Continuous Wave Laser Beam Research Articles

Crystal Growth and Dissolution Dynamics of l-Phenylalanine Controlled by Solution Surface Laser Trapping

We present sequential behavior of nucleation, growth, and dissolution of an l-phenylalanine plate-like crystal which is induced by a focused continuous-wave near-infrared laser beam in unsaturated solution. Upon the laser irradiation into the air/solution interface, the single crystal is generated from the focus and continuously grows two-dimensionally while being trapped by the laser. The crystal growth is stopped when the laser power is decreased. The crystal size is kept constant for a certain time period, and then the crystal starts dissolution. The dissolution is also induced by moving the crystal from the focus at the air/solution interface. When the crystal is shifted far from the original position where the crystallization is induced, the crystal starts dissolution at a certain distant position. Based on the demonstrations of the crystal size change during the laser manipulation, we conclude that the l-phenylalanine crystal is surrounded by a highly concentrated domain of a few hundreds of micrometers consisting of l-phenylalanine liquid-like clusters.

Far-field diffraction patterns and optical limiting properties of bisdemethoxycurcumin solution under CW laser illumination

In this work, nonlinear optical properties of bisdemethoxycurcumin solution were studied using diffraction ring patterns method. Multiple diffraction rings observed as a continuous wave (CW) laser beam passes through a bisdemethoxycurcumin solution. The nonlinear refractive index, n2, and change in refractive index, Δn, for sample were determined from the number of observed rings, and are found to be 0.8327 × 10−6 cm2/W and 0.00946 respectively. The evolution of the diffraction ring patterns are numerically studied using the Fresnel–Kirchhoff diffraction integral theory. The experimental findings are in good agreement with theoretical analysis. Also the optical limiting properties of the sample were measured at 473 nm. The obtained results proved that the sample bear good optical limiting property.

Laser-assisted tunable optical nonlinearity in liquid-phase exfoliated MoS2 dispersion

The paper aims to explain the effect of laser irradiation on the nonlinear optical (NLO) response of MoS2 nanosheets. MoS2-layered nanostructures were prepared by liquid-phase exfoliation (LPE) in deionized (DI) water. The characterization of MoS2 dispersion proves the formation of 2-3-layered 2H-MoS2 nanosheets with less than 100 nm lateral dimension. The NLO response of prepared dispersion was explored using the Z-scan technique with 532 nm continuous wave (CW) laser beam at 30, 50, 70 mW powers. The main finding of this research is that the nonlinear refractive index (n2) of MoS2 dispersion is a laser-assisted tunable quantity. It has been shown that the nonlinear refractive index of MoS2 nanosheets is altered up to 48% of its initial value only by 1-h laser irradiation with 30 mW power.

Effect of vibration frequency and displacement on melt expulsion characteristics and geometric parameters for ultrasonic vibration-assisted laser drilling of steel

Recently, the applications of ultrasonic vibration assistance to laser-based manufacturing processes are rapidly proliferating. Ultrasonic vibration-assisted laser drilling (UVLD) process involves simultaneous application of high frequency vertical vibrations to the workpiece while being irradiated with a continuous wave laser beam. In UVLD, the ultrasonic vibration assistance causes expulsion of droplets from the laser melted surface, resulting in the formation of deep holes. In this paper, systematic analysis of the effects of ultrasonic vibration frequency (20–40 kHz) and displacement (16–32 µm) on melt expulsion characteristics in early stages of drilling and geometric/quality features of the holes for UVLD of AISI 316 is presented. Based on the analysis of initiation of droplet ejection from the melt pool and particle size of the ejected droplets, mechanisms of droplet ejection based on capillary wave theory are proposed. It was observed that while increasing both ultrasonic vibration frequency and displacement resulted in reduction in droplet ejection initiation time and the formation of deeper holes for the given laser irradiation time (100 ms), the effect of vibration displacement was much more pronounced than the frequency on the variation.

Continuous-wave line laser thermography for monitoring of rotating wind turbine blades

This article presents a continuous-wave line laser thermography system for monitoring of rotating wind turbine blades. The proposed continuous-wave line laser thermography system non-destructively inspects rotating blades by generating thermal waves on the target blades using a continuous-wave line laser beam and simultaneously recording the corresponding thermal wave propagation using an infrared camera. The continuous-wave line laser thermography system is positioned at a fixed point, and the blades are automatically scanned using the continuous-wave line laser thermography system as the blades rotate under normal operational conditions. A coordinate transform algorithm named “time–space-integrated coordination transform” is developed for precise damage evaluation in rotating blades. Time–space-integrated coordination transform transforms spatially and temporally varying thermal images taken by the infrared camera to only temporally varying thermal images viewed from the perspective of the fixed blade positions. The effectiveness of the proposed continuous-wave line laser thermography system is experimentally validated by detecting hidden delamination on lab-scale rotating blades. In the experiments, artificial delaminations with diameters of 15 and 30 mm are successfully visualized with no false alarms while the blades are rotating at 10 r/min.

Pseudopolymorph Control of l-Phenylalanine Achieved by Laser Trapping

We demonstrate pseudopolymorph control of l-phenylalanine (l-Phe) with laser trapping method by tuning laser power, polarization, and initial solution concentration. When a continuous-wave near-infrared laser beam of 1064 nm was focused at an air/solution interface of l-Phe D2O solutions with different saturation, l-Phe crystallization was always observed within 30 min-irradiation, even from unsaturated solution. Either whisker- or plate-like crystals were generated depending on given conditions, and identified by Raman spectroscopy to be two l-Phe pseudopolymorphs of monohydrate and anhydrous forms, respectively. The absolute control of l-Phe pseudopolymorphism was achieved by changing the initial solution concentration. In unsaturated solution, laser trapping always produced only one anhydrous crystal at the focus, which can never be produced on spontaneous nucleation at ordinary temperatures and pressures, while in supersaturated solution, a number of monohydrate crystals were densely distributed in an...

Bubble generation and molecular crystallization at solution surface by intense continuous-wave laser irradiation

We demonstrate bubble generation outside the focus induced by irradiating a focused 1064 nm continuous-wave laser beam into the surface of water and l-phenylalanine H2O solutions. In the former case of water, bubbles stay at positions distant from the focus during the irradiation, and their size and location are controllable by the laser power. In the latter solution, bubbles move outward toward the surrounding area, and subsequently crystallization takes place at the focus. We discuss these behaviors from the viewpoints of the temperature elevation accompanying the decrease in air solubility as well as the optical trapping of l-phenylalanine clusters giving a single crystal.

Estimation of thermocapillary force during laser trapping of confined microbubbles in a liquid

A theoretical model is introduced to determine the thermocapillary force acting on a microbubble, which adheres to the wall of a container filled with a liquid, during trapping using a focused continuous-wave (CW) laser beam. The model is developed by considering all possible forces acting on the microbubble, which also includes the optical force, the viscous force, and the friction force. The thermocapillary force, estimated from the relative velocity of the trapped microbubble with respect to the container, compares favorably with theoretical predictions based on the temperature gradient induced by the focused laser beam. The proposed experiment can be also used to determine the contact angle and/or the coefficient of friction of the microbubble at the microbubble–container interface. Our results should be useful in the design of efficient systems using microbubbles for drug delivery and water treatment systems.

Time-resolved infrared photoluminescence spectroscopy using parametric three-wave mixing with angle-tuned phase matching.

A setup for time-resolved photoluminescence spectroscopy, based on parametric three-wave mixing in a periodically poled lithium niobate crystal, is characterized. Special attention is given to adjusting the phase matching condition by angle tuning of the luminescent light relative to a strong, continuous-wave laser beam within the crystal. The detection system is capable of operating at room temperature and in a wavelength range from 1.55 to 2.20µm. Its sensitivity is compared to a commercial photomultiplier, and its capability of nanosecond time resolution is demonstrated.

The influence of beam-cone-angle on the high energy laser induced damage of optical thin film

A continuous wave (cw) laser beam with extremely high power density is needed in the experimental study of the optical film’s thermal damage. In order to achieve such high power density, the incident beam generally needs to converge. In this situation, the cone-angle of the converged beam is inevitable, which may affect the damage process of the optical film. A thin-film Fabry–Perot filter is taken as an example. The influence of the beam cone angle on the thermal damage of the optical film is theoretically studied. Under the irradiation of high power cw laser, the film absorbs the laser energy and the heat accumulates continuously in the film. The cone-angle changes the laser intensity distribution, i.e. the heat source, in the multilayer film. The temperature distribution and the temperature rising process are also related to the cone-angle. Only when the cone’s half angle is smaller than 2°, the influence of the cone-angle may be ignored.

Thermal nonlinearities for three curcuminoids measured by diffraction ring patterns and Z-scan under visible CW laser illumination

The Gaussian visible Continuous-wave (CW) laser beam propagation in three curcuminoids compounds has led to diffraction ring patterns. These patterns believed to be originated due to self-phase modulation. The study focuses on the effect of input power on the diffraction ring patterns. As a result of increasing input power each circular ring pattern flattened in the upper part due to the convection. These results are reproduced numerically using the Fresnel-Kirchhoff integral. It appears that each ring pattern evolve with time from circular to flattened ones. The thermal nonlinear refractive indexes of the curcuminoids are calculated based on diffraction ring patterns and the Z-scan technique.

Direct Laser Writing of Gold Nanostructures: Application to Data Storage and Color Nanoprinting

We have demonstrated a simple way to fabricate gold islands by using the laser direct writing method. The gold nano-islands were formed by the optically induced local thermal effect, resulting from the excitation of a continuous-wave laser beam on gold layer. By moving the laser focusing spot, it was possible to write desired plasmonic texts and images on demand at a nanoscale. By changing the exposure dose, the size of gold nano-islands was controlled, resulted in different colors. This demonstration paves the way for many interesting applications, such as plasmonic data storage and nano-scaled color printing.

Laser surface hardening of 11% Cr ferritic stainless steel and its sensitisation behaviour

11% Cr ferritic stainless steel conforming to EN 1.4003 standard was surface hardened by a continuous-wave fibre laser beam. Both single-pass and multi-pass laser hardening was investigated. Different laser parameters were compared and their influence on hardness, microstructure, geometry of the hardened zone and sensitisation was investigated, especially for overlapping passes. The experiments showed that a surface hardness which is double that of the base material hardness was obtainable via martensitic phase transformation and high cooling rate, in spite of the low carbon and nitrogen content. This behaviour could be predicted from the chemical composition using the Kaltenhauser Ferrite Factor. Hardening at higher power levels gives more coarse-grained lath martensite but does not increase the hardness. Sensitisation was not a problem in single-pass hardening. However, the production of overlapping tracks could be detrimental to corrosion resistance in 11% Cr steel due to the formation of chromium carbides and nitrides.

Quantitative detection of oxygen in reduced graphene oxide by femtosecond laser-induced breakdown spectroscopy.

This paper proposes a simple, direct, and fast method for the quantitative detection of oxygen in reduced graphene oxide (r-GO) by femtosecond laser-induced breakdown spectroscopy (fs-LIBS). First, GO was reduced by continuous-wave (CW) laser beams with different powers; subsequently, the oxygen content in the r-GO was detected through the intensity of oxygen obtained by fs-LIBS. The fit of the observed data and errors by LIBS was compared with the results of x-ray photoelectron spectroscopy (XPS), and the fs-LIBS results correlate well with the XPS results; it indicated that fs-LIBS can realize quantitative analysis of the GO-reduction degree. The method provides a convenient and time-efficient way for detecting the reduction degree of r-GO and can extend the applications of r-GO with different reduction degrees.

Single-photon three-dimensional microfabrication through a multimode optical fiber.

Two-photon polymerization (TPP) processes have enabled the fabrication of advanced and functional microstructures. However, most TPP platforms are bulky and require the use of expensive femtosecond lasers. Here, we propose an inexpensive and compact alternative to TPP by adapting an endoscopic imaging system for single-photon three-dimensional microfabrication. The wavefront of a visible continuous-wave laser beam is shaped so that it focuses into a photoresist through a 5 cm long ultra-thin multimode optical fiber (∅70 μm, NA 0.64). Using this device, we show that single-photon polymerization can be confined to the phase-controlled focal spot thanks to the non-linearity of the photoresist, likely due to oxygen radical scavenging. Thus, by exploiting this non-linearity with a specific overcuring method we demonstrate single-photon three-dimensional fabrication of solid and hollow microstructures through a multimode fiber with a 1.0-μm lateral and 21.5-μm axial printing resolution. This opens up new possibilities for advanced and functional microfabrication through endoscopic probes with inexpensive laser sources.

Third - Order Nonlinear Optical Properties and Optical Limiting Behavior of Celestin Blue B Dye Doped Polymer Films

Pure Poly (methylmethacrylate) (PMMA) polymer film and Celestin Blue B dye doped polymer films at different concentrations were prepared using casting technique. UV - Vis spectra were recorded to characterize the optical properties of the Celestin Blue B dye doped PMMA polymer films. The magnitudes of both real and imaginary parts of third - order nonlinear susceptibility (χ (3)) of Celestin Blue B dye doped polymer films were determined using the z - scan technique with a continuous wave laser beam at wavelength 532 nm. The nonlinear refractive index (n2) and the nonlinear absorption coefficient (β) of the Celestin Blue B dye doped polymer films were calculated. It was found that the prepared films exhibited saturable absorption (SA) and self - defocusing effect. The optical power limiting behavior also investigated for Celestin Blue B dye doped PMMA polymer films at different concentrations and the optical power limiting threshold values were determined. Results indicate that the Celestin Blue B dye doped PMMA polymer film is a promising material for future photonic device applications.

Novel Quaternary TlGaSn2Se6 Single Crystal as Promising Material for Laser Operated Infrared Nonlinear Optical Modulators

The studies of the laser operated third order nonlinear optical features of novel TlGaSn2Se6 crystal were done. The main efforts were devoted to a search of a possibility to apply these crystals as laser operated optoelectronic material. For this reason, the third harmonic generation of the Nd:YAG pulse laser 1064 nm as the fundamental beam with varied energy density of up to 200 J/m2 was studied. As a source of laser operated light, we have used the cw laser (532 nm), exciting the material above the energy gap. Additionally, the influence of middle-energy Ar+ ions on the XPS spectra of the TlInSn2Se6 surface has been explored. We have shown that the main contribution of the Se4p states is manifested in the upper part of the valence band of TlInSn2Se6 We have established that for the TlGaSn2Se6 crystal there exists a possibility of variation of the third harmonic generation efficiency using illumination by external continuous wave laser beam. The discovered effect makes it possible to utilize TlGaSn2Se6 crystal in advanced optoelectronic laser operated devices.

Influence of copper ions on structural and non-linear optical properties in manganese ferrite nanomaterials

A series of Mn1-xCuxFe2O4 (x = 0, 0.15, 0.30, 0.45, 0.60 and 1) particles were prepared using chemical co-precipitation method with metal nitrates as precursor materials. Samples were synthesized under various annealing temperatures and 800 °C was found to be the optimal temperature for phase formation. Powder XRD analyses confirm the formation of spinel manganese ferrites along with the α-Fe2O3 phase which got reduced with increase in copper concentration. Samples were characterized using spectroscopic and microscopic techniques. UV-Diffuse reflectance spectroscopy was employed to calculate the band gap which varied between 1.51 eV and 1.83 eV. HR-SEM images reveal the spherical nature of the particles. Ferromagnetic nature of these materials was confirmed from vibrating sample magnetometer (VSM) measurements. Z-scan technique was employed to measure the non-linear optical properties. The non-linear refraction, non-linear absorption and non-linear susceptibility are found to be of the order of 10−8 cm2/W, 10−4 cm/W and 10−6 esu respectively. The samples showed a defocusing effect which was utilized to explain the optical limiting behavior at the same wavelength using the continuous-wave laser beam. The results show that these materials have potential for exploitation towards device applications like optical limiting and switching.

Quantifying Remote Heating from Propagating Surface Plasmon Polaritons.

We report a method to electrically detect heating from excitation of propagating surface plasmon polaritons (SPP). The coupling between SPP and a continuous wave laser beam is realized through lithographically defined gratings in the electrodes of thin film gold "bow tie" nanodevices. The propagating SPPs allow remote coupling of optical energy into a nanowire constriction. Heating of the constriction is detectable through changes in the device conductance and contains contributions from both thermal diffusion of heat generated at the grating and heat generated locally at the constriction by plasmon dissipation. We quantify these contributions through computational modeling and demonstrate that the propagation of SPPs provides the dominant contribution. Coupling optical energy into the constriction via propagating SPPs in this geometry produces an inferred temperature rise of the constriction a factor of 60 smaller than would take place if optical energy were introduced via directly illuminating the constriction. The grating approach provides a path for remote excitation of nanoconstrictions using SPPs for measurements that usually require direct laser illumination, such as surface-enhanced Raman spectroscopy.

Study of Nonlinear Optical Properties of Disperse Yellow – 7 Dye-doped Polymer Films using CW Laser

The materials with an ability of self-focusing/defocusing through their light intensitydependent refractive index and phase shift properties are potential candidates for all-optical photonic devices. Several organic materials including dye-doped polymer films are attracting many researchers due to their advantages in terms of enhanced efficiency, and acceptable mechanical properties to fabricate useful devices. In this paper, we have reported the nonlinear optical properties like nonlinear absorption and nonlinear refraction of an organic dye Disperse Yellow - 7 (DY-7) doped in Polymethyl methacrylate-methacrylic acid (PMMA-MA) polymer matrix using open aperture and closed aperture Z-scan experimental methods by means of low power continuous wave (CW) laser beam. The optical limiting properties of these films are also studied using Type 1 and Type 2 configurations at different input powers using continuous wave (CW) laser beams of 532 nm wavelength. The nonlinear refractive index n2, nonlinear absorption coefficient β, changes in refractive index with input intensity, and the magnitude of third-order optical nonlinearity of the dye-doped film are experimentally determined. The sample is tested for optical power limiting in which the input limiting threshold and saturated output power level for both type 1 and type 2 optical limiting configurations are recorded. DY-7 dye-doped in PMMA-MA polymer film has shown saturation absorption at lower input irradiance and reverse saturation absorption at higher input irradiance along with thermal nonlinearity and hence found to be a potential candidate for the third harmonic property based photonic devices.