CC BY
2*
ALT'23
The 30th International Conference on Advanced Laser Technologies
LM-O-21
Laser cavitation in liquid hydrocarbons at a high pulse repetition
rate
E.V. Zavedeev, V.V. Kononenko, K.K. Ashikkalieva, N.R. Arutyunyan, V.I. Konov
Prokhorov General Physics Institute of the Russian Academy of Sciences, 38 Vavilova St., Moscow, 119991, Russian
Federation
Optical breakdown in liquids is quite complex process which includes a number of fast dynamic components: from the formation of a dense nonequilibrium plasma to cavitation. In solutions, suspensions, and even in pure liquids the chemically "pure" synthesis of various nanomaterials and nanocomposites can be realized at laser intensity exceeding ~1013 W/cm2. Physical and chemical rearrangement of the structure of molecules proves possible due to the highest degree of the liquid ionization (up to 1022 cm-3 and higher), which initiates many new effects from laser exposure.
The experiments presented are stimulated by a study of laser synthesis of linear carbon chains in liquid hydrocarbons. We describe the main laws of the formation and evolution of a cavitation bubble, which inevitably occurs during an avalanche optical breakdown in liquid hydrocarbons (in hexane and in ethyl alcohol). The main attention is paid to the effects of interplay of this bubble with the laser beam and the features of cavitation that develops when using laser sources with a high pulse repetition rate (up to 500 kHz), which, in turn, is caused by the need to increase the productivity of laser synthesis of polyines. The ionization and breakdown of liquids were carried out in a cuvette using intense picosecond (~10 ps) radiation emitted by a Huaray Olive-1064-40 laser (wavelength of 1064 nm). The focusing aperture was NA=0.27. Using optical microscopy, the cavitation process was traced (Fig. 1a). At pulse repetition rates >~10 kHz, a tendency was found for formation of single relatively large (up to ~100 ^m) superbubble instead of multiple microbubbles (Fig. 1b). An even more interesting effect is that the formed superbubble remains for a long time (up to minutes) inside the beam caustic (in front of the laser waist), thus blocking the light focusing and stopping laser synthesis. Possible mechanisms of the described processes are discussed.
Fig. 1. Optical microscopy of laser cavitation in hydrocarbons: a) "normal" cavitation; b) formation of superbubble. The light was propagating from left to right, red lines indicate an approximate boundaries of the laser caustic.
This work was supported by the Russian Science Foundation (project no. 19-12-00255-P).
LM-O-24
