PERFORMANCE CHARACTERISTICS OF A LOW TEMPERATURE CELL WHICH IS COOLED BY A CLOSED CYCLE HELIUM REFRIGERATOR

Abstract

We have fabricated and tested a low temperature cell which is mounted directly on the second stage of a CTI-Cryogenics Model 22C $CRYODYNE^(R)$ CRYOCOOLER. The vacuum system consists of a room temperature vacuum shroud, a radiation shield maintained at 77K and the cell which is mounted directly to the second stage of the cryocooler. The ultimate cell temperature is 12.4 Kelvin, and the low temperature limit increases at a rate of 5.6 Kelvin /Watt. The absorption path length of the cell is 3.35 cm, and the window clear aperture is 1.27 cm. The cell temperature with typical experimental conditions of approximately 29 milliTorr of helium, slow flowing gas and a heated injector is 22 Kelvin. We performed a series of experiments in which we measured the R(2), P(4) and P(5) transitions in the (1-0) fundamental band of carbon monoxide. In these experiments we focused our tunable diode laser to a spot size of approximately one millimeter in the plane of the injector, and we collected absorption data for different image locations measured relative to the injector tip. At each cell location we recorded absorption spectra for each of the three CO transitions in order to obtain translational temperatures from the Doppler width and rotational temperatures from the relative intensities of the three transitions. These experiments were performed with a cell temperature maintained at 42.9 Kelvin. Results from these experiments will be presented.