Cw Laser Light Research Articles

Gold Nanoparticles for Photothermal and Photodynamic Therapy.

Cancer cells exposed to 13 nm gold nanoparticles and irradiated with cw laser light at 532 nm are shown to undergo cell death via two competing causes. When cells contain relatively high quantities of gold nanoparticles and/or receive a high dose of light, photothermal effects dominate, which are independent of the cellular location of the gold nanoparticles and affect all cells in the irradiated area due to the rapid diffusion of heat. In contrast, at lower doses of nanoparticles and light, the photogeneration of singlet oxygen triggers cell death only in cells that contain a sufficient number of nanoparticles. The parallel occurrence of both effects will need to be considered carefully when designing practical therapy applications. In particular, the photodynamic effect should allow for a cell-type-specific treatment modality that can distinguish between cancer and normal cells using suitable targeting ligands on the nanoparticle surface, providing a highly selective route for cancer therapy.

Investigation of variation in fluorescence intensity from rhodamine 6G dye in a trapped and levitated liquid micro-drop

Variation in fluorescence intensity from rhodamine 6 G dye was investigated. A small volume of dye solution, in the form of a trapped and levitated micro-drop, was optically excited with a 400 μW, 532 nm wavelength cw-laser light. The dye was dissolved in methanol and glycerol for a concentration of 10 mg/ml or 21 mMole per liter. With the optical excitation, initially the fluorescence intensity was observed to rise with time, and then it decayed, along with a steady shift of fluorescence peak from 562 nm to 543 nm. The observation of initial enhancement in fluorescence from start to 7 min of excitation, can partly be due to the low excitation power, less dimer formation and gradual rise in molecular population to excited state therefore slower rate of change (increase) of fluorescence intensity was observed with time. Simulation studies indicate that the photo bleaching was taking place from all the energy states of the dye molecules, which is an extension of the concept that the photo bleaching takes place at the excited triplet state whereas the fluorescence takes place due to transition between excited singlet states and ground states. A steady shift in fluorescence peak position, from 562 nm to 543 nm, was observed during the fluorescence life of the dye, at a rate of 0.0113 nm/s during fluorescence enhancement and 0.026 nm/s during photo-bleaching. The steady blue shift of fluorescence indicate insignificant dimer formation.

Eff ect of Different Laser Irradiation Parameters on the Viability of Bacillus Species

The genus Bacillus is present everywhere in the environment, it has environmental, industrial, and medical signifi cance. This heterogeneous group of bacteria shares unique characteristics, one of these is the resistance to physical and chemical agents. Laser light is one of the most interesting physical agents with a wide range of applications in all scientifi c fi elds. It has the ability to alter bacterial growth by triggering inhibitory or stimulatory mechanisms. In this study, laser parameters were varied to evaluate the eff ect of each one on the viability of Bacillus species. CW or chopped (532 nm) laser light at diff erent irradiation periods were examined. Results showed that tested bacterial species’ response to green laser light varied. Bacterial viability was dropped with increasing chopping frequency and exposure time. In conclusion, high repetition rate and prolonged exposure time increase the lethal eff ects of this type of laser

Amplification of pulsed light with arbitrary frequency chirps on nanosecond timescales.

We have developed a system for producing amplified pulses of frequency-chirped light at 780nm on nanosecond timescales. The system starts with tunable cw laser light and employs a pair of fiber-based phase modulators, a semiconductor optical amplifier, and a tapered amplifier to achieve chirp rates exceeding 3 GHz/10ns and peak powers greater than 1W. Driving the modulators with an arbitrary waveform generator enables arbitrary chirp shapes, such as two-frequency linear chirps. We overcome the optical power limitations of the modulators by duty cycling and avoid unseeded operation of the tapered amplifier by multiplexing the chirped pulses with "dummy" light from a separate diode laser.

Analysis of the spatial intensity distribution of a CW laser light through tissue-like turbid media

We analyze the two-dimensional spatial intensity distribution of a CW laser light with Gaussian profile through tissue-like turbid media via calculation and experiment. The results show that the spatial intensity distribution of laser depends on the scattering coefficient, absorption coefficient, and the anisotropy factor of the turbid media. The full width at half maximum (FWHM) of the normalized intensity of the light spatial intensity distribution increases with an increase of the scattering coefficient. But the FWHM of the spatial intensities’ distribution of the CW laser light through turbid media does not increase monotonously with an increase of the anisotropy factor. Besides, the spatial intensity distribution is dependent on the absorption coefficient when considering a given scattering coefficient. The two-dimensional spatial intensity distribution narrows with an increase of absorption coefficient. As one of the potential applications, we finally perform an experiment to image an object hidden behind a turbid medium.

In-situ study of the processes of damage to the tungsten surface under transient heat loads possible in ITER

Experiments on the effect of fast heat loads on the surface of tungsten were carried out on the BETA facility at the Budker Institute. Tungsten samples were uniformly heated by an electron beam with a heat flux factor below the melting threshold. During and shortly after exposure, the 2D surface temperature distribution was measured, as well as the temperature history on selected surface areas. Active diagnostics using the scattering of CW laser light on a surface exposed by the electron beam allowed us to monitor the damage dynamics. At the heating stage, an increase in the surface roughness occurred, caused by inhomogeneous elastic and plastic deformations of the heated layer. As the cooling progressed, the residual plastic deformations remained. Simultaneously with the modification of the surface, bending of samples with a thickness of 3-4 mm occurred. The bending dynamics of the sample was measured by the intensity of a converging laser beam reflected from the back surface of the sample, polished to a mirror state. The residual sag due to bending increases with the heat load similarly as residual roughness of the front surface of the sample. These data, together with simultaneously measured temperature dynamics and the spatial heating profile, can provide an experimental basis for the numerical calculation of the residual stresses in the sample. The data obtained in situ were compared with those measured outside the vacuum chamber with X-ray diffraction, optical profiler, and optical interferometer. At the stage of cooling, after a sufficient intensity of heating, the second stage of damage took place — the cracking of the surface layer. The time before the start of this relatively fast process usually exceeded the time to achieve a DBTT by 1–4 orders of magnitude.

Nonlinear Scattering of Near-Infrared Light for Imaging Plasmonic Nanoparticles in Deep Tissue

Nonlinear optical microscopy can obtain three-dimensionally resolved images within a specimen by exploiting the nonlinear light–matter interaction between the excitation light and sample. However, the image contrast significantly degrades with increasing observation depth because the emitted signal attenuates during light propagation through layers of the tissue before being detected. To obtain high contrast images from deep tissue, we developed saturated excitation (SAX) microscopy using the nonlinearity of near-infrared (NIR) plasmonic scattering from gold nanoshells and gold nanorods. SAX microscopy selectively detects the nonlinear component from the scattering signal generated by nanoparticle probes located at the center of the focal spot. By using this technique, background signals generated at out-of-focal positions are effectively removed. In addition, emitted signals in the NIR from nanoparticle probes efficiently transmit through biological tissue and are ideally suited to image deep parts of the tissue. We experimentally confirmed that scattering intensities from a single gold nanoshell and gold nanorod exhibit nonlinear relations with the excitation intensity of CW laser light at 780 and 1064 nm, respectively. We also demonstrated improvements of image contrast and spatial resolution at the depth of 400 μm in a phantom of muscle tissue by selectively detecting the nonlinear scattering signal component from gold nanoshells.

Atom femtosecond optical trap based on spectrally filtered laser radiation

We have examined the use of alkali metal (rubidium) vapour for spectral filtering of broadband pulsed laser light that is used to produce a femtosecond pulsed optical dipole trap. It has been shown that, even at large detuning of the centre emission frequency from the frequency of atomic transitions, spectral components present in the wings of the laser emission line are capable of heating localised atoms, thus reducing their lifetime in the atomic trap. Using atomic vapour for filtering the laser emission spectrum, we have suppressed its spectral components resulting in heating. This has made it possible to increase the lifetime of atoms in the pulsed optical dipole trap to a value comparable to their lifetime in an optical trap formed by narrow-band cw laser light.

Nonlinear depolarization of light in optical communication fiber

We report the experimental observation of a novel transmission phenomenon in optical long-haul communication systems. Unpolarized ASE depolarizes via nonlinear fiber interactions a cw laser light during their copropagation which leads to small but measurable ultrafast polarization state fluctuations at the fiber output. We provide a phenomenological approach and a theory that qualitatively corroborates our experimental results. One of our major findings suggests that the applicability of the often used Manakov equation needs to be scrutinized for highly accurate studies of nonlinear polarization state evolutions in noisy environments. The described phenomenon leads to a qualitatively different microscopic understanding of nonlinear light propagation in fiber and can contribute toward an explanation for today’s commonly perceived gap between simulated and experimentally obtained system performance in optical data transmission.

Nonlinear Optical Surface Plasmon Resonance in Amorphous Arsenic Sulfide Films

AbstractFour‐layer surface plasmon resonance configuration that includes a thin film from As2S3 is studied. By numerical calculations and experiment, it is established that the shape of the resonance curve is very sharp. The changes in the optical transmission are investigated and it is found that when querying the structure with 514 nm CW laser light, nonlinear changes of the optical transmission with hysteresis loop occur. Large nonlinear change of reflectivity is observed near 10–12 mW power. Such behavior can be applied for the elaboration of optoelectronic devices.

Investigating the nonlinear optical properties of poly eosin-Y phthalate solution under irradiation with low power visible CW laser light

In this work, the study of the nonlinear optical properties of poly eosin-Y phthalate solution using the diffraction ring patterns and the Z-scan methods are presented. The diffraction ring patterns were observed when a low power laser beam of wavelength of 473 nm passed through the poly eosin-Y phthalate solution. It was found that the number of rings and diameter of the outer-most ring in each pattern depends on the incident intensity of the laser beam and type of the beam wave front. The Fresnel-Kirchhoff diffraction integral theory was used to simulate the diffraction ring patterns and found good agreement with experimental results. Both diffraction ring patterns and closed aperture Z-scan techniques were used to calculate the nonlinear refractive index, while open aperture Z-scan was used to calculate the nonlinear absorption coefficient of the poly eosin-Y phthalate solution. The possibility of using the sample as an optical limiter is tested.

Laser induced structural phase transitions in Cu3SbS4 thin films

We investigate the laser-induced structural phase transition of Cu3SbS4 to CuSbS2. The Cu3SbS4 thin films were synthesized by a two-stage process of sputtering and subsequent sulfurization. The as-grown films were characterized by x-ray diffraction and Raman spectroscopy to investigate the phase purity of the material. The Cu3SbS4 thin films were irradiated with 532 nm CW laser light at different power densities and in situ Raman spectroscopy was used to investigate the phase transitions. Experimental results show an evidence of local CuSbS2 phase formation from Cu3SbS4 phase in the laser annealed areas above a critical power density. Heat transfer equations solved using COMSOL Multiphysics were used to estimate the surface temperature during the laser irradiation process.

Evidence for degenerate mirrorless lasing in alkali metal vapor: forward beam magneto-optical experiment

We report experimental evidence of degenerate mirrorless lasing in the forward direction under excitation of a dilute atomic Rb vapor with a single linearly polarized cw laser light resonant with cycling Fe > Fg atomic D2 transitions. Light polarized orthogonally to the laser light is generated for the input light intensity exceeding a threshold value of ∼3 mW cm−2. Application of a transverse magnetic field directed along the input light polarization reveals a sharp ∼20 mG wide magnetic resonance centered at B = 0. Increasing the incident light intensity from 3 to 300 mW cm−2, the generated light undergoes rapid amplitude increase followed by a decline and resonance broadening. Such nonlinear behavior of the observed magnetic resonance is attributed to the population inversion on optical transitions between magnetic sublevels established under linearly polarized excitation. We present observations that indicate that a combination of nonlinear-optical effects occurs in this system, including degenerate mirrorless lasing and four-wave mixing.

Write – Read all-Optical System Based on Diffraction Ring Patterns in Aloe, Cresson and Taramira Vegetable Oils.

Multiple diffraction ring patterns appeared in Aloe , Cresson and Taramira oils under irradiation with cw blue (473 nm ) laser light beam . No ring patterns appeared in these oils using the green cw ( 532 nm) and red cw ( 635nm ) laser light beams . As a result of irradiation of these oils with the blue beam together with the green or with red beam or with both green and red beams together, blue and green , blue and red , and blue , green and red rings appeared respectively at very low input powers of the green and red beams . The number of rings produced by the green and red lights are totally controlled by the blue beam input power and not by their input powers . By this technique .we have established a write ( by the blue beam ) – Read ( by the green and red beams ) all optical system in these three oils

Made Easy: CW Laser Light Widely Tunable Across the Visible

AbstractA remarkable number of photonic applications call for continuous‐wave (cw) laser light that is widely tunable throughout the visible range of the spectrum. However, this spectral region remains difficult to access with conventional tunable laser devices. This is why recently commercialized sources based on cw optical parametric oscillator (OPO) technology gain market awareness – and become increasingly recognized as cost‐effective and user friendly turn‐key solutions.

Linear, nonlinear and optical limiting properties of carbon black in epoxy resin

Films of an epoxy resin doped carbon black were prepared by casting method onto BK7 glass substrates. The surface morphology of these films were investigated together with the nonlinear optical properties under CW laser light irradiation of 532 nm wavelength using diffraction ring pattern and Z-scan techniques. The prepared samples exhibited strong self-defocusing effect and good optical limiting behavior.

Operation by optoelectronic features of cadmium sulphide nanocrystallites embedded into the photopolymer polyvinyl alcohol matrices

Laser operation by optical third harmonic generation at Er:Yb glass laser fundamental wavelength 1540 nm for the cadmium sulphide (CdS) nanocrystallites (NC) with average sizes 13 nm, 20 nm, 50 nm embedded into the poly(vinyl alcohol) (PVA) photopolymer matrices was discovered. The 300 mJ intensity modulated continuous wave (cw) Nd:YAG 1060 nm laser was used for photoinduced changes. The content of CdS NC was chosen to be 3%, 6%, 9%, 12%. The CdS NC have been synthesized using electrolytic procedure and their structural and morphological features were monitored by X-ray diffraction and transmission electron microscopy (TEM). The dependences of the THG versus the cw laser light power density at 1060 nm was studied and has shown an existence of the maxima which are strongly dependent on the NC sizes. Generally with decreasing NC sizes the laser stimulated THG was increased. The relaxation of the photoinduced changes was explored. The effect may be used for laser operation by coherent harmonic generation in the CdS/polymer nanocomposites.

Observation of dust particles ejected from the tungsten surface by transient heat flux with small-angle scattering of cw laser light

A new test facility for experimental simulation of transient heat load expected in the ITER divertor during unmitigated events is developed. Application of a long-pulse (0.1–0.3ms) wide-aperture (up to 2cm2) electron beam as a heating device provides powerful energy loads at a tungsten target with FHF> 250MJm−2s−0.5. Dynamics of tungsten particles in the ablation plume is investigated with a novel for PSI experiments small-angle laser light scattering technique. The threshold of intense droplet generation and dynamics of particles sizes are estimated.

Observation of photoacoustic/photothermal effect with a liquid-core optical ring resonator

Photothermal/photoacoustic (PT/PA) spectroscopy provides useful knowledge about optical absorption, as well as the thermal and acoustical properties of a liquid sample. For microfluidic biosensing and bioanalysis where an extremely small volume of liquid sample is encapsulated, simultaneous PT/PA detection remains a challenge. In this work, we present a new optofluidic device based on a liquid-core optical ring resonator (LCORR) for the investigation of PT and PA effects in fluid samples. A focused 532 nm pulsed light optically heats the absorptive fluid in a capillary to locally create a transient temperature rise, as well as acoustic waves. A 1550 nm CW laser light is quadrature-locked to detect the resonance spectrum shift of the LCORR and study thermal diffusion and acoustic wave propagation in the capillary. This modality provides an optofluidic investigative platform for biological/biochemical sensing and spectroscopy.

Low-level laser therapy stimulates the oxidative burst in human neutrophils and increases their fungicidal capacity.

Low-level laser therapy (LLLT) is known to enhance mitochondrial electron transfer and ATP production; thus, this study asked whether LLLT could stimulate the oxidative burst in human neutrophils (PMN) and improve their ability to kill microorganisms. Blood from healthy human subjects was collected and PMN were isolated from the samples. PMN were treated in vitro with 660nm or 780nm CW laser light at 40mW power and increasing energies up to 19.2J and were subsequently incubated with Candida albicans cells. Generation of hydroxyl radicals, hypochlorite anions and superoxide anions by PMN were checked using fluorescent probes and chemiluminescence assays; a microbicidal activity assay against C. albicans was also performed. LLLT excited PMN to a higher functional profile, which was translated as superior production of reactive oxygen species (ROS) and increased fungicidal capacity. The most efficacious energy was 19.2J and, interestingly, the 660nm light was even more efficacious than 780nm at increasing the respiratory burst of PMN and the fungicidal capacity. Human neutrophils (PMN) were stimulated in vitro with 660nm or 780nm CW laser light at 40mW of power and a total energy of 19.2J. Low-level laser therapy (LLLT) excited PMN to a higher functional profile, which was translated as a superior production of reactive oxygen species (ROS) such as hydroxyl radicals (HO• ) and hypochlorite anions (ClO- ) (Figure) and increased fungicidal capacity against Candida albicans cells.