CATAPHORESIS IN HELIUM-CADMIUM LASER DISCHARGE TUBE

Side light measurements were made to determine the density distribution of cadmium in a discharge tube similar to that used in the helium-cadmium laser. The tube had an electrode at either end and a single cadmium source near the center. The discharge causes the cadmium vapor to flow toward the cathode, the flow being greater at higher currents. At currents greater than 20 mA almost no cadmium is found a few cm from the cadmium source in the discharge region between it and the anode. In contrast to this, large amounts of cadmium are found in the discharge region between the source and the cathode. It is concluded that an approximately uniform density of metal vapor may be maintained in a helium-cadmium laser by placing a single cadmium source near the anode and passing currents greater than 50 mA through the tube. A very simple theory gives a qualitative explanation of the gross features of the density distribution curves. © 1970 The American Institute of Physics.