The foundation of offshore wind turbines, port protection systems, steel sheet piles, river barriers, water gates, and even pipelines can all be directly processed in water. Another application area is the dismantling of abandoned nuclear reactors, in which case laser technology can gently dismantle steel structures underwater while minimizing the dissolution of radioactive materials.
The ocean, which accounts for 70% of the Earth's surface, stores precious wealth and enormous energy, and human exploration of ocean resources has never stopped. With the deepening development of laser technology, the industry has gradually focused on marine applications in recent years.
Professor Christoph Leyens, Director of the Fraunhofer Institute for Materials and Beam Technology in Germany, stated that in the future, humans must make greater use of offshore reserves to develop and expand environmentally friendly energy sources. To this end, the research institute is promoting new technologies for metal underwater laser processing.
Professor Christoph Leyens
The foundation of offshore wind turbines, port protection systems, steel sheet piles, river barriers, water gates, and even pipelines can all be directly processed in water. Another application area is the dismantling of abandoned nuclear reactors, in which case laser technology can gently dismantle steel structures underwater while minimizing the dissolution of radioactive materials.
Demonstration of underwater laser cutting of stainless steel
Underwater laser cutting requires green or blue laser. This is because the long wave laser used on land scatters too strongly in water, and the energy disappears very quickly. In contrast, short wave lasers can still maintain focus underwater. Since manufacturers such as Tongkuai, Coherent Gaoyi, Laserline, and NUBURU began offering green and blue lasers with power in the kilowatt range, underwater laser cutting has become an efficient and low maintenance alternative to the previously used mechanical cutting process.
Dr. Madlen Borkmann
Dr. Madlen Borkmann, the manager of the laser cutting group at the research institute, said: We are currently testing thicker materials and higher laser power. Unlike onshore laser cutting, underwater laser cutting does not require external gas supply: water squeezes molten metal out of the incision. Water may seem like an obstacle, but it is beneficial for processing. Reducing the burden of gas configuration is an important prerequisite for compact and highly maneuverable underwater robots.
Cutting, welding, and cleaning the ship's hull
Underwater laser processing is a key focus of the Hanover Laser Center (LZH). The underwater technology team of the center is developing innovative laser processes for offshore applications in special pressure tanks used for deep-sea simulation at the underwater technology center in Hanover and the test area on Helgoland Island in the North Sea.
Schematic diagram of self-protection flux cored wire arc welding operation
This includes self-protection flux cored wire arc welding. This is a process that allows for continuous laser welding directly from the wire spool. It can replace the existing manual electrode welding process, as electrode replacement often interrupts the immersion process in this process. In addition, LZH is also developing a low pollution underwater separation process for dismantling retired nuclear power plants.
LZH has also collaborated with partners such as the Fraunhofer Institute for Manufacturing Technology and Advanced Materials and Laserline to develop an environmentally friendly laser process for cleaning ship hulls. Laserline provides a blue light diode direct emitter for illuminating the hull and removing shells, algae, and other organisms. The dirt on the hull not only increases the flow resistance, thereby increasing the fuel consumption of the ship, but also introduces new species, threatening the local ecosystem.
Results of samples irradiated with laser and samples not irradiated with laser
This process uses short wave laser radiation to kill dirt without damaging the hull coating. Dead creatures will be carried away by the current on their next voyage. The automation system for this process has also been put on the agenda: the laser system will be installed on magnetic tracks to scan and illuminate the hull underwater. These tracks are usually used in dry docks. At present, the project is applying this technology to underwater laser therapy.
Hannover Laser Center showcases underwater robot laser cutting at exhibition
Exploring raw materials in the deep sea
Laser also contributes to future exploration of the deep sea. So far, immense pressure and absolute darkness have hindered human exploration of the deep sea. In fact, the map resolution of many planets is higher than that of deep oceans. But photonics has also created new possibilities here. Among other things, it is also related to the exploration of underwater raw materials. To this end, LZH is collaborating with the Leibniz Institute of Plasma Science and Technology to further develop laser-induced breakdown spectroscopy (LIBS) methods. This analysis method has been widely used in the aerospace and recycling industries, emitting high-energy short laser pulses onto materials and forming plasma under their influence.
Laser induced breakdown spectroscopy is a rapid chemical analysis technique that uses short laser pulses to generate microplasma on the surface of a sample. Collecting emitted light through a set of optical lenses and fibers
Through spectral analysis, the exact composition of the material can be determined. The research team has developed a new dual pulse technology to enable the use of this process in deep-sea conditions. The first laser pulse generates a bubble on the surface of the material, and the second pulse evaporates the material into plasma, which is then read out by a spectrometer. Although the concept is simple, the pressure conditions in the deep sea make this process complex. This requires a detailed interaction of pulse energy, pulse duration, and distance between two pulses to generate a spectrum with appropriate intensity and meaning.
A research group from the Chinese Academy of Sciences is also studying laser induced plasma in the deep sea. The research team used a different method to generate laser-induced plasma under immense pressure (60 MPa) at the bottom of the ocean. The research team introduced high-pressure helium gas into the surface of the studied material. They use high-energy lasers in gas to generate meaningful spectra for LIBS analysis.
As part of the NERITES project, LZH scientists have developed a compact LIBS system suitable for a water depth of 100 meters
Research has found that there are different patterns of increasing laser energy in high-pressure water and gas environments. Plasma imaging shows that shortening the laser transmission distance in high-pressure gas can improve signal strength. This project is part of China's National Key Research and Development Program, demonstrating the strategic importance of exploring raw materials in deep sea environments. This is because the deep sea contains a large amount of valuable minerals and metals, which are exactly what is needed for the development of electric vehicles and renewable energy.
Unknown animal populations and undeveloped ecosystems
The purpose of using LIBS is to enable real-time analysis of the material composition of rocks and nodules on site. Laser analysis can replace expensive underwater robot sampling and laboratory analysis, or replace large-scale raking of potential raw materials, in order to search for raw materials in a targeted and gentle manner. Therefore, mining can be limited to valuable areas. Otherwise, it is possible that the biodiversity of deep-sea ecosystems may have already been destroyed or even destroyed before people have recognized and understood them.
While exploring raw materials, the research team is also striving to uncover the eternal darkness of the deep sea and study the animals living there. For this, they also used lasers. In this case, a long wave red light source is very helpful because animals living there cannot detect it. Therefore, they will not be disturbed, and researchers can observe and understand their natural behavior.
Coherent provided a laser source for this project at the Monterey Bay Aquarium Research Institute. It provides enough light to record deep-sea videos and explore the creatures living there. Other teams are using photon methods such as Raman spectroscopy and laser-induced native fluorescence (LINF) to analyze minerals and organic suspended matter at different water depths and seabeds.
This relates to a fundamental understanding of ecosystems, interconnections, and the material cycle of life. Photonics is a key technology to achieve this goal. Because it allows for large-scale real-time analysis directly on-site, saving researchers time in selective sampling and transporting samples to the laboratory.
Source: Yangtze River Delta G60 Laser Alliance
