image: Figure | Femtosecond UV-C photonics. Schematic configuration for generation and detection of femtosecond UV-C laser pulses in free space. A message is coded by a UV-C laser source-transmitter and decoded by a sensor-receiver. The sensor is based on an atomically-thin semiconductor grown by molecular beam epitaxy on a 2-inch sapphire wafer (inset).
Credit: B.T. Dewes et al.
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 (Ga2O3). 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.
Journal
Light Science & Applications