Cw Argon Laser Research Articles

An Efficient Ultrasonic-Assisted Synthesis and Nonlinear Optical Property of Donor (D) -π-Acceptor (A) Chalcone (DDFP)

Abstract 3-(3,4-dimethoxyphenyl)-1-(2,5-dimethylfuran-3-yl)prop-2-en-1-one (DDFP), is prepared by the equimolar ratio of 1-(2,5-dimethylfuran)ethan-1-one and 3,4, dimethoxy benzaldehyde under ultrasonic irradiation. Structure of DDFP was established by the FT-IR, 1H and 13C-NMR spectroscopic methods and elemental analysis. The nonlinear optical properties of this dye using the z-scan technique with a cw argon ion laser at 514.5 nm are studied. Both the closed and open aperture z-scan data is used to estimate the nonlinear refractive index n2 and the nonlinear absorption coefficient β respectively. The measurements are carried out at five concentrations as well as at five laser powers. The values obtained are relatively very high and vary linearly with concentration. The studies on optical limiting behavior of this dye are also reported here.

Synthesis, linear and nonlinear optical properties of a new dimethine cyanine dye derived from phenothiazine

Dimethine cyanine dye (PTZIS) based on phenothiazine as the core donor and indolium salt as the acceptor has been synthesized and fully characterized. UV-Vis absorption and fluorescence properties of PTZIS were studied in different solvents. Absorption spectra revealed a large bathochromic shift of the intramolecular charge transfer (ICT) absorption band of PTZIS compared with those in the non-halogenated solvents. Also, the optical data of PTZIS showed a large Stokes shift compared with those in the non-halogenated solvents, indicating a great influence on the geometry of the emissive excited state. The nonlinear optical properties of PTZIS in ethanol solution at different concentrations and different laser powers have been studied using the Z-scan technique with a continuous wave (cw) argon ion laser at 514.5 nm. The closed aperture Z-scan data was used to estimate the nonlinear refractive index n2, while the open aperture scan provided the nonlinear absorption coefficient β. The values obtained are relatively very high and vary linearly with concentration.

Microwave assisted synthesis, spectroscopic studies and non linear optical properties of bis-chromophores

Bis chromophores were synthesized by the terephthalaldehyde with (4-nitrophenyl) acetonitrile/(4-flurophenyl) acetonitrile under microwave irradiation. Bis-chromophores were obtained in good to excellent yields. The structures of bis-chromophores were established by FT-IR, 1H NMR, 13C NMR, EI-MS and elemental analyses. Physical chemical properties such as singlet absorption, extinction coefficient, stokes shift, oscillator strength and dipole moment, were investigated by UV–Vis and fluorescence spectroscopy measurements. Further we also measured the nonlinear refractive index and nonlinear absorption coefficients of these compounds using the single beam z-scan technique with a cw argon ion laser at 514.5nm at different concentrations in DMSO solvent. The third order nonlinear susceptibility was estimated from these measurements and it shows high nonlinearity. The high negative refractive index makes these compounds suitable for optical limiting application.

Bidirectional Photoresponse of Surface Pretreated Azobenzene Liquid Crystal Polymer Networks

We report on the photodriven, polarization-controlled response of UV-pretreated azobenzene-based liquid crystal polymer networks (azo- LCN) of polydomain orientation to higher wavelength CW argon-ion laser light (Ar(+)) of 457-514 nm. The significant absorbance of the azo-LCN cantilever in the UV is used to form an approximately 1 microm thick cis-isomer rich skin. Subsequent exposure to the Ar(+) laser drives a bidirectional bending process that is the result of two distinguishable photochemical processes. First, 457-514 nm laser light (regardless of polarization state) drives cis-trans photoisomerization of the UV-pretreated surface, restoring the order of the azobenzene liquid crystalline moieties. Mechanically, the cis-trans process results in an expansion on the exposed surface that forces the cantilever to undergo a rapid bend away from the laser source. Once a sufficient number of trans-azobenzene moieties are regenerated, continued Ar(+) illumination promotes both the trans-cis and cis-trans processes enabling trans-cis-trans reorientation. In this particular system and conditions, trans-cis-trans reorientation enables polarization controlled mechanical bending of different angles towards the Ar(+) source. Photomechanical responses of UV-pretreated azo-LCN demonstrate the viability of photogenerated effects in UV-rich environments such as space.

Local crystallization in an oxyfluoride glass doped with Er3+ ions using a continuous argon laser

Local crystalline formation in erbium doped oxyfluoride glass has been obtained under a cw Argon laser irradiation up to 1.8 W pumping power. By exciting at 514 nm, the emission from 800 nm and 850 nm corresponding to the 4S3/2(2H11/2)→4I13/2 electronic transitions have been analyzed both inside and outside the irradiated area. The changes in the emission spectra indicate that the high power Ar laser irradiation has resulted in a localized desvitrification process. The temperature dependence of the fluorescence intensity ratio of the 800 nm and 850 nm emission bands has been used to determine the temperature of the irradiated zone. Moreover, the average lifetime of the 4S3/2(2H11/2) thermalized levels have been measured as a function of the excitation spot position. An important decrease is observed at the irradiated area. These results confirm that a localized cristalline phase has been created by the laser action.

Motion of a red blood cell in interference field

The motion of a red blood cell suspended in blood plasma in a two-beam plane interference field was studied experimentally. A cw Argon Ion laser was used. A model is proposed to describe the observed motion. The model is based on a balance between the optical gradient force and the drag force, and yields the location of the cell as a function of time, starting from a stationary position at an arbitrary distance from a dark fringe until becoming trapped at the center of the closest bright fringe. It is suggested that the discrepancy between the predictions of the model and the observed motion is attributable to the influence of the wall close to which the cell flows.

Highly efficient lasing at difference frequencies in a nematic liquid crystal

Highly efficient lasing at difference frequencies is obtained in a nematic liquid crystal excited by several visible lines from a cw argon laser with a total power of 0.08—1.5 W. The maximum conversion efficiency was ≈1% and the quadratic susceptibility was ≈2×10-6 m V-1. The field of application of the approximate mechanism of quadratic nonlinearity and frequency conversion considered in the paper requires specification. The nonlinear conversion of radiation in a nematic crystal has specific features compared to lasing at difference frequencies in solid crystals.

Synthesis, characterization and local changes induced by a cw argon laser in silica glass xerogel doped with transition metal ions

We report on the synthesis, characterization and local changes induced by a cw argon laser in SiO2 xerogel doped with low metal ion concentrations, and obtained by the sol–gel process. The V, Mn and Cr metal ions were introduced into the SiO2 matrix as inorganic salts and as an oxide in the case of Mo. The characterization of these materials showed that an amorphous system with high porosity was obtained; the metals were incorporated as ions with several different oxidation states, and the thermal diffusivity was around 10−9m2/s. In these xerogel monoliths it is possible to induce local changes in the refractive index with the incidence of a focused laser beam at 488nm, about 80μm in diameter, with power intensities from 1 to 48mW and an incidence time from 0.5 to 5min. After this process, a high contrast in the transmitted light between the processed area and the homogenous matrix is obtained, resulting in an optical memory effect.

Fabrication of Poly-silicon Thin Films on Glass and Flexible Substrates using Laser Initiated Metal Induced Crystallization of Amorphous Silicon

AbstractPoly-silicon thin films on glass and Kapton® substrates are fabricated using laser initiated metal induced crystallization method. Amorphous silicon films of 200 nm thickness were deposited on the two substrates. The films were capped with 200 nm aluminum films. The annealing laser was a cw Argon-ion laser system. Laser power densities ranging from 4 to 9 W/cm2 were used in the annealing process. The samples were irradiated for various periods of time. X-ray diffraction patterns from the initial results indicated the crystallization of the films. Scanning electron microscopy showed dendritic growth in the annealed samples. The composition analysis of the samples indicated aluminum-silicon alloy regions in the films.

Direct detection of chlorosilylene and time resolved study of some of its reactions in the gas-phase using a new photochemical precursor

Chlorosilylene, ClSiH, was prepared by 193 nm laser flash photolysis of 1-chloro-1-silacyclopent-3-ene in the gas phase. ClSiH was monitored in real time at 457.9 nm using a CW argon ion laser. The kinetics of reactions of ClSiH with C 2H 4, CH 2 CHCMe 3, C 2H 2, Me 2O, SO 2, HCl, MeSiH 3, Me 2SiH 2, Me 3SiH, MeGeH 3, Me 2GeH 2 and precursor have been studied at ambient temperatures for the first time. Addition reactions of ClSiH and reactions with lone pair donors are faster than insertion reactions. Surprisingly ClSiH inserts faster into Si–H than Ge–H bonds. ClSiH is intermediate in reactivity between SiH 2 and SiCl 2. Relative reactivities of ClSiH and SiH 2 vary considerably.

Modal content and noise characteristics of a cw argon ion laser with an optical feedback: Numerical simulations of experimental results

We have shown that significant reduction of the optical noise can occur in a cw argon ion laser when the laser cavity is coupled to an empty external cavity. When the external cavity was terminated by a phase conjugate mirror, noise reduction reaching 15 dB for the frequency components below 1 MHz and reaching 58 dB at the frequencies of the beating of the longitudinal modes has been observed experimentally. It was also possible to reduce the number of oscillating longitudinal modes from ∼40 to 2 without loss of optical power. A numerical model taking into account the description of the lineshape by a Voigt profile and the presence of an optical feedback has been developed. The numerical results were found to be in good agreement with experimental results.

Efficient laser synthesis of single-walled carbon nanotubes through laser heating of the condensing vaporization plume

Significant improvement in the production rate of high-purity single-walled carbon nanotubes using the laser-oven method is reported. The effects of using continuous wave (cw) and kilohertz frequency Nd:YAG lasers at 1064 nm as well as a cw argon ion laser at 514.5 nm to excite the vaporized plume during the pulsed-laser synthesis of single-walled carbon nanotubes have been studied. Production rates exceeding 400 mg/h of nanotube deposits have been achieved. Raman spectroscopy, transmission electron microscopy, isothermal gas adsorption and thermo-gravimetric analysis indicate single-walled nanotube purity approaching 80% and metal catalyst contamination of less than 6% by weight. Gas adsorption measurements using nitrogen and argon have been performed to help characterize the bundle structure of the SWNT. Possible insights into the nanotube synthesis mechanism have been discussed.

CW Argon-ion laser initiated aluminum induced crystallization of amorphous silicon thin films

ABSTRACTCW Argon-ion laser initiated aluminum induced crystallization (AIC) of RF magnetron sputtered amorphous silicon (a-Si) thin films has been investigated. It was found that lasers could be effectively used to initiate AIC process at very low threshold power densities. An argon-ion laser (λ=514.5 nm) was used to anneal Al/a-Si/glass structures with varying power densities ranging between 55 and 125 W/cm2 and exposure times ranging from 10 to 120 s. X-ray diffraction analysis showed the resulting films to be polycrystalline. The crystallization rate increased both with power density and exposure time. Environmental scanning electron microscopy (ESEM) analysis showed that the surface features change with increasing power density and irradiation time. A dendritic growth pattern was observed in the initial stages of interaction between the films. A strong crystalline Raman peak at around 520 cm-1 was observed in the Raman spectra of the crystallized samples.

Photoluminescence investigation of energy up-conversion in KY 1− xEr xF 4

Using a CW argon-ion laser operating at 488 nm and a pulsed 532 nm laser, we find up-conversion of Er 3+ energy in KY 1− x Er x F 4. Among three samples with x=0.1, 0.05, and x=0.0005 that show energy up-conversion, x=0.1 and 0.05 samples were confirmed to have up-conversion caused by energy transfer. By measuring temporal dependence of the photoluminescence (PL) we show that, with energy transfer, 4S 3/2 state is up-converted into 2H(2) 9/2 and 2P 3/2 state by taking energy from other ions in 4F 9/2 state. The incident laser power dependence of the up-converted PL intensity indicates that the up-converted states have mutual annihilation at high density via energy transfer.

Polymeric humidity sensor based on laser carbonized polyimide substrate

This research demonstrated some of the capabilities of a laser carbonized polyimide substrate functioning in an all-polymer humidity sensor. Most polymeric chemical sensors are based on alumina or silica substrates with gold or silver deposited wiring. These sensor substrates are relatively expensive and complicated to manufacture. A Kapton-based all-polymer substrate is a possible alternative for use in future chemical and biological sensing applications. The substrate was carbonized to form electrically conducting filaments using a focused cw argon ion laser beam operating at 364 and 514 nm. The substrate was coated with a hygrosensitive polymer and tested varying humidity, test frequency, test voltage, and temperature. Two separate hygrosensitive polymer coatings were tested: 2-hydroxy-3-methacryloxypropyltrimethylammonium chloride (HMPTAC) and polyethylene oxide doped with lithium perchlorate (PEO-LiClO 4). Humidity detection was used as a proof of concept for future research into chemical and biological agent detection. Results demonstrate the Kapton-based sensor performed as well as an alumina gold substrate and indicate the all-polymer substrate is a viable sensor substrate for future use in chemical detection systems.

The spatial structure of the lowest ion-acoustic instability modes in the high-current discharge of CW argon ion lasers

The cross-sectional structure of the two lowest ion-acoustic instability modes in the positive column of a cylindrical, high-current discharge, traditionally used as an active medium in CW ion gas lasers, has been investigated. The diameter and length of the discharge column in our experiments were 16 mm and 1 m, respectively, and the discharge current was 250–350 A. Under these conditions, the observed mode frequencies were ν1 = 190 kHz and ν 2 = 390 kHz. To obtain the spatial structure of these modes, time-resolved integral projections of spontaneous argon-plasma emission were measured in planes normal to the discharge axis. From the power spectra of the measured projections, the structures of the modes ν1 and ν 2 were reconstructed using computerized tomography algorithms. Based on available theoretical models of the instability, the modes have been identified as the (1, 1) and, tentatively, the (1, 2) modes of oscillation.

Visible laser self-focusing in hybrid glass planar waveguides

We report that self-focusing occurs with simultaneous self-inscription of a cylindrical waveguide when 514.5-nm light from a cw argon-ion laser propagates in a solgel-derived silica methacrylate hybrid glass planar waveguide. Spatially localized free-radical polymerization of methacrylate substituents is initiated in the path of the guided wave. This causes intensity-dependent refractive-index changes that lead to self-lensing and focusing. A channel waveguide evolves in the matrix, which supports fundamental and higher-order optical modes and suppresses diffraction of the beam.

Dopplerglobal velocimetry data in circular jets

A two-component Doppler global velocimeter (DGV)system has been improved through the use of vapour-limitediodine cells that have temperature-independent responses, alongwith nonpolarizing beam splitters and lower f-number lenses.Two-component DGV velocity measurements have been obtained fora 1 inch diameter uniform circular jet flow at a nominal exit velocity of 60 m s-1, as well as for an annular jet and aswirling jet. These data generally agree with earlier pointDoppler velocimeter and hot wire anemometer results towithin about 2-4 m s-1, and display a total variabilityfrom a smooth curve of ±2-3 m s-1. This level ofaccuracy has been obtained for a system that uses a cw argonion laser and eight-bit CCD cameras and digitizers. Exceptions tothis level of accuracy are noted in regions of significantsecondary scattering, due to scattered laser light that isreflected off the lip of the jet nozzle, as well as in regionsof low smoke seeding levels, resulting in low signal-to-noiseratios. A significant amount of the variability of the datafrom a smooth curve is due to the flat field correction.

A comparative study of the gaseous products generated by thermal and ultra-violet laser pyrolyses of the polyimide PMDA-ODA

Thermal and UV-laser pyrolyses of the commercial thin film polymer PMDA-ODA (Kapton®) were studied to determine the gaseous products evolved and to elucidate a potential mechanism for decomposition. Thermal pyrolysis covered a temperature range from 800 to 1300 °C in 100 degree increments. Non-ablative laser pyrolysis was conducted using a continuous wave (cw) argon ion laser at 363.6 nm. The results from the UV-laser pyrolysis show that the principal gaseous products evolved are CO, CO 2, C 2H 2, H 2NNH 2, CH 4 and HCN. The only gaseous products observed in the thermal pyrolysis study are CO and CO 2. While the amount of carbon dioxide evolved was relatively constant, the concentration of carbon monoxide increased with temperature. These results help provide essential information for the analysis of the chemical properties of the commercial polyimide Kapton® and a better understanding of this carbonization process.

Kinetics and reaction mechanisms of laser-assisted chemical vapor deposition of polycrystalline silicon dots from silane

Polycrystalline silicon dots have been deposited on silicon-coated SiO2 substrates from silane irradiated with a continuous wave (cw) argon ion laser and a cw CO2 laser. Various experimental configurations were adopted for laser-assisted chemical vapor deposition of Si dots. The cw argon ion laser was focused either directly on the surface of absorbent polycrystalline Si films acting as substrates (front side visible laser illumination) or penetrated through the transparent SiO2 plate and focused at the SiO2–Si interface (rear side visible laser illumination). The cw CO2 laser beam penetrated through the transparent polycrystalline Si film and was absorbed into the SiO2 plate (front side IR laser illumination). The deposition rate of polycrystalline Si dots was investigated as a function of the laser power (or surface temperature which was proportional to the laser power) and silane pressure. With the direct visible laser irradiation of Si/SiO2 substrates (front side laser illumination), at a surface temperature in the range 700–1000 °C, the growth kinetics of polycrystalline Si dots was found to be limited by surface reactions. The reaction mechanism proposed for chemical vapor deposition of Si films from pyrolysis of silane in conventional reactors can be invoked to explain the kinetic data, i.e., the rate-limiting step is the release of hydrogen from the Si surface. Visible photon interactions with reactive species were found to promote the release of hydrogen since this kinetic regime was not observed with other experimental configurations investigated. The deposition rate of polycrystalline Si dots produced at a surface temperature in the range 1100–1410 °C was proportional to the laser power or surface temperature and silane pressure. In addition, the deposition rate was independent of the experimental configuration used. In other words, only pyrolytic effects are involved in the laser-induced deposition of Si dots even with the IR laser light which is absorbed by silane molecules. With the gas phase in the fluid regime, the rate-limiting step was probably the diffusion of reactive species through the boundary layer developed in the vicinity of the surface of the deposition zone. Silylene radicals, SiH2, formed in the gas phase from inelastic collisions between excited silane molecules seem to be the major reactive species. A reaction mechanism of laser-assisted chemical vapor deposition of polycrystalline Si dots involving the formation and diffusion of silylene radicals through silane which acts as a buffer gas with respect to silylene radicals is proposed and discussed in this article.