Integrated UV-C Source-Sensor Platform Based on Efficient Ultrafast Fourth Harmonic Generator and Two-Dimensional Sensor

The UV-C spectrum offers a plethora of uses such as air/water purification [1] and free space optical communication [2]. An efficient fourth harmonic (FH) generator is presented, suitable for ultrafast NIR lasers with a pulse energy of < 100 μJ. We demonstrated our FH generator as an efficient source to investigate the photo response of a novel two-dimensional GaSe sensor. Fig. 1a) outlines the experimental setup. We used a Carbide CB5 with a pulse duration of 237 fs, a central wavelength of 1024 nm and a tuneable repetition rate from 0–60 kHz. Two separate second harmonic generation processes in a BiBO crystal (1 mm thick) and a BBO crystal (0.3 mm thick) generated the FH at 256 nm. As can be seen in Fig. 1b) the measured fundamental to FH conversion efficiency reached 20 ± 0.05%, generating 2.38 μJ of UV-C light. To the best of our knowledge, this is the highest reported efficiency for these laser parameters. Similar FH setups [3], [4] typically refocus the SH into the second crystal. The work presented here demonstrates that a single-focus geometry can provide a simpler and more efficient route to FH for these laser parameters. A more compact system using nJ pulse energies, such as those generated by an oscillator, could also be developed using a similar approach as in [3].