Laser sources in the 140 to 7500 GHz frequency range

The techniques and operating principles that have enabled laser systems to generate power at frequencies in the 140-7500 GHz range from pulsed and CW optically pumped rotational-transition lasers are reviewed. State-of-the-art performance is summarized in terms of both output power and tunability. It is noted that the first laser for the FIR spectral region was the HCN system which lases at six frequencies around 900 GHz. Optically pumped CO2 lasers are considered, and the possibility of providing continuous coverage of a large portion of the FIR spectrum is identified. Criteria for choosing a new candidate molecule for FIR operation include a large permanent dipole moment 'mu' about equal to 1 Debye and a coincidence between the CO2 pump laser frequency and molecular absorption line to better than 60 MHz. Application of these lasers to scale model measurements is used to illustrate problems associated with the present frequency range.