The analysis of harmonic generation during ultrashort lR pulses filamentation in polymer

We report the analysis of femtosecond laser modification of poly( methyl methacrylate) (PMMA) by detection of optical signals emitted from the sample coaxially with laser beam. The influence of pulse duration, energy and burst pattern on recorded spectra was investigated using TruMicro 2000 laser. We present images of internal structures in polymer as well as the spectra of conical emission created as result of laser - polymer interaction. Generation of a broadband continuum signal was detected and analysed in a function of position of the focal plane. Furthermore, third harmonic generation and second harmonic of fundamental 1030 nm wavelength was detected and the origin of these signals is discussed. We present possibility of the material modification process monitoring by in situ spectral analysis of light coming out from the sample. The deposited pulse energy fraction was analysed.