by S. Kudryashov, A. Samokhvalov, S. Shelygina, A. Karabutov, G. Tsibidis, D. Pankin, V. Veiko
Laser Physics Letters, 17, 105302, 1-6.
The ultrasonic characterization of the propagation of femtosecond laser pulses in pure transparent water and colored phenol-red dye solutions at variable concentrations indicates their thermoacoustic pressure generation due to intrinsic multi-photon absorption in the low-power sub-filamentation regime and sub-linear pressure response of sub-critical plasma via free-carrier absorption in the filamentation regime. Multi-photon absorption appears to be concentration dependent for water and dye solutions, while plasma absorption demonstrates a universal trend for all these liquids. In the filamentation regime, through the non-linear laser-matter interactions, not only new optical frequencies (intense white-light supercontinua) were generated, but supercontinuum-based ultrafast broadband spectroscopy in the filaments also revealed many additional transient absorption bands of the dye molecules, induced via power-dependent and concentration-independent stimulated Raman scattering.
