Tritiated surface contamination forms on ion chamber surfaces due to the isotope exchange between tritium in the ambient with protium on the surface. This creates a large background signal which impedes low level measurement. Ion chambers may be periodically cleaned to reduce the background, but this increases the risks of exposure to radiation and ion chamber breakage. We have previously described the use of ultraviolet LED light illumination as means to decontaminate ion chambers in a safe, hand-free manner. In this report, we further investigate the process for decontamination and the underlying mechanisms governing this process using in situ FTIR.

The development of CMOS-compatible nonlinear optical materials is essential for the continued growth of integrated photonics. This work investigates B-substituted AlN as a novel material platform with suitability towards UV light generation using second harmonic generation. The linear and nonlinear optical properties are characterized as a function of B composition. An enhancement of second harmonic generation coefficients with B substitution is observed, accompanied by a minor reduction in the bandgap. A waveguide structure is fabricated and used to measure loss in sputter-deposited films. A quasi-phase-matched ferroelectric domain pattern is produced and efficient second harmonic generation of UV light demonstrated.

GaN is a promising material for studying exciton-polaritons at room temperature due to its large exciton binding energy and high oscillator strength. In this study, we present a new approach to fabricating triangular GaN structures by selective area growth method using metal organic chemical vapor deposition that enables the observation of superscar mode polaritons. The superscar mode is an optical cavity mode found in polygonal structures that has a longer optical path and higher quality factors compared to the whispering gallery mode. We conducted angle-resolved micro-photoluminescence with varying excitation power to investigate the processes of polariton formation and condensation.

Micro- and nanopatterning of metal oxide materials is an important process to develop electronic or optoelectronic devices. ZnO is a material of choice for its semiconducting and photoluminescence properties. We have developed and investigated a new process that relies on direct write laser patterning in the DUV range to prepare photoluminescent microstructures of ZnO at room temperature, under air. This process is based on a synthesis of colloidal ZnO nanocrystals (NCs) with a careful choice of the ligands on the surface to obtain an optimal (i) stability of the colloids, (ii) redissolution of the non-insolated parts and (iii) cross-linking of the DUV-insolated parts. The mechanisms of photocrosslinking are studied by different spectroscopic methods. This room temperature process preserves the photoluminescence properties of the NCs and the wavelength used in DUV allows to reach a sub-micrometer resolution, which opens new perspectives for the integration of microstructures on flexible substrates for opto-electronic applications. We also show that this concept can be extended to other metal oxide nanoparticles.

Light-matter interactions in the deep ultraviolet (DUV) wavelength region exhibits a variety of optical effects such as luminescence, photoisomerization, and polymerization in many materials. Here, we present the use of two-photon excitation (TPE) using a visible wavelength laser to realize the photo-polymerization of molecules at an excitation energy equivalent to DUV light. The DUV excitation initiates direct photo-polymerization of DUV-absorbing moieties without any addition of photo-activating agents such as photo-initiators and sensitizers. Together with 3D fabrication capabilities associated with TPE, our technique allows 3D fabrication of a wider variety of materials including organic and inorganic materials such as ZrO2 and TiO2[1]. A series of fine 3D structures were created with the smallest resolved line-space features of 80 nm. The initiator-free direct laser writing of 3D nanostructures offers a distinct tool for creating nanodevices including optoelectronics, bio-compatible devices, 3D metamaterials, and more. [1] A. Taguchi, et al, “Mutiphoton-excited DUV photolithography for 3D nanofabrication,” ACS Applied Nano Materials 3(11): 11434-11441 (2020).

We proposed a cost-effective and compact optical setup for laser Interference lithography. The system is based on the special designed wave-front splitting prisms with only one spatial filter for two and tree coplanar beams interference. This configuration allows to reduce the total size of the setup. Employing a low coherence laser diode source allows to reduce the price and the size of the setup as well. The coherence length of the source was improved by Littrow type external cavity configuration. The patterning on large area (1 cm2) with sub-micron resolution was successfully demonstrated.

Far-UVC light with a wavelength of 230 nm or less are harmless to human body and have a strong inactivating effect for virus. We demonstrated 230-236nm AlGaN-based far-UVC LEDs for the purpose of virus inactivation in the human working space. We achieved the external quantum efficiency (EQE) of more than 1.5 % by introducing polarization doped p-type AlGaN layer for a 236 nm LED. We mounted 80 pieces of 230 nm LEDs in parallel to produce a panel with an output power approximately 220 and 90 mW measured under pulse and CW operation, respectively.

UV laser diodes have many advantages over existing gas lasers and solid-state lasers, such as compact size, high efficiency, low power consumption, controllable wavelength, and no use of rare noble gases, and are therefore attracting much attention for their practical application. In this presentation, we introduce our AlGaN-based laser diode in the UV-B region (wavelength of 280~315 nm), which has been difficult to realize in the past. Two bottlenecks existed in the realization of this device: the difficulty of realizing a layer structure that simultaneously realizes the formation of a favorable optical cavity and the high carrier density injection required for laser oscillation, and the difficulty of obtaining high-quality AlGaN crystals with low carrier injection that provide a large optical gain. Our group has solved these problems by using a structure with polarized doping in the p-cladding layer and a high-quality lattice-relaxed AlGaN template, and demonstrated laser oscillation by current injection. I would like to discuss the details of these breakthroughs. I would also like to introduce the latest device performance.

Hexagonal boron nitride (hBN) is a two-dimensional van der Waals material and is composed of boron and nitrogen atoms in a hexagonal lattice. hBN is the wide-bandgap semiconductor with a band of 6.4 eV and shows efficient band edge cathodoluminescence at 215 nm as well as lasing behavior. Here I will present the efficient DUV electroluminescence (EL) in band edge emission at 215 nm as well as broad 303-333 nm emission peaks from hBN van der Waals heterostructure. We observed that 303-333 nm broad emissions with phonon replica of optical phonon energy of hBN based on the Franck-Condon principle, which are attributed to the electric field induced color centers and its highly localized excitons features. These results demonstrate the promising developments of a highly efficient solid-state DUV light source at the nanoscale and allow the development of the key architectures for DUV nanophotonic, bio-sensing, high-precision metrology, and quantum information.

The demand for gas sensors is increasing as interests in air quality monitoring related to environmental pollution and industrial safety grow. The semiconductor metal oxide (SMO) type sensor is preferred for its low cost, high sensitivity, mass production, and small size, but it suffers from poor selectivity. To solve this issue, an ultra-low-power electronic nose (e-nose) system was developed using ultraviolet (UV) micro-LED (μLED) gas sensors and a convolutional neural network (CNN). This e-nose system was highly selective, with a gas classification accuracy of 99.32%, and had a gas concentration regression error of 13.82% for five different gases. The μLED-based e-nose system is battery-driven, has a total power consumption of 0.38 mW, and is expected to be widely used in environmental internet of things (IoT) applications.