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The possibility of using interband transitions to achieve maser action is considered. The criterion for maser action is presented in a way which allows the most direct use of optical absorption data. The absorption constant for interband transitions, which is negative corresponding to induced emission when a population exists, is related to the normal absorption constant for direct, indirect, and indirect exciton transitions. Using available absorption data, it is shown that in Ge maser action, using either the indirect or indirect exciton transitions, would be prevented by absorption due to free carriers. In GaAs, or other materials with a direct band gap, however, it is entirely possible that maser action could be achieved.
W. P. Dumke (Sat,) studied this question.