Localized Measurement of a Sub-Nanosecond Shockwave Pressure Rise Time

Abstract

In a growing number of applications fast and localized pressure measurement in aqueous media is desired. To perform such measurements a custom made single-mode fiber optic probe hydrophone (FOPH) was designed and used to measure the pressure pulse generated by laser induced breakdown in water. The sensor enabled sub-nanosecond pressure rise time measurement. Both the rise time and the duration of the shockwave were found to be shorter in the direction perpendicular to the breakdown generating laser beam, compared to the shockwave observed in the parallel direction. Simultaneous highframerate imaging was used to qualitatively validate the novel hydrophone data and to observe the shockwave evolution. The measurements were performed also on pressure pulses emitted during generation of miniature (150 µm diameter) laser-induced bubbles at very small distances (down to 40 µm), further demonstrating the capabilities of the small-size sensor and the ability to measure locally. The results improve understanding of laser induced breakdown shockwave characteristics dependence on laser pulse energy and duration.

Ultrafast measurement of laser-induced shock waves

“…Distance d and angle are sufficient to characterize the fiber position with respect to the source since any transversal offset can be converted to a new (slightly larger) distance between the source and the fiber center and a new fiber positioning angle. This relation is explained in more detail in [23] , together with the analysis of frequency response which is not repeated, as it was shown there that it only plays a role on longer time scales, which are not of interest here.…”

“…The main reason for choosing the single-mode fiber over the multimode is the size of the active area (fiber core) which is much smaller in the case of a single-mode fiber (5 µm), enabling spatially and temporally very local measurements [23] . However, there is still some broadening of the measured signal, the main contributing factor being due to geometry: the fact that both, the sensing element of the hydrophone as well as the shock wave source are not points but each of them has a finite dimension.…”

Near threshold nucleation and growth of cavitation bubbles generated with a picosecond laser

“…Transient shock wave pressure was measured using a custom-build fiber optic probe hydrophone (FOPH) operating at a 1030 nm wavelength, guiding the light in a single-mode fiber with 5 μm core and 125 μm cladding diameters. The FOPH has been tested and validated in measuring of a sub-nanosecond shock wave pressure rise times [21] and in combination with the multi-frame multi-exposure shock wave imaging for velocity and pressure measurements [22] .…”

Interferometric Fiber Optic Probe for Measurements of Cavitation Bubble Expansion Velocity and Bubble Oscillation Time

“…Fiber optic probe hydrophones (FOPHs) are well-known measurement systems [ 1 , 2 , 3 , 4 ], commonly used in medicine and in all fields where there is a need to measure fast transient pressure waves or shock waves with high amplitude and broad bandwidth [ 5 ]. To generate an optically induced ultrasonic wave, a high-energy pulsed laser and a breakdown of the liquid medium is usually employed, leading to the formation of cavitation bubbles, followed by the emission of a shock wave after the bubble has collapsed [ 6 , 7 ].…”