Fibre laser hydrophones for cosmic ray particle detection

Abstract

The detection of ultra high energetic cosmic neutrinos provides a unique means to search for extragalactic sources that accelerate particles to extreme energies. It allows to study the neutrino component of the GZK cut-off in the cosmic ray energy spectrum and the search for neutrinos beyond this limit. Due to low expected flux and small interaction cross-section of neutrinos with matter large experimental set-ups are needed to conduct this type of research. Acoustic detection of cosmic rays may provide a means for the detection of ultra-high energetic neutrinos. Using relative low absorption of sound in water, large experimental set-ups in the deep sea are possible that are able to detect these most rare events, but it requires highly sensitive hydrophones as the thermo-acoustic pulse originating from a particle shower in water has a typical amplitude as low as a mPa. It has been shown in characterisation measurements that the fibre optic hydrophone technology as designed and realised at TNO provides the required sensitivity. Noise measurements and pulse reconstruction have been conducted that show that the hydrophone is suited as a particle detector.

Electroseismic Scholte‐wave analysis: A potential method for estimating shear‐wave velocity structure of shallow‐water seabed sediments

“…Scholte waves propagating at a velocity of ∼246.3 m/s are the main component of these evanescent ES waves, the maximum amplitude of which is 8.89 × 10 −3 Pa (79 dB re μPa). This amplitude falls within the range detectable by common seismic instruments such as fibre optic hydrophones (Buis et al, 2014). In addition, we observe acoustic waves propagating at a speed of 1500 m/s at very near offsets, but their amplitude is considerably lower than that of the Scholte waves.…”

“…(2020), the utilization of a low‐frequency fibre optic hydrophone employing weak value amplification reveals remarkable sensitivity, allowing it to detect underwater acoustic disturbances as weak as 1.3 $${{{\mathrm{\mu Pa}}} \mathord{/ {\vphantom {{{\mathrm{\mu Pa}}} {\sqrt {{\mathrm{Hz}}} }}} \kern-\nulldelimiterspace} {\sqrt {{\mathrm{Hz}}} }}$$ at 10 Hz. Therefore, the ES pressure field remains measurable with common seismic instruments such as fibre optic hydrophones (Buis et al., 2014). Figure 3a shows that the main wave types in the ES pressure field are Scholte waves; other wave patterns (guided waves, reflected waves and refracted waves) are too weak to be observed.…”

“…An essential parameter for measuring weak ES signals is the self‐noise of the recording system, commonly known as the ‘noise floor’. For instance, fibre laser hydrophones typically exhibit a self‐noise level ranging from 20 to 50 dB re μPa, slightly lower than the underwater ambient noise at sea state zero (Buis et al., 2014). Based on the simulation results presented in the ‘Pekeris model’ and ‘Complex multi‐layer model’ sections, the pressure field converted by EM waves can reach maximum amplitudes of about 10 −3 Pa (60 dB re μPa), significantly exceeding the recording system's noise floor (Buis et al., 2014).…”

“…Hz at 10 Hz. Therefore, the ES pressure field remains measurable with common seismic instruments such as fibre optic hydrophones (Buis et al, 2014). Figure 3a shows that the main wave types in the ES pressure field are Scholte waves; other wave patterns (guided waves, reflected waves and refracted waves) are too weak to be observed.…”

Fiber optic hydrophones for acoustic neutrino detection

“…It has been advocated that fiber optic hydrophone technology is a promising means to establish a sensitive, cost-effective and large scale sensor network [9][10][11], that could provide the basis of a future neutrino telescope. This technology is based on fiber lasers and hydrophone sensors that are integrated on a single optical fiber as shown in Fig.…”