Cr:Tm:Ho:YAG (2.1 μm) and Nd:YAG (1.444 μm) pulsed-laser lithotripsy of bile duct stones

The Nd:YAG (1.444 m) and Cr:Tm:Ho:YAG (2.1 m) free-running laser systems of the output energy of 300 mJ per pulse and repetition rate 1 Hz have been developed and used for bile duct stones fragmentation study in vitro. A total of 67 human bile duct stones of known sizes, collected from surgical sources were used in the experiments. Insensitivity of the stones fragmentation to the type of the laser used, and insensitivity of the fragmentation efficiency to the type of stone, was observed. No pathological changes of the tissue were observed for non-human soft tissue laser irradiation (in vitro) by 1, 2, and 5 pulses of the Cr:Th:Ho:YAG radiation of the fluency of 1.6 J/cm². The lasers are found to be good candidates for laser lithotripsy.     

Laser-induced deposition of Ni lines on ferrite in NiSO4 aqueous solution

Maskless deposition of nickel lines on single crystalline Mn-Zn ferrite (MnO:ZnO:Fe₂O₃=31:17:52) has been investigated in a NiSO₄ aqueous solution by Ar⁺ laser irradiation. A high deposition rate of up to 36.4m/s was achieved by a single scan of laser beam. The purity of deposited nickel layers is up to 86%. In particular, well-defined values of laser power and laser irradiation time were necessary for effective deposition. The deposition process was found to be a thermochemical process.On leave from D. S. Scanner Co., Ltd., 5-3-7. Fukushima, Osaka 553, Japan     

Green Fluorescent Protein (GFP) as a Marker for Cell Viability After UV Irradiation

Generation of Chinese Hamster Ovary (CHO) cell lines stably expressing green fluorescent protein (GFP) was achieved using a plasmid vector that encoded the red-shifted pCX-xGFP under the control of a strong hybrid promoter composed of a CMV enhancer and a -actin/-globin gene promoter. Cotransfection of the promoter-less pSV2-Neo helper plasmid transmitting neomycin resistance was followed by selection with the antibiotic G418. Constitutive GFP expression could be visualized in living and fixed cells using fluorescence spectroscopy, fluorescence microscopy, and flow cytometry. DNA repair-proficient (AA8) and deficient (UV5) CHO strains were used for survival tests after UVC irradiation. Cells carrying the GFP construct (AA8-pGFP, UV5-pGFP) show the same response to UV irradiation (colony forming ability) as their nontransformed parental cell lines (AA8, UV5). Using GFP as a marker for cell viability, cells were harvested after certain postirradiation growth periods and the numbers of GFP expressing cells and fluorescence intensities were determined by FACS analysis. Generally, GFP fluorescence in irradiated cells is not seen when cell membranes are damaged (leak-out of the soluble GFP). Irradiated cells without membrane damage express GFP continuously (leading to a dose-dependent increase in GFP contents).     

Photodynamic damage study of HeLa cell line using ALA

The present study evaluates the photodynamic damage with 5-aminolevulinic acid (5-ALA) using HeLa as experimental model. HeLa cell line was irradiated with red light (He-Ne laser, λ = 632.8 CW nm). The influence of different incubation times and concentrations of 5-ALA, different irradiation doses and various combinations of photosensitizer and light doses on the cellular viability of HeLa cells were studied. The optimal uptake of photosensitizer ALA in HeLa cells was investigated by means of PpIX fluorescence intensity by exciting the HeLa cell suspension at 450 nm and a detection wavelength set at 690 nm. Cells viability was determined by means of trypan blue solution. The spectrometric measurements showed that the maximal cellular uptake of 5-ALA occurred after 4 h in vitro incubation. We found that the combination with 5-ALA and laser irradiation leads to time/concentration-dependent increase of cells death and also energy doses-dependent enlarge the cells death. The fluorescence intensity after PDD of carcinoma cells reduce when compared with the control group. The fluorescence emission spectral profiles after PDD of carcinoma cells showed a dip around 425–525 nm when compared with the control group. This may be due to the damage of mitochondria component of cells. The percentage of HeLa cells after PDD shows that the percentage of cells survival rate as function of laser dose (power). Hence it is clear that at 200 μg/ml ALA and 20 mW laser irradiation, more than 70% of HeLa cells were dead after 15 min.     

Research of the Mode Instability Threshold in High Power Double Cladding Yb‐doped Fiber Amplifiers

We experimentally investigate the behavior of the mode instability (MI) threshold in the double cladding Yb‐doped fiber amplifier when the amplifier is pumped by broad linewidth laser diodes and narrow linewidth laser diodes respectively. It is found that the MI threshold increases by 26% when the amplifier is pumped by the broad linewidth laser diodes. Experiment results show that the MI threshold is affected by the local heat load rather than the average or the total heat load. The calculation shows that the local heat deposit actually plays the key role to stimulate the MI behaviour. At the MI threshold position in the fiber, the local heat deposit also changes dramatically. The effect of the thermal conductivity on the MI threshold is also studied. Our investigation shows that the MI threshold increases from 1269 W to 1950 W when the thermal conductivity of the fiber amplifier is increased from 0.3  to 5 . Through optimizing the pump linewidth and the cooling efficiency of the gain fiber, the MI threshold is doubled in our experiment.     

Simulations of a photopumped X-ray laser using the H-like Cl−Li-like Se scheme

Calculations of the modal photon densities and gain in a photopumped Cl XVII-Se XXXII X-ray laser are presented. In this paper we undertake a realistic simulation of the generation of both Cl and Se plasmas, using a high-power optical laser, which includes radiation from both Ly-α fine-structure components of H-like Cl pumping the 2p_3/2-5d_5/2 transition in Li-like Se. The calculations are performed in two dimensions in a realistic geometry taking into account plasma gradients. This gives information about the spatial extent and time evolution of X-ray lasing gain on the 5-4 transitions in Li-like Se. We find that gain (about ) is expected only when the optical laser includes a pre-pulse. Calculations show that the absorption of pumping radiation in the pumped plasma can reduce the gain by 20%. Time-dependent calculations have shown that the gain is reduced by 30% in comparison to the steady-state calculations. The effect of the spectral profile and self-radiation of 5d_5/2-2p_3/2 transition in Li-like Se reduces the gain by about 2%.     

Extrinsic fluorescence as a sensitive method for studying photo-degradation of high density polyethylene part I

Artificial ageing of high density polyethylene (HDPE) exposed to ultra-violet irradiation has been investigated by fluorescence spectroscopy. In the case of HDPE, fluorescence spectroscopy requires the addition of fluorophore, (rhodamine 101 laser dye). The spectral features of fluorescence are very sensitive to the interaction between the exited molecules and the polymer matrix. Under wavelength close to 254 nm, the diffusion of oxygen can introduce groups such as CO, CO and C(O)O into the molecular chains. Thus entail structural and chemical modifications such as polymeric chain breaking, cross linking and oxidation. In the present work, we clearly illustrate the fact that fluorescence spectroscopy is very worthwhile in particular to follow the early stages of photo-degradation.     

Analysing Cytochrome c Aggregation and Fibrillation upon Interaction with Acetonitrile: an in Vitro Study

The propensity of native state to form aggregated and fibrillar assemblies is a hallmark of amyloidosis. Our study was focused at analyzing the aggregation and fibrillation tendency of cytochrome c in presence of an organic solvent i.e. acetonitrile. In vitro analysis revealed that the interaction of cytochrome c with acetonitrile facilitated the oligomerization of cytochrome c via the passage through an intermediate state which was obtained at 20 % v/v concentration of acetonitrile featured by a sharp hike in the ANS fluorescence intensity with a blue shift of 20 nm compared to the native state. Oligomers and fibrils were formed at 40 and 50 % v/v concentration respectively as indicated by a significant hike in the ThT fluorescence intensity, red shift of 55 nm in congo red binding assay and an increase in absorbance at 350 nm. They possess β-sheet structure as evident from appearance of peak at 217 nm. Finally, authenticity of oligomeric and fibrillar species was confirmed by TEM imaging which revealed bead like aggregates and a meshwork of thread like fibrils respectively. It could be suggested that the fibrillation of bovine cytchrome c could serve as a model protein to unravel the general aggregation and fibrillation pattern of heme proteins.

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Photophysical properties and laser performance of photostable UV laser dyes

The photophysical properties such as singlet absorption and fluorescence spectra, the fluorescence quantum yield and fluorescence decay time as well as the laser performance data such as the tuning range, the conversion efficiency, and the photochemical stability of 12 sterically hinderedp-quaterphenyls have been measured in ethanol and/or dioxane at room temperature. The sterically hinderedp-quaterphenyls exhibit shorter laser dye emissions in the 330–380 nm range than the parent compoundp-quaterphenyl. The conversion efficiencies of the sterically hinderedp-quaterphenyls range between 1 and 21%. The photochemical stability of the sterically hinderedp-quaterphenyls is by a factor of 10 to 20 better in dioxane than in ethanol. 2-Methyl-5-tert. butyl-p-quaterphenyl and 2,5,2,5-tetramethyl-p-quaterphenyl are among the most stable UV laser dyes known today.     

Multiple layer formation of bovine serum albumin on silver nanoparticles revealed by dynamic light scattering and spectroscopic techniques

It is well known that when nanoparticles (NPs) are exposed to biological fluid, it results into formation of nanoparticle protein corona, which has been the subject of extensive studies for the development of targeted drug delivery. In this work, we demonstrated the dynamic light scattering, fluorescence, and UV-visible spectroscopy as quantitative and qualitative tools to monitor adsorption of BSA protein onto silver nanoparticles (AgNPs). The adsorption resulted in significant gradual increase in average hydrodynamic radius of BSA-AgNP corona from 24 to 35 nm and its attainment of equilibrium point (saturation) that correlated with albumin concentration enables condition for bound and unbound protein adsorption to be interpreted. Using DLS, the dissociation constant (K_D) was obtained for soft corona to be 2.09?±?0.30 μM. The UV-visible and fluorescence spectroscopy results were correlated with DLS. Loss of percent helicity in secondary structure of adsorbed BSA was monitored in both coronas as compared to native protein. Both coronas were found to be biocompatible with RBC membrane. Further, the results of adsorption isotherm model were used to validate the multilayer formation of albumin protein on silver nanoparticles. The obtained results would be relevant in the drug design development for tumor-targeted therapy.

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Experimental investigation of infrared fluorescence of molecular gases under the action of CO2-laser radiation

In the paper, the experimental investigation is carried out of the IR fluorescence of organic substances of different classes in the range 600–3000 cm^–1 under the action of the continuous radiation of a CO₂ laser with a power of 40 W/cm². The procedure is given for obtaining the fluorescence spectra. For all the substances investigated, the magnitudes of the effective absorption cross section were determined experimentally at the generation frequency of the laser. Fluorescence is observed only in the case when _v 0; if _v 0, fluorescence is absent. It is shown that the fluorescence intensity depends significantly on the magnitude of the absorption cross section at the laser frequency. A comparison of the fluorescence and absorption spectra shows that only vibrations allowed in the IR region appear in the emission; in a number of cases, a sharp increase of the fluorescence intensity of certain overtones and compound vibrations is observed: when the frequencies are multiples of the laser emission.Translated from Izvestiya Uchebnykh Zavedenii, Fizika, No. 3, pp. 50–53, March Vysshikh 1979.     

Spectroscopic Studies of Fluorescence Effects in Bioactive 4-(5-Heptyl-1,3,4-Thiadiazol-2-yl)Benzene-1,3-Diol and 4-(5-Methyl-1,3,4-Thiadiazol-2-yl)Benzene-1,3-Diol Molecules Induced by pH Changes in Aqueous Solutions

This paper presents the results of stationary fluorescence spectroscopy and time-resolved spectroscopy analyses of two 1,3,4-thiadiazole analogues, i.e. 4-(5-methyl-1,3,4-thiadiazol-2-yl)benzene-1,3-diol (C1) and 4-(5-heptyl-1,3,4-thiadiazol-2-yl)benzene-1,3-diol (C7) in an aqueous medium containing different concentrations of hydrogen ions. An interesting dual florescence effect was observed when both compounds were dissolved in aqueous solutions at pH below 7 for C1 and 7.5 for C7. In turn, for C1 and C7 dissolved in water at pH higher than the physiological value (mentioned above), single fluorescence was only noted. Based on previous results of investigations of the selected 1,3,4-thiadiazole compounds, it was noted that the presented effects were associated with both conformational changes in the analysed molecules and charge transfer (CT) effects, which were influenced by the aggregation factor. However, in the case of C1 and C7, the dual fluorescence effects were visible in a higher energetic region (different than that observed in the 1,3,4-thiadiazoles studied previously). Measurements of the fluorescence lifetimes in a medium characterised by different concentrations of hydrogen ions revealed clear lengthening of the excited-state lifetime in a pH range at which dual fluorescence effects can be observed. An important finding of the investigations presented in this article is the fact that the spectroscopic effects observed not only are interesting from the cognitive point of view but also can help in development of an appropriate theoretical model of molecular interactions responsible for the dual fluorescence effects in the analysed 1,3,4-thiadiazoles. Furthermore, the study will clarify a broad range of biological and pharmaceutical applications of these compounds, which are more frequently used in clinical therapies.

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Graphical Abstract Upper left corner – C7 molecule at high pH, right upper corner - fluorescence emission spectrum for C7 dissolved in H₂O at high pH (7–12) - single fluorescence. Bottom left corner – C7 molecule at low pH (1–7), lower right corner - fluorescence emission spectrum for C7 dissolved in water at low pH – two fluorescence emissions. The circles indicate the group related to dissociation of molecules at low and high pH and the additional long circles indicate C1 or a molecule with a shorter acyl chain.

     

Controllable femtosecond laser‐induced dewetting for plasmonic applications

Dewetting of thin metal films is one of the most widespread method for functional plasmonic nanostructures fabrication. However, simple thermal‐induced dewetting does not allow to control degree of nanostructures order without additional lithographic process steps. Here we propose a novel method for lithography‐free and large‐scale fabrication of plasmonic nanostructures via controllable femtosecond laser‐induced dewetting. The method is based on femtosecond laser surface pattering of a thin film followed by a nanoscale hydrodynamical instability, which is found to be very controllable under specific irradiation conditions. We achieve control over degree of nanostructures order by changing laser irradiation parametrs and film thickness. This allowed us to exploit the method for the broad range of applications: resonant light absorbtion and scattering, sensing, and potential improving of thin‐film solar cells.

     

74% Slope efficiency from a diode-pumped Yb3+:LiNbO3:MgO laser crystal

An optimization of the laser action performance from a diode-pumped Yb³⁺-doped LiNbO₃:MgO crystal has been carried out. In this sense, efficient laser action at 1.06 m when pumping with a fiber-coupled laser diode at 980 nm has been demonstrated, achieving laser slope efficiencies as high as 74%. The influence of output mirror transmittance on both pumping threshold and laser slope efficiency has been investigated, and the parameters of relevance in laser dynamics (emission cross section and optical losses) have been determined. Under the experimental conditions leading to maximum slope efficiency, the pump power at threshold was 300mW, and the pump-to-laser conversion efficiency was 40%. PACS 42.55.Xi; 42.55.Rz; 42.60.Lh     

Effect of Doping on the Properties of Hydrogenated Amorphous Silicon Irradiated with Femtosecond Laser Pulses

A comparative analysis of the effect of femtosecond laser irradiation on the structure and conductivity of undoped and boron-doped hydrogenated amorphous silicon (a-Si: H) is performed. It is demonstrated that the process of nanocrystal formation in the amorphous matrix under femtosecond laser irradiation is initiated at lower laser energy densities in undoped a-Si: H samples. The differences in conductivity between undoped and doped a-Si: H samples vanish almost completely after irradiation with an energy density of 150–160 mJ/cm².     

Lasing of Nd3+ in sapphire

We present a rare‐earth‐doped sapphire laser. Single‐crystalline α‐Al₂O₃ films doped with trivalent neodymium have been grown by pulsed laser deposition on undoped sapphire substrates. The Nd³⁺ doping concentrations of the films have been varied between 0.3 at.% and 2 at.%. Epitaxial growth was proven by structural and optical characterization of the films. The samples exhibit strongly polarization dependent emission transitions from the ⁴F_3/2 manifold with a fluorescence lifetime of 108 μs and peak emission cross sections of 1.1 × 10⁻¹⁸ cm² around 1100 nm. Lasing at 1096.5 nm was achieved under Ti:sapphire‐pumping in a planar waveguide configuration with a maximum cw output power of 137 mW and a slope efficiency of 7.5% with respect to the incident pump power.

     

Emissive pattern formation by the photoreaction of poly(p-phenylene vinylene)

The vinylene unit of a p-phenylene polymer was photo-oxidized under atmospheric oxygen to provide emittive patterns. Thin films of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-p-phenylene vinylene] (MDMO-PPV) were directly photo-patterned by UV light through a photo-mask having 1 μm-wide lines. The absorption and fluorescence studies on the MDMO-PPV film by UV irradiation indicated that the photo-patterning was mainly originated from the oxidation of the vinylic bonds to give carbonyl (CO) containing polymers. The patterned MDMO-PPV film was applied to an electroluminescent cell, which showed 20 μm-wide luminescent line patterns at applied potential of 5 V.     

The DNA content of mouse two-cell embryos can be measured by microfluorimetric image analysis under conditions of cell viability

Video-enhanced fluorescence imaging was used to quantify the DNA content in live two-cell mouse embryos. DNA was stained with the vital fluorophore Hoechst 33342. Conditions of dye concentration and irradiation were such that two-cell embryos could be kept in the constant presence of the dye for about 24 h without a major effect on their furtherin vitro viability. Total nuclear fluorescence intensity of stained two-cell embryos was measured twice under these conditions, i.e., in G1 (1 h after cleavage) and in G2 (15–18 h after cleavage), by image analysis. After correcting for the fluctuations in excitation intensity and for the spatial nonhomogeneities of the optical system (lenses and sensor), the mean total nuclear fluorescence intensity was about twofold higher in G2 than in G1 (R=1.99 to 2.25), and this increase was abolished by the addition of aphidicolin, an inhibitor of replication. The fluorescence increase did not depend on the Hoechst concentration in the range of 10–40 ng/ml, i.e., in the range of embryo viability. The coefficient of variation of the total nuclear fluorescence intensity measured under these conditions was rather large (10 to 20%). Nevertheless, the mean value of fluorescence intensity in G1 of nuclei of a given pool represents an appropriate reference to measure the increase in fluorescence intensity between G1 and G2.