Influence Of Laser Wavelength Research Articles

Revealing Subsurface Damage Morphology and Patterns in areal Ultrashort Pulse Laser Machining of Glass

Material removal rates as well as surface and subsurface quality are key aspects for the industrial application of ultrashort pulse (USP) laser machining. However, revealing so-called subsurface damage (SSD) is challenging. The presented study visualizes and quantifies subsurface damage patterns in areal USP laser ablation of fused silica (FS) and glass N-BK7 (BK). For the first time, using high-resolution optical coherence tomography (OCT) as non-destructive and three-dimensional (3D) evaluation method, SSD morphologies of areal laser machining induced damages are analysed. Influences of laser wavelength, beam geometry and processed material are investigated. Discovered differences of damage morphologies and depth in FS and BK point out the relevance of selecting suitable process parameters. Based on the evaluation of volumetric OCT data, the authors were able to quantify damage morphologies using the surface texture ratio as well as power spectral density functions. One important finding for the quantification and comparability of damage depths in USP laser processing is the influence of applicable evaluation thresholds. In comparison to area thresholds of 0.001% being applicable to OCT measurements, more lenient thresholds of e.g. 1% commonly applied in destructive SSD measurement methods in average result in a reduction of measured damage depths by a factor of ~ 2. This potentially leads to an underestimation of damage depths depending on methods on thresholds used. The presented measurement and evaluation methods as well as gained process insights are important assets for the future optimization of low-damage USP laser micromachining of brittle materials. Moreover, the general applicability and relevance of OCT-based morphological damage analysis in laser material processing is shown.

Influence of laser wavelength on the powder bed fusion of pure copper

Influence of laser wavelength on the powder bed fusion of pure copper

Investigation of picosecond laser-induced graphene for dopamine sensing: Influence of laser wavelength on structural and electrochemical performance

This research focuses on a straightforward synthesis method for laser-induced graphene using green (532 nm) and UV (355 nm) picosecond laser irradiation of graphene oxide dispersion. Structural analysis revealed that the laser operating at 355 nm is more favorable to producing a product with a higher content of the restored sp2 network, a higher graphene in-plane crystallite size, a higher concentration of pyrrolic N, and higher values of the optical bandgap. Conversely, the 532 nm laser yielded a sample with higher concentrations of epoxy groups, sp3 defects, and amorphous carbon. Electrochemical analysis for dopamine determination showed potential for both samples as electrode materials. However, the analytical parameters of the sample treated with the 355 nm laser surpass those of the 532 nm laser. It was assumed that the enhanced electrochemical activity results from the presence of pyrrolic N and vacancies in the structure of the sample treated with the 355 nm laser.

Assessment of global detection capability of oceanographic lidar

The profiling of marine bio-optical properties by oceanographic lidar is of great significance to the monitoring of the marine environment and the study of the global carbon cycle. In this study, the global detection capability of oceanographic lidar is analyzed with different specifications. To evaluate the detection performance, a simulator on multi-platform is developed. Based on the quasi-single elastic scattering approximation lidar equation and the bio-optical models, the simulator can generate different kinds of outputs, such as lidar signal profiles, signal-to-noise ratio profiles, maximum detectable depth distributions. The optical properties profiles of the global ocean could be derived from the global chlorophyll-a concentration profile data set, which is used as the input to the simulator. The simulation results are compared with the measurements from airborne lidar in the South China Sea, which verifies the reliability of the simulator. The global detection capability of spaceborne lidar with different power aperture products is simulated, and the influence of laser wavelength is analyzed. The results show that, for the simulated spaceborne lidar with typical specifications at 486 nm, there are probabilities ranging from 0.66 to 0.85 that the upper boundary of the thermocline can be detected on a global scale. In the cleanest open ocean, the lidar has a good capability to penetrate the upper boundary of the thermocline, while it cannot penetrate the subsurface chlorophyll maximum layers, in which the global penetration ratio is 0.93 under the simulation specifications at 486 nm. Finally, the influence of repetition frequency is analyzed, and the results show that reducing the pulse repetition frequency at the same average power can effectively reduce the background light of cumulative profiles and improve the signal-to-noise ratio.

Influence of Laser Wavelength in Simultaneous Patterning of Fluorinated Ethylene Propylene and Copper Electrode Surface Towards Performance Enhancement of Triboelectric Nanogenerator

Triboelectric nanogenerators (TENGs) are promising cost‐effective energy harvesters useful to scavenge vibration or mechanical movements from various domains. Ranging from condition monitoring of machines to motion sensing of humans, its applications are enormous in the internet of things scenario. Enhancing the performance of small‐sized TENGs is of great demand, and pulsed laser‐assisted texturing is an efficient and proven method to enhance the output of energy harvesters. This work studies simultaneous laser patterning of fluorinated ethylene propylene (FEP) dielectric material and the underneath copper electrode with three different wavelengths (355, 532, and 1064 nm) of the Nd3+:YAG laser and the device's electrical performance is analyzed. The maximum enhancement is observed in the case of 355 nm laser‐assisted patterning on FEP and Cu electrode with a laser fluence of 10 J cm−2. The improvement is least in the case of 1064 nm laser‐assisted patterning. Laser patterning on the underlying electrode with this new approach is able to produce an enhancement in the TENG output. However, patterning on the FEP top surface is critical in the process.

Large-Dynamic-Range and High-Stability Phase Demodulation Technology for Fiber-Optic Michelson Interferometric Sensors.

A large-dynamic-range and high-stability phase demodulation technology for fiber-optic Michelson interferometric sensors is proposed. This technology utilizes two output signals from a 2 × 2 fiber-optic coupler, the interferometric phase difference of which is π. A linear-fitting trigonometric-identity-transformation differential cross-multiplication (LF-TIT-DCM) algorithm is used to interrogate the phase signal from the two output signals from the coupler. The interferometric phase differences from the two output signals from the 2 × 2 fiber-optic couplers with different coupling ratios are all equal to π, which ensures that the LF-TIT-DCM algorithm can be applied perfectly. A fiber-optic Michelson interferometric acoustic sensor is fabricated, and an acoustic signal testing system is built to prove the proposed phase demodulation technology. Experimental results show that excellent linearity is observed from 0.033 rad to 3.2 rad. Moreover, the influence of laser wavelength and optical power is researched, and variation below 0.47 dB is observed at different sound pressure levels (SPLs). Long-term stability over thirty minutes is tested, and fluctuation is less than 0.36 dB. The proposed phase demodulation technology obtains large dynamic range and high stability at rather low cost.

Three-dimensional echo distribution analysis of multi-band and oblique Gaussian beams propagating through cat-eye optical system

The cat-eye effect in optical systems enables active laser detection at long distances and high orientation precision. However, few studies focus on the influence of a multi-band laser with a large incident angle on the echo distribution. This study proposes a three-dimensional echo distribution calculation model of an obliquely incident multi-band laser based on the Collins diffraction integral formula and aperture function expansion as the sum of complex Gaussian functions. The echo distributions for different detection ranges are calculated by coupling the size of the detector in a cat-eye optical system into the model. In the numerical simulation, the influences of laser wavelength, incident angle, and target detector parameter are quantitatively analysed by introducing a target-missing quantity of echo spot and peak light intensity. The results show that the peak light intensity decreases with an increase in incident laser wavelength. When the incident angle increases to a particular value, the peak light intensity decreases sharply, and the target-missing quantity of the echo spot centroid is positively correlated with the incident angle. We can effectively extract important information, such as the working band and detector size, from the cat-eye target echo using this model and provide a trajectory prediction theory for the active detection of a cat-eye target moving at high speed.

Influence of laser wavelength on the optical and structural properties of MoS2 nanoparticles prepared via laser irradiation in ethylene glycol

MoS2 nanoparticles (NPs) were prepared by nanosecond (ns) laser ablation in ethylene glycol using a Q-switched neodymium:ytterbium aluminum garnet laser at 1064 and 532 nm laser wavelengths. The influence of laser wavelengths in ns laser production of MoS2 NPs is not yet fully understood. The shape, structure, crystalline phase, stability, and optical and photoluminescence (PL) properties of NPs were studied using TEM, dynamic light scattering, scanning electron microscopy with energy-dispersive x-ray, x-ray diffraction (XRD), ultraviolet–visible (UV–Vis), PL, Fourier transform infrared, and Raman spectroscopy. The UV–Vis absorption spectroscopy showed that the optimum laser wavelength for preparing MoS2 NPs is 1064 nm. Also, the absorption peak intensity of MoS2 NPs prepared at 1064 nm was 3.95 times higher than that at a 532 nm wavelength. In the case of ablation with 1064 nm, the most of NPs had spherical shapes and well dispersed compared with 532 nm. While the samples had the same crystalline structure for both wavelengths, as the laser wavelength increased, the mean particle size decreased from 22 to 13 nm. This is because of a photofragmentation phenomenon.

Influence of laser wavelength on surface enhanced Raman spectroscopy using Mn based nano-particles produced by laser ablation synthesis in 4,4′ Bipyridine solution (LASiS)

In this work surface Raman spectroscopy of Mn based nano-particles produced by laser ablation technique in 4,4′ Bipyridine (Bipy: C10H8N2) aqueous environment is studied using three Raman spectroscopes with different laser wavelengths of 532, 632.8 and 785 nm. Transmission electron microscopy (TEM), X-ray diffraction (XRD), UV–visible spectroscopy (UV-Vis), dynamic light scattering (DLS) and Fourier transformations infra-red spectroscopy (FTIR) produced the characteristics of the obtained samples. Results of TEM and DLS showed that spherical Mn based nano-particles with a diameter of 40 nm and nano-rods with different lengths were produced. A value of − 23.61 mV for zeta potential and a mobility of − 1.84 × 10−8 m2s−1V−1 showed the instability of the produced nano-particles in the solution which can be stabilized by ultrasonic treatment of the solution. The absorption spectra showed two peaks at 400 and 422 nanometer wavelengths that may be assigned as transverse and longitudinal plasmonic oscillations of the nano-rod particles, respectively. The most intense peak in the XRD pattern of nano-particles in Bipy solution was assigned as MnO2(131) and no Mn peak was observed. Raman and FTIR analyses should not result in similar data for molecules with center of symmetry. This is confirmed in the results of this work for Bipy as such molecule. High enhancement of the Raman peaks of Bipy was achieved using all three different laser wavelengths. The influence of laser wavelength on different main Raman shifts of Bipy is discussed and related to the correlation between the laser wavelength and size of the nano-particles. In particular, and consistent with this and previous results some combined Raman shifts are also observed using 632.8 nm laser wavelength.

Influence of Laser wavelength on morphological and optical properties of ZnO nanoparticles prepared by laser ablation in water

Nanoparticles (NPs) of Zinc oxide (ZnO) were prepared utilizing pulsed laser ablation of a Zinc metal plate in deionized water without utilizing surfactant. The effect of Laser wavelength on the characterization of ZnO was investigated. The 1064-nm and 532-nm wavelength beams produced from a Q-switched Nd: YAG laser at 10 ns pulse duration were employed. The SEM images displayed that the average diameter of the Zinc oxide NPs generated by the laser wavelength 532-nm are larger than the 1064-nm laser wavelength nanoparticles. Various sizes were observed of round ZnO nanoparticles in the SEM image. As the laser wavelength increased, the density of the nanoparticles in water increased. UV–vis analyses revealed that the absorption peak located at 342 nm (1064nm) and 344 nm (532nm). The nanoparticles formed at 1064 nm exhibited higher absorbance than the nanoparticles formed at 532 nm. The optical band gap is considered to be 3.42 eV for 1064 nm and 3.4 eV for 532 nm.

Investigation of the mechanism and influence of laser wavelength and energy on laser opto-ultrasonic dual detection.

Laser opto-ultrasonic dual (LOUD) detection, which uses laser irradiation of samples to generate spectral and ultrasonic signals simultaneously, can perform multimodal detection of element composition and structural property. As such, it has been applied to the detection of additive manufacturing (AM) components. Further, optimized parameters lead to better detection results. To the best of our knowledge, however, there is no study on the effect of laser properties on LOUD detection. Therefore, we studied the mechanism and influence of laser wavelength and energy on LOUD detection. In this work, the intensity, signal-to-noise ratio (SNR), and stability evolution of the laser excitation spectrum and ultrasonic signals at different wavelengths and energies were analyzed. It was found in the plasma evolution that high electron number density means a large amount of ablated mass generated, which was favorable for laser ultrasonic excitation and can produce higher SNR and a more stable signal. However, it also led to more atoms of the ground-state, which resulted in the self-absorption effect and reduced spectrum intensity in the spectrum analysis. Therefore, with self-absorption correction, better stability, and higher signal intensity, an SNR of spectral and ultrasonic signals can be obtained using 355 nm laser excitation at optimal energy. As a result, in the quantitative analysis of Cu and Si elements by LOUD detection, the determination coefficients (R2) were higher than 0.995, and the average relative errors were less than 2.5%, the limit of detection could reach the order of 100 ppm. Further, the defect size of 0.55 mm in the wire +arc additive manufacturing sample was detected by LOUD detection, and the average relative error was 5.59% compared with the digital radiography results, which indicate that laser wavelength and laser energy affect the intensity and stability of spectral and ultrasonic signals in LOUD detection, which means selecting appropriate laser parameters is important to obtain a high precision detection.

Influence of laser wavelength on the modification of friction between 100Cr6 steel and polytetrafluoroethylene by femtosecond laser-induced periodic surface structures

The authors report on surface modification by laser-induced periodic surface structures of different periodicities and modulation depths to modify dry and lubricated tribological properties. Using 220 fs laser pulses in the infrared (λ1=1030nm), visible (λ2=515nm), and ultraviolet (λ3=343nm) spectral regions, the authors periodically structure two-dimensional areas with periodicities in the range between 300 and 950 nm and modulation depths between 30 and 180 nm, respectively. The coefficient of friction is measured by performing a linear reciprocating ball-on-disk test with polytetrafluoroethylene balls on such structured 100Cr6 bearing steel. This configuration reveals a modified friction behavior using load forces between 50 and 1000 mN and a translation speed of 4 mm/s. In general, the results show an increased coefficient of friction in the presence of the applied periodic structures. In particular, in the case of dry environmental conditions, laser-induced periodic surface structures with an increasing spatial period lead to an increase in the coefficient of friction. In addition, for a sliding direction perpendicular to the alignment of the periodic structures, a higher coefficient of friction is found in comparison to a parallel movement. While in the case of lubricated friction, an increased coefficient of friction is also found; yet, it reveals a less pronounced dependency of the sliding direction as compared to dry conditions. For lubricated linear reciprocating movements, the coefficient of friction decreases under increasing load forces, which results in a load depended friction reduction.

Terahertz radiation emission from three-color laser-induced air plasma

Based on the photocurrent model, terahertz (THz) radiation generation in three-color (fundamental ($$\omega $$), second-harmonic ($$2\omega $$), and third-harmonic ($$3\omega $$)) laser-induced air plasma is studied using particle in cell simulation. Our simulation results show that the amplitude of THz radiation in the three-color laser scheme is several times larger than the amplitude of THz radiation in the two-color laser scheme (fundamental ($$\omega $$), second harmonic ($$2\omega $$)). In addition, the effect of the phase difference between the first and second harmonics $$\left( \varphi _{2} \right) $$ and the phase difference between the fundamental and third harmonics $$\left( \varphi _{3} \right) $$ on THz generation is investigated in order to obtain the optimum conditions. It is indicated that the effect of $$\varphi _{3}$$ on THz radiation strongly depends on $$\varphi _{2}$$ in the three-color scheme and it is found that the THz radiation is maximum in the case with $$\varphi _{2}=\pi / 6$$ and $$\varphi _{3}= \pi / 6$$. The influence of laser wavelength and pulse duration on THz generation is also studied. Our results reveal that the THz radiation increases proportionally to the square of the laser wavelength. Moreover, it is shown that THz radiation increases by increasing pulse duration.

Influence of Laser Wavelength and Solution Type on the Optical Absorbance of Colloidal AG Nanoparticles Synthesized by Laser Ablation

Influence of Laser Wavelength and Solution Type on the Optical Absorbance of Colloidal AG Nanoparticles Synthesized by Laser Ablation

Non-sequential double ionization of triatomic molecules OCS in intense laser fields

We investigated the non-sequential double ionization of the OCS molecule at both 800 nm and 1200 nm laser fields. For the double ionization with different laser wavelengths, an alternating high and low yields were observed in the yields dependence on the laser intensity. To get insight of this phenomenon, the mechanisms of the strong field double ionization were analyzed in details. An abnormal change of the mechanism was identified at 1200 nm laser fields as the laser intensity increases. With further discussions, the influence of laser wavelength on the NSDI was studied.

Influence of laser wavelength and laser energy on depth profiling of easel painting samples

The depth-resolved analysis by means of the laser-induced breakdown spectroscopy (LIBS) is a useful tool in the investigation of multi-layered structures of paintings. The LIBS technique is considered micro-destructive, as it is associated with the formation of the ablation crater. It is important to optimize the laser pulse parameters to minimize the crater size and also to avoid some possible side effects of the laser radiation, such as the material redeposition and the light- or heat-induced pigment discoloration. In the present work, mock-up painting samples were used to investigate the influence of laser radiation characteristics on the ablation process. The first LIBS set-up contains a Nd:YAG laser at the second harmonic frequency (laser wavelength 532 nm, pulse duration ~ 10 ns) and the second set-up is comprised of a modified laser-ablation system equipped with a Nd:YAG laser at the fourth harmonic frequency (laser wavelength 266 nm, pulse duration ~ 5 ns). The influence of different laser wavelengths and different laser energies on the properties of the craters was examined. The effects caused by the laser-ablation process were described.

Laser-Induced Breakdown Spectroscopic (LIBS) Analysis of Trace Heavy Metals Enriched by Al2O3 Nanoparticles.

We demonstrated a unique method for the detection of heavy metals, such as Ni, Cr, and Cd, at trace level in aqueous solutions by laser induced breakdown spectroscopy (LIBS) enriched by aluminum oxide (Al2O3) nanoparticles (NP) adsorption. Al2O3 NPs were used for the sample phase transformation and heavy metals pre-concentration because of its excellent adsorption capacity and sparse spectral lines. The influence of laser wavelength and laser irradiance on the signal intensity was investigated. With 45 mL solutions used for enrichment and adsorption, limits of detection obtained for Ni, Cr, and Cd were 9.61, 8.49, and 71.6 μg/L under 532 nm laser ablation, and 22.5, 20.4, and 83.8 μg/L under 1064 nm laser ablation, respectively. The relative standard deviations of all elements were about 12% or 13%. Moreover, Al2O3 NPs adsorption enrichment of target elements was verified and the detection sensitivity was improved by increasing the amount of sample solutions.

Pulsed UV Laser Processing of Carbosilane and Silazane Polymers.

Freestanding SiCNO ceramic pieces with sub-mm features were produced by laser crosslinking of carbosilane and silazane polymer precursors followed by pyrolysis in inert atmosphere. Three different pulsed UV laser systems were investigated, and the influence of laser wavelength, operating power and scanning speed were all found to be important. Different photoinitiators were tested for the two lasers operating at 355 nm, while for the 266 nm laser, crosslinking occurred also without photoinitiator. Pre-treatment of glass substrates with fluorinated silanes was found to ease the release of green bodies during solvent development. Polymer crosslinking was observed with all three of the laser systems, as were bubbles, surface charring and in some cases ablation. By focusing the laser beam several millimeters above the surface of the resin, selective polymer crosslinking was observed exclusively.

Wavelength dependence of laser plasma interaction related to shock ignition approach

AbstractThis paper provides a summary of recent research connected with the shock ignition (SI) concept of the inertial confinement fusion which was carried out at PALS. In the experiments, Cu planar targets coated with a thin CH layer were used. Two-beam irradiation experiment was applied to investigate the effect of preliminary produced plasma to shock-wave generation. The 1ω or 3ω main beam with a high intensity >1015W/cm2generates shock wave, while the other 1ω beam with the intensity below 1014W/cm2creates CH pre-plasma simulating the pre-compressed plasma related to SI. Influence of laser wavelength on absorbed energy transfer to shock wave was studied by means of femtosecond interferometry and measuring the crater volume. To characterize the hot electron and ion emission, two-dimensional (2D) Kα-imaging of Cu plasma and grid collector measurements were used. In single 1ω beam experiments energy transport by fast electrons produced by resonant absorption made a significant contribution to shock-wave pressure. However, two-beam experiments with 1ω main beam show that the pre-plasma is strongly degrading the scalelength which leads to decreasing the fast electron energy contribution to shock pressure. In both the single 3ω beam experiments and the two-beam experiments with the 3ω main beam, do not show any clear influence of fast electron transport on shock-wave pressure. The non-monotonic behavior of the scalelength at changing the laser beam focal radius in both presence and absence of pre-plasma reflects the competition of plasma motion and electron heat conduction under the conditions of one-dimensional and 2D plasma expansion at large and small focal radii, respectively.

Influence of laser wavelength and beam profile on the coagulation depth in a soft tissue phantom model

In laser tissue soldering (LTS), a protein solution is thermally denatured and cross-linked to obtain a strong bond between tissues or tissue and a wound dressing. However, if the extension of the heat-affected zone is too large, wound healing is impaired by thermal tissue injuries. Therefore, heat input and coagulation depth have to be limited. We investigate the influence of wavelength and beam profile on coagulation depth using a soft tissue phantom in case of weakly (980 nm) and strong (1540 nm) absorbed laser radiation. The soft tissue phantom is doped with polystyrene (PS) beads to obtain similar scattering properties as natural tissue. The propagation of the laser radiation in the phantom is simulated by Monte–Carlo method and the optical penetration (OPD) depth calculated from isophotes. The simulation results are compared with the experimental determination of the coagulation volume. The results reveal that scattering effect of tissues on laser radiation increases the losses of a Gaussian beam profile laterally leading to a half-sphere coagulation volume. The depth profile of the coagulation follows approximately the intensity distribution of the laser beams as long as scattering effects are weak. As scattering effects become significant, as for 980-nm radiation, the intensity distribution of the laser beam in the tissue deviates from the original one, leading to different profile of the coagulation depth.