Liquid Nitrogen Camera heads.



PixCellent provides camera heads for use with its cooled CCD camera systems that are designed to give the ultimate in photon counting performance by providing cooling to very low temperatures. Each type of camera head consists of a CCD, cooled by liquid nitrogen. The electron multiplying CCDs used by  PixCellent  Imaging Limited are all frame transfer devices and so do not need a mechanical shutter in front of them.. The camera heads provided with fixing holes to enable them to be attached to the user's Experimental setup.

The CCDs used in PixCellent's systems are cooled in order to reduce the amount of thermally generated dark current. Accumulation of dark current severely limits the performance of an uncooled system. By lowering the temperature of the CCD, the dark current is reduced by a factor of about 10 for every 20C drop in CCD temperature. Consequently, sensitivity and dynamic range are greatly extended. Cooling to below about -120C gives no further advantage in terms of dark current and can reduce the far red sensitivity of the CCD.

Liquid nitrogen cooling

Liquid nitrogen cooled heads offer the ultimate performance in terms of sensitivity and dynamic range. Dark current from the chip is reduced to levels of only a few electrons per pixel per hour in some cases by cooling the CCD to approximately -120C.  The liquid nitrogen cooled heads contain a CCD mounted in a vacuum-sealed housing to minimise heat loss. The CCD is connected by a cold "finger" to a container filled with liquid nitrogen. This effectively cools the CCD to a user selectable and accurately stabilised temperature from -60C to -120C., reducing dark current to the absolute minimum. Periodic re-filling with liquid nitrogen is necessary and the heads may require occasionalre-pumping with a rotary/diffusion or turbo vacuum pump, depending on usage.  The liquid-nitrogen heads we use have been designed for applications where space is limited and may be used in a sideways as well as a downward looking configuration. Additional fill tube inserts are available to allow inverted operation (with slightly reduced liquid nitrogen hold times). Drawing is available here.

Table 1: Liquid nitrogen cooled camera head performance characteristics

High Performance LN Head  
Cooling method Liquid nitrogen  
Dark counts with standard CCD 10 electron/pixel/hour at -120C  
Weight (kg) 4.2 (empty) plus maximum of 1.0 for a full liquid nitrogen fill.  
Height x Diameter (mm) 267mm long (body) plus >120 mm for LN fill access , front plate 122 mm diameter. Side access for electrical connectors and for re-pumping. Rear access space required for re-pumping and re-filling of the Dewar  
Optical distance of CCD from front face  (mm) 8.0 mm  
Mounting points available on front face C-mount, K-mount. Other mounts can be provided on request.  
Mounting points available on side of head 12 holes on circle on shutter plate  
Nominal CCD temperature -60C. to -120C.  

Drawings are available as follows:

LN/K high performance dewar

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Site last updated: 20 November 2011.