Abstract

FIR/sub-mm laser emission (70 to 250 micron) from p-Ge in E⊥ B fields is enhanced when Voigt configuration is used. We recently demonstrated that permanent magnets provide an easier realization of the Voigt configuration than do the traditional superconducting solenoids.^1,2 We report here an additional advantage resulting from the relatively open permanent magnet architecture. Large Cu blocks can be pressed in contact with two faces along the full 5-cm length of the Ge rod. These blocks serve simultaneously as electrodes for the high-power electric pulses and as heat sinks. Because the thermal conductivity of Cu is almost three orders of magnitude higher at 4 K than that of liquid helium, which also has the disadvantage of forming insulating bubbles, the blocks serve effectively to pump out the Joule heat generated in the crystal during the laser operation. A dramatic six-fold increase in the maximum repetition rate (Fig. 1), a 100-fold increase in the total emission pulse energy at low repetition rate (Fig. 2), and a significant increase in the allowed electric-field range are observed (Fig. 2). Because lasing is observed up to 10 K, the Cu blocks can themselves be the cold finger of a closed-cycle refrigerator. Hence, a solid-state FIR/sub-mm laser without need for liquid helium as a coolant can be considered for the first time to our knowledge. The data presented here suggest strongly that such a laser will have significant advantages over the usual Faraday/superconducting-solenoid/liquid-helium design in terms of pulse energy and repetition rate, as well as being considerably more economical and practical to use

© 1996 Optical Society of America