FIAT LUX
Shining light on titanium’s unique properties
A new method uncovers how titanium’s subatomic features influence its physical properties
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Shining intense infrared laser pulses on titanium generates higher-frequency light, revealing how its optical properties change in different directions due to variations in electron movement and bonding.
view moreCredit: Yokohama National University
A research team at Yokohama National University has developed a way to study how the orientation and behavior of electrons in titanium influence its physical characteristics. Their findings, published in Communications Physics on December 18, 2024, could pave the way for the development of more advanced and efficient titanium alloys.
Titanium is a very valuable metal because of its remarkable resistance to chemical corrosion, lightweight nature, and high strength-to-weight ratio. Its biocompatibility makes it ideal for medical applications, such as implants, prosthetics, and artificial bones, while its strength and durability are useful in aerospace and precision manufacturing.
To get an idea of how titanium's atoms and electrons generate these properties, the researchers used a process called high harmonic generation. “When we shine intense infrared laser pulses on a solid material, the electrons inside that material emit light signals at frequencies higher than that of the original laser beam,” explains the study’s first author, Professor Ikufumi Katayama of Yokohama National University’s Faculty of Engineering. “These signals help us study how the electrons behave and how the atoms are bonded.”
High harmonic generation is difficult with titanium and other metals, because the free electrons which make them excellent electrical conductors also interact strongly with the laser field and screen it in the material. This weakens the light signals, reducing their clarity and making it harder to collect data. “We carefully tuned the laser settings to reduce the screening effect, allowing us to clearly observe how titanium’s electronic structure behaves,” says Katayama.
The researchers used computer simulations to study the light signals emitted in response to the laser. They found that most of them came from electrons moving within certain zones called energy bands. These bands act like tracks where electrons can move freely. The direction of the laser and the way the titanium atoms are arranged affected how these electrons moved and bonded.
Titanium has a special uniaxial structure that can change with alloying, and its properties, like strength and flexibility, depend on the direction in which a force is applied. In other words, titanium behaves differently depending on the direction you push or pull on it. It turns out that this is because the way that the titanium atoms are arranged means the electrons don’t move the same way in all directions. When a laser hits titanium, the way the electrons absorb energy changes, affecting how they bond in different directions.
The researchers also found that fewer signals were emitted when electrons moved between different energy bands, showing that electron behavior is affected by the way atoms align. This difference determines whether the bonds are strong or weak, and thus how flexible or tough titanium is.
“By mapping how these bonds change with direction, we can understand why titanium has such unique mechanical properties,” says the study’s lead author, Dr. Tetsuya Matsunaga of the Japan Aerospace Exploration Agency. “That helps us understand how to design stronger titanium alloys that work better under different conditions, which could help create stronger, more effective materials for industries like aviation, medicine, and manufacturing.”
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Yokohama National University (YNU or Yokokoku) is a Japanese national university founded in 1949. YNU provides students with a practical education utilizing the wide expertise of its faculty and facilitates engagement with the global community. YNU’s strength in the academic research of practical application sciences leads to high-impact publications and contributes to international scientific research and the global society. For more information, please see: https://www.ynu.ac.jp/english/
Journal
Communications Physics
Article Title
Three-dimensional bonding anisotropy of bulk hexagonal metal titanium demonstrated by high harmonic generation
Metrology gets a new twist
Light Publishing Center, Changchun Institute of Optics, Fine Mechanics And Physics, CAS
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Conceptual notion of twisted light probing a complex medium. An artistic illustration of twisted OAM light passing through a medium, where the OAM spectrum acts as a sensor to monitor its effects. The signature can be read out and analyzed using machine learning and AI algorithms to recognize or sense key features of the medium, as exemplified in the context of a turbulent atmosphere.
view moreCredit: Mingjian Cheng, Wenjie Jiang, Lixin Guo, Jiangting Li and Andrew Forbes
Metrology serves as the cornerstone of modern industry, providing the key standards by which we measure the world. Optical metrology, in particular, has historically leveraged on the notion of interference, essentially unchanged since the days of Thomas Young more than 200 years ago. However, can one glean more information by extrapolating the concept of fringes to other degrees of freedom?
In a recent paper published in Light: Science & Applications, a team of scientists led by Prof. Lixin Guo from Xidian University have shared their perspectives on the past, and future of optical metrology involving orbital angular momentum (OAM). The paper explores fundamental principles, applications, and seminal advancements in the field. The researchers demonstrate how twisted light carrying OAM can be used for new paradigms in measurement, for instance, 3D particle position tracking, utilizing a modern interpretation of the Doppler effect by observing frequency shifts that depend on both OAM and polarization.
“The original Doppler effect could only track movement toward or away from the observer, but the incorporation of orbital angular momentum in both scalar and vector light allows motion tracking in all directions, including rotational movement,” says Prof. Andrew Forbes, a corresponding author from South Africa. “This advancement has revolutionized the metrology of dynamic systems.”
It is not only the shift in paradigm for existing tools but also the invention of completely new instruments that is propelling the field forward. One such example is the concept of an OAM spectrum serving as the 'signature' of a system: when OAM light passes through a complex medium, its OAM is altered, resulting in changes to the shape of the OAM spectrum (see Figure 1).
"This OAM fingerprint of the medium contains a wealth of information that can be harnessed," says Dr. Mingjian Cheng, the lead author. As the review highlights, if the OAM spectrum is interpreted by machine learning and AI, it opens the door to real-time analysis and recognition of complex media, with OAM light serving as a probe, a topic that is gaining traction very fast.
The review not only covers metrology with classical light but also utilizing OAM in quantum entangled superpositions and single-photon states. Transitioning into the quantum domain holds the potential to reduce noise and enhance accuracy and precision with fewer measurements. However, this aspect of the field remains in its early stages of development.
"Quantum metrology using OAM is still an emerging field with numerous untapped opportunities," says Prof. Andrew Forbes.
The comprehensive review spans a wide range of applications, from nano-sensing at the microscopic scale to measuring black holes at the cosmic scale. It provides an authoritative overview that will prove invaluable to both entry level and experienced researchers alike.
Journal
Light Science & Applications
Article Title
Metrology with a twist: probing and sensing with vortex light
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