Nonlinear bubble nucleation and growth following filament and white-light continuum generation induced by a single-shot femtosecond laser pulse into dielectrics based on consideration of the time scale

Abstract

Bubble nucleation and growth following plasma channeling (filament) and white-light continuum in liquid irradiated by a single-shot fs-pulse were experimentally investigated with close observation of the time scale. Making full use of a new confocal system and time-resolved visualization techniques, we obtained evidence suggestive of a major/minor role of the non-linear/thermal effects during the fs-pulse-induced bubble's fountainhead (10−13 s) and growth (10−7 s), which was never observed with the use of the ns-pulse (i.e., optic cavitation). In this context, the fs-pulse-induced bubble is not an ordinary optic cavitation but rather is nonlinear-optic cavitation. We present the intrinsic differences in the dominant-time domain of the fs-pulse and ns-pulse excitation, and intriguingly, a mere hundred femtoseconds' excitation predetermines the size of the bubble appearing several microseconds after irradiation. That is, the nucleation happens temporally beyond a six-order-of-magnitude difference.

Improvement of Optical Fiber Probing in Multiphase Systems, and the Possibility of Practical Application in Chemical Engineering Processes

“…The second peak (blue line, named the 'pre-signal') arises from a phenomenon in which some of the beams reflecting at the bubble's frontal surface re-enter the S-TOP. The pre-signal clearly and strongly appears when the S-TOP touches a bubble at its center region in parallel with the bubble's minor axis (Mizushima et al, 2013).…”

“…The I spike takes the maximum at x/r mj =0 (i.e., the center of the bubble), at θ=0 (i.e., parallel with the bubble's minor axis) and at φ=0 (i.e., parallel with the bubble's minor axis). This characteristic of the pre-signal enables researchers to selectively and optionally extract signals at the center region of bubbles almost in parallel with the bubble's minor axis by the S-TOP ("Pre-signal threshold method, " Mizushima et al, 2013). As a result, as demonstrated in the paper of Mizushima et al (2013), by using this method in the data analysis, the random errors of bubble chord length and velocity due to an uncertain penetration of the S-TOP are markedly decreased.…”

“…optical ber probe A few group have attempted the simultaneous measurement of velocity, chord length and number density of components of the dispersed phase such as bubbles and droplets by using a single-tip (mono-tip) optical fiber probe (e.g., Saito et al, 2009;Mizushima et al, 2013;Mizushima and Saito, 2015). The sensing tip of a single-tip optical fiber probe (S-TOP) developed by Saito et al (2009) is ground into a wedge with an angle of 28-32°.…”

Electrodeless hydrogen production from seawater using femtosecond laser pulses

“…The single bubble collapsed and dissolved into liquid in the sparse regime; however, when the bubbles were close to each other, they coalesced into a larger bubble. The bubble nuclei distribution at the foci of the femtosecond pulse is lengthened/shortened along its optic axis 21 by the Kerr effect, 22 which depends on the liquid's nonlinear refractive index ( n 2 ). 23 Through observation, the salinity seems to have an advantage over the bubble growth.…”

Filamentary plasma grating induced by interference of two femtosecond laser pulses in water

“…For example, Rhodamine B dyes were used to generate two-photon fluorescence to monitor multiple filaments in methanol [12]. On the other hand, liquids have high optical nonlinearities and low filamentation thresholds, which give rise to conspicuous phenomena such as conical emission, white-light continuum generation [13], multiple filaments competition [14], and laser filamentation induced bubbles [15][16][17]. It remains unexplored whether these phenomena will cause unfavorable influence on the formation of filamentary plasma gratings in liquids.…”