Generation of submillimeter radiation by mixing of optical wavelengths

One approach to the problem of generating signals in the submillimeter range is to start from the large outputs available both at centimeter wavelengths or below one micron wavelength, and synthesize them by using non-linear media. The first alternative involves harmonic generation of microwave fundamental frequencies, and experience has shown that it is very difficult to obtain acceptable conversion efficiency above doubling or tripling. The second approach has become possible since the advent of high power masers in the optical and near infrared regions of the spectrum. These signal generators are capable of pulsed outputs of many kilowatts, and their frequency stabil ity is quite sufficient to provide monochromatic beat notes at wavelengths thousands of times larger.