Dynamics of a TEA CO2 laser with a cubic nonlinear medium in the cavity: from frequency stabilisation to chaos

A method for controlling the frequency of radiation from a single-mode TEA CO₂ laser with external signal injection is proposed, justified, and has been realised experimentally. It allows the output frequency of the laser to be stabilised (to within ~0.1 MHz) during the time interval of maximum power, i.e. during the leading spike, by introducing a suitable nonlinear medium (InAs plate) into the laser cavity. The transition from a single-mode frequency-stable to a multimode lasing regime with regular and chaotic pulsations of the output power could occur because of internal injection excitation of adjacent transverse and longitudinal modes by radiation which was chirped due to the nonlinearity of the intracavity optical components even in the case of initially single-mode emission.