Multiple Sampling Raman Cold Cell

Recently a low temperature sample cell for a laser excited Raman spectrophotometer was described1 in which the laser beam was positioned in the horizontal plane of the optic axis, and the incident beam entered the side of the sample chamber (Fig. 2 of Ref. 1). This variable temperature cryostat could be used with other types of spectrophotometers provided that the sample compartment was open at the top. Such a cold cell is unsuitable for the more recent Raman spectrophotometers such as the Jarrell-Ash model 25–300 in which the sample compartment is enclosed as a part of the instrument. In the model 25–300, the distance from the optic axis to the top of the sample compartment (measured to the upper optical bench) is about 8.5 in. Thus, a cryostat of the size described in Ref. 1 could not be mounted vertically without removing the upper optical bench and cutting a hole in the top of the compartment. In addition, optimum use of the light collecting system consisting of an f/0.95 camera lens which collects and collimates the scattered light requires a distance of no more than 12 mm between the sample and the rear element of the lens. This places a severe requirement on the allowed maximum distance between the sample and outer surface of the exit window of a cryostat.