There is provided in a first form, an apparatus. The apparatus includes a detector array having a plurality of elements, the detector array comprising a photosensitive material and a photosensitive region disposed about and distinct from the plurality of elements. Electrical circuitry is coupled to each of the elements of the detector array. The electrical circuitry is configured to generate a set of first signals, each first signal of the set of first signals is based on optical energy impinging on a respective one of the plurality of elements of the detector array. The photosensitive region is coupled to the electrical circuitry and the electrical circuitry is configured to generate a second signal having a first value if no portion of optical energy impinging on the plurality of elements of the detector array impinges on the region disposed about the plurality of elements of the detector array. The second signal has a second value, distinct from the first value, if a portion of an optical energy impinging on the plurality of elements of the detector array impinges on the photosensitive region disposed about the plurality of elements of the detector array, the portion of the optical energy impinging on the photosensitive region disposed about the plurality of elements exceeds a threshold energy.