Helium-cadmium Laser Research Articles

Green Afterglow of Undoped SrAl2O4.

Undoped SrAl2O4 nanocrystals were obtained via solution combustion using urea as fuel. The afterglow properties of undoped SrAl2O4 were investigated. Green afterglow from undoped SrAl2O4 is visible to the human eye when the 325 nm irradiation of a helium–cadmium laser (13 mW) is ceased. The afterglow spectrum of undoped SrAl2O4 is peaked at about 520 nm. From the peak temperature (321 K) of the broad thermoluminescence glow curve, the trap depth of trap levels in undoped SrAl2O4 is estimated to be 0.642 eV using Urbach’s formula. Based on first-principles density functional calculations, the bandstructures and densities of states are derived for oxygen-deficient SrAl2O4 and strontium-deficient SrAl2O4, respectively. Our results demonstrate that the green afterglow of undoped SrAl2O4 originates from the midgap states introduced by oxygen and strontium vacancies. The observation of green afterglow from undoped SrAl2O4 helps in gaining new insight in exploring the afterglow mechanisms of SrAl2O4-based afterglow materials.

Bragg Gratings Inscribed in Solid-Core Microstructured Single-Mode Polymer Optical Fiber Drawn From a 3D-Printed Polycarbonate Preform

This paper reports the first microstructured solid-core fiber drawn from a 3D-printed preform and the first fiber Bragg gratings inscribed in a fiber of this type. The presented fiber is made of polycarbonate and displays single-mode behavior. The fiber attenuation was the lowest reported so far for a POF drawn from a 3D-printed preform across a broad range of wavelengths. In addition, extensive fiber characterization results are presented and discussed including: fiber attenuation, mode simulations, dynamic thermomechanical analysis and thermo-optic coefficient. Fiber Bragg gratings are successfully inscribed in the produced fiber using three different lasers: a continuous wave helium-cadmium laser, a pulsed femtosecond frequency doubled ytterbium laser and ultra-violet nanosecond krypton fluoride laser. Mechanical testing of the fiber showed that the 3D printing approach did not introduce any unexpected or undesirable characteristics.

Effect of nonionizing rays on growth, chemical constituents, and molecular aspects of Catharanthus roseus plant

Background and objective Catharanthus roseus (L.) is a perennial tropical plant and is considered one of the important ornamental and medicinal plants of the family Apocynaceae. It is used as an anticancer and antidiabetic agent. Catharanthus leaves are used for menorrhagia and rheumatism. The laser rays are used as a physical method to improve the germination, the plant growth, and the vigor of the seeds. The study aimed to evaluate vegetative growth, flowering, and marker gene on Catharanthus leaves and to investigate its chemical constituents under the effect of laser rays. Materials and methods The pot experimental study was carried out at greenhouse of National Research Centre, Giza, Egypt, on C. roseus. Two types of laser [helium cadmium (He-Cd) and argon (Ar) laser] were used at different exposure times (0, 4, 8, and 12 min), and various morphological, flowering, chemical constituents were determined. Inter-simple sequence repeat (ISSR) marker was used to illustrate the effect of He-Cd and Ar laser on C. roseus at different exposure time. Results Generally, the highest values of number of leaves, plant height, root length, fresh and dry weight of leaves, and number of days to flower, photosynthetic pigments, proline %, carbohydrate, vinblastine, and vincristine were obtained with 8 and 12 min of He-Cd laser treatments. Conversely, 4-min He-Cd and 8-min Ar laser time exposure recorded decrease in photosynthetic pigments, proline %, and carbohydrate concentration. ISSR showed that mean polymorphic percentage was 25%. ISSR investigation demonstrated that the control, He-Cd laser exposure for 8 min, and Ar laser exposure for 12 min of Catharanthus plant produced unique positive markers, which were found to be mutant specific. Conclusion It was concluded that laser rays with different time exposure had potential effect on growth, flowering, chemical constituents, and the production of Catharanthus plant.

Dynamic characteristics of the plasma of a helium-cadmium laser

In this work the dynamic characteristics of a helium-cadmium laser are investigated in the process of entering the working regime. The study of the spectra of oscillations of the coherent radiation power in combination with the study of the spectrum of discharge current oscillations is carried out. The spectra of lateral spontaneous emission were also studied using a small-size diffraction spectrometer in the process of entering the laser into operating mode.

Low-temperature degradation and defect relationship in yttria-tetragonal zirconia polycrystal ceramic

In this work, the relationship between tetragonal to monoclinic phase transformation and photoluminescence spectrum were studied for 3 mol% yttria-tetragonal zirconia polycrystal samples sintered in air and argon atmosphere at 1500°C. A low-temperature degradation study was conducted under autoclave conditions containing superheated steam at 180°C and 10 bar vapour pressure for periods up to 12 hours. Photoluminescence studies were conducted using a photoluminescence spectroscope with helium–cadmium laser at a wavelength of 325 nm as the excitation source, and the phase content in the zirconia samples was measured using X-ray diffractometer. The studies concluded that argon gas sintered samples have higher structural vacancy than air sintered samples; the argon gas sintered sample showed a more rapid phase transformation than the air sintered sample and also showed that the defect associated with oxygen vacancies in the zirconia lattice increases with increasing aging time.

Discovering a Laser

An enthusiastic recounting of the early days of the helium cadmium laser—a twisting path with many characters that started at the University of Utah.

Photocatalytic Nanolithography of Self-Assembled Monolayers and Proteins

Self-assembled monolayers of alkylthiolates on gold and alkylsilanes on silicon dioxide have been patterned photocatalytically on sub-100 nm length-scales using both apertured near-field and apertureless methods. Apertured lithography was carried out by means of an argon ion laser (364 nm) coupled to cantilever-type near-field probes with a thin film of titania deposited over the aperture. Apertureless lithography was carried out with a helium–cadmium laser (325 nm) to excite titanium-coated, contact-mode atomic force microscope (AFM) probes. This latter approach is readily implementable on any commercial AFM system. Photodegradation occurred in both cases through the localized photocatalytic degradation of the monolayer. For alkanethiols, degradation of one thiol exposed the bare substrate, enabling refunctionalization of the bare gold by a second, contrasting thiol. For alkylsilanes, degradation of the adsorbate molecule provided a facile means for protein patterning. Lines were written in a protein-resistant film formed by the adsorption of oligo(ethylene glycol)-functionalized trichlorosilanes on glass, leading to the formation of sub-100 nm adhesive, aldehyde-functionalized regions. These were derivatized with aminobutylnitrilotriacetic acid, and complexed with Ni2+, enabling the binding of histidine-labeled green fluorescent protein, which yielded bright fluorescence from 70-nm-wide lines that could be imaged clearly in a confocal microscope.

Ultraviolet lithography on sloped surfaces utilizing diamond turned holograms

A lithography method by means of a diamond turned hologram (DTH) is presented, that allows patterning of sloped surfaces. The DTH is manufactured by a modified diamond turning process, using a piezoelectric actuator, the nano fast tool servo, which modulates the depth of cut within submicrometer range at a frequency up to 10 kHz. In order to machine a DTH to be applied as phase masks for ultraviolet lithography, workpiece materials have to feature a sufficient reflectivity and excellent machinability. Ultra-fine grained aluminium was identified as most suitable workpiece material, since its reflectivity measures around 80 % and a homogenous structure can be machined. The employed DTH is used in a lithography setup in conjunction with a helium cadmium laser emitting at a wavelength of λ = 325 nm. Patterns up to a linewidth of 30 μm were successfully and consistently transferred on a photoresist coated planar substrate with a tilt angle of 30° with respect to the optical axis.

Tunable solid‐state fluorescence emission and red upconversion luminescence of novel anthracene‐based fluorophores

Novel, tunable solid‐state emitters based on anthracene groups were synthesised and characterised by spectroscopy and elemental analysis. Their solid‐state photoluminescence properties were studied. These fluorophores display interesting solid‐state emission properties with an emission at wavelengths ranging from 550 to 650 nm when excited by a 325 nm helium–cadmium laser at room temperature. In particular, among them, 1,6‐di(9‐anthryl)hexa‐1,5‐diene‐3,4‐dione, 2‐[4‐(2‐benzoxazolyl)phenyl]‐4,5‐bis[2‐(9‐anthryl)vinyl]‐1H‐imidazole and 2,3‐bis[2‐(9‐anthryl)vinyl]quinoxaline show red, yellow and green emission, respectively, at 650, 584 and 550 nm. The results demonstrated that the luminescent colours can be tuned from red to yellow and green by simply varying molecular structure. Besides, 1,6‐di(9‐anthryl)hexa‐1,5‐diene‐3,4‐dione also exhibited an upconverted red fluorescent emission peak at around 675 nm under femtosecond excitation at 800 nm.

Solid-state Fluorescence Emission and Second-Order Nonlinear Optical Properties of Coumarin-based Fluorophores

Some coumarin-based fluorophores were synthesized and characterized by elemental analysis, (1)H NMR, (13)C NMR and MS. The solid-state photoluminescence properties were studied. The benzocoumarins display interesting solid-state emission properties with an emission at wavelengths ranging from 532 to 645 nm, when excited by a 325 nm helium-cadmium laser at room temperature. The results demonstrated that the luminescent colors can be tuned from green to red by simply varying molecular structure. The benzocoumarin-phenyl boronic acid hybrid, 4-(3-oxo-3-(2 -oxo-2H-1-naphtho[2,1-b]pyran-3-yl)-prop-1-enyl)phenyl boronic acid, showed obvious fluorescence response to water. Whereas the free compound was very weakly fluorescent in tetrahydrofuran (THF), the addition of water leads to an appearance of strong blue-green fluorescence and a dramatic increase of emission intensity. Besides, 3-(3-(3,4,5-trimethoxyphenyl)-prop-2-enoyl)-2H-1-benzopyran-2-one exhibited second order nonlinear optical response to laser pulses. A noticeable second harmonic generation (SHG) under pulsed excitation at 1064 nm was observed. Preliminary nonlinear measurements on powder samples showed that the second harmonic generation efficiency is roughly 5.8 times that of potassium dihydrogen phosphate (KDP).

Origin of Blue Photoluminescence from Naturally Oxidized Porous Silicon

Upon the 325 nm excitation from a helium-cadmium laser, the photoluminescence (PL) from aged porous silicon was investigated with fluorescence spectroscopy. Each PL spectrum of the aged porous silicon films contained two luminescent bands, one of the luminescent bands peaked at about 466.7 nm whereas the other luminescent band peaked at about 596.1 nm. The origin of the blue PL from aged porous silicon was discussed, and our results indicated that the blue photoluminescence of porous silicon films originated from the silicon oxide itself.

Specific features and mechanisms of photoluminescence of nanostructured silicon carbide films grown on silicon in vacuum

The light-emitting properties of cubic silicon carbide films grown by vacuum vapor phase epitaxy on Si(100) and Si(111) substrates under conditions of decreased growth temperatures (Tgr ∼ 900–700°C) have been discussed. Structural investigations have revealed a nanocrystalline structure and, simultaneously, a homogeneity of the phase composition of the grown 3C-SiC films. Photoluminescence spectra of these structures under excitation of the electronic subsystem by a helium-cadmium laser (λexcit = 325 nm) are characterized by a rather intense luminescence band with the maximum shifted toward the ultraviolet (∼3 eV) region of the spectral range. It has been found that the integral curve of photoluminescence at low temperatures of measurements is split into a set of Lorentzian components. The correlation between these components and the specific features of the crystal structure of the grown silicon carbide layers has been analyzed.

One Dimensional Aluminum Nitride Nanostructures: Synthesis, Structural, and Luminescence Properties

Aluminum nitride (AIN) is a direct bandgap semiconductor with a bandgap about 6.1 eV at room temperature, the largest among semiconductors. This paper emphasizes experimental results of the growth and optical properties of AIN nanostructures by direct nitridation. The nitridation process was performed by chemical vapor deposition method with nitrogen (N2) gas flow. AIN nanostructures were analyzed by scanning electron microscope (SEM) equipped with energy-dispersive X-ray (EDX) spectroscope and photoluminescence (PL) spectroscopy. AIN nanowires with different widths from ultrathin to thick were synthesized with this method. All of the samples had high purity without presence of any other material in EDX spectrum. The PL spectra were obtained by a 325-nm helium-cadmium (He-Cd) laser as the excitation source showing high-intensity light emitting visible wavelengths for these structures at room temperature.

Broadband luminescence and emission enhancement

Three novel quinoline– and fluorene–coumarin hybrids were prepared and characterised by Fourier Transform–infrared spectroscopy, proton and carbon nuclear magnetic resonance spectroscopy, mass spectrometry, elemental analysis and ultraviolet–visible spectrophotometry. Their photoluminescence properties were investigated. All of these hybrid molecules exhibited a broadband emission from ca. 450 to 800 nm when excited by a 325 nm helium–cadmium laser at room temperature. Importantly, the fluorene–coumarin hybrid shows a very bright red emission at ca. 650 nm and displays up to a 10-fold increase in fluorescence emission intensity, as compared with the other samples. The experimental results confirm that remarkable enhancements in the fluorescence emission intensity can be obtained by introducing a fluorene group into the azo-bridged coumarin-based π-conjugated framework. The geometry structures and frontier orbitals are calculated by the ab initio Hartree–Fock method.

Photoprotection in Plants Involves a Change in Lutein 1 Binding Domain in the Major Light-harvesting Complex of Photosystem II

Nonphotochemical quenching (NPQ) is the fundamental process by which plants exposed to high light intensities dissipate the potentially harmful excess energy as heat. Recently, it has been shown that efficient energy dissipation can be induced in the major light-harvesting complexes of photosystem II (LHCII) in the absence of protein-protein interactions. Spectroscopic measurements on these samples (LHCII gels) in the quenched state revealed specific alterations in the absorption and circular dichroism bands assigned to neoxanthin and lutein 1 molecules. In this work, we investigate the changes in conformation of the pigments involved in NPQ using resonance Raman spectroscopy. By selective excitation we show that, as well as the twisting of neoxanthin that has been reported previously, the lutein 1 pigment also undergoes a significant change in conformation when LHCII switches to the energy dissipative state. Selective two-photon excitation of carotenoid (Car) dark states (Car S(1)) performed on LHCII gels shows that the extent of electronic interactions between Car S(1) and chlorophyll states correlates linearly with chlorophyll fluorescence quenching, as observed previously for isolated LHCII (aggregated versus trimeric) and whole plants (with versus without NPQ).

Efficient Photoluminescence from Thin Films of Polypyrrole

A soluble polypyrrole without any substituent groups was obtained by controlling the oxidation level of polypyrrole in the presence of oxygen. Upon the exposure to the 325 nm ultraviolet excitation from a helium-cadmium laser, thin films of the non-substituted polypyrrole could give off strong photoluminescence with its peak at about 530 nm. To elucidate the origin of the recorded strong photoluminescence, we measured the absorption spectra of the polypyrrole thin films with ultraviolet-visible absorption spectroscopy and our data indicated the appropriately oxidized polypyrrole are free of polarons. With the help of the electronic structures calculated with Hückel tight-binding method, the intense photoluminescence is interpreted in terms of the direct electronic transitions from the conduction band to valence band of the conjugated polymer.

Origin of the Photoluminescence of a Banana-Shaped Liquid Crystal

We have investigated the optical absorption and photoluminescence (PL) of a classical banana-shaped liquid crystal, 1,3-phenylene-bis[4-(4'-nonyloxy)phenyliminomethyl]benzoate, in dilute solutions of tetrahydrofuran. Upon the 325 nm excitation from a helium-cadmium laser, the dilute tetrahydrofuran solutions of the banana-shaped compound gives off strong PL with its peak located at about 380 nm (3.26 eV). Interestingly the PL spectrum of the banana-shaped compound has a long tail that extends beyond 500 nm. In order to explore the origin of the PL, we have calculated the electronic structures of the three chromophores in the banana-shaped compound: the central benzene ring (chromophore A), the carbonyl linkage (chromophore B), and the Schiff base bridged two benzene rings in the branched arms of the molecule (chromophore C). Our results have shown that chromophore C is responsible for the 380 nm PL band where the chromophore B is responsible for the long tail in the recorded PL.

Photoluminescence of Pyrrole Oxidized in Hydrogen Peroixde

The optical absorption and photoluminescence (PL) of 5-(2-pyrrolyl)-2-pyrrolidinone were investigated with ultra-visible absorption spectroscopy and photoluminescence spectrscopy. Upon the 325 nm excitation from a helium-cadmium laser, strong blue PL was recorded for the 5-(2-pyrrolyl)-2-pyrrolidinone. The peak of the PL was located at about 425 nm (2.92 eV). The origin of the strong PL can be assigned to isolated carbonyl group.

Narrowband 1.5-μm Bragg filter based on a polymer waveguide with a laser-written refractive-index grating

We report the fabrication of narrowband frequency-selective filters for the 1.5-μm telecom window, which include a single-mode polymer waveguide with a submicron Bragg grating inscribed by a helium-cadmium laser. The filters have a reflectance R > 98 % and a nearly rectangular reflection band with a bandwidth Δλ≈0.4nm. They can be used as components of optical multiplexers/demultiplexers for combining and separating signals in high-speed dense wavelength-division multiplexed optical fibre communication systems.

CAMP Mediators of Pulsatile Insulin Secretion from Glucose-stimulated Single β-Cells

Pulsatile insulin release from glucose-stimulated beta-cells is driven by oscillations of the Ca(2+) and cAMP concentrations in the subplasma membrane space ([Ca(2+)](pm) and [cAMP](pm)). To clarify mechanisms by which cAMP regulates insulin secretion, we performed parallel evanescent wave fluorescence imaging of [cAMP](pm), [Ca(2+)](pm), and phosphatidylinositol 3,4,5-trisphosphate (PIP(3)) in the plasma membrane. This lipid is formed by autocrine insulin receptor activation and was used to monitor insulin release kinetics from single MIN6 beta-cells. Elevation of the glucose concentration from 3 to 11 mm induced, after a 2.7-min delay, coordinated oscillations of [Ca(2+)](pm), [cAMP](pm), and PIP(3). Inhibitors of protein kinase A (PKA) markedly diminished the PIP(3) response when applied before glucose stimulation, but did not affect already manifested PIP(3) oscillations. The reduced PIP(3) response could be attributed to accelerated depolarization causing early rise of [Ca(2+)](pm) that preceded the elevation of [cAMP](pm). However, the amplitude of the PIP(3) response after PKA inhibition was restored by a specific agonist to the cAMP-dependent guanine nucleotide exchange factor Epac. Suppression of cAMP formation with adenylyl cyclase inhibitors reduced already established PIP(3) oscillations in glucose-stimulated cells, and this effect was almost completely counteracted by the Epac agonist. In cells treated with small interfering RNA targeting Epac2, the amplitudes of the glucose-induced PIP(3) oscillations were reduced, and the Epac agonist was without effect. The data indicate that temporal coordination of the triggering [Ca(2+)](pm) and amplifying [cAMP](pm) signals is important for glucose-induced pulsatile insulin release. Although both PKA and Epac2 partake in initiating insulin secretion, the cAMP dependence of established pulsatility is mediated by Epac2.