Imaging Sensors

The image sensors for our camera systems are two-dimensional photon-detectors with a minimum dimension of 256 x 256 pixels and a pixelsize of a few 10 micrometers

Image Sensor Types

CCD - Charge Coupled Devices

CCD sensors (CCD = Charge Coupled Device) are two-dimensional photon detectors. They have highest sensitivity at the visible wavelengths with some sensitivity even at near-ultraviolet or near-infrared wavelengths. CCD sensors are known for their linear signal response.

EM-CCD - Electron Multiplying CCD

EM-CCDs (Electron Multipliplying Charge Coupled Devices) are CCD sensors which provide charge amplification (or electron multiplication) in an additional internal shift register. The enhanced sensitivity allows to detect single photons and makes them powerful devices for astronomical observations of faint objects with short exposure times as required by speckle observations.

Infrared imaging sensors

Imaging sensors for near and mid-infrared wavelengths (1-30 µm) are photon detectors which deliver a real two-dimensional image similar to a CCD sensor. We use sensors with sizes of 256 x 256 to 2048 x 2048 pixels. The infrared imaging sensor and all other parts of an infrared camera housing must be cooled to avoid any thermal radiation which would degrade astronomical observations. For sensors at a wavelength range below 5 µm cooling with liquid nitrogen is sufficient, however sensors for longer wavelengths need to be cooled down to 10 K and less. Infrared imaging sensors are constructed differently to CCDs. They consist of a semiconductor layer and a multiplexer which has a readout cell for each pixel. The cells provide the charge-to-voltage conversion and a logic for resetting the pixel charge after an exposure. The multiplexer itself has a matrix structure which routes the output signal of each addressed pixel to the output contact pins.

Imaging sensors in use

NICMOS

Application: Speckle-Cameras
Number of Pixels: 256 x 256, arranged in 4 quadrants
Pixel size: 40 μm x 40 μm
Wavelength: 1 - 2.5 μm
Quantum efficiency: > 50%
Operating temperature: 77 K
Readout Noise: 35 e-
Pixel Clock: max. 500 kHz

PICNIC

Application: Speckle-Cameras
This device is comparable to the NICMOS imaging sensor, but the readout noise is only 20 e-

HAWAII-1

Application: Speckle-Cameras, AMBER, LINC-NIRVANA
Number of Pixels: 1024 x 1024, arranged in 4 quadrants
Pixel size: 18.5 μm x 18.5 μm
Wave length: 1 - 2.5 μm
Quantum efficiency: > 50%
Operating temperature: 77 K
Readout Noise: 10 e-
Pixel Clock: max. 600 kHz

HAWAII-2RG

Application: MATISSE
Number of Pixels: 2048 x 2048, arranged in 32 stripes
Pixel size: 18 μm x 18 μm
Wave length: 1 - 5.3 μm
Quantum efficiency: > 50%
Operating temperature: 40 K
Readout Noise: 10 e- or 70 e-
Pixel Clock: 100 kHz or 1 MHz

AQUARIUS

Application: MATISSE
Number of Pixels: 1024 x 1024, arranged in 2 times 32 stripes
Pixel size: 30 μm x 30 μm
Wave length: 5 - 27 μm
Quantum efficiency: > 50%
Operating temperature: 6 - 10 K
Readout Noise: 200 e-
Pixel Clock: 1 - 3 MHz

 
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