<title>Second harmonic of Ti:sapphire femtosecond laser as a possible tool for pointlike 3D optical information recording</title>

Abstract

We show that irradiation by the second harmonic (SH) of Ti:Sapphire femtosecond laser provides well-defined spots with micrometer diameter by controllable manner in pure PMMA. Combined effect of SH and fundamental frequency (FF) radiation of Ti:Sapphire laser yields significant decrease in recording time. These results relate to 3D bitwise optical information storage. Usually in order to produce irreversible detectable changes, either single amplified Ultra-Short Laser Pulse (USLP) irradiation of pure matrix or multi-shot irradiation of matrix with dyes by nonamplified USLP is employed. In our present experiments the 1.5 percent transformation of nonamplified Ti:Sapphire laser radiation into the Sh has been obtained by means of BBO crystal with thickness of 300micrometers . The SH beam was then focused within the PMMA matrix by a lens with NA equals 0.55. The onset of emission corresponds to the onset of detectable irreversible changes in PMMA detected by optical microscope. The SH provides two-photon electronic transition to the absorption band of PMMA. Theoretical analysis of experimental data shows that preliminary matrix excitation by SH is followed by a self-developing process. This process can be driven not only by SH radiation but by potentially more powerful FF radiation as well.