He-Ne-Cd laser with two color output

Results are presented of experiments including a parametric study on a laser operating with a mixture of He, Ne, and Cd, and lasing at both 6328 Å (Ne I) and 4416 Å (Cd II), The laser uses a d. c. discharge and uniform cadmium concentration is obtained by a cataphoresis technique (1). In experiments on a 2.5 mm bore tube, 1 meter long, it was found possible to obtain useful outputs in both the neon and cadmium lines simultaneously. Two factors are important in such operations: Normal optimum He-Ne laser operation is at lower He pressures than those optimum for He-Cd lasers, and secondly the He-Ne laser output normally saturates at lower discharge currents. However, it is found that at the higher wall temperature at which the He-Cd laser operates, optimum conditions for the He-Ne laser change (2) and are more compatible with those of He-Cd operation. Preliminary results with cadmium of natural isotopic abundance, indicate that an optimum He-Ne-Cd gas fill for this type of laser allows operation in three modes determined by the operating current: 1) Low current operation (25-35m A), characterized by 6328 Å output approximately 80% of that obtained with the laser tube containing He-Ne only, and well optimized for 6328 Å output, 2) High current operation (90 mA and above), characterized by 4416 Å output ap proximately 70% of that obtained with the laser tube containing He-Cd only and well optimized for 4416 Å output, and 3) Intermediate currents (40-80 mA), where both lines lase simultaneously. At equal power outputs, the 6328 Å and 4416 Å lines are 25% ard 20% respectively of optimum. Arbitrary ratios of red to blue can be obtained by variation of operating current. These results will be analyzed in terms of the discharge properties of the mixture and their effect on gain.