Ultraviolet-C (UV-C) light is widely used for water, air, and surface disinfection. It enables high-contrast imaging and precise targeting of biological tissues due to its strong interaction with organic molecules, and it is used to study ultrafast molecular dynamics, ionization processes, and nonlinear optical effects that are often inaccessible at longer wavelengths. Despite its vast potential, use of UV-C technology remains limited due to a lack of suitable photonic components. Although lasers have advanced significantly, UV-C lasers are still scarce. A newly demonstrated UV-C source-sensor platform, developed by a team from the University of Nottingham and Imperial College London, integrates nonlinear optical crystals that produce femtosecond (fs) laser pulses in the UV-C range with a new class of photodetectors built with 2D semiconductors. The developed platform for generating and detecting UV-C laser pulses on fs timescales could enable applications spanning materials processing and high-contrast bioimaging. The UV-C source exploits phase-matched, second-order, nonlinear processes through cascaded, second harmonic generation in nonlinear crystals. This generates the fourth harmonic of an fs laser, producing UV-C pulses with energies up to about 2 μJ. The optimization of crystal thicknesses leads to a modular, cascaded fourth harmonic generation with a conversion efficiency of 20% from the near-NIR to the UV-C. A new platform for the generation and detection of ultrashort ultraviolet-C (UV-C) laser pulses on femtosecond (fs) timescales could unlock opportunities for transforming optical wireless communication systems, material processing applications, and medical imaging. Courtesy of the University of Nottingham. “We have exploited phase-matched, second-order processes in nonlinear optical crystals for the efficient generation of UV-C laser light,” professor John Tisch said. “The high conversion efficiency marks a significant milestone and provides a foundation for further optimization and scaling of the system into a compact source.” The fs UV-C pulses are detected at room temperature by photodetectors that are based on the semiconductors gallium selenide (GaSe) and gallium oxide (Ga2O3). The electronic properties of these materials are well-suited for low-power sensors and for providing a fast temporal response. In addition to being able to detect UV-C fs pulses, the 2D semiconductor sensors show reliable performance over a variety of pulse energies and pulse repetition rates. To date, this capability has not been demonstrated with traditional semiconductors or 2D semiconductor materials. “This work combines for the first time the generation of femtosecond UV-C laser pulses with their fast detection by a new class of 2D semiconductors,” professor Amalia Patané, who led the sensor development, said. “These can operate over a wide range of pulse energies and repetition rates, as required for many applications.” As proof of concept, the researchers used fs UV-C pulses to demonstrate a free-space communication system, where a message was encoded by the fs laser source-transmitter and decoded by the 2D sensor-receiver. The ability to generate and detect light in the UV-C range is useful for many applications. For example, the short wavelength of UV-C light enables superresolution microscopy, allowing nanoscale imaging. Its strong absorption by materials makes UV-C useful for material processing applications, including surface activation, cleaning, and photolithography. UV-C light is also used in spectroscopy and environmental monitoring, where it enables the detection and quantification of trace substances through unique fluorescence and absorption signatures. Beyond these applications, UV-C’s strong atmospheric scattering properties open new possibilities in non-line-of-sight communication systems for data transmission in obstructed environments. The sensing capabilities of GaSe and Ga2O3 could inspire new, integrated source-sensor platforms for applications where machine-to-machine communication is key. “The detection of UV-C radiation with 2D materials is still in its infancy,” researcher Ben Dewes said. “The ability to detect ultrashort pulses, as well as to combine the generation and detection of pulses in free-space, helps pave the way for communication between autonomous systems and robotics.” The photodetectors have a simple planar structure and are suitable for monolithic integration with other components on photonic integrated circuits. The manufacturing and processing of the materials used to generate fs UV-C pulses are scalable and affordable. With its efficient generation of UV-C laser light by nonlinear optical processes, the source-sensor platform has broad value. “A compact, efficient, and simple UV-C source will benefit the wider scientific and industrial community, stimulating further advances,” researcher Tim Klee said. The research was published in Light: Science & Applications (www.doi.org/10.1038/s41377-025-02042-2).