Ne Laser Research Articles

Improvement of the antifungal activity of Litsea cubeba vapor by using a helium–neon (He–Ne) laser against Aspergillus flavus on brown rice snack bars

The aim of this study was to improve the antifungal activity of the volatile Litsea cubeba essential oil and its main components (citral and limonene) on brown rice snack bars by applying He–Ne laser treatment. Different volumes (50–200μL) of L. cubeba, citral or limonene were absorbed into a filter paper and placed inside an oven (18L). Ten brown rice snack bars (2cm wide×4cm long×0.5cm deep) were put in an oven and heated at 180°C for 20min. The shelf-life of the treated snack bars at 30°C was assessed and sensory testing was carried out to investigate their consumer acceptability. A count of total phenolic content (TPC) and Fourier transform infrared spectroscopy (FTIR) on the properties of essential oil, citral, and limonene before and after the laser treatment was studied for possible modes of action. It was found that the laser treatment improved the antifungal activity of the examined volatile L. cubeba and citral with Aspergillus flavus inhibition by 80% in comparison with those of the control not treated with the laser. L. cubeba vapor at 100μL with the laser treatment was found to completely inhibit the growth of natural molds on the snack bars for at least 25days; however, without essential oil vapor and laser treatment, naturally contaminating mold was observed in 3days. Results from the sensory tests showed that the panelists were unable to detect flavor and aroma differences between essential oil treatment and the control. Laser treatment caused an increase in TPC of citral oil whereas the TPC in limonene showed a decrease after the laser treatment. These situations could result from the changing peak of the aliphatic hydrocarbons that was revealed by the FTIR spectra.

Photodecomposition, photomutagenicity and photocytotoxicity of retinyl palmitate under He–Ne laser photoirradiation and its effects on photodynamic therapy of cancer cells in vitro

ObjectiveOur aim was to study photodecomposition, photomutagenicity and cytotoxicity of retinyl palmitate (RP), a principal storage form of vitamin A in humans and animals, under He–Ne laser photoirradiation. Moreover, the effect of different concentrations and timing protocol of antioxidants on photodynamic therapy (PDT) is contradictory, so the effect of RP (as antioxidant) on the PDT cytotoxicity was studied. MethodsPhotomutagenicity was tested by Ames test. Photodecomposition was studied by UV–vis spectroscopy. Cytotoxicity was measured with MTT-assay. Moreover, the effect of PDT, using hematoporphyrin derivatives (HpD) as photosensitizer under He–Ne laser irradiation (10J/cm2), was studied on HeLa cells either with or without RP (1–100μM) which incubated with the cells for short or long incubation period (1h or 24h) prior to PDT. ResultsNo photodecomposition of RP alone was obseved whereas there is a little photodecomposition of RP only in presence of HpD under irradiation with He–Ne laser. Moreover, no photomutagenicity was observed in Salmonella typhimurium strains under laser irradiation in presence or absence of HpD. RP alone (1–100μM) significantly decrease the viability of HeLa cells. Laser irradiation of HeLa cells pre-incubated with RP alone for 24h showed further significant decrease in viability of the cells. While RP incubations for 1h before PDT had slight effect on the cells, 24h incubation before PDT enhanced the cytotoxicity of PDT on HeLa cells. ConclusionsRP can be used 24h before PDT to enhance its effects. RP is not mutagenic under irradiation with He–Ne laser.

Waveguides and proportional beam splitters in bulk poly(methyl methacrylate) produced by direct femtosecond-laser inscription

Waveguides fabricated by direct femtosecond-laser inscription were reported in bulk poly(methyl methacrylate) (PMMA). Optimization of waveguide structures was conducted and 1×2 beam splitters with equal and proportional splitting ratio were fabricated. Three-dimensional structures of 1×4 beam splitters were also achieved based on 1×2 beam splitters. The largest change of the refractive index between femtosecond laser modified area and unmodified area was estimated to be 1.1×10−3. The minimum insertion loss of the single-mode waveguide measured with the He–Ne laser at the wavelength of 632.8nm was 4.32dB and propagation loss was calculated to be as low as 3.57dB/cm.

Laser images recording on aerosol-synthesized single-walled carbon nanotube films

It is shown that images on semitransparent conducting films of aerosol-synthesized single-walled carbon nanotubes (SWCNTs) can be recorded using focused low-power radiation of a He–Ne laser operating at a wavelength of 632.8 nm. Both free-standing films and those deposited on glass or polymer substrates can be used. Laser recording of images on the polymer-supported films is possible due to their transparency increased as a result of chemical reactions between iron nanoparticles encapsulated in SWCNTs and the products of local thermal decomposition of the polymer. Recording on the free-standing SWCNT films and those supported on glass substrates was performed upon acid treatment of the film surface.

Crystal growth, spectral, structural, optical and thermal properties of semi-organic single crystal: Tetrakis (thiourea) cadmium(II) nitrate

The semi-organic third-order nonlinear optical tetrakis (thiourea) cadmium(II) nitrate (TTCN) single crystal was grown by solution growth method. The grown crystal was found to be in monoclinic crystal system by using single crystal X-ray diffraction study. The spectral studies of infrared, 1H NMR, 13C NMR studies were used to confirm the functional groups. UV–visible spectral study was recorded in the range of 190–900nm and found good optical transmittance in the visible region. Z-scan technique was employed to determine the nonlinear refractive index, nonlinear optical absorption and third-order nonlinear susceptibility of the grown crystal using He–Ne laser. TG–DTA analysis revealed that the decomposition steps, compound stability and melting point of the crystal.

Photoionization spectrum of 85RbCs molecules produced by short range photoassociation

We present photoionization (PI) spectrum of ultracold ground state 85RbCs molecules formed by spontaneous decay from J=1, v=8 rovibrational level of (2)Π0−3 short range excited state molecules, which are produced from a space-adjustable dark spontaneous force optical trap. PI spectrum is obtained by scanning PI laser when photoassociation laser is locked by utilizing transfer cavity technique based on an ultrastable He–Ne laser as a reference laser. We calculated vibrational distribution of RbCs molecules in metastable ground state and corresponding transition probabilities to RbCs+ ion in (1)Σ+2 state. An enlarged PI spectrum with relative clear peaks is assigned to v=24–33 vibrational levels of molecular ion state. The method we used in PI spectrum analysis is also adoptable for other states of RbCs molecules or other kinds of molecules.

Photo-induced degradation and thermal decomposition in ZnSnF6·6H2O:Mn4+ red-emitting phosphor

ZnSnF6·6H2O:Mn4+ red-emitting hexahydrate phosphor is synthesized by the chemical reaction method, and its unique structural and optical properties are investigated using X-ray diffraction measurement, photoluminescence (PL) analysis, PL excitation spectroscopy, and electron spin resonance (ESR) spectroscopy. The Mn4+-activated phosphor exhibits remarkable degradation in the PL intensity under Xe lamp exposure and also by the coherent laser beam irradiation with the following order of degradation: Ar+ (488nm)>He–Cd (325nm)>He–Ne laser (632.8nm). The mechanism of degradation is considered to be due to a change in the valence state of manganese ions from Mn4+ to Mn5+ by the photooxidation and/or disproportionation. The ESR measurement supports decreased Mn4+ spin density in the Xe-lamp exposed, degraded sample. The changes in the structural and PL properties are also observed after thermal annealing above ∼100°C and explained by the thermal-annealing-induced dehydration/decomposition of the host material.

Determination of beam incidence conditions based on the analysis of laser interference patterns

Beam incidence conditions in the formation of two-, three- and four-beam laser interference patterns are presented and studied in this paper. In a laser interference lithography (LIL) process, it is of importance to determine and control beam incidence conditions based on the analysis of laser interference patterns for system calibration as any slight change of incident angles or intensities of beams will introduce significant variations of periods and contrasts of interference patterns. In this work, interference patterns were captured by a He–Ne laser interference system under different incidence conditions, the pattern period measurement was achieved by cross-correlation with, and the pattern contrast was calculated by image processing. Subsequently, the incident angles and intensities of beams were determined based on the analysis of spatial distributions of interfering beams. As a consequence, the relationship between the beam incidence conditions and interference patterns is revealed. The proposed method is useful for the calibration of LIL processes and for reverse engineering applications.

Increase in the power of a commercial He−Ne laser under combined pumping

Almost double (a factor of about 1.75) increase is obtained in the power of the radiation with a wavelength of 633nm using combined pumping of the LG-38 He−Ne laser by the direct and inductive (3 MHz) currents. It is found that the maximum power is attained at a lower (by about 30%) direct current.

Experimental profiling of a non-truncated focused Gaussian beam and fine-tuning of the quadratic phase in the Fresnel Gaussian shape invariant

An especially dedicated homodyne profiler is used for recording the intensity distribution of focused non-truncated Gaussian beams. The spatial distributions are obtained at planes in the vicinity of the back-focal plane of a focusing lens placed at different distances from a He–Ne laser beam with a Gaussian intensity profile. Comparisons of the experimental data with those obtained from the analytical equations for an ideal focusing lens allow us to propose formulae to fine-tune the quadratic term in the Fresnel Gaussian shape invariant at each interface of the propagated field. We give analytical expressions to calculate adequately the propagation of the field through an optical system.

Optimization of waveguide structures for beam splitters fabricated in fused silica by direct femtosecond-laser inscription

Abstract The Type-I waveguides fabricated by femtosecond laser inscription were reported in fused silica. Optimization of waveguide structures was conducted for fabricating 1×2 and 1×4 beam splitters. The change of the refractive index between femtosecond laser modified area and unmodified area was estimated to be 9×10 −4 . The minimum loss of the waveguides measured with the He–Ne laser at the wavelength of 632.8 nm was determined to be as low as 1.34 dB.

Growth of organic benzimidazole (BMZ) single crystal by vertical Bridgman technique and its structural, spectral, thermal, optical, mechanical and dielectric properties

Benzimidazole (BMZ) single crystal was successfully grown by the vertical Bridgman technique (VBT). The crystal system was identified and lattice parameters have been measured from the powder X-ray diffraction (PXRD) measurement. Fourier transforms infrared spectral studies have been carried out to find out the functional groups of BMZ crystal. The optical transmittance and the cut-off wavelength of BMZ were identified using UV–Vis NIR studies and the cut-off wavelength was found to be 294nm. The dielectric permittivity and dielectric loss as a function of frequency and temperature was measured for the grown BMZ crystal. Vickers microhardness analysis was carried out to identify the mechanical stability of the grown crystal. Chemical etching study was carried out using different etchants and the etch pit density (EPD) was calculated and compared. The third order nonlinear optical property of BMZ crystal was studied by using Z-scan technique with He–Ne laser (632.8nm). The magnitude of nonlinear refractive index (n2), nonlinear absorption (β) and third order nonlinear susceptibility (χ3) have been found to be in the range of 10−11m2/W, 10−4m/W and 10−5esu respectively. Photoluminescence spectrum was recorded using a xenon lamp in the range of 330–585nm and it exhibits ultraviolet light emission.

Thermally stimulated third-order optical nonlinearity in Cd-doped CuO–PVA thin films under cw laser illumination

We report synthesis, linear and third-order nonlinear optical properties of Cd-doped CuO–PVA nanocomposite thin films. Cd-doped CuO nanoparticles (NPs) were obtained by chemical synthesis method, and spin coating technique was used to obtain thin films in polyvinyl alcohol matrix. X-ray diffraction (XRD) shows formation of crystalline CuO having monoclinic phase with average particle size of 10 nm. Ultraviolet–visible (UV–Vis) spectroscopy attests formation of NPs by witnessing strong blue shift in the excitonic absorption. Absorption wavelength of CuO NPs shifts from 365 to 342 nm for Cd doping of 1–5 wt%. Both XRD and UV–Vis data confirm decrease in particle size with increase in Cd-doping concentration. Thin films have been characterized by Z-scan technique under continuous-wave He–Ne laser, and enhanced values of nonlinear refractive index n 2 and nonlinear absorption coefficient β have been obtained. Enhancements in the nonlinear optical properties have been attributed to the thermal effect due to strong linear absorption coefficient combined with increased thermo-optic coefficient. Contributing mechanisms such as photoacoustic effect, surface states effect and dielectric effect due to dopant and thin film structure have been discussed.

Continuous wave laser induced third-order nonlinear optical properties of conducting polymers

We report the studies on the third-order optical nonlinearity and optical power limiting properties of conducting polymers viz., poly(o-anisidine) and polypyrrole. Continuous wave (CW) He–Ne laser operating at 633 nm was used as the source of excitation. Ultraviolet-Visible (UV– VIS) spectroscopy measurement reveals that the absorption bands are continuous and wide and hence can be used for photovoltaic applications. Fourier transform infrared spectroscopy (FTIR) was performed to elucidate the structure of polymers. Z-scan technique was employed to determine the real and imaginary parts of third-order nonlinear susceptibility v(3), nonlinear absorption coefficient beff, and nonlinear index of refraction n2. The estimated values of beff, n2, and v(3) are of the order of 1022 cm/W, 1025 esu, and 1027 esu, respectively. The presence of large number of electron donating groups in the structure, leads to efficient charge transfer and results in the increase in conjugation length. The increase in conjugation length in turn increases the v(3) value. Induced self-diffraction rings were observed when the samples were exposed to laser beam due to thermal lensing and refractive index change. Good optical limiting and clamping behavior was achieved for various sample concentrations. These studies indicate that the polymers are a suitable candidate for photonic applications. POLYM. ENG. SCI., 00:000–000, 2015. VC 2015 Society of Plastics Engineers

He–Ne laser induced changes to CN-85 polymer track detector

In this work, the induced changes in cellulose nitrate (CN-85) polymer track detector have been investigated. CN-85 samples were irradiated with He–Ne laser at different fluences. These investigations have been carried out using UV–Vis spectroscopy, photoluminescence (PL) spectroscopy and X-ray diffraction (XRD). In addition, the wetting property and surface free energy (SFE) of the irradiated samples have been studied by measuring the contact angle. The UV–Vis spectra showed that the absorption edge shifted towards longer wavelength region with increasing irradiation. This means that the optical band gap energy was decreased by increasing the laser beam doses. The correlation between the number of carbon clusters and the optical band gap energy is discussed. The PL spectra indicated a decrease in the integrated photoluminescence intensity of irradiated samples compared with the pristine one. XRD intensity showed a dominant amorphous with a partly crystalline phase. The surface wettability was evaluated by contact angle method (for water, dimethyl-formamide and glycerol), as well as, the surface free energy which was estimated using Owens–Wendt method. Furthermore, the surface roughness has been studied.

Characterization of thermal diffusivity and optical properties of Ag nanoparticles

Thermal diffusivity of silver nano-fluid synthesized using radiation technique at a concentration of 5.889×10−3M and irradiated with γ-radiation at different doses was measured. The measurements were performed by thermal lens method. A diode laser (λ=532nm) was used as an excitation beam while a He–Ne laser beam (λ=632.8) was utilized as a probe beam. The thermal diffusivity of Ag nano-fluid samples measured at room temperature increase with the increasing nanoparticles size ranging from 44nm to 64nm. A similar behavior of nonlinear refractive index measured using a single beam z-scan are presented and discussed.

Virtual instrumentation in LabVIEW for multiple optical characterizations on the same opto-mechanical system

In this work we propose a virtual instrumentation, user-friendly, computer-controlled instrumentation and data analysis techniques, allowing an instantaneous comparison between theoretical predictions, simulations and actual experimental results. These applications in LabVIEW programming software show a virtual explosion in data acquisition and control system from the laboratory. We consider a versatile opto-mechanical system θ–2θ by using the p-polarized light from a He–Ne laser in which the surface plasmon resonance, Brewster and Brewster-Abelès methods, and scattering measurements are driven by LabVIEW software that produces fast, simple and accurate measurements of samples. The application can be used for both education and specific research purposes.

On-line molecular iodine isotopologue detection in gaseous media during spent nuclear fuel reprocessing using a laser-induced fluorescence method

The paper reports on on-line measurement of the 127I129I, and concentrations during spent nuclear fuel (SNF) reprocessing using a laser-induced fluorescence method. A He–Ne laser (632.8 nm) was used as a fluorescence excitation source. The detection limits obtained for molecular iodine isotopologue concentrations demonstrate the possibility of using this method for iodine control both in gaseous technological media generated during SNF reprocessing and after passing through the gas purification system (in atmosphere emission).

Nonlinear optical measurements of conducting copolymers of aniline under CW laser excitation

Synthesis and measurements of third-order optical nonlinearity and optical limiting of conducting copolymers of aniline are presented. Single beam z-scan technique was employed for the nonlinear optical studies. Continuous wave He–Ne laser operating at 633nm was used as the source of excitation. Copolymer samples exhibited reverse saturable absorption (RSA) process. The nonlinear refraction studies depict that the copolymers exhibit self-defocusing property. The estimated values of βeff, n2 and χ(3) were found to be of the order of 10−2cm/W, 10−5esu and 10−7esu respectively. Self-diffraction rings were observed due to refractive index change when exposed to the laser beam. A good optical limiting and clamping of power of ∼0.9mW and ∼0.05mW was observed. Therefore, copolymers of aniline emerge as a potential candidate for photonic device applications.

Phonon modes and local polar distortions in nanoclusters of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals probed by terahertz reflectance spectra and Raman scattering

Optic phonons and lattice vibrations of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals near the morphotropic phase boundary (MPB) are determined by terahertz (THz) reflectance spectra in a temperature range of 5.5–300 K. Raman scattering is measured with a He–Ne laser with a wavelength of 632.8 nm as the exciting source. On cooling from 300 K, the A1 component of the splitting TO1 mode hardens, which follows the Cochran law with a critical softening temperature of 761–861 K. Moreover, the E component of the soft mode is heavily damped around 0.81 THz (27 cm − 1). Additional polar phonon modes, which are forbidden in the cubic structure, are activated due to the broken cubic symmetry in polar clusters.