Publication database

Here we developed a real-time photoacoustic tomography (PAT) imaging acquisition device based on the linear array transducer utilized on ultrasonic devices. Also, we produced a phantom including diverse contrast media and acquired PAT imaging as the light source wavelength was changing to see if the contrast media reacted. Indocyanine green showed the highest reaction around the 800-nm band, methylene blue demonstrated the same in the 750-nm band, and gold nanoparticle showed the same in the 700-nm band. However, in the case of superparamagnetic iron oxide, we observed not reaction within the wavelength bands used herein to obtain imaging. Moreover, we applied selective filtering to the acquired PAT imaging to remove noise from around and reinforce the object’s area. Consequentially, we could see the object area in the imaging was effectively detected and the image noise was removed.

We have observed extreme ultraviolet (EUV) spectra from terbium (Tb) ions in optically thin and thick plasmas for a comparative study. The experimental spectra are recorded in optically thin, magnetically confined torus plasmas and dense laser-produced plasmas (LPPs). The main feature of the spectra is quasicontinuum emission with a peak around 6.5-6.6 nm, the bandwidth of which is narrower in the torus plasmas than in the LPPs. A comparison between the two types of spectra also suggests strong opacity effects in the LPPs. A comparison with the calculated line strength distributions gives a qualitative interpretation of the observed spectra.

The picosecond laser-induced ripple formation on the stainless steel surface upon irradiation with linearly-polarized single-pulse and dual-wavelength cross-polarized double-pulse trains in air was studied experimentally. The characteristic switching of the ripple period and orientation were observed depending on the inter-pulse delay in the dual-wavelength cross-polarized double-pulse train irradiation experiments.

Nanostructured composites of inorganic and organic materials are attracting extensive interest for electronic and optoelectronic device applications. Here we report a novel method for the fabrication and patterning of metal selenide nanoparticles in organic semiconductor films that is compatible with solution processable large area device manufacturing. Our approach is based upon the controlled in situ decomposition of a cadmium selenide precursor complex in a film of the electron transporting material 1,3,5-tris(N-phenyl-benzimidazol-2-yl)-benzene (TPBI) by thermal and optical methods. In particular, we show that the photoluminescence quantum yield (PLQY) of the thermally converted CdSe quantum dots (QDs) in the TPBI film is up to 15%. We also show that laser illumination can form the QDs from the precursor. This is an important result as it enables direct laser patterning (DLP) of the QDs. DLP was performed on these nanocomposites using a picosecond laser. Confocal microscopy shows the formation of emissive QDs after laser irradiation. The optical and structural properties of the QDs were also analysed by means of UV-Vis, PL spectroscopy and transmission electron microscopy (TEM). The results show that the QDs are well distributed across the film and their emission can be tuned over a wide range by varying the temperature or irradiated laser power on the blend films. Our findings provide a route to the low cost patterning of hybrid electroluminescent devices.

In this paper, experiments are described in which cylindrical vacuum insulator samples and samples inclined at 45° relative to the cathode were stressed by microsecond timescale high-voltage pulses and illuminated by focused UV laser beam pulses. In these experiments, we were able to distinguish between flashover initiated by the laser producing only photo-electrons and when plasma is formed. It was shown that flashover is predominantly initiated near the cathode triple junction. Even dense plasma formed near the anode triple junction does not necessarily lead to vacuum surface flashover. The experimental results directly confirm our conjecture that insulator surface breakdown can be avoided by preventing its initiation [J. G. Leopold et al., Phys. Rev. ST Accel. Beams 10, 060401 (2007)] and complement our previous experimental results [J. Z. Gleizer et al., IEEE Trans. Dielectr. Electr. Insul. 21, 2394 (2014) and J. Z. Gleizer et al., J. Appl. Phys. 117, 073301 (2015)].

The picosecond laser irradiation of diamond-like carbon (DLC) film on the silicon wasinvestigated. The DLC films were irradiated by Nd:YVO₄ laser with the infrared (1064 nm, fluency 1.02 J/cm²) and ultraviolet (355 nm, fluency 0.79 J/cm²) wavelengths with 1, 10, and 100 pulse numbers per spot. The energy dispersive X-ray spectroscopy and microRaman spectroscopy measurements indicated that the full ablation area of the DLC was narrower than laser beam radius of the 1064 nm wavelength with 10 and 100 pulses. The increase of the oxygen concentration was obtained near the ablation areas after irradiation with the first harmonic. The microRaman and SEM measurements demonstrated that the DLC film was fully ablated in the laser spot when the third harmonic was used. The formation of silicon carbide (SiC) in the center of the irradiated spot was found after 100 pulses.

Hybrid particles are of great significance in terms of their adjustable optical, electronic, magnetic, thermal and mechanical properties. As a novel technique, laser ablation in liquids (LAL) is famous for its precursor-free, “clean” synthesis of hybrid particles with various materials. Till now, almost all the LAL-generated particles originate from the nucleation-growth mechanism. Seed-growth of particles similar to chemical methods seems difficult to be achieved by LAL. Here, we not only present novel patch-joint football-like AgGe microspheres with a diameter in the range of 1 ~ 7 μm achievable by laser ablation in distilled water but also find direct evidences of their layered seed growth mechanism. Many critical factors contribute to the formation of AgGe microspheres: fast laser-generated plasma process provide an excellent condition for generating large amount of Ge and Ag ions/atoms, their initial nucleation and galvanic replacement reaction, while cavitation bubble confinement plays an important role for the increase of AgGe nuclei and subsequent layered growth in water after bubble collapse. Driven by work function difference, Ge acts as nucleation agent for silver during alloy formation. This new seed-growth mechanism for LAL technique opens new opportunities to develop a large variety of novel hybrid materials with controllable properties.

Conventional photoluminescence (PL) yields at most one emitted photon for each absorption event. Downconversion (or quantum cutting) materials can yield more than one photon by virtue of energy transfer processes between luminescent centers. In this work, we introduce Gd₂O₂S:Tm³⁺ as a multi-photon quantum cutter. It can convert near-infrared, visible, or ultraviolet photons into two, three, or four infrared photons of ∼1800 nm, respectively. The cross-relaxation steps between Tm³⁺ ions that lead to quantum cutting are identified from (time-resolved) PL as a function of the Tm³⁺ concentration in the crystal. A model is presented that reproduces the way in which the Tm³⁺ concentration affects both the relative intensities of the various emission lines and the excited state dynamics and providing insight in the quantum cutting efficiency. Finally, we discuss the potential application of Gd₂O₂S:Tm³⁺ for spectral conversion to improve the efficiency of next-generation photovoltaics.

We report ultra-broadband supercontinuum generation in high-confinement Si3N4 integrated optical waveguides. The spectrum extends through the visible (from 470 nm) to the infrared spectral range (2130 nm) comprising a spectral bandwidth wider than 495 THz, which is the widest supercontinuum spectrum generated on a chip.

The present study assessed the ability of optogenetics techniques to provide a better understanding of the control of insulin secretion, particularly regarding pancreatic β-cell function in homeostasis and pathological conditions such as diabetes mellitus (DM). We used optogenetics to investigate whether insulin secretion and blood glucose homeostasis could be controlled by regulating intracellular calcium ion concentrations ([Ca²⁺]i) in a mouse pancreatic β-cell line (MIN6) transfected with the optogenetic protein channelrhodopsin-2 (ChR2). The ChR2-transfected MIN6 (ChR2-MIN6) cells secreted insulin following irradiation with a laser (470 nm). The increase in [Ca²⁺]i was accompanied by elevated levels of messenger RNAs that encode calcium/calmodulin-dependent protein kinase II delta and adenylate cyclase 1. ChR2-MIN6 cells suspended in matrigel were inoculated into streptozotocin-induced diabetic mice that were then subjected to a glucose tolerance test. Laser irradiation of these mice caused a significant decrease in blood glucose, and the irradiated implanted cells expressed insulin. These findings demonstrate the power of optogenetics to precisely and efficiently controlled insulin secretion by pancreatic β-cells ‘on demand', in contrast to techniques using growth factors or chemical inducers. Optogenetic technology shows great promise for understanding the mechanisms of glucose homeostasis and for developing treatments for metabolic diseases such as DM.