Spatial mapping of collisionally cooled carbon monoxide molecules in a cold cell

We used a collisional cooling cell which was designed to mount directly on the second stage of a CTI-cryogenics Model 22C CRYODYNE CRYOCOOLER. The cell was maintained at approximately 14 K for all measurements reported here. The absorption path length in the cell was 4.2 cm and the window clear aperture was 1.27 cm. The position of the injector was designed to be adjustable, so we could probe the cold gas cloud from the exit plane of the injector along a vertical line to approximately 11 mm downstream from the injector. We also probed the cloud in a horizontal direction, orthogonal to the previous direction. Our beam is imaged to a spot diameter of approximately 1 mm in the center of the cell. Gas temperatures as low as 24 K were measured approximately 11 mm from the nozzle and temperatures of approximately 40 K were measured close to the exit plane of the nozzle. Carbon monoxide was used for all measurements. (C) 1999 Elsevier Science B.V. All rights reserved.