On the Efficiency of Ruby Laser Pumping

Abstract

The paper deals with the efficiency considerations of optical pumping in ruby laser in general and that of ruby rod in particular. The absorption of the incident light in ruby depends upon the path length and the frequency of incident light. Based on both these aspects, the efficiency has been calculated for different cross-sections of the rod. There are two sets of results, one each for the ultraviolet and the green-blue absorption bands of ruby. The radiation curves of a standard pumping source at a black body radiation temperature of 6580°K were utilized because it radiates between 2500 and 8000 Å which covers both the absorption bands of ruby. The efficiencies computed vary from 9·9 to 23·7 per cent in the green band for rod diameters of 0·3–1·3 cm. For the same diameter range the efficiencies in the ultraviolet band are 5·9- 11·6 per cent.

Once the theoretical efficiency of the rod is known the overall efficiency of the laser can be determined easily. It is the product of three efficiencies, the efficiency of the rod, cavity and the pump source. This has been illustrated by taking a specific design case. The theoretical computations show an overall efficiency of the order of 4 per cent for a composite rod having a diameter of 1·2 cm, which is consistent with the practical efficiency. The analysis has been done only for ruby. This, however, is applicable for any solid state lasing material provided the range of the absorption band and the absorption coefficients are known.