An argon ion laser using a thermionic hollow cathode

The principle of operation of an argon laser based upon a thermionic hollow cathode discharge (HCD) is described. The HCD argon laser is shown to be a simple, durable, long-lived device capable of high power output. An essential feature of this design is that it is a demountable, flowing gas device. In its simplest form, the HCD laser consists of an anode and cathode, both of which are tantalum tubes, located some 10 to 20 cm apart along the axis of a one kilogauss solenoid. Commercial grade argon flows in through the cathode tube and is pumped out through a high conductance sideport by a 15-cfm forepump. The discharge is maintained by copious electron emission from the inner surface of the cathode. The emission appears to come from a ring a few tube diameters inside the cathode tip. The emitting area operates at approximately 2500°K and the emission mechanism is probably a combination of thermionic and field emission.