Intensity Of Incident Laser Beam Research Articles

Self‐Excited Free‐Standing VO2 Film for Infrared Optical Limiter

AbstractEffective optical limiters (OLs) are necessary devices for the protection of various sensitive photo‐detectors, cameras, infrared sensors, or even the human eyes once encountering unexpected high‐intensity illumination or laser blinding attacks. Vanadium dioxide (VO2) shows pronounced infrared switching behavior across the phase transition, which is considered as an idea optical limiter for broad‐band infrared laser protection. However, the self‐adapting optical limiter function based on VO2 is quite difficult to realize since the open‐state absorptance of the VO2 layer is always very low, which makes the laser irradiation cannot trigger the phase transition quickly. In the current study, a self‐excited VO2 infrared optical limiter is proposed, which is integrated by a transferred VO2 layer, InGaAs micro/nano wires, and a local heater. Based on the“optical response–electric heating” strategy, the phase transition of VO2 layer can be quickly triggered once the incident laser beam intensity exceeds the pre‐set threshold value. In addition, this integrated device has an excellent switching ratio, flexible controllability, and stability. This work achieves a practical VO2 optical limiter device and provides a promising strategy for developing VO2‐based integrated multifunctional devices in the future.

Diffraction ring patterns of the acid blue 29 in different solvents

The spatial self-phase modulation effect was exploited to study the nonlinear optical parameters of the acid blue 29 dye solutions. The acid blue 29 dye was used as samples and it was dissolved in four different alcohols. The trend in these experiments to investigate the influence of solvent structure on the formation and the temporal evolution of the far field self-diffraction ring patterns of the Gaussian laser beam passing through the studied samples. The nonlinear refractive index (n2), birefringence (Δn2) and thermo-optic coefficient [dn/dT] were determined from the obtained self-diffraction ring patterns. Our results have indicated that the difference between the numbers of diffraction rings is attributed to the type of the solvents and to the incident laser beam intensity.

Twisted laser beam propagation in a novel one-dimensional photonic crystal defected by an absorbent plasma layer

A novel tunable filter including the absorbent plasma layer affected by twisted electromagnetic beam propagation is indicated. The presented photonic crystal is composed by SiO2 and free space with one absorbent plasma defect layer, and that the transmittance and reflectance spectra are studied by using Transfer Matrix Method. It is found out that the transmittance spectrum can be adjusted by the plasma absorption rate, vortex charge number or intensity of incident laser beam. The dependence of the transmittance, reflectance and absorptivity spectra to the transverse coordinate is surveyed, particularly when a change in vortex charge number is applied.

The study of nonlinear optical properties of rhodamine B dye and TiO2 nanoparticles doped in PMMA polymer

In this research, A thin film of Rhodamine B dye and TiO2 Nanoparticles doped in PMMA Polymer has been prepared by a casting method. The sample was spectrum absorption by UV-Vis. The nonlinear optical properties were measured by Z- scan technique using Nd:YAG laser with (1064 nm) wavelength. The nonlinear refractive index (n2) and nonlinear absorption coefficient (β) were estimated for the thin film for different energies of the laser, n2 and β were decreased with increasing intensity of incident laser beam. Also, the type of β was two-photon absorption and n2 negative nonlinear reflective.

Light induced phase change in Cu2−xZn1.3SnS4 thin films

Cu2ZnSnS4 and its alloy based thin film solar cells have shown better photovoltaic performance under Cu-poor and Zn-rich conditions. However, the effect of Cu-stoichiometry on the coexistence of kesterite (KS), stannite and/or partially disordered kesterite (PD-KS) phases and their influence on photovoltaic performance is not clearly understood. Raman studies were carried out on Cu2−xZn1.3SnS4 (x = 0, 0.3, and 0.5) thin films by changing the intensity of the incident laser beam. It was observed that both Cu-stoichiometry and incident laser beam intensity induce a disorder in the system. Disorder induced transformation of KS (I4¯) to PD-KS (I4¯2m) is explained by Raman studies.

Investigation of the Soret coefficient in magnetic fluids using the Z-scan technique

The generalized thermal lens model formalism, which includes on it the thermodiffusion phenomenon, is used to determine the Soret coefficient ( S T) of a cationic surfacted ferrofluid. The single-beam Z-scan experiment is employed to obtain both the magnitude and sign of S T. Besides S T, the method allows the determination of the parameter ∂ n / ∂ I , where n and I are the sample index of refraction and the incident laser beam intensity on the sample. This parameter accounts for the third-order nonlinear optical effects which yield in the sample an instantaneous modification of the index of refraction, proportional to the intensity of the local light.

Fluorescent probes for monitoring the pulsed‐laser‐induced photocuring of poly(urethane acrylate)‐based adhesives

AbstractFluorescence spectroscopy was used to study the kinetics of polymerization of acrylic adhesive formulations exposed to a 355‐nm pulsed emission from an Nd‐YAG laser. Nine fluorescent probes were used for monitoring the laser curing, showing different sensitivities. In general, the fluorescence intensity emission increased as crosslinking occurred. In addition, solvatochromic fluorescent probes showed a blueshift in their emission. A relative method was applied for the evaluation of the polymerization rates in three different acrylic systems. Special features of pulsed‐laser‐induced polymerization were treated in detail, such as the influence of the laser pulse frequency and the incident laser beam intensity. The polymerization rate slowed down as the pulse repetition rate decreased. An inhibition period due to oxygen quenching was observed, and it was highly dependent on the laser repetition rate and the nature of the photoinitiator. The effect of the laser beam intensity on the kinetics of such fast reactions was studied. In general, increasing the laser energy improved the rate of polymerization. The degree of cure improved as the polymerization rate increased as a result of faster crosslinking, rather than relaxation volume kinetics. Moreover, a saturation rate effect occurred that depended on the photoinitiator. The different behaviors of the two photoinitiators in the curing of the same acrylic formulation was explained on the basis of primary radical termination. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1227–1238, 2004

ESR studies on laser beam irradiated polyethyleneterephtalate

Electron spin resonance investigations on polyethyleneterephtalate irradiated with a YAG-Nd laser are reported. The dependence of electron spin resonance spectra on the incident laser beam intensity (power) is studied. It is noticed that the concentration of free radicals has a sigmoidal dependence on the crystal current, presenting saturation at high incident powers. The nature of free radicals induced by laser irradiation is discussed.

Read-Out Signal Simulation of an Optical Disk Having an Oxide Super-Resolution Film

The read-out signal simulation of an optical disk having a cobalt-oxide super-resolution film was performed to find the optimum condition for a higher recording density of the super-resolution disk. A simple model of the complex refractive index change in a super-resolution film due to its temperature was applied, which can explain experimental data. It was found that this type of super-resolution disk must increase its reflectivity as the incident laser-beam intensity rises. To confirm this experimentally, a new super-resolution disk with an added Ge–N layer was prepared, and its read-out signals were measured, which agreed well with the calculated results.

An instrument for measuring high-power laser beam profiles and beam attenuation

An instrument has been developed for measuring high-power laser beam profiles and the amount of beam attenuation during radiative ignition of solid propellants. The detector houses a 1.0 mm square PZT (lead-zirconate-titanate) sensing element that responds to changes in incident laser beam intensity. A chopper wheel with three slots was employed to produce the changes in beam intensity required by the element. The resultant output signal is a series of ‘‘spikes’’ whose height corresponds to the level of beam intensity. Profiles of a high-power CO2 laser beam were obtained by using the detector to acquire a series of radial data points which were then graphed to yield the beam profile. Experiments were also conducted to measure the amount of attenuation of the laser beam during the ignition of solid propellants. This was done by mounting a small sample of propellant on a thin plate above the detector, cutting a 1.5 mm hole through the propellant and the plate, and aligning the hole with the sensing element. The gases and particles evolved during ignition and subsequent combustion of the propellant attenuated the laser beam as it passed through the gaseous plume and the small hole in the sample before being measured by the sensor. The intensity measured by the sensor was then used to quantify the level of transmittance of the beam through the gaseous plume to the propellant sample surface. Results are presented and discussed for a beam profile test and two attenuation tests performed on different energetic materials.