Semiconductor lasers

Since the announcement of the GaAs diode laser in November 1962, laser action has been achieved in diodes of a variety of III–V and IV–VI direct‐gap semiconductors. The wavelength of the emitted radiation varies over the range from 6300 Å for the III–V mixed semiconductor $\mathrm{Ga}({\mathrm{As}}_x{P}_{\text{1−x}})$ to 85 000 Å for the IV–VI semiconductor PbSe. The semiconductor diode laser has the advantages that its size is small, that it converts electric power directly into coherent light, and that its output can be modulated by simply modulating the diode current. Figure 1 shows an artist's sketch of a GaAs diode laser in a pill‐type package. Such a laser, when operated between 4° and 20°K, has emitted up to 6 W of continuous coherent radiation at close to fifty percent power efficiency, and the radiation has been modulated at frequencies up to 11 Gc. At room temperature such a laser can be used on a pulse basis and 20 W of coherent radiation can be emitted in 50 nsec pulses. When operated continuously at currents not too high above threshold, GaAs lasers can operate stably in one mode of the Fabry‐Perot cavity formed by the cleaved face, shown in Fig. 1, and the parallel face on the opposite end of the laser. The width of such a cavity mode has been measured to be less than 50 Mc/sec or less than 1.5 parts in ${10}^7$ of the output frequency.