193-nm Laser Research Articles

Optical clearing of living brains with MAGICAL to extend i nvivo imaging.

SummaryTo understand brain functions, it is important to observe directly how multiple neural circuits are performing in living brains. However, due to tissue opaqueness, observable depth and spatiotemporal resolution are severely degraded in vivo. Here, we propose an optical brain clearing method for in vivo fluorescence microscopy, termed MAGICAL (magical additive glycerol improves clear alive luminance). MAGICAL enabled two-photon microscopy to capture vivid images with fast speed, at cortical layer V and hippocampal CA1 in vivo. Moreover, MAGICAL promoted conventional confocal microscopy to visualize finer neuronal structures including synaptic boutons and spines in unprecedented deep regions, without intensive illumination leading to phototoxic effects. Fluorescence emission spectrum transmissive analysis showed that MAGICAL improved in vivo transmittance of shorter wavelength light, which is vulnerable to optical scattering, thus unsuited for in vivo microscopy. These results suggest that MAGICAL would transparentize living brains via scattering reduction.

Fourth-harmonic-generation of 266-nm ultraviolet nanosecond laser with NaSr3Be3B3O9F4 crystal

Ultraviolet (UV) 266-nm nanosecond (ns) laser was obtained through fourth-harmonic-generation by using new nonlinear optical crystals of NaSr3Be3B3O9F4 (NSBBF) with different lengths. Since NSBBF crystals are prone to crack during laser experiments, we added a water-cooling device under NSBBF crystal in the experiment, and compared the experimental results under conditions of water cooling and no water cooling. Moreover, different laser focusing effects were explored to optimize the experimental conditions. The maximum optical conversion efficiency from 532 to 266 nm was 4.8% with the pump power of 2.8 W. The maximum average output power of the 266-nm UV laser was 420 mW when the 532-nm pump power was 23.82 W. The study provides research ideas and experimental basis for NSBBF crystal to realize higher-power 266-nm ns laser output.

Time-resolved Infrared Characterization on the Photolysis of Roussin's Red Phenyl Ester in Different Solvents

Roussin's red esters (RRE) are regarded as a precursor to the release of a nitrogen monoxide upon irradiation. The 355-nm nanosecond pulsed laser was employed to initiate the photolysis of Roussin's red benzyl ester, Fe2(μ-SPh)2(NO)4, in different solvent compositions monitored with time-resolved step-scan Fourier-transform infrared spectroscopy. Density functional theory assisted in predicting the energetics and assignments of vibrational bands of the photolytic intermediates. The photolysis in cyclohexane (cHex) gives rise to two downward bands at 1785 and 1760 cm–1 owing to parent depletion coupled with an upward band at 1805 cm–1 that accounts for the symmetric NO stretch of Fe2(μ-SPh)2(NO)3. In a binary solvent of cHex/THF = 2/1, a quick coordination of THF to Fe2(μ-SPh)2(NO)3 forms Fe2(μ-SPh)2(NO)3(THF), which contributes to the two upward NO-associated vibrations at 1738 and 1717 cm–1. Similarly, the two upward features at 1740 and 1718 cm–1 attributed to Fe2(μ-SPh)2(NO)3(DX) were observed in a mixed solvent of cHex/1,4-dioxane(DX) = 2/1. In this work, we deliver direct spectroscopic evidence that cyclohexane serves as a weakly interactive medium to solvate the transient species, whereas THF and DX are capable of coordinating to the vacant sites of the photolytic intermediates via lone pair electrons on oxygen, leading to different transient species and cascading products. The combination of theoretical and time-resolved IR spectroscopic approaches successfully conquers the difficulties in the prediction of photolysis of RRE, suggesting further applicability in tracking the photochemistry of iron-containing species at the molecular level. Moreover, the distinct photolytic products characterised in the steady-state spectra ascertain the solvent-controlled selectivity in the organic reactions.

Sensitive analysis of doxorubicin and curcumin by micellar electromagnetic chromatography with a double wavelength excitation source.

Doxorubicin has been extensively used to treat cancers, and there are recent findings that the anticancer activities can be enhanced by curcumin. Although the two compounds have native fluorescence, they can hardly be quantified directly simultaneously using the laser-induced fluorescence (LIF) detection method. To avoid complex fluorescence derivatization and introduction of interfering components, a highly sensitive double wavelength excitation source LIF (D-W-Ex-LIF) detector composed of a 445-nm and 488-nm commercial laser diode was constructed to detect them simultaneously. Rhodamine 6G was selected as an internal standard, because its fluorescence can be excited at 445nm and 488nm. The native fluorescence of doxorubicin and curcumin and their resolution were enhanced by introducing mixed micelles. The optimal electrophoretic separation buffer was 10mM borate buffer containing 20mM Triton X-100, 5mM sodium dodecyl sulfate, and 30% (v/v) methanol at pH9.00. Therefore, the developed method was specific, accurate, and easily operable. Its limits of detection for doxorubicin and curcumin in human urine samples were 4.00 × 10-3 and 1.00 × 10-2μg/mL, respectively, and the limits of quantification were 1.00 × 10-2 and 3.00 × 10-2μg/mL, respectively. The recoveries were 94.9-109.1%. Graphical abstract.

High surface laser-induced damage threshold of SrB4O7 single crystals under 266-nm (DUV) laser irradiation.

Under 266-nm (deep ultraviolet, DUV) laser irradiation, an SrB4O7 (SBO) single crystal has been found to exhibit a surface laser-induced damage threshold (LIDT) of ∼ 16.4 J/cm2, which is higher than those of a synthetic silica glass (4.8 J/cm2) and a calcium fluoride (CaF2) crystal (11.4 J/cm2). By catalyst-referred etching (CARE), the LIDT of an SBO crystal can also be improved to around 24.1 J/cm2, which is 1.4 and 6.0 times higher compared to an unetched crystal and a silica glass, respectively. With high surface LIDTs, SBO single crystals can then be used as optical window materials for high-power DUV laser systems.

Role of water vapour in the absorption of nanosecond 266-nm laser pulses by atmospheric air

The absorption of the Nd : YAG fourth harmonic in air and binary mixtures of water vapour with nitrogen and oxygen at atmospheric pressure has been measured as a function of pulse energy (peak intensity). The mixtures obtained by adding equal amounts of water vapour to dry nitrogen and oxygen have been found to differ significantly in absorption. Preliminary quantitative data have been obtained for two- and three-photon absorption cross sections of water and oxygen molecules: σ(2)(H2O) = (4 ± 1) ± 10–49 cm4 s and σ(3)(O2) = (5.6 ± 1.4) ± 10–78 cm6 s2. The absorption of 266-nm pulses with peak intensities from 0.05 to 2 GW cm–2 in the near-surface atmosphere has been shown to be determined by two-photon absorption in water vapour and three-photon absorption in oxygen. In moist air containing 1 % water vapour, the absorption coefficient for 266-nm laser pulses exceeds that in dry air by four to five times. There is no absorption in nitrogen. We have developed a technique for photoacoustic measurements of multiphoton absorption cross sections in single-component gases and gas mixtures.

Changes in Autofluorescence Level of Live and Dead Cells for Mouse Cell Lines.

Label-free characterization of cell subpopulations is a very promising biomedical approach. Nowadays, there are several label-free methods based on different physical properties such as size, density, stiffness, etc. allowing the characterization of biological objects. However, fluorescence properties are the most suitable feature for the label-free study of tissue and cells. Understanding the autofluorescence level peculiarities of normal and pathological / live and dead cells can become a helpful tool for cells' metabolic activity, viability evaluation, and diagnostics of a number of diseases. In this study, we applied a series of mouse cell lines (RAW 264.7 - macrophages, L929 - fibroblasts, C2C12 - myoblasts, and B16-F10 - melanoma) to compare cell autofluorescence of live and dead cells under 488nm laser excitation and found the difference between their autofluorescence depending on a cell state and type.

ZnO Microwire-Based Fiber-Tip Fabry-Pérot Interferometer for Deep Ultraviolet Sensing

We propose a simple deep ultraviolet (UV) sensor consisting of a conventional single-mode optical fiber capped with a ZnO microwire. The ZnO microwire positioned on the fiber-tip acts as a Fabry-Pérot interferometer, of which the reflection spectrum can be employed for UV light monitoring. When ZnO microwire is exposed to UV irradiation, variations in the concentration of photogenerated carriers will result in the change of the refractive index (RI) of the ZnO microwire, and thus interference wavelengths of the proposed device exhibits red-shift with a sensitivity of 0.288 nm/(W·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ) under 266-nm deep UV laser irradiation. Meanwhile, a fast response time of 0.56 ms is experimentally obtained. The results may pave a new way for fast responsive, highly spatial-resolved optical fiber UV sensors.

Enhancement of ultra-violet light absorption of surface-textured silicon induced by nanosecond laser irradiations

The process of inducing crystallization on the surface of a 50-nm-thick amorphous Si (a-Si) thin film was analyzed by applying a Nd:YAG (λ = 355 nm) nanosecond laser with an asymmetric Gaussian shape at a pulse repetition rate of 14 kHz and pulse duration of 5.5 ns. Single-laser-pulse irradiation with a peak fluence of 124 mJ/cm2 resulted in the formation of circular Si nanoparticles on the surface, which was observed to have multiple domains with varying degrees of surface roughness and crystallinity. Additionally, the light absorption significantly increased at the center of irradiation, where the density of the nanoparticles was maximized. Specifically, at the ultraviolet wavelength of 380 nm, the absorption was 85%, which is approximately twice that for the non-laser-treated a-Si (i.e., 42%). These results are attributable to the anti-reflection effect of the Si nanoparticles, and have been validated by numerical simulations. Although the intensity and absorption were observed to be heterogeneous, it is suggested that uniform crystallinity can be achieved by optimizing the scan pitch and laser fluence; these conditions would enable application of a 355-nm nanosecond laser to the laser crystallization process for organic light-emitting diode displays or photovoltaic devices.

Effects of Pulse Duration and Heat on Laser-Induced Periodic Surface Structures

Compared with traditional nanotexturing methods, an ultrashort-pulsed laser is an efficient technology of fabricating nanostructures called laser-induced periodic surface structures (LIPSS) on material surfaces. LIPSS are easily fabricated when the pulse duration is shorter than collisional relaxation time (CRT). Accordingly, ultrashort-pulsed lasers have been mainly used to study LIPSS, but they unstably irradiate while requiring high costs. Although long-pulsed lasers have low cost and high stability, the phenomena (such as the effect of pulse duration, laser wavelength, and heat) of the LIPSS fabricated using short-pulsed lasers with the pulse duration close to the maximum CRT, which is greater than femtosecond, have not been clarified. However, the nanosecond pulse laser has been reported to produce LIPSS, but those were unclear and ununiform. In this study, the short-pulsed laser with the pulse duration of 20 ps, which is close to the maximum CRT, was employed to clarify the effects of pulse duration and heat on the fabrication of LIPSS and to solve problems associated with ultrashort-pulsed lasers. First, a finite-difference time-domain simulation was developed at 20-ps pulse duration to investigate the effects of irradiation conditions on the electric-field-intensity distribution. Subsequently, experiments were conducted using the 20-ps pulse laser by varying conditions. The aspect ratio of the LIPSS obtained was greater than that of the LIPSS fabricated using ultrashort-pulsed lasers, but LIPSS were not fabricated at 355- and 266-nm laser wavelength. In addition, the short-pulsed laser experienced thermal influences and a cooling material was effective for the fabrication of LIPSS with high-aspect-ratio. This demonstrates the effects of pulse duration close to the CRT and heat on the fabrication of LIPSS.

Laser-Power Dependence of Poly-Silicon Crystallization Using 355-nm Nanosecond Laser Annealing

We report the laser-power dependence of a poly-silicon thin film fabricated using a 355-nm nanosecond laser annealing. The temperature distribution in the annealed thin film was investigated using thermal simulations as the laser power was varied to obtain the optimum laser conditions for crystalizing an amorphous silicon film. Based on the simulation results, laser annealing experiments were conducted for a 100-nm-thick amorphous silicon film deposited on a SiO2/Si wafer by using a Q-switched 355-nm nanosecond diode-pumped solid-state laser. The characteristics of the annealed silicon film were investigated using Raman spectroscopy and atomic force microscopy, which showed that both the crystal quality and the roughness of the annealed film increased as the laser was power increased. The experimentally obtained optimum laser power condition was found to be consistent with the simulation results. The demonstrated 355-nm nanosecond laser annealing is expected to provide a versatile solution for low-temperature poly-silicon processes.

Photochemical reactions between 1,4-benzoquinone and O2•.

The superoxide anion radical (O2•-) is one of the most predominant reactive oxygen species (ROS), which is also involved in diverse chemical and biological processes. In this study, O2•- was generated by irradiating riboflavin in an O2-saturated solution using an ultraviolet lamp (λem = 365 nm) as the light source. The photochemical reduction of 1,4-benzoquinone (p-BQ) by O2•- was explored by 355-nm laser flash photolysis (LFP) and 365-nm UV light steady irradiation. The results showed that the photodecomposition efficiency of p-BQ was influenced by the riboflavin concentration, p-BQ initial concentration, and pH values. The superoxide anion radical originating from riboflavin photolysis served as a reductant to react with p-BQ, forming reduced BQ radicals (BQ•-) with a second-order rate constant of 1.1 × 109 L mol-1 s-1. The main product of the photochemical reaction between p-BQ and O2•- was hydroquinone (H2Q). The present work suggests that the reaction with O2•- is a potential transformation pathway of 1, 4-benzoquinone in atmospheric aqueous environments.

Fixed versus live endothelial cells: The effect of glutaraldehyde fixation manifested by characteristic bands on the Raman spectra of cells.

This work shows an impact of glutaraldehyde (GA) fixation on endothelial cells. Raman spectroscopy imaging was used as a method to monitor biochemical content of the cells due to GA fixation since this is an approach frequently used for studying cells by means of Raman imaging. To get a deeper insight into the changes and to understand them better the measurements of live and fixed cells were performed using two lasers, i.e. 488 and 532nm. It has been demonstrated that GA fixation affects lipids, proteins, nucleic acid and carbohydrates to small extent. The application of 488nm laser line seems to be more efficient for live cells due to the small impact of cytochrome resonance on Raman spectra, however 532nm line is more beneficial for fixed cells due to higher quantum efficiency of the detector, thus leading to higher intensity of Raman bands. Generally, the changes due to fixation are not pronounced but cannot be ignored and the knowledge about them can help in a proper interpretation of data collected for fixed versus live cells.

Enhanced one- and two-photon pumped amplified spontaneous emissions of Ag-SiO2 core-shell nanowire composite embedded CH3NH3PbBr3 in SiO2 mesopores

Benefiting from high-performance of photoelectric, hybrid organic-inorganic perovskite shows great development potential. We introduce a composite nanostructure of monolayer well-organized mesoporous silica, with a wrapped silver nanowire as a core. A gain material, methyl ammonium lead bromide (MAPbBr3) was embedded in mesoporous silica (mSiO2). Using 400-nm and 800-nm femtosecond lasers for pumping, which were corresponding to one-photon and two-photon regimes, the laser sign peaks appeared at 549 nm and 546 nm. The amplified spontaneous emissions (ASE) were observed, as well, giant enhancements of ASE can be obtained due to the localized field of surface plasmon resonance caused by silver-core. Compared with composites without silver nanowire cores to enhance the field distribution, the thresholds are significantly down to ∼62% and 32% of original values under 400-nm and 800-nm femtosecond lasers pump, respectively.

HCN emission by a Polydesmid Millipede Detected Remotely by Reactive Adsorption on Gold Nanoparticles Followed by Laser Desorption/Ionization Mass Spectrometry (LDI-MS).

Hydrocyanic acid (HCN) is a well-known defensive allomone in the chemical arsenal of millipedes in the order Polydesmida. The presence of HCN in the headspace vapor of adult Xystocheir dissecta (Wood, 1867), a common millipede from the San Francisco Bay Area, was traced by laser desorption/ionization-mass spectrometry (LDI-MS). To accomplish this, the headspace vapor surrounding caged, live millipedes was allowed to diffuse passively over gold-nanoparticle (AuNP) deposits placed at various distances from the emitting source. The stainless steel plates with AuNP deposits were removed and irradiated by a 355-nm laser. The gaseous ions generated in this way were detected by time-of-flight mass spectrometry. The intensity of the mass spectrometric peak detected at m/z 249 for the Au(CN)2- complex anion was compared to that of the residual Au- signal (m/z 197). Using this procedure, HCN vapors produced by the live millipedes could be detected up to 50 cm away from the source. Furthermore, the addition of H2O2, as an internal oxygen source for the gold cyanidation reaction that takes place in the AuNP deposits, significantly increased the detection sensitivity. Using the modified H2O2 addition procedure, HCN could now be detected at 80 cm from the source. Moreover, we found a decreasing intensity ratio of the Au(CN)2-/Au- signals as the distance from the emitting source increased, following an exponential-decay distribution as predicted by Fick's law of diffusion. Graphical abstract.

General design and experiment for separated final optics assembly on high energy laser system

Final optics assembly (FOA) is paramount to high energy laser system. It took more than ten years for the National Ignition Facility (NIF) and Laser Megajoule Facility (LMJ) to optimize their FOA and improve output capability. However, the final optical damage limited the output capability of the NIF and LMJ. Contamination is the dominant factor which can dramatically reduce their damage threshold. Accordingly, in this work we propose a separated FOA which mainly locates in the atmosphere and is convenient for contaminants sources management. In addition, we adopts an on-line cleaning system to improve clean status of FOA and achieves longevity lifetime of final optics. The experiment result of the separated FOA demonstrates that even more than one thousand particle contaminants are generated by each laser shot of 6 J/cm2, the on-line cleaning system can take major of them away and maintain cleanliness of separated FOA at ISO Class 3. Our separated FOA can stably operate under a 351-nm laser shot of 6 J/cm2 (21.7 ns shaped-pulse), which is significant to improve the output capability of high energy laser system.

Characterization of Silver-Doped LiF Crystal Grown by Czochralski Technique for Dark Matter Search Application

In this article, the growth, luminescence, and scintillation properties of a silver-doped LiF crystal grown by the Czochralski technique are studied. The absorption spectrum of the crystal is measured at room temperature and optical energy bandgap of the crystal is calculated as ~5.2 eV. The luminescence and scintillation properties of the crystal are studied at different temperatures (10–550 K) under the excitations with X-ray, 266-nm laser, 280-nm light emitting diode (LED), and 90Sr beta source. The crystal shows a violet emission (~405 nm) under the excitation of a 280-nm LED source. The luminescence decay time of the crystal is measured from room temperature (300 K) to 10 K under the excitation of the 266-nm laser source. The decay time curves are fit with 2-exponential (300–200 K) and 3-exponential (175–10 K) decay functions. The shortest ( $27.2~\mu \text{s}$ ) and the longest decay time ( $42.8~\mu \text{s}$ ) of the crystal are obtained at 300 and 75 K, respectively. Thermoluminescence (TL) measurements were carried out from 10 to 300 K and 325 to 550 K in order to investigate the presence of trap centers. The different kinematic parameters such as order of kinematics, trap depth, and frequency factor are calculated for the observed TL peaks. The scintillation light yield of the crystal is measured with a continuous single photon counting technique using a 90Sr beta source in the temperature range from 300 to 10 K. In this article, we will emphasize the potentiality of a Li-based crystal for dark matter search applications.

Non-linearities in Superconducting Tunnel Junction Radiation Detectors and Their MCA Readout

The response of cryogenic high-resolution detectors to a short-pulse laser consists of a Poisson-distributed set of equidistant peaks that correspond to integer numbers of absorbed photons. Since the laser has a negligible intrinsic line width, the peaks can be used for detailed characterization of both the detector and the data acquisition system. We have characterized our superconducting tunnel junction (STJ) photon detectors in the UV and soft X-ray range with a pulsed 355-nm laser at rates up to 5000 counts/s. The observed peaks are described by a Gaussian to very high accuracy, with a width between ~ 1 and ~ 3 eV FWHM depending on the detector area and the absorbed energy. For high statistics, centroids can be determined with a precision of order 1 meV over an energy range of several 100 eV. This allows identifying and correcting for non-linearities in the digitizer that can otherwise limit the calibration accuracy.

Achieving high-resolution of 21 nm for STED nanoscopy assisted by CdSe@ZnS quantum dots

Although quantum dots (QDs) show strong photoluminescence and high photostability, they are not widely used as probes for stimulated emission depletion (STED) nanoscopy because the excitation of the doughnut-shaped STED beam always generates background noise (the so-called “halo”) that hampers superresolution microscopy. In this study, we attempted to use commercially available CdSe@ZnS QDs with green emission (QD526) as a probe in STED nanoscopy. A lateral resolution of 21.0 nm for a single QD was obtained when using a 488-nm excitation laser and a 592-nm depletion laser. The high resolution achieved was mainly attributed to the fact that no halo was generated around the STED spots. This was also confirmed through spectral analysis in that no spontaneous fluorescence was detected when the QDs were irradiated by the 592-nm laser. The results indicated that the halo could be avoided effectively in QD-assisted STED nanoscopy by tuning the wavelength of the emission peak of the QDs and the depletion laser. This study provides insights into how to easily avoid the halo in QD-assisted STED nanoscopy and how to improve the nanoscopy resolution.

Efficient synthesis of NIR emitting bis[2-(2'-hydroxylphenyl)benzoxazole] derivative and its potential for imaging applications.

Unassymetric bis[2-(2'-hydroxyphenylbenzoxole)] bis(HBO) derivatives with a DPA functionality for zinc binding have been developed with an efficient synthetic route, using the retrosynthetic analysis. Comparison of bis(HBO) derivatives with different substitution patterns allows us to verify and optimize their unique fluorescence properties. Upon binding zinc cation, bis(HBO) derivatives give a large fluorescence turn-on in both visible (λem≈536nm) and near-infrared (NIR) window (λem≈746nm). The probes are readily excitable by a 488nm laser, making this series of compounds a suitable imaging tool for in vitro and in vivo study on a confocal microscope. The application of zinc binding-induced fluorescence turn-on is successfully demonstrated in cellular environments and thrombus imaging.