Real-time monitoring of the energy deposition under the tight focusing of femtosecond laser radiation into a bulk transparent dielectric based on third harmonic signal

It has been found that the third harmonic generated under the tight focusing of a near-infrared (1.24-$\mu$m) femtosecond laser pulse indicates the energy deposition into the bulk transparent dielectric and can be used as a feedback system in the process of microstructuring. A third harmonic signal is sensitive to a change in both the size of a laser-induced microplasma and the free-electron density, which allows the detection of the microplasma with submicron longitudinal sizes. It has been shown that the method based on the third harmonic is universal and can be applied in both single-pulse and two-color microstructuring.