Detector for determining the location of a laser spot

1. A detector for determining the location of a pulsed laser spot reflected from a scene, which comprises a CCD sensor for imaging the scene comprising an array of pixels arranged in rows and columns, a serial read-out register arrangement, and charge transfer electrodes capable of transferring signal charge packets from pairs of adjacent pixels to read-out register arrangement locations representative of the row location of respective ones of the pairs and the column location of the respective others, wherein the charge transfer electrodes are arranged to transfer one of each pair of adjacent signal charge packets to the read-out register arrangement along the row direction of the array, and the other along the column direction of the array.

2. A detector as claimed in claim 1 , in which the transfer paths in the row and column directions have intersecting charge storage locations arranged to store signal charge packets representative of both row location and column location, but at different times.

3. A detector as claimed in claim 1 , in which the read-out register arrangement includes read-out registers along adjacent edges of the array.

4. A detector as claimed in claim 1 , including control means for reading out the CCD continuously, with no separate integration period.

5. A detector as claimed in claim 1 , in which the pixels of the pairs from which row location is derived are arranged in different rows of the array to the pixels of the pairs from which column location is derived.

6. A detector as claimed in claim 5 , in which the rows of the array which generate pixel row location intersect the columns of the array containing the pixels from which column location is derived at regions having charge transfer electrodes capable of transferring signal charge packets in both the row and column direction.

7. A detector as claimed in claim 6 , in which the CCD array has two-phase charge transfer electrodes, which are controlled such that transfer of signal charge packets in the row direction alternate with those in the column direction.

8. A detector as claimed in claim 1 , in which the pixels of the pairs from which row and column location is derived are arranged in the same rows as each other.

9. A detector as claimed in claim 8 , in which the pixels of the pairs of adjacent pixels from which row and column location is derived alternate with each other along rows and along columns of the array.

10. A detector as claimed in claim 9 , in which the CCD array has three-phase charge transfer electrodes, and regions between the pixels from which row and column information is derived in both the row and column direction have electrodes corresponding to two of the phases.

11. A detector as claimed in claim 10 , in which the order of those two phase electrodes alternates at successive regions along the row direction and in the column direction.

12. A detector as claimed in claim 11 , in which each set of three-phase pulses is arranged to be followed by another set in which the order of the second and third phases is reversed.

13. A detector as claimed in claim 10 , in which each clocking cycle includes two sequences of the three phase voltages, with the order of the second and third voltage phases reversed between the two sequences.

14. A detector as claimed in claim 1 , including a narrow-band optical filter tuned to pass the laser frequency, arranged at the front of the detector.

15. A detector as claimed in claim 1 , including means to produce a defocused image of the spot on the detector.

16. A detector as claimed in claim 1 , in which the point spread function due to diffusion of charge in undepleted substrate before collection in a potential well is arranged to be approximately a pixel pitch.

17. A detector system including a detector as claimed in claim 1 and further comprising a laser source for generating the laser spot.