Photonic devices operating in the ultraviolet UV-C range (100−280 nm) have diverse applications from super-resolution microscopy to optical communications, and their advances promise to unlock new opportunities across science and technology. In particular, UV-C’s strong atmospheric scattering properties open new possibilities in non-line-of-sight communication systems, e.g., enabling data transmission in obstructed environments. Despite its vast potential, the widespread adoption of UV-C technology remains limited by lack of suitable photonic components.
In a new paper published in Light: Science & Applications , a team of scientists led by Professor Amalia Patané (University of Nottingham) and Professor John W. G. Tisch (Imperial College London) have developed a new platform for the generation and detection of ultrashort UV-C laser pulses. The new system integrates an ultrafast UV-C laser source with UV-C sensors based on atomically-thin (two-dimensional) semiconductors (2DSEM). The source exploits phase-matched second-order nonlinear processes via cascaded second-harmonic generation in nonlinear crystals to produce UV-C pulses of femtosecond duration, less than 1 trillionth of a second. These pulses are detected at room temperature by photodetectors based on the 2DSEM gallium selenide (GaSe) and its wideband gap oxide layer (Ga 2 O 3 ). All materials are compatible with scalable manufacturing processes. As a proof of concept, they demonstrate a free-space communication system: a message is encoded by the laser source-transmitter and decoded by the 2D sensor-receiver.
Professor Patané, who led the development of the sensors, summarizes their findings: “ This work combines for the first time the generation of femtosecond UV-C laser pulses with their fast detection by 2D semiconductors. Unexpectedly, the new sensors exhibit a linear to super-linear photocurrent response to pulse energy, a highly desirable property, laying the foundation for UV-C-based photonics operating on femtosecond timescales over a wide range of pulse energies and repetition rates .” Ben Dewes, PhD student at Nottingham, notes: “The detection of UV-C radiation with 2D materials is still in its infancy. 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 the further development of UV-C photonic components.”
Professor Tisch, who led the research on the laser source adds: “ We have exploited phase matched second-order processes in nonlinear optical crystals for the efficient generation of UV-C laser light. The high conversion efficiency marks a significant milestone and provides a foundation for further optimization and scaling of the system into a compact UV-C source. ” Tim Klee, PhD student at Imperial, remarks: “ A compact, efficient and simple UV-C source will benefit the wider scientific and industrial community, stimulating further research on UV-C photonics. ”
In summary, the generation and detection of femtosecond UV-C laser pulses demonstrated in this work can dramatically impact many innovative applications. The sensing capabilities of 2D materials can stimulate the development of new integrated source-sensor platforms for specific applications, such as free-space communication between autonomous systems and robotics. These systems are also compatible with monolithic integration in photonic integrated circuits for different technologies spanning from broad-band imaging to spectroscopy on femtosecond timescales.
Light Science & Applications