Strange behavior of laser-excited gold a revolutionary discovery and multiple applications

Imagine a group of people holding hands, gently swaying together, but when they are suddenly pushed, they link their arms together more tightly to withstand the push, and shake faster to resist the disturbance.

Likewise, researchers from the US Department of Energy's SLAC National Accelerator Laboratory found that the push that gold atoms receive when exposed to intense laser pulses helps tighten the bonds between its molecules and make them vibrate faster, unlike what is common for other materials.

While many materials, such as silicon, typically collapse when exposed to a laser, researchers in the new study published in the journal Science Advances observed that gold becomes harder and more flexible, a phenomenon known as phonon hardening.

"Phonon" refers to the vibrational energy that is transmitted through a solid material. When materials are exposed to external forces or changes in temperature, the atoms inside the material vibrate, and these vibrations can be described in terms of "phonons."

“Phonon hardening” refers to a phenomenon in which the vibrational behavior of atoms within a material changes in response to external stimuli, such as intense laser pulses. This change leads to an increase in the material’s rigidity due to changes in the way phonons propagate through the crystal lattice.

For decades, simulations have hinted at the possibility of this phenomenon, but using SLACK National Accelerator Laboratory's LCLS coherent light source, researchers were finally able to demonstrate phonon hardening in practice.

Why LCLS?

The Coherent Light Source (LCLS) is the most powerful X-ray laser device in the world, and it is unique in its working mechanism that relies on the following:

Free electron laser technology : Unlike traditional laser devices that use mirrors to amplify light generated by atoms or molecules, the device uses high-energy electron beams that travel at a speed close to the speed of light, and these electrons are accelerated through a linear accelerator to obtain energy.

Generating X-ray pulses : Once the electrons are accelerated enough, they are directed into a long, wavy magnet array. In the wavy mode, the electrons are forced to oscillate back and forth, emitting intense bursts of X-rays in the process. This radiation is coherent, which means that the waves emitted of individual electrons are synchronized, resulting in intense and highly focused X-ray pulses.

Tunable X-ray Spectrum : One of the features of the LCLS device is its ability to produce X-rays with a wide range of wavelengths and energies. Scientists can adjust the wavelength of the X-ray pulses by adjusting the energy of the electron beam or the strength of the magnetic field, and allows Adjustability allows researchers to adapt X-rays to the specific needs of their experiments.

Ultra-fast time resolution : This is another important aspect. The X-ray pulses generated by the LCLS are extremely short, lasting only a femtosecond. This ultra-fast time scale allows scientists to capture snapshots of ultra-fast processes - such as chemical reactions. Or changes in atomic structure - in unprecedented detail.

SLAC National Accelerator Laboratory operates the world's most powerful X-ray laser (National Accelerator Laboratory)

From preparation to proof

The process of using this unique device to demonstrate the different behavior of gold when exposed to an intense laser went through several steps explained by the researchers in the study, which are:

Experimental setup:

The researchers began by preparing thin gold films for use in experiments, which were designed to be thin to allow precise control and observation of the material's behavior under intense laser excitation.

Targeting with laser optical pulses:

The researchers used laser optical pulses to irradiate thin gold films, and these laser pulses provided the intense energy needed to excite the gold atoms and induce phonon solidification.

Capture snapshots at the atomic level:

After irradiating the gold films with optical laser pulses, the researchers used the ultrafast X-ray pulses of the Coherent Light Source (LCLS) device to capture atomic-level snapshots of how the material responded. These X-ray pulses were able to capture incredibly fast processes. This allowed researchers to monitor the behavior of gold atoms with high precision.

X-ray diffraction measurements:

The researchers used X-ray diffraction techniques in a coherent light source (LCLS) instrument to measure the structural response of gold when excited by a laser. X-ray diffraction is a powerful tool for studying the arrangement of atoms in matter and how they change under different conditions. By analyzing the diffraction patterns produced by the X-ray pulses, the researchers were able to gain insight into the atomic arrangements and stability of the gold films under extreme conditions.

Note “phonon hardening”:

Through their experiments, the researchers observed the phenomenon of “phonon hardening” in gold. This phenomenon indicates the strengthening of the material’s bonds and an increase in phonon energies when exposed to intense laser pulses. By observing changes in the vibrational behavior of gold atoms, the researchers were able to provide concrete evidence of “phonon hardening” in gold. Gold when exposed to harsh conditions.

Data analysis and interpretation:

Finally, the researchers analyzed the data collected from their experiments to interpret the results, and compared their observations with theoretical predictions and previous simulations to verify the validity of their results. The experimental evidence they obtained confirmed the phenomenon of “phonon hardening” in gold, which constitutes a challenge to previous concepts and opens new horizons for research. In materials science.

3 potential applications

In a press release issued by the US Department of Energy's National Accelerator Laboratory (SLAC), the researchers expressed their happiness with their results, and the statement quoted three important applications that could emerge from this discovery:

Improved techniques in laser manufacturing and materials manufacturing : Understanding how materials such as gold respond to intense laser pulses at the atomic level can lead to the development of improved techniques in laser manufacturing and materials manufacturing. By taking advantage of insights gained from studying phonon solidification, researchers may be able to enhance the accuracy, efficiency and reliability of processes that involve cutting, engraving and shaping materials using lasers.

Developing more flexible materials : The discovery of phonon solidification in gold opens new possibilities for designing more flexible materials. By harnessing the mechanisms behind this phenomenon, researchers may be able to engineer materials with strength, durability, and resistance to harsh conditions, and these materials can find applications in various industries, Including aerospace, automotive, electronics and construction, where durability and reliability are critical requirements.

Exploring similar phenomena in other metals : Researchers believe that similar phenomena can exist in other metals, such as aluminum, copper, and platinum. Further exploration of phonon solidification in these materials provides valuable insights into their behavior under extreme conditions, and paves the way for the development of new materials with distinctive properties. This knowledge can have wide-ranging implications for various technological applications and scientific progress.

Questions that need answers

For his part, Khaled Farhat, a researcher in materials science at the Egyptian Zagazig University, praises the results reached by the researchers, but on the other hand, he believes that experiments should be completed to answer some questions, stressing that this is necessary so that the discovery can be used in many applications.

Among these questions that Farahat mentioned in a telephone interview with Al Jazeera Net are those related to “improvement and control strategies,” and he says: “Is it possible to control or improve phonon hardening to enhance its beneficial effects in materials,” indicating that the answer to this question is from This will help mitigate potential challenges or limitations in practical applications.

He explains that researchers also need to answer a question related to “long-term stability and reliability,” as researchers need to know “how phonon hardening affects the long-term stability and reliability of materials under different operating conditions.”

"Experiments that study the stability and reliability of materials subjected to phonon solidification over long periods would provide crucial insights for evaluating the feasibility and durability of materials in real-world applications," he says.