Green Radiation Research Articles

Oxidative phenylamination of 5-substituted 1-hydroxynaphthalenes to N-phenyl-1,4-naphthoquinone monoimines by air and light "on water".

A number of N-phenyl-1,4-naphthoquinone monoimines 6–10 were prepared by on-water oxidative phenylamination of 1,5-dihydroxynaphthalene (1) and 5-acetylamino-1-hydroxynaphthalene (5) with oxygen-substituted phenylamines under aerobic conditions and either solar or green LED radiation, in the presence of rose bengal as singlet oxygen sensitizer. As compared to the conventional oxidative phenylamination procedures, this novel synthetic method offers the advantage of aerobic conditions “on water” instead of hazardous oxidant reagents currently employed in aqueous alcoholic media.

High contrast laser marking of alumina

Alumina serves as raw material for a broad range of advanced ceramic products. These elements should usually be identified by some characters or symbols printed directly on them. In this sense, laser marking is an efficient, reliable and widely implemented process in industry. However, laser marking of alumina still leads to poor results since the process is not able to produce a dark mark, yielding bad contrast.In this paper, we present an experimental study on the process of marking alumina by three different lasers working in two wavelengths: 1064nm (Near-infrared) and 532nm (visible, green radiation). A colorimetric analysis has been carried out in order to compare the resulting marks and its contrast. The most suitable laser operating conditions were also defined and are reported here. Moreover, the physical process of marking by NIR lasers is discussed in detail. Field Emission Scanning Electron Microscopy, High Resolution Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy were also employed to analyze the results. Finally, we propose an explanation for the differences of the coloration induced under different atmospheres and laser parameters. We concluded that the atmosphere is the key parameter, being the inert one the best choice to produce the darkest marks.

Secondary Radiation in Color Optical Filter Glasses by the Action of Plasma

This paper presents the results of experimental investigations and theoretical analysis of secondary physical phenomena that occur at interaction of electrical discharges in impulse (EDI) plasma radiation with color optical filter glasses. It was established that infrared filters (of type IKS) emit a violet secondary radiation, and dark filter (of type TS) emits a green secondary radiation. Detected phenomena can be explained by secondary radiation emission due to multi-photonic excitation of SiO2 molecules and direct-inverse translating from one energy level to another. One of the resonance oscillatory levels (of the absorption bands) for molecules of SiO2 is 780 cm-1. Thus, for infrared filters the number of absorbed infrared photons is 33, and for dark glasses is 24. In this case, the wave length of secondary radiation is 388.5 nm (violet color) and 534.2 nm (green color) respectfully. This phenomenon can be applied in construction of equipment functioning based on monochromatic light radiation.

Type-I frequency-doubling characteristics of high-power, ultrafast fiber laser in thick BIBO crystal

We report on experimental realization of optimum focusing condition for type-I second-harmonic generation (SHG) of high-power, ultrafast laser in "thick" nonlinear crystal. Using single-pass, frequency doubling of a 5 W Yb-fiber laser of pulse width ~260 fs at repetition rate of 78 MHz in a 5-mm-long bismuth triborate (BIBO) crystal we observed that the optimum focusing condition is more dependent on the birefringence of the crystal than its group-velocity mismatch (GVM). A theoretical fit to our experimental results reveals that even in the presence of GVM, the optimum focusing condition matches the theoretical model of Boyd and Kleinman, predicted for continuous-wave and long-pulse SHG. Using a focusing factor of ξ=1.16 close to the estimated optimum value of ξ=1.72 for our experimental conditions, we generated 2.25 W of green radiation of pulse width 176 fs with single-pass conversion efficiency as high as 46.5%. Our study also verifies the effect of pulse narrowing and broadening of angular phase-matching bandwidth of SHG at tighter focusing. This study signifies the advantage of SHG in "thick" crystal in controlling SH-pulse width by changing the focusing lens while accessing high conversion efficiency and broad angular phase-matching bandwidth.

Thermal Effects in High-Power Continuous-Wave Single-Pass Second Harmonic Generation

We present a theoretical model which describes the effects of thermal load distribution on single-pass second harmonic generation (SP-SHG) of high-power continuous-wave (cw) radiation in MgO:sPPLT nonlinear crystal to provide green output at 532 nm. Numerical simulations are performed based on real practical values and actual operating conditions associated with a recent SP-SHG experiment, generating 10 W of cw green radiation using a Yb-fiber laser. The model is used for four oven configurations to simulate the implications of thermal effects on SH power. The observed asymmetric feature of the phase-matching curves, particularly at higher fundamental powers up to 50 W, are characterized and explained by considering the generation of heat due to crystal absorption. The concept of optical path difference (OPD) is introduced to study the formation of thermal lens and its effects on the displacement of focal point inside the thermally loaded crystal. We further study the dependence of the SH power on the different oven schemes by increasing the input fundamental power up to 50 W. It is found that a top-sinked oven design is the optimum configuration for achieving maximum SHG efficiency without saturation. Comparison of the simulation results with experimental data confirms the validity of the theoretical model.

Optical phase locking of two infrared continuous wave lasers separated by 100 THz.

We report on phase locking of two continuous wave IR laser sources separated by 100 THz emitting around 1029 and 1544 nm, respectively. Our approach uses three independent harmonic generation processes of the IR laser frequencies in periodically poled MgO:LiNbO3 crystals to generate second and third harmonics of those two IR sources. The beat note between the two independent green radiations generated around 515 nm is used to phase lock one IR laser to the other, with tunable radio frequency offset. In this way, the whole setup operates as a mini-frequency comb emitting four intense optical radiations (1544, 1029, 772, and 515 nm), with output powers at least three orders of magnitude higher than the available power from each mode emitted by femtosecond lasers.

Studies on Spatial, Spectral, and Energy Characteristics of Copper-HBr Laser Radiations

This paper presents, for the first time, a study on the pulse-to-pulse variation in the spatial, spectral, and energy characteristics (pointing instability, divergence, intensity, as well as the emission line-width and their fluctuations) of both green and yellow radiations of a copper-HBr laser (Cu-HBrL). The experimental study was performed in a high power (specific power: 70 W/L, total power: 72 W), 18 kHz repetition rate Cu-HBrL for different wall plug electrical input powers (6-9.5 kW) and HBr concentrations (5%-9%). These observations are supplemented with studies on near field spatial intensity and temporal profiles under all working conditions. It is observed that the characteristics are widely different for the two radiation components. The experimental observations are supported by comprehensive analysis in terms of input power coupling, laser gain and its radial distribution, thermally induced wave-front aberrations, optical noise contribution, and laser kinetics.

High-power, fiber-pumped, picosecond green source based on BiB3O6

We report a stable, high-power, high-repetition-rate, picosecond green source at 532 nm in a compact and practical design based on single-pass second-harmonic generation (SHG) of a mode-locked ytterbium fiber laser in the nonlinear material BiB3O6. Using a 10-mm-long crystal, we have generated as much as 5.4 W of picosecond green radiation at 80 MHz for a fundamental average power of 14.2 W at a single-pass SHG conversion efficiency of 38%. The green output power exhibits excellent passive stability of 0.24% rms over 15 h, has a TEM00 spatial profile with M2 < 1.93, and a beam pointing stability <9 μrad over 1 h without active control.

Effect of magnesium on the burning characteristics of boron particles

Boron is an attractive fuel for propellants and explosives because of its high energy density. However, boron particles are difficult to combust because of inhibiting oxide layers that cover the particles. The use of magnesium as additives has been shown to promote boron oxidation. In this study, laser ignition facility and thermobalance were used to investigate the effect of magnesium on the burning characteristics of boron particles. The influences of magnesium addition on sample combustion flame, boron ignition delay time, boron combustion efficiency and initial temperature of boron oxidation. Results show that all Mg/B samples exhibit the same type of flame structure, i.e., a bright plume surrounded by green radiation which is interpreted as BO2 emission. The combustion flame intensity of a sample increases with the increasing magnesium content of boron particles. An increase in magnesium content results in a decrease and a subsequent increase in boron ignition delay time. (Mg/B)0.2 has a minimum ignition delay time of ~48ms. Boron combustion efficiency increases with increasing magnesium addition. (Mg/B)0.5 shows a maximum boron combustion efficiency of ~64.2%. Magnesium addition decreases the initial temperature of boron oxidation.

Synthesis, growth and characterization of picolinic acid hydrochloride: A novel semiorganic nonlinear optical single crystal

Nonlinear optical single crystals of picolinic acid hydrochloride (PHCL) were grown by the slow evaporation method. The grown crystal was subjected to a single crystal X-ray diffraction analysis, to confirm that it belongs to the orthorhombic structure. The Nonlinear Optical (NLO) property of the crystal is confirmed with the emission of green radiation from the crystal under the illumination of laser radiation (106.4 nm) from a Q switched Neodymium: Yttrium Aluminum Garnet (Nd: YAG) laser. The optical transmission range of the grown crystal was measured by Ultraviolet-Visible-Near Infrared (UV-VIS-NIR) with the lower cut-off wavelength as 195 nm. The mechanical strength of the grown crystal was analyzed using Vickers microhardness tester. The dielectric constant and dielectric loss of picolinic acid hydrochloride are measured in the frequency range of 50 Hz to 5 MHz at different temperatures. Key words: Crystal growth, Nonlinear Optical (NLO), optical transmission, single crystal X-ray diffraction (XRD), mechanical properties, dielectric studies.

Growth and Flowering before and after Storage of African Marigold and Salvia Seedlings Stored under Different Light Conditions

This study was conducted to investigate the growth and flowering of African marigold (Tagetes erecta L.) and salvia (Salvia splendens F. Sello ex Ruem & Schult.) seedlings before and after storage under fluorescent lamps and green LED radiation conditions with different light intensities during storage. The both seedlings were kept under a storage room controlled at <TEX>$8^{\circ}C$</TEX> air temperature and <TEX>$40{\pm}10%$</TEX> relative humidity conditions. Light intensities were maintained at 15 and <TEX>$30{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$</TEX> during storage. In lighting treatments, dry weight of African marigold at 28 days after storage was not significantly different, and decreased approximately 29% compared to pre-storage under dark treatment. There was no significant difference in the leaf area of salvia seedlings stored under dark condition compared to before storage, but the leaf area under green light radiation with higher light intensity (treatment GH) was two times greater than before storage. The survival rate after transplanting of African marigold stored under dark condition was 10%, and days to flowering increased compared to those stored under fluorescent and green light with higher light intensity (treatment FLH, GH). Comparing to before storage, growth and flowering of the both seedlings after storage were significantly promoted by the light exposure during storage. The present experimental results show that the light intensity should be decided to maintain minimum growth during lighting storage and storage quality of the seedlings such as flowering promotion and extended blooming period after lighting treatment during storage period from the above results.

Growth and characterization of pure and doped organic nonlinear optical single crystal: l-Alanine alaninium nitrate (LAAN)

The pure l-alanine alaninium nitrate (LAAN) single crystals and LAAN crystals doped with lanthanum oxide (La2O3), sodium chloride (NaCl), urea (CH4N2O), glycine (C2H5NO2) and thiourea (CH4N2S) were grown by slow evaporation method. The X-ray diffraction analysis, scanning electron microscopy (SEM), energy dispersive X-ray (EDAX) analysis, UV–vis spectral analysis, dielectric studies and powder SHG measurement are studied systematically. The slight changes in the lattice parameters were observed for the doped crystals compared to pure LAAN crystal. The incorporation of doping into the crystal lattice was confirmed by energy dispersive X-ray analysis. There is no change in the transmission window due to doping and the percentage of transmission in doped samples was found to increase as compared to that of pure LAAN crystal. The dielectric constant of pure crystal was found to be less than that of doped crystals. The AC conductivity was found to increase after doping and with the increase in temperature. A green radiation of 532nm was observed from the pure and doped LAAN crystals confirming the second harmonic generation (SHG) of the crystals.

Bright white upconversion luminescence in Ho3+/Yb3+/Tm3+ triple doped CaWO4 polycrystals

Abstract Ho 3+ /Yb 3+ /Tm 3+ triple doped CaWO 4 polycrystals are synthesized by a sample high temperature solid state method. The crystal structure of the polycrystals is characterized by means of X-ray diffraction.Under single-wavelength diode laser excitation of 980 nm, the bright white light consists of the blue, green, and red upconversion radiations which correspond to the transitions 1 G 4 → 3 H 6 of Tm 3+ ions, 5 S 2 / 5 F 4 → 5 I 8 and 5 F 5 → 5 I 8 of Ho 3+ ions, respectively. The pump power plays an important role in the blue upconversion emission intensity, and it helps to the adjustment of the white upconversion emission chrominance. The calculated color coordinates display that white light can be achieved by adjusting pump powers. The CIE coordinate close to (0.33, 0.33) is potentially suitable for the widely realistic application in the field of displays, lasers, and lighting technology. The possible upconversion mechanisms are investigated and discussed.

Influence of Yb3+ doping concentration on upconversion luminescence of Er3+ in Lu2O3 phosphor

Cubic phase Lu2O3:Er3+/Yb3+ nanocrystal phosphors were prepared by sol–gel method. Fourier transform infrared (FT-IR) spectra were measured to evaluate the vibrational feature of the samples. Green and red radiations were observed upon 980nm diode laser excitation. Laser power and Er3+ or Yb3+ doping concentration dependence of upconversion luminescence were studied to understand upconversion mechanisms. Excited state absorption, cross relaxation and energy transfer processes are the possible mechanisms for the visible emissions.

Studies on the spectral purity of copper–hydrogen bromide laser radiations

This paper presents, for the first time to the best of our knowledge, the linewidth, frequency, and stability characteristics of a copper-HBr laser. These spectral purity attributes were found to be critically linked with the electrical input power and HBr concentration, unlike that of the optical resonator. Variation in green and yellow radiation linewidths from 4 to 4.5GHz and from 6.5 to 8.8GHz, linewidth fluctuations from 50 to 150MHz and from 60 to 530MHz as well as frequency fluctuations from 10 to 100MHz and from 410 to 10MHz were observed when varying the input power and HBr concentration. These results are comprehensively analyzed in terms of isotopic shift, hyperfine splitting, line broadening, and temperature and gain distribution effects relevant to this laser.

Effect of pulse to pulse variation of divergence, pointing and amplitude of copper vapor laser radiations on their second harmonic and sum frequency conversion

This paper presents the effect of single pulse stability of divergence angle, beam pointing angle and amplitude of green and yellow radiation pulses of an unstable resonator copper vapor laser (CVL) oscillator in the sum frequency (SF) mixing and second harmonic (SH). The conversion efficiency of sum frequency generation was lower compared to second harmonic processes despite larger fundamental power being used in sum frequency experiments. However the net UV power obtained at the sum frequency was higher than both of the second harmonic UV frequencies. Lower sum frequency generation (SFG) conversion efficiency compared to second harmonic generation (SHG) of individual CVL radiation is attributed to difference in single pulse stability of beam pointing, divergence and amplitude fluctuation of both CVL radiations in addition to commonly known fact of spatio-temporal mis-match. At the same fundamental input power, higher SH conversion efficiency of yellow compared to green is attributed to its better single pulse stability of beam pointing and divergence.

A method used to overcome polarization effects in semi-polar structures of nitride light-emitting diodes emitting green radiation

Polarization effects are studied within nitride light-emitting diodes (LEDs) manufactured on standard polar and semipolar substrates. A new theoretical approach, somewhat different than standard ones, is proposed to this end. It is well known that when regular polar GaN substrates are used, strong piezoelectric and spontaneous polarizations create built-in electric fields leading to the quantum-confined Stark effects (QCSEs). These effects may be completely avoided in nonpolar crystallographic orientations, but then there are problems with manufacturing InGaN layers of relatively high Indium contents necessary for the green emission. Hence, a procedure leading to partly overcoming these polarization problems in semi-polar LEDs emitting green radiation is proposed. The (1122) crystallographic substrate orientation (inclination angle of 58∘ to c plane) seems to be the most promising because it is characterized by low Miller–Bravais indices leading to high-quality and high Indium content smooth growth planes. Besides, it makes possible an increased Indium incorporation efficiency and it is efficient in suppressing QCSE. The In0.3Ga0.7N/GaN QW LED grown on the semipolar (1122) substrate has been found as currently the optimal LED structure emitting green radiation.

Fluorescence-based versus reflectance proximal sensing of nitrogen content in Paspalum vaginatum and Zoysia matrella turfgrasses

Newly developed non-destructive fluorescence-based indices were used to evaluate nitrogen (N) fertilization rates and leaf nitrogen content in Paspalum vaginatum and Zoysia matrella turfgrasses. They were defined by combinations of the red (RF) and far-red (FRF) chlorophyll fluorescence signals excited under ultraviolet (UV), green (G) or red (R) radiation, as follow: Flavonol index, FLAV=log(FRFR/FRFUV); Chlorophyll indices, CHL=FRFR/RFR and CHL1=FRFG/FRFR; Nitrogen Balance Indices, NBI=FRFUV/RFR and NBI1 = FRFG⋅FRFUV/FRFR2. Measurements were performed in situ by using a portable optical sensor able to scan 1m2 plots, with a 0.2m resolution, under 6 different nitrogen rates, from 0 to 250kgha−1, with four replicates each. From the same plots, reflectance spectra were recorded and several reflectance-based indices calculated. Most of them, as well as the fluorescence-based indices of chlorophyll, CHL and CHL1, had a quadratic response to N rate with a flattening above 150kgha−1 and 100kgha−1 for P. vaginatum and Z. matrella, respectively. The fluorescence-based NBI1 index was the only one able to discriminate all the 6 N levels applied to both P. vaginatum and Z. matrella plots. This result is due to the character of NBI1 as a ratio between an index of chlorophyll and an index of flavonols that present opposite responses to N rates. The spatial heterogeneity within and between plots treated with different levels of N was well represented by the map of the NBI indices. When the NBI1 and NBI were regressed against leaf N content linear fits were obtained with high regression coefficients in both P. vaginatum (R2=0.85–0.87, RMSE=0.23–0.24% N) and Z. matrella (R2=0.75–0.78, RMSE=0.20–0.22% N). The best relationships between leaf N content and reflectance-based indices, found for R730/R1000 (R2=0.71, RMSE=0.43% N) and MCARI (R2=0.80, RMSE=0.22% N) for P. vaginatum and Z. matrella, respectively, were curvilinear and, therefore, less effective than NBI indices in the estimation of N. Nevertheless, a reflectance vegetation index suitable as proxy of leaf N common to both turf species was not found. Our results indicate the high potential of the fluorescence-based method and sensors for the in situ proximal sensing of N status in the management of N fertilization in turfgrass.

High power Q-switched intracavity sum-frequency generation and self-Raman laser at 559 nm

We report a diode-end-pumped acousto–optically Q-switched composite YVO4/Nd:YVO4/YVO4 crystal self-Raman yellow–green laser, based on the intracavity sum-frequency generation of the fundamental and first-Stokes fields in LiB3O5 crystal. Maximum average output power at 559nm is 3.55W at the incident pump power of 32W and pulse repetition frequency (PRF) of 30kHz, with an optical conversion efficiency of 11%. The highest pulse energy and peak power are 129μJ and 10.5kW at 20kHz PRF, respectively. The power stability of yellow–green radiation is better than 2% for 40min at an average output power around 3W.

Enhanced optical and electrical stability of thermally carbonized porous silicon

In the current paper, the intrinsic instability of physical properties of porous silicon (PS) was minimized using a thermal carbonization (TC) method. A typical PS showed an obvious quenching of its photoluminescence (PL) properties under long-term laser radiation. To resolve this problem, an ultra-thin stabilizing layer was grown on the porous structure under an acetylene gas flow. During the TC process at high temperatures, carbon atoms were detached from the acetylene molecules and dissolved in the porous structure. Thermally carbonized PS (TC-PS) layer changed the PL peak position of PS slightly due to the formation of Si–C species on porous surface after acetylene exposure. The effects of TC-PS layer in electrical properties of fabricated photodetectors were studied. The photocurrent of freshly prepared PS decreased under prolonged green laser radiation (532nm, 5mW), but the TC-PS sample showed more stable electrical characteristics under the same conditions.