Negative pressure, although rare and challenging to detect, is an important phenomenon in physics. Researchers at the Max Planck Institute for the Science of Light (MPL) in Erlangen have recently made a groundbreaking discovery by using liquid-filled optical fibers and sound waves to measure negative pressure. In collaboration with the Leibniz Institute of Photonic Technologies in Jena (IPHT), the scientists in the Quantum Optoacoustics research group, led by Birgit Stiller, have gained valuable insights into thermodynamic states. This article delves into the new method they have developed and how it can advance our understanding of negative pressure in various fields.
Pressure, as a physical quantity, is encountered in different disciplines such as meteorology, medicine, and everyday life. It is defined as a force per unit area acting perpendicular to a surface. In closed systems, very high pressure can lead to explosive reactions, while very low pressure can cause the implosion of the system. Normally, pressure is always positive. However, liquids exhibit a peculiar characteristic – they can exist in a metastable state with a negative pressure value. In this state, even a slight external influence can cause the collapse of the system into different states.
The scientists at MPL and IPHT have combined two unique techniques to measure negative pressure in liquids. In their study, published in Nature Physics, nanoliters of liquid were encapsulated within a fully closed optical fiber, allowing for both highly positive and negative pressures to be measured. The specific interaction of optical and acoustic waves in the liquid enabled the sensitive measurement of pressure and temperature in different states of the liquid. Sound waves acted as sensors to explore this unique state of matter with high precision and detailed spatial resolution.
When a liquid is subjected to negative pressure, its volume decreases. However, adhesive forces keep the liquid inside the glass fiber capillary, creating a “stretching” effect. The liquid is pulled apart and behaves like a stretched rubber band. Previous measurement setups for negative pressure required complex equipment and safety precautions, particularly when working with toxic liquids. The method developed by the researchers, using light and sound waves, allows for precise pressure measurements in a simple setup using a fiber as thin as a human hair.
The Quantum Optoacoustics research group at MPL utilized sound waves to detect temperature, pressure, and strain changes along the optical fiber. This technique enables spatially resolved measurements, providing an image of the situation inside the fiber at a centimeter-scale resolution. The researchers believe that their method opens up new possibilities for exploring thermodynamic dependencies in this fiber-based system. It also allows for the monitoring of chemical reactions in toxic liquids and the investigation of nonlinear optical phenomena in the unique thermodynamic state of materials.
The discovery of this new method for measuring negative pressure presents exciting possibilities for further research. The tightly sealed liquid core fibers used in this study offer access to high pressures and other thermodynamic regimes. Prof. Markus Schmidt from IPHT in Jena emphasizes the importance of investigating and tailoring further nonlinear optical phenomena in this type of fiber. These phenomena can unlock previously unexplored and potentially new properties of materials in unique thermodynamic states.
The researchers at MPL and IPHT have made significant strides in understanding and measuring negative pressure using liquid-filled optical fibers and sound waves. Their new method offers a simple and precise way to explore this rare phenomenon with high spatial resolution. The ability to examine negative pressure opens up avenues for research in various fields, contributing to our broader understanding of pressure and its effects in different systems. With further advancements in measurement techniques and the exploration of nonlinear optical phenomena, scientists can uncover new properties and applications of materials in unique thermodynamic states.
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