Visible Light Emission From Dye Molecular Grains via Infrared Excitation Based on the Nonadiabatic Transition Induced by the Optical Near Field

We observed light emission in the visible wavelength range (lambda = 600-690 nm) from aggregated 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM) dye molecule grains excited by infrared light (lambda_ex = 805 nm). The domains of visible light emission were localized at the surface and edges of the dye grains, where the optical near field was strengthened. The emitted visible light intensity decayed exponentially according to the time constants tau₁ = 0.45 ns and tau² = 1.37 ns, which were equivalent to those of conventional fluorescence excited by visible light at lambda_ex = 402 nm. The emitted light intensity increased with the infrared excitation intensity, in agreement with the theoretical results of the exciton-phonon polariton model. This confirmed that the visible light emission originated from the nonadiabatic transition process due to optical near-field features. The frequency upconversion efficiency for excitation from infrared (lambda_ex = 805 nm) to visible (lambda = 600-690 nm) in the film of the DCM molecular grains was experimentally estimated to be higher than that of the second harmonic generation (SHG) from a potassium dihydrogen phosphate (KDP) crystal. In particular, it was higher when the fundamental light power density was lower than 100 W/cm². Visible light emission from the grains of the rhodamine 6G (N-{2-[2-(2-aminoethoxy)ethoxy]ethyl} rhodamine 6G-amide bis[trifluoroacetate]) dye molecule was also observed in the infrared light (lambda_ex = 805 nm). Our results demonstrated the universality of the nonadiabatic transition process.     

Spectroscopic imaging and the characterization of the autofluorescence properties of human bronchus tissues using UV laser diodes

Ultraviolet laser diodes (UV-LD) were used for the excitation source of autofluorescence (AF) measurements and spectroscopic imaging of the AF originating from the human bronchus was obtained. The AF spectra from normal bronchus tissues were measured and a clear AF spectrum was obtained by using a short wavelength (400 nm) laser diode; the overlap of the AF signal and excitation source could be substantially eliminated. In order to study the origin of AF intensity deterioration from bronchus tissue due to the formation of tumor tissues, the fluorescence spectrum was measured for various AF substances under various conditions. The blue AF signal of elastin and NADH solutions, which could not be easily studied by conventional excitation light sources, as well as the green AF became weak by adding lactic acid. The AF spectrum was measured for 512/spl times/512 pixels and the intensity mapping as a function of emission wavelength was obtained. Two-dimensional information of the AF signal intensity distribution for a certain wavelength component was measured. The feature originating from a region as small as about 100 /spl mu/m could be recognized. Numerical calculations of the data were performed and precise features of the AF were revealed.     

Growth of InGaN self-assembled quantum dots and their applicationto lasers

We have successfully grown InGaN self assembled quantum dots (QD's) on a GaN layer, using atmospheric-pressure metalorganic chemical vapor deposition (MOCVD). The average diameter of the QD's was as small as 8.4 nm, and strong emission from the QD's was observed at room temperature. Next, we have investigated a structure in which InGaN QD's were stacked to increase the total QD density. InGaN QD's were formed even when the number of stacked layers was ten. As the number of layers increased, the photoluminescence (PL) intensity increased drastically. Moreover, we have fabricated a laser structure with InGaN QD's embedded into the active layer. A clear threshold of 6.0 mJ/cm² was observed in the dependence of the emission intensity on the excitation energy at room temperature under optical excitation. Above the threshold, the emission was strongly polarized in the transverse electric (TE) mode, and the linewidth of the emission spectra was reduced to below 0.1 nm (resolution limit). The peak wavelength was around 405 nm. These results indicate lasing action at room temperature     

Investigations on the VUV emissions of Ne-Xe-Cs gas mixturesexcited by an electrical discharge

UV emissions of Ne-Xe-Cs mixtures excited by a pulsed electrical discharge were investigated experimentally as a function of gas pressure and gas composition. For the studied discharge plasmas no fluorescence emissions originating to the radiative decay of the ionic excimer molecule (XeCs)⁺ at 160 nm were observed. Discharge excitation seems to be unsuitable for the generation of this ionic excimer. Previously reported fluorescence emissions due to the radiative transitions in the discharge-excited (XeCs)⁺ molecule could not be confirmed in our experimental conditions. An upper Limit for the unknown rate constant of the formation reaction Xe*+Cs⁺+Ne→Xe⁺Cs+Ne was given     

Vacuum ultraviolet emissions from the ionic excimer molecules(KrCs)+ and (HeAr)+ by low-energy electron-beamexcitation

Vacuum ultraviolet fluorescence emissions from the ionic excimer molecules (KrCs)⁺ and (HeAr)⁺ were studied in detail by low-energy electron-beam excitation, measurements were performed as a function of gas composition, gas pressure, and deposited energy in order to investigate the kinetic mechanisms of these molecules. The rate constants of the formation and competitive reactions were determined from the observed fluorescence signal decay. Estimations of the total fluorescence yield and of the gain coefficient for these molecules are given     

Intraoperative application of optical spectroscopy in the presenceof blood

A simple but effective method of spectral processing was developed to minimize or remove the effects of the presence of superficial blood on tissue optical spectra and, hence, enhance the performance of optical-spectroscopic-based in vivo tissue diagnosis and surgical guidance. This spectral-processing algorithm was developed using the principles of absorption-induced light attenuation wherein the ratio of fluorescence intensity (F) and the hth power of diffuse reflectance intensity (Rd) at a given emission wavelength λ_m is immune to spectral distortions induced by the presence of blood on the tissue surface. Here, the exponent h is determined by the absorption coefficients of whole blood at the excitation and emission wavelengths. The theoretical basis of this spectral processing was verified using simulations and was experimentally validated. Furthermore, the optical spectra of brain tissues collected in vivo was processed using this algorithm to evaluate its impact on brain tissue differentiation using combined fluorescence and diffuse reflectance spectroscopy. Based on the simulation, as well as experimental results, it was observed that using F/Rd^h h can effectively reduce or remove spectral distortions induced by superficial blood contamination on tissue optical spectra. Thus, optical spectroscopy can also be used intraoperatively for applications such as surgical guidance of tumor resection     

Measurement of the space charge field in transformer oil using itsKerr effect

Nonuniform electric fields >80 kV/cm, have been measured via a relative optical intensity measurement by exploiting the Kerr effect in transformer oil. Transformer oil was used as a Kerr medium in these measurements. Neither a knowledge of the Kerr coefficient nor the actual value of maximum transmitted intensity are required to obtain the absolute value of the electric fields. Electric fields were measured with ac and dc excitations. Space charges resulting from charge injection have been found in transformer oil at room temperature under electric stresses >150 kV/cm with ac excitation and 90 kV/cm under dc excitation. The magnitudes of space charges in transformer oil with ac applied voltages varied from 2 to 50 nC/cm³. The magnitudes of space charges with dc excitation varied from 60 pC/cm³ to 10 nC/cm³. The results illustrate the limitations of the electro-optic technique for investigations of the interfacial electric fields (gas-solid) with transformer oil as the Kerr medium     

Miniature erbium:ytterbium fiber Fabry-Perot multiwavelength lasers

We demonstrate stable simultaneous lasing of up to 29 wavelengths in miniature 1- and 2-mm-long Er³⁺:Yb³⁺ fiber Fabry-Perot lasers. The wavelengths are separated by 0.8 (100 GHz) and 0.4 nm (50 GHz), respectively, corresponding to the free spectral range of the laser cavity. The number of lasing wavelengths and the power stability of the individual modes are greatly enhanced by cooling the laser in liquid nitrogen (77 K). The polarization modes and linewidth of each wavelength are measured with high resolution by heterodyning with a local oscillator. The homogeneous linewidth of the Er³⁺:Yb ³⁺ fiber at 77 K is determined to be ~0.5 nm, from spectral-hole-burning measurements, which accounts for the generation of a stable multiwavelength lasing comb with wavelength separations of 0.4 nm     

不同波长光激发下氧化锌纳米线的发光特性研究

用汽相传输法制备了氧化锌(ZnO)纳米线,并在室温条件下,测量了在不同波长光的激发下,样品的光致发光谱.实验结果表明,当用325 nm的光激发ZnO纳米线时,观察到峰值波长约为392 nm的紫光峰峰值强度强,峰值波长约为445 nm的蓝光峰峰值强度较弱和峰值波长约为486 nm的蓝绿光峰峰值强度弱;当增加激发光波长到380 nm时,发射光谱变成峰值波长约为520 nm的半高宽较宽、峰值强度较强的带状光谱.同时对发光峰产生的机理进行了分析.     

Optical investigation of high-field conduction and prebreakdown ina dielectric liquid

Light emission studies of the high-field conduction and prebreakdown phenomena in a mixture of mono and dibenzyl-toluene (M/DBT), used as polypropylene impregnant in the all-film capacitor technology, have been undertaken to gain insight into the underlying physical mechanisms responsible for these processes. The absorption spectrum of this fluid, in the UV region, shows the appearance of structured bands at 348, 366 and 386 nm indicating a luminescence process via anthracene and 9-methylanthracene impurities at a concentration of 3×10^-3 mol/l. Optical and electrical measurements were performed simultaneously on the electrically stressed fluid. Electroluminescence of the impurities contained in M/DBT has been investigated using a new uniform field electrode arrangement. The light inception stress was determined to be ~ 20 μm^-1 for ac excitation (50 Hz). Configurations with different interfacial situations were studied and we have evidenced a correlation between charge injection and electroluminescence activity. Spectral analysis of the light radiated by streamers in M/DBT in a needle-plane electrode geometry, under step voltage (1 to 50 μs, 30 kV) revealed, for both polarities, the presence of H₂ and C₂ characteristic bands emerging from a continuum corresponding to the dissociation and recombination of molecular fragments     

1.047-μm Yb:Sr5(PO4)3F energystorage optical amplifier

The pumping and gain properties of Yb³⁺-doped Sr₅ (PO₄)₃F (Yb:S-FAP) are reported. Using a tunable, free running 900-nm Cr:LiSAF oscillator as a pump source for a Yb:S-FAP rod, the saturation fluence for pumping was measured to be 2.2 J/cm² based on either the spatial, temporal, or energy transmission properties of the Yb:S-FAP rod. The emission peak of Yb:S-FAP (1047.5 nm in air) is shown to overlap with that of Nd:YLiF₄ (Nd:YLF) to within 0.1 nm, rendering Yb:S-FAP suitable as an effective power amplifier for Nd:YLF oscillators. The small signal gain, under varying pumping conditions, was measured with a cw Nd:YLF probe laser. These measurements implied emission cross sections of 6.0×10^-20 and 1.5×10^-20 cm ² for π and σ polarized light. Respectively, which fall within the error limits of the previously reported values of 7.3×10^-20 and 1.4×10^-20 cm² for π and σ polarized light, obtained from purely spectroscopic techniques. The effects of radiation trapping on the emission lifetime have been quantified and have been shown to lead to emission lifetimes as long as 1.7 ms, for large optically dense crystals. This is substantially larger than the measured intrinsic lifetime of 1.10 ms. Yb:S-FAP crystal boules up to 25×25×175 mm in size, which were grown for the above experiments and were found to have acceptable loss characteristics (<~1%/cm) and adequately large laser damage thresholds at 1064 nm (~20 J/cm² at 3 ns). Overall, diode-pumped Yb:S-FAP amplifiers are anticipated to offer a viable means of amplifying 1.047-μm light, and may be particularly well suited to applications sensitive to overall laser efficiencies, such as inertial confinement fusion energy applications     

Highly strained GaInAs-GaAs quantum-well vertical-cavitysurface-emitting laser on GaAs (311)B substrate for stable polarizationoperation

We have realized high-quality GaInAs-GaAs quantum wells (QWs) with high strain of over 2% on GaAs (311)B substrate for a polarization controlled vertical-cavity surface-emitting laser (VCSEL). By increasing the In composition in GaInAs, the optical anisotropy in photoluminescence (PL) intensity was increased. The anisotropy of 50% was obtained at 1.15 μm emission wavelength. We have demonstrated edge-emitting lasers and VCSELs emitting at over 1.1 μm on GaAs (311)B substrate for the first time. The 1.15-μm edge-emitting laser showed a characteristic temperature of 210 K and the threshold current density of 410 A/cm². The threshold current and lasing wavelength of VCSELs are 0.9 mA and 1.12 μm, respectively. The orthogonal polarization suppression ratio was 25 dB and CW operation up to 170°C without a heat sink was achieved     

Improved output performance of high-power VCSELs

The intention of this paper is to report on state-of-the-art high-power vertical-cavity surface-emitting laser diodes (VCSELs), single devices as well as two-dimensional (2-D) arrays. Both approaches are studied in terms of electrooptical characteristics, beam performance, and scaling behavior. The maximum continuous wave (CW) output power at room temperature of large-area bottom-emitting devices with active diameters up to 320 μm is as high as 0.89 W, which is to our knowledge the highest value reported for a single device. Measurements under pulsed conditions show more than 10-W optical peak output power. Also, the CW performance of 2-D arrays has been increased from 0.56 W for 23 elements to 1.55 W for 19 elements due to significantly improved heat sinking. The extracted power densities spatially averaged over the area close to the honeycomb-like array arrangement raised from 0.33 kW/cm² to 1.25 kW/cm². Lifetime measurements have proven acceptable reliability for over 10000 h at a degradation rate of less than 1% per 1000 h. The emission wavelength of bottom-emitting devices is restricted to about 900 nm or higher due to fundamental absorption in the GaAs substrate. Windowing of the substrate has been studied to allow for shorter wavelength emission     

Luminescence Characteristics of YAG Glass–Ceramic Phosphor for White LED

Luminescence characteristics of Ce:Y₃Al₅O₁₂ (YAG) glass-ceramic (GC) phosphor for a white LED were investigated. The GC phosphor was obtained by a heat treatment of a Ce-doped SiO₂-Al₂ O₃-Y₂O₃ mother glass between 1300degC and 1500degC for the prescribed time period. The quantum efficiency (QE) of Ce³⁺ fluorescence in the GC materials, the color coordinate, and the luminous flux of electroluminescence of LED composite were evaluated with a blue LED (465 nm) set in an integrating sphere. The QE increased with increasing ceramming temperature of the as-made glass. The color coordinates (x, y) of the composite were increased with increasing thickness of the GC mounted on a blue LED chip. The effect of Gd₂O₃ substitution on the optical properties of the GC materials was also investigated. The excitation and emission wavelengths shifted to longer side up to Gd/(Y + Gd) = 0.40 in molar composition. As a result, the color coordinate of the LED with GdYAG-GC of various thickness shifted to closer to the Planckian locus for the blackbody radiation. These results were explained by partial substitution of Gd³⁺ ions in the precipitated YAG microcrystals, leading to the increase of lattice constant of unit cell, which was confirmed by XRD.     

Light propagation in tissue during fluorescence spectroscopy withsingle-fiber probes

Fluorescence spectroscopy systems designed for clinical use commonly employ fiberoptic probes to deliver excitation light to a tissue site and collect remitted fluorescence. Although a wide variety of probes have been implemented, there is little known about the influence of probe design on light propagation and the origin of detected signals. In this study, we examined the effect of optical fiber diameter, probe-tissue spacing and numerical aperture on light propagation during fluorescence spectroscopy with a single-fiber probe. A Monte Carlo model was used to simulate light transport in tissue. Two distinct sets of excitation-emission wavelength pairs were studied (337/450 nm and 400/630 nm). Simulation results indicated that increasing fiber diameter or fiber-tissue spacing increased the mean excitation-emission photon pair pathlength and produced a transition from high selectivity for superficial fluorophores to a more homogeneous probing with depth. Increasing numerical aperture caused an increase in signal intensity, but axial emission profiles and pathlengths were not significantly affected for numerical aperture values less than 0.8. Tissue optics mechanisms and implications for probe design are discussed. This study indicates that single-fiber probe parameters can strongly affect fluorescence detection and should be considered in the design of optical diagnostic devices     

OH radical measurement in a pulsed arc discharge plasma observed bya LIF method

Hydroxyl radicals generated by a pulsed arc discharge were measured by laser-induced fluorescence (LIF) with a tunable KrF excimer laser. It was shown that not only OH but excited O₂ (O₂ ^*) and excited NO (NO^*) had absorption lines within a tunable range of the KrF laser, so that LIF signals of O₂ ^* and NO^* were observed as well as OH signals. It was demonstrated that OH could be detected without disturbance by LIF signals of O₂^* or NO^* through the A-X(3,0):P₂(8) excitation; OH density was measured under various conditions in the post-discharge region. The influences of humidity, discharge current, and O₂ concentration on OH density and OH decay rate were studied in H₂ O/O₂/N₂ mixture. The results provided some possible channels of OH production and reaction with other molecules in humid air. The absolute density of OH was estimated     

Emission mechanism in rubrene-doped molecular organiclight-emitting diodes: direct carrier recombination at luminescentcenters

The emission mechanism in molecularly doped organic light-emitting diodes, where the emitting layer is composed of N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) as the host and 5,6,11,12-tetraphenylnaphthacene (rubrene) as the dopant, is investigated in terms of energy transfer and direct carrier recombination. Hole trapping by rubrene is identified by current versus voltage and mobility measurements in single-layered devices. Shallow traps are formed and are found to be filled by injected holes at electric field above 2×10⁵ V/cm. Electroluminescence observed in single-layered devices indicate that electrons can be injected directly into the hole transporter, TPD. In double-layered devices composed of TPD and tris-(8-hydroxyquinolinato) aluminum(III) (Alq₃), the penetration depth of electrons into undoped TPD is determined to be ⩽5 nm from the Alq₃ interface. Upon doping with rubrene, the emission zone is extended to 20 nm due to the increase in the electron penetration depth. This is attributed to the transition of the electron hopping sites from TPD to rubrene molecules. At high-rubrene concentration, electron transport occurs via hopping on the rubrene molecules. The dominant emission mechanism in rubrene-doped TPD is attributed to the electron-hole recombination at the dopant molecule. This is maximized by hole trapping and electron transport of rubrene     

氩气中灼烧ZnS和卤化钾混合物制备ZnS基蓝光粉的研究

在Ar保护下灼烧ZnS和KX（X为Cl、Br、Ⅰ）的混合粉体制备ZnS基蓝光粉,并研究了KBr的添加对ZnS荧光粉发光性能的影响。用X射线衍射仪（XRD）、扫描电子显微镜（SEM）和荧光光谱仪（FS）对样品进行表征。结果表明,在337nm波长光激发下,添加卤化钾的ZnS荧光粉发射出明亮蓝光,发射峰位于464nm处。随着KBr添加量的增大,荧光粉发光强度呈现先增大后减小的变化规律,KBr添加量为10％（原子分数）时荧光粉蓝光最强。     

Inverse method 3-D reconstruction of localized in vivofluorescence-application to Sjogren syndrome

The development of specific fluorescently labeled cell surface markers have opened the possibility of specific and quantitative noninvasive diagnosis of tissue changes. We are developing a fluorescence scanning imaging system that can perform a “noninvasive optical biopsy” of the Sjogren syndrome (SS) which may replace the currently used histological biopsy. The diagnosis of SS is based on the quantification of the number of topical preadministered fluorescent antibodies which specifically bind to the lymphocytes infiltrating the minor salivary glands. We intend to scan the lower lip, and for each position of the scan, generate a two-dimensional (2-D) image of fluorescence using a charge-coupled device (CCD) camera. We have shown previously that our diffuse fluorescent photon migration theory predicts adequately the positions and strengths of one and two fluorescent targets embedded at different depths in tissue-like phantoms. An inverse reconstruction algorithm based on our theoretical findings has been written in C⁺⁺ and uses 2-D images to predict the strength and location of embedded fluorophores. However, due to large numbers of variables, which include the optical properties of the tissue at the excitation and emission wavelengths, and the positions and strengths of an unknown number of fluorophore targets, the validity of the final result depends on assumptions (such as the number of targets) and the input values for the optical parameters. Our results show that the number of fluorophore targets reconstructed for each scan is limited to two, and at least the scattering coefficient at the excitation wavelength is needed a priori to obtain good results. The latter can be obtained by measurements of spatially resolved diffuse reflectance at the excitation wavelength that provides the product of the absorption and scattering coefficients     

A new method to determine the absolute mode number of a mode-locked femtosecond-laser comb used for absolute optical frequency measurements

The generation of optical frequency combs, directly referenced to the SI second, can be used to make measurements of optical frequencies. This provides a supreme method for the realization of the meter. However, an approximate knowledge of the frequency of the radiation is normally needed for such measurements in order to determine the integral order of the comb component used. Such information is usually obtained by prior wavelength measurements of the radiation under study. This paper demonstrates a new method to determine the absolute mode number in optical frequency measurements using mode-locked femtosecond lasers, thus eliminating the need for complementary wavelength measurements. Measurements of the frequency of an iodine-stabilized He-Ne laser at /spl lambda/=633 nm and a Nd:YAG laser at /spl lambda/=532nm are given as examples.