Theory of operation

Aug. 1, 1998
The light source of the laser range finder is a collimated diode laser with an output beam of divergence less than 1 mrad. It produces a spot A on the first obstacle located at the distance D from the source (see figure). The triangle IAC is formed by the reference base B perpendicular to distance D and the retrodiffused ray AC, which forms angle a with a line parallel to D. A lens L of focal length f is located with its optical center at point C. The retrodiffused light from A is collected by

Theory of operation

The light source of the laser range finder is a collimated diode laser with an output beam of divergence less than 1 mrad. It produces a spot A on the first obstacle located at the distance D from the source (see figure). The triangle IAC is formed by the reference base B perpendicular to distance D and the retrodiffused ray AC, which forms angle a with a line parallel to D. A lens L of focal length f is located with its optical center at point C. The retrodiffused light from A is collected by the lens via an interference filter (IF) and focused in at A` on a charge-coupled device (CCD).

For A at infinity, A` is at the focus F` of the lens. To reduce loss of focus at short distances, the CCD line is not perpendicular to the optical lens axis; it forms an angle q with D. The q angle inclination is given by tan q = B/f and the position of the image center A` is x` = F`A`, which is given by

x`/sin a = f/sin (q - a)

with tan a = B/D

The CCD has 2048 pixels, each 11 µm wide, and the x` maximum value is 2048 ¥ 1.1 ¥ 10-5 m = 2.25 ¥ 10-2 m or 22.5 mm. With the numerical value of B = 60 mm and f = 30 mm, the minimal measurable distance is D = 30 [1+(4500)1/2]/22.5 100 mm and, in this case, the angle a is given by arctan 60/100 31°.

As the laser beam divergence a` is about 0.8 mrad, at a long distance it can be considered that the A` image at the focal point is at least equal to fa` = 24 µm, which is at least two pixels. The interference filter, which reduces natural light perturbations, is tilted about 15° against the lens plane to match incidences on the filter. In fact the lens is not a simple one but a large-field optical system.

R. R.

Sponsored Recommendations

March 31, 2025
Enhance your remote sensing capabilities with Chroma's precision-engineered optical filters, designed for applications such as environmental monitoring, geospatial mapping, and...
March 31, 2025
Designed for compatibility with a wide range of systems, Chroma's UV filters are engineered to feature high transmission, superior out-of-band blocking, steep edge transitions...
March 31, 2025
Discover strategies to balance component performance and system design, reducing development time and costs while maximizing efficiency.
March 31, 2025
Explore the essential role of optical filters in enhancing Raman spectroscopy measurements including the various filter types and their applications in improving signal-to-noise...

Voice your opinion!

To join the conversation, and become an exclusive member of Laser Focus World, create an account today!