Lambert Instruments

Developed for faint object detection by using Speckle Interferometry and Photon Counting techniques. The Instrument contains a Hybrid Image Intensifier (2 stages: GenII & GenI), which is fibre-optically coupled to a high frame rate CCD-Camera. The Photocathode of the Intensifier is thermo-electrically cooled down to -25°C.

Background
The faintest objects to detect will generate a photon stream of 15000 photons/cm²/s at the detectors input face. The goal is to detect at least 3000 photons/s with a time resolution of 1-10 ms.

Assuming a Detective Quantum Efficiency of 10 %, the above mentioned detection goal would require a detector surface of at least 2 cm². At a camera frame rate of 200 frames/s this means an average of 15 events per frame to be detected.

If the detector would be a photocathode operating at room temperature, the dark current corresponding to a photocathode surface area of 2 cm² would be in the order of 500 electrons per frame. It is necessary to reduce the dark current to a value much smaller than the signal, being 15 electrons per frame. This can be realized very effectively by cooling the photocathode. Cooling down from +25°C to -25°C will reduce the dark current from 500 electrons down to 4 electrons per frame.

By selection of the image intensifier for low dark current, a dark count rate of less than 1 count/frame was achieved at a frame rate of 220 frames/s and at -25°C photocathode temperature.

Features:

• Photon Imaging
• Less than 1 e-/frame Dark Current"
• 50,000 Intensifier Photon Gain
• 256 x 256 pixel Frame Transfer CCD
• 220 frames/s Frame Rate