We are familiar with ultraviolet-C (UV-C) light through its use in sterilising water, air and surfaces. But beyond this, UV-C light remains under-exploited, owing to challenges in creating compact systems capable of both generating and detecting intense, ultrafast UV-C light.

A recent study, titled ‘Fast ultraviolet-C photonics: Generating and sensing laser pulses on femtosecond timescales’, published by Dewes and colleagues in Light: Science & Applications, addresses this challenge directly. Combining advances in non-linear optics with scalable two-dimensional semiconductor sensors, the authors demonstrate an integrated platform capable of producing and detecting UV-C laser pulses lasting only a few hundred femtoseconds (a femtosecond is one quadrillionth of a second).

Ultrafast light

Many physical, chemical and biological processes unfold on timescales far shorter than a nanosecond. Ultrafast lasers, producing pulses lasting femtoseconds, help probe these processes. A femtosecond is short enough to resolve molecular vibrations, electronic transitions and ionisation dynamics.

Femtosecond lasers are now routine in the infrared and visible regions. But in the case of UV-C, direct sources such as excimer lasers are bulky and energy-intensive, while compact semiconductor lasers have limited output power. Detection poses an additional challenge, as conventional UV sensors often lack the speed or spectral discrimination needed for femtosecond operation.

femtosecond pulses

In the non-linear optical approach, the starting point is a commercially available ytterbium-based laser operating at 1,024 nanometres in the near-infrared. The pulses last 236 femtoseconds, with repetition rates of up to 60 kilohertz.

The conversion to UV-C proceeds through cascaded second-harmonic generation. Infrared pulses pass through a bismuth triborate crystal, and their frequency is doubled to produce visible light at 512 nanometres. The frequency is doubled again in a beta-barium borate crystal, yielding ultraviolet pulses at 256 nanometres. Harmonic separators suppress residual infrared and visible light, ensuring a clean UV-C output.

Through careful optimisation of crystal thickness and spacing, the authors achieve a fourth-harmonic conversion efficiency of about 20 per cent. For a compact femtosecond system, this is exceptionally high. The resulting UV-C pulses have durations of around 243 femtoseconds and energies of up to 2.38 microjoules.

2D semiconductors

For detection, the authors have developed photodetectors based on two-dimensional semiconductors — gallium selenide, which has a high absorption coefficient in the UV-C range, allowing even nanometre-scale layers to absorb light efficiently, and gallium oxide, which exhibits enhanced selectivity for UV-C wavelengths and suppressed sensitivity to visible light.

The detectors use a metal–semiconductor–metal geometry with interdigitated gold electrodes. In the gallium oxide devices, the semiconductor layer is integrated with graphene on a silicon-carbide substrate. When a UV-C pulse is absorbed, electron–hole pairs are generated and separated by an applied electric field, producing a measurable photocurrent.

The gallium selenide devices show a linear relationship between the UV-C pulse energy and the integrated photocurrent, indicating a stable and predictable response over a wide operating range.

By contrast, the gallium oxide devices exhibit an unusual super-linear response. As the pulse energy or repetition rate increases, the detector responsivity rises more rapidly than expected.

The authors attribute this to electronic processes within the semiconductor and at its interface with graphene. As a result, detector performance improves under stronger illumination, which is valuable for ultrafast applications.

High-impact uses

In biomedical imaging and diagnostics, the short wavelength of UV-C light enables spatial resolution beyond the limits of visible microscopy, while femtosecond pulses allow time-resolved observation of rapid biochemical processes such as protein dynamics, DNA damage and photo-induced cellular responses.

In materials science and semiconductor manufacturing, ultrafast UV-C spectroscopy provides direct access to electronic structure, defect states and charge recombination dynamics in wide-bandgap materials and oxides.

The ultrashort pulses enable nanoscale fabrication and repair without significant heat diffusion, detection of trace pollutants and hazardous substances, and portable systems for laboratory-on-chip applications.

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Published on January 12, 2026