Theory of a tunable Raman laser

Mobile electrons in semiconductors, when subjected to a magnetic field, Raman scatter at a frequency which is shifted from that of the incident light by twice the electron cyclotron frequency. This process may provide the mechanism for a tunable Raman laser. A formula is derived for the threshold pump power required to stimulate such Raman emission. -type InSb pumped by a 10.6-μ CO2laser appears to be a good combination for achieving laser action. Pump powers of 1 to 10 MW/cm²are required for operation in the wavelength range of 12 to 25 μ. Such power densities have been achieved with pulsed CO2lasers. Stimulated Raman emission at wavelengths beyond 60 μ is also a possibility. The threshold pump power in the range is comparable to that in the near infrared. However, magnetic fields greater than 100 kGs are required to shift the Raman frequency into the far infrared.