Reiner Hofmann

CONICA (Coude Near Infrared Camera) is the high spatial resolution camera for the VLT unit telescope 1. It was originally designed to operate at the Coude focus but will now be installed at one of the Nasmyth focii together with the adaptive optics system NAOS. Like SHARP I and SHARP II it will mainly produce diffraction limited images. But CONICA has an extended wavelength range of 1 - 5 µm spectral range and also has extended spectroscopic capabilities (cooled K-band Fabry-Perot, several grisms). The camera is being built by a consortium of the MPIA Heidelberg and MPE, where MPE is in charge of the detector with its control and readout electronics and the LN2 cooled shutter.

The CONICA detector will be an Aladdin array (InSb, 1024 x 1024 pixel) from SBRC. For the fast readout modes (speckle interferometry and 5 µm imaging) the data rate can be as high as 40 MB/s. Therefore, the 32 channels have to be read in parallel and a system with 32 16-bit ADCs with a maximum conversion rate of 2 MHz has been designed and is now beeing tested.

For the array tests, a special dewar has been built which uses a closed cycle cooler to keep the array at a temperature of around 30 K and the optical components at about 77 K. The main feature of this dewar is the easy access to the array and the short cool and heating times due to a nitrogen precool system and several heaters installed inside the dewar. The dewar is shown on the picture during the first vacuum tests.

For exposure times shorter than the readout time of the array (about 50 to 100 ms), the cold shutter has to switch the beam at the location close to the pupil stop (beam diameter approx. 12 mm) within less than 10 ms. Several drive mechanisms have been tested under cryo-vacuum conditions. The best solution uses the data pickup system of a 3.5" hard disk drive. The shutter together with its control electronics and the position sensors is presently under test.

Lenzen, R., Hofmann, R.: Status of the High Resolution Near Infrared Camera CONICA for the VLT (ESO). SPIE Proceedings, Vol. 2475, 268 - 278 (1995)