Researchers develop a novel method to generate deep

Second harmonic generation

The researchers have overcome these challenges by using a process called ‘second harmonic generation,’ which relies on the fact that the frequency of a photon, or particle of light, is proportional to its energy. By using a specially designed waveguide that can control the orientation of the aluminum-nitride crystal, the researchers were able to merge two photons with half the energy into one photon with twice the energy, and thus, twice the frequency. This way, they could produce deep-UV light with a very narrow wavelength range that is safe for humans but lethal for germs.

Hiroto Honda, the study's lead author, explains that their novel approach to generating deep-UV light incorporates methods from semiconductor manufacturing. This enables accurate manipulation of the aluminum-nitride crystal's orientation, a feat that was challenging to accomplish previously.

Aluminum-nitride bilayer channel

The apparatus features a vertical polarity-inverted aluminum-nitride bilayer channel waveguide that has a width of less than one micron. A waveguide is essentially a conduit made of transparent substance, designed in such a way that it allows specific frequencies of light to pass through effortlessly. This waveguide is engineered to optimize the nonlinear optical characteristics of the material, thereby maximizing the efficiency of second harmonic generation.

The researchers tested their device by pumping visible light with a wavelength of 458 nm into the waveguide and measuring the output light at 229 nm, which is in the far-ultraviolet range. They found that their device had a conversion efficiency of 0.12%, which is comparable to or higher than previous methods of deep-UV light generation.

The researchers hope that their device can pave the way for compact and efficient deep-UV disinfection tools that can be used in various settings without compromising human safety.

The study was published in the journal Applied Physics Express.

Study abstract:

Far-UV light sources have attracted much attention for human-safe viral inactivation and bacterial disinfection. Due to large optical nonlinearity and transparency to this wavelength region, AlN is a promising material for compact and low-cost far-UV second harmonic generation (SHG) devices. In this study, a transverse quasi-phase-matched AlN channel waveguide with vertical polarity inversion was designed and fabricated. From wavelength spectra and a pump power dependence of an SH intensity, far-UV SHG via the largest nonlinear optical tensor component d33 was successfully confirmed under ultrashort pulse laser excitation.