Sign-tunable anomalous Hall effect induced by two-dimensional symmetry-protected nodal structures in ferromagnetic perovskite thin films.

Magnetism and spin-orbit coupling are two quintessential ingredients underlying topological transport phenomena in itinerant ferromagnets. When spin-polarized bands support nodal points/lines with band degeneracy that can be lifted by spin-orbit coupling, the nodal structures become a source of Berry curvature, leading to a large anomalous Hall effect. However, two-dimensional systems can possess stable nodal structures only when proper crystalline symmetry exists. Here we show that two-dimensional spin-polarized band structures of perovskite oxides generally support symmetry-protected nodal lines and points that govern both the sign and the magnitude of the anomalous Hall effect. To demonstrate this, we performed angle-resolved photoemission studies of ultrathin films of SrRuO3, a representative metallic ferromagnet with spin-orbit coupling. We show that the sign-changing anomalous Hall effect upon variation in the film thickness, magnetization and chemical potential can be well explained by theoretical models. Our work may facilitate new switchable devices based on ferromagnetic ultrathin films.

Deep learning-based statistical noise reduction for multidimensional spectral data.

In spectroscopic experiments, data acquisition in multi-dimensional phase space may require long acquisition time, owing to the large phase space volume to be covered. In such a case, the limited time available for data acquisition can be a serious constraint for experiments in which multidimensional spectral data are acquired. Here, taking angle-resolved photoemission spectroscopy (ARPES) as an example, we demonstrate a denoising method that utilizes deep learning as an intelligent way to overcome the constraint. With readily available ARPES data and random generation of training datasets, we successfully trained the denoising neural network without overfitting. The denoising neural network can remove the noise in the data while preserving its intrinsic information. We show that the denoising neural network allows us to perform a similar level of second-derivative and line shape analysis on data taken with two orders of magnitude less acquisition time. The importance of our method lies in its applicability to any multidimensional spectral data that are susceptible to statistical noise.

A photoacoustic finder fully integrated with a solid-state dye laser and transparent ultrasound transducer.

The standard-of-care for evaluating lymph node status in breast cancers and melanoma metastasis is sentinel lymph node (SLN) assessment performed with a handheld gamma probe and radioisotopes. However, this method inevitably exposes patients and physicians to radiation, and the special facilities required limit its accessibility. Here, we demonstrate a non-ionizing, cost-effective, handheld photoacoustic finder (PAF) fully integrated with a solid-state dye laser and transparent ultrasound transducer (TUT). The solid-state dye laser handpiece is coaxially aligned with the spherically focused TUT. The integrated finder readily detected photoacoustic signals from a tube filled with methylene blue (MB) beneath a 22 mm thick layer of chicken tissue. In live animals, we also photoacoustically detected both SLNs injected with MB and subcutaneously injected melanomas. We believe that our radiation-free and inexpensive PAF can play a vital role in SLN assessment.

Development of a Minimally Invasive and Non-invasive Lipolysis Laser System for Effective Fat Reduction.

Introduction: Obesity is a global problem because it causes various complications. Methods for reducing fat for healthy life are being studied. In this study, we developed a minimally invasive and non-invasive lipolysis laser system for effective fat reduction. Methods: The laser had the wavelengths of 1980 nm and 2300 nm which have very good absorption of fat and water. We developed a minimally invasive laser system that breaks down fat by direct irradiation of fat tissue. This minimally invasive laser system uses a 808 nm diode laser and Nd:YVO4 to generate the 1064 nm wavelength, which is the pumping source of the nonlinear crystals. It is a mid-infrared lipolysis laser system having two wavelengths of 1980 nm and 2300 nm by controlling the temperature of nonlinear crystals. We also developed a non-invasive laser system that reduces fat with hyperthermia treatment by raising the temperature of adipocytes with a 1060 nm penetrating depth into the skin. In this non-invasive laser system, the In gallium arsenide (GaAs) diode laser is irradiated on the skin with an area of 4 × 8 cm2 through the hand-piece. The cooling system in the hand-piece protects the skin from burns. We studied the effectiveness and safety of each system through animal experiment. We studied the effects of lipolysis when these two systems were combined. Results: This research uses new wavelengths (1980 nm, 2300 nm) to increase the fat reduction effect with low energy (1.3 W). After using the 1060 nm (1.1 W/cm2) wavelength laser, when the 1980 nm and 2300 nm (1.3 W) laser were used, a lipolysis effect of about 35 % was obtained. Conclusion: We have developed a 1.3 W mid-infrared (1980 nm, 2300 nm) laser with good lipolysis effect with low power.

In Vivo Dual-Modal Photoacoustic and Ultrasound Imaging of Sentinel Lymph Nodes Using a Solid-State Dye Laser System.

Photoacoustic imaging (PAI) is being actively investigated as a non-invasive and non-radioactive imaging technique for sentinel lymph node (SLN) biopsy. By taking advantage of optical and ultrasound imaging, PAI probes SLNs non-invasively with methylene blue (MB) in both live animals and breast cancer patients. However, these PAI systems have limitations for widespread use in clinics and commercial marketplaces because the lasers used by the PAI systems, e.g., tunable liquid dye laser systems and optical parametric oscillator (OPO) lasers, are bulky in size, not economical, and use risky flammable and toxic liquid dyes. To overcome these limitations, we are proposing a novel dual-modal photoacoustic and ultrasound imaging system based on a solid-state dye laser (SD-PAUSI), which is compact, convenient, and carries far less risk of flammability and toxicity. Using a solid-state dye handpiece that generates 650-nm wavelength, we successfully imaged the MB tube positioned deeply (~3.9 cm) in chicken breast tissue. The SLNs were also photoacoustically detected in the in vivo rats beneath a 2.2-cm-thick layer of chicken breast, which is deeper than the typical depth of SLNs in humans (1.2 ± 0.5 cm). Furthermore, we showed the multispectral capability of the PAI by switching the dye handpiece, in which the MB-dyed SLN was selectively highlighted from the surrounding vasculature. These results demonstrated the great potential of the SD-PAUSI as an easy but effective modality for SLN detection.

A multi-layer electro-optic field probe.

We present a novel design method and sensing scheme for an electro-optic field probe using multi-stratified layers of electro-optic wafers. A serial stack of cascaded layers is found to be capable of enhancing the performance of interferometric electro-optic light modulation that utilizes the slopes of interference fringe patterns and field-induced electro-optic phase retardations within wafers. The absolute sensitivity of the probe is also characterized with a micro-TEM cell that generates electric fields distributions with accurate, calculable strength for use in probe calibration. The sensitivity of a multi-layered probe-per unit electro-optic wafer volume--was enhanced by 6 dB compared to that of a single-layer one.

Threshold features of a Brillouin Stokes comb generated in a distributed fiber Raman amplifier.

We study threshold features of a Brillouin-shifted Stokes comb generated in a distributed fiber Raman amplifier. When the input power of Brillouin pump is linearly increased in high Raman gain, the first Stokes wave grows exponentially at much lower threshold power and then experiences an appreciable power decrease in the vicinity of the Brillouin comb's threshold. This power reduction of the first Brillouin Stokes, which we did not see mentioned in previous reports, was caused by a power transfer to higher-order lines and initiated Brillouin comb generation. Moreover, the effects of Raman pump power and pumping direction on the threshold of a Brillouin comb are investigated.