A range of optically pumped, far infra-red (FIR) lasers are available for applications that require coherent radiation in the spectral range of 40 microns to 1.22 mm, the TeraHertz (0.25 to 7.5 THz) frequency range.

FIR laser frequencies arise from rotational transitions in an excited vibrational state of a polar gas molecule at low pressure. The optically pumped FIR laser relies on the selective absorption of tunable infra red radiation to create the population inversion between rotational states and hence generate laser action. In practice, a small number of molecules are chosen to provide discrete frequencies across the entire FIR spectrum from 40μm upwards.

Output powers of 150mW and 500mW at the 118.8 μm and 184.3 μm methanol (CH3OH) lines can be guaranteed depending on the model of the Edinburgh Instruments CO2 pump laser used. The FIR lasers are Invar bar stabilised and are available with either single or dual output. The products range from the FIR 295, FIR 395 (Twin FIR output), to the FIRL 100.