to determine the distance to the object. The receiver detector, the laser cavity optical system for producing the eye-safe laser beam, and the visible aiming beam, produced by a laser diode and collimating optics, cannot be mounted on an optical bench coaxially, they must be separated.
Prior art rangefinding applications typically use complex and expensive multiple-bounce dichroic beamsplitters to yield coaxial laser transmitter and aiming beam optical paths and separate the received laser beam from the transmitted beams. Splitting the transmitted paths from the receiver path typically requires dichroic optical coatings on the beamsplitter. Prior art beamsplitters may require as much as four tightly toleranced regions of different optical coatings. Prior art beam steering methods typically require repackaging of the aiming light to accommodate complex beamsplitters with added cost and weight to the overall opto-mechanical package.
Critical to rangefinder applications is the angular alignment of the three laser beam paths must be held to tight tolerances. This places difficult alignment and retention requirements on the optical elements typically used to combine the two transmitted paths. For example, one laser is often transmitted through a beamsplitter (usually tilted at 45 E) and combined with the first beam. This causes the angular alignment sensitivity and retention of the beamsplitter to be twice as sensitive as the angular requirement between the two beams, requiring costly optical alignment at manufacturing time.
In use, each of the two LOS paths must be steered from their respective nominal position. The two LOS paths and the received path are manipulated in unison in a manner that ensures that all paths have essentially the same deviation from their nominal position. Prior art beam steering methods for multi-wavelength systems require wedges or prism pairs for LOS steering.