At the Laser Zentrum Hannover, Germany, Marcel Rieck and his team are adapting laser-induced breakdown spectroscopy (LIBS) for some of the most hostile settings imaginable, from the crushing pressures of the deep sea to the vacuum of space. Their work, featured in projects such as LIBS60, ROBUST, and the EU initiative NERITES, aims to bring real-time elemental analysis to places where traditional methods fail.
In this conversation, Rieck explains how his group has overcome the physical challenges of underwater plasma formation, why dual-pulse technology was a breakthrough, and how LIBS could become a cornerstone of future ocean intelligence systems.
How would you define an “extreme environment” from an analytical perspective?
From an analytical perspective, an environment is considered "extreme" when environmental conditions such as high pressure, low or high temperatures, or special environmental media such as water or strong radiation, impair the stability of measuring systems and the reproducibility and reliability of measurements.
What can we learn by making measurements in extreme environments – and what makes LIBS especially well suited to that task?
Taking direct measurements in extreme environments provides access to unbiased, real-time information about the chemical composition and physical properties of materials that are difficult to replicate in a laboratory setting.
LIBS is particularly well suited for this purpose as it requires no sample preparation – enabling real-time data collection in locations where conventional sampling would be extremely difficult or impossible. This allows us to more effectively observe and understand the effects of environmental conditions. At the same time, time-consuming transport and preparation steps are eliminated, resulting in significant time and cost savings, as well as conserving resources. The combination of scientific insight and technological benefits makes LIBS particularly fascinating, especially in the context of the deep sea, where every measurement system is pushed to its limits.
What are the main physical challenges of underwater LIBS – and how did you overcome them?
All measurement processes that take place outside controlled laboratory conditions are challenging, especially when there are significant variations in temperature, pressure or the surrounding medium. Underwater, additional special physical conditions apply: the medium itself influences plasma formation and requires adapted system technology.
Since plasma cannot form spontaneously in water, we use double-pulse LIBS technology. The first laser pulse generates a short-lived gas bubble (cavity) in which the second pulse ignites the plasma. The high hydrostatic pressure at greater depth significantly affects the formation and lifetime of this cavity, placing high demands on the housing, optics, and stability of the overall system.
During the initial field tests, the spectra were barely visible and only signal noise could be measured. It was only when we switched to dual-pulse operation that we were able to detect stable emission lines, representing a real breakthrough for our research.
How did you develop the system?
In the laboratory, we simulated the extremely high hydrostatic pressure using a pressure chamber. This allowed us to develop, test and optimize the system technology.
Contrary to the initial assumption that higher pulse energy would lead to better measurement quality, our tests showed that the opposite was true. Excessive pulse energy shifts the breakthrough point in the water – the so-called critical energy – closer to the sensor. This alters plasma formation and reduces signal quality.
In addition, we observed that each laser pulse slightly ablates material, which causes a gradual turbidity of the surrounding water. This effect further complicates underwater measurements, as it changes the local optical conditions and can influence subsequent plasma formation.
This was a key insight for us, as it highlighted how sensitive the entire LIBS system is – not only to optical parameters like focal length, beam expansion, and working distance, but also to the dynamic interaction between the plasma and its environment.
Real-world applications took place in the Pacific Ocean and the Baltic Sea at depths of up to 4,000 meters.
In what ways might this work shape the future of underwater observation and preservation?
The LIBS sensor is central to the continuous monitoring of underwater sites. This enables changes in material composition or signs of contamination to be detected at an early stage, long before any visible damage occurs.
As part of the NERITES monitoring system, LIBS complements traditional laboratory analysis, enabling direct, on-site detection of elemental concentrations. This allows the condition of cultural heritage objects to be assessed more accurately and enables the impact of environmental factors, such as corrosion or water contamination, to be tracked over time.
Ultimately, this continuous data collection opens up new possibilities for the targeted protection of underwater cultural heritage and the development of sustainable conservation strategies.
In addition, in the long term, we envisage underwater LIBS playing a pivotal role in ocean intelligence systems, which are networks of autonomous vehicles and observatories that continuously monitor the ocean's chemistry. LIBS offers the unique ability to rapidly analyze multiple elements directly from natural surfaces, complementing physical and biological sensors.
Just how deep can we go with LIBS?
In principle, there is no strict depth limit for LIBS. If the laser and detector are housed in pressure-resistant enclosures, the system could, in theory, operate at full ocean depth. In practice, however, both technical and physical factors pose challenges at depths of several thousand meters.
The increasing hydrostatic pressure shortens the lifetime of the cavity, which affects plasma formation and signal intensity. At the same time, maintaining reliable optics, materials, and power supply under such extreme conditions requires highly robust system design.
Interestingly, many of these technical challenges are also encountered in other fields of research, such as Mars exploration missions. Projects such as MOMA (Mars Organic Molecule Analyzer) demonstrate the difficulty of performing precise analyses under extreme conditions with limited technology. Ultimately, both underwater LIBS and planetary analytics aim to enable reliable measurements where laboratory conditions are unavailable.
Are there any other extreme environments where you’d like to explore LIBS applications?
LIBS also has enormous potential for use in other extreme environments beyond the deep sea. As I mentioned, applications in planetary research, such as on the surface of Mars, are particularly exciting. The chemical composition of rocks there could reveal whether conditions conducive to life exist or existed. Beyond that, LIBS could also be valuable in challenging terrestrial environments, such as high-radiation nuclear zones, high-temperature industrial sites, or even during subsurface exploration – for example, in geothermal drilling, tunneling, or oil and gas exploration – where rapid, in-situ chemical analysis is crucial.
What’s next for this field?
We now know that LIBS can deliver reliable data even under the most extreme conditions. The biggest challenge is no longer proving its functionality, but developing smaller, more autonomous systems that can be more easily integrated into existing platforms.
Marcel Rieck spoke at the Colloquium Spectroscopicum Internationale (CSI 2025) in Ulm, Germany, in July 2025, where he presented on “LIBS in Extreme Environments.”
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