Hybrid silicon avalanche quadrant detector

A method and apparatus for retrofitting an airborne laser tracker with a er ranging capability is described. A silicon avalanche detector is mounted within the silicon quadrant receiver of a laser tracker for an aircraft. The silicon avalanche detector is mounted behind the metalized quadrant electrodes of the quadrant detector in a position which permits the avalanche detector to receive radiation passing between the quadrant electrodes. An increased instrument sensitivity is achieved which provides an increased ranging capability for the airborne laser tracker.

What is claimed is:

1. An airborne laser tracker with a target ranging capability including an optical system having an optical axis and receptive of laser radiation from a target comprising: a first detector means disposed adjacent said optical axis for detecting radiation received by said optical system, said first detector means including spaced electrodes upon which a portion of said received radiation impinges, another portion of said received radiation passing through spaces between said electrodes; and second detector means for target ranging mounted in fixed relation with respect to said first detector means, said second detector means disposed behind said first detector means along said optical axis in substantial alignment with said first detector means for intercepting said another portion of said radiation for detecting radiation transmitted between electrodes of said first detector means, said second detector means having a sensitivity greater than that of said first detector means and an aperture smaller than that of said first detector means.

2. The airborne laser tracker of claim 1 wherein said second detector comprises a silicon avalanche detector.

3. The airborne laser tracker of claim 1 wherein said first detection means is a quadrant detector having four spaced electrodes, the spaces between said electrodes defining a cruciform and said second detector means is axially disposed in alignment with the point of intersection of said cruciform.

4. The airborne laser tracker of claim 2 wherein said second detector means is a silicon avalanche detector the aperture of which is smaller than that of said first detector means.

5. The airborne laser tracker of claim 4 wherein said optical system comprises:

transparent dome means for enclosing said optical system and for transmitting radiation from said target;

filter means for selectively passing radiation of predetermined wavelengths;

collector lens means for receiving radiation passed by said filter;

reflector means for reflecting radiation exiting from said collector lens means back through said collector lens means; and

immersion lens means in direct contact with said collector lens means for receiving said reflected radiation.

6. The airborne laser tracker of claim 1 wherein said both said detector means are encapsulated in a common housing.

7. The airborne laser tracker of claim 5 wherein said detectors are encapsulated in a common housing glued directly to said immersion lens.