532-nm Nanosecond Laser Research Articles

Analysis and comparison of laser cutting performance of solar float glass with different scanning modes

Cutting quality and efficiency have always been important indicators of glass laser cutting. Laser scanning modes have two kinds, namely, the spiral and concentric circle scanning modes. These modes can achieve high-performance hole cutting of thick solar float glass using a 532-nm nanosecond laser. The mechanism of the glass laser cutting under these two different scanning modes has been described. Several experiments are conducted to explore the effect of machining parameters on cutting efficiency and quality under these two scanning modes. Results indicate that compared with the spiral scanning mode, the minimum area of edge chipping (218340 µm2) and the minimum Ra (3.01 µm) in the concentric circle scanning mode are reduced by 9.4% and 16.4% respectively. Moreover, the best cutting efficiency scanning mode is 14.2% faster than that in the spiral scanning mode. The best parameter combination for the concentric circle scanning mode is as follows: Scanning speed: 2200 mm/s, number of inner circles: 6, and circle spacing: 0.05 mm. This parameter combination reduces the chipping area and sidewall surface roughness by 8.8% and 9.6% respectively at the same cutting efficiency compared with the best spiral processing parameters. The range of glass processing that can be achieved in the concentric circle scanning mode is wider than that in the spiral counterpart. The analyses of surface topography, white spots, microstructures, and sidewall surface element composition are also performed. The study concluded that the concentric circle scanning mode shows evident advantages in the performance of solar float glass hole cutting.

Q-switched double frequency Nd:YAG 532-nm nanosecond laser vs. double frequency Nd:YAG 532-nm picosecond laser for the treatment of solar lentigines in Asians.

Solar lentigines are common pigmentary lesions. Q-switched lasers are effective treatment options but postinflammatory hyperpigmentation (PIH) is common in darker skin. The objective of the study is to compare the efficacy and safety in solar lentigines of Asian skin treated by Q-switched potassium titanyl phosphate (KTP) 532-nm nanosecond laser vs. KTP 532-nm picosecond laser for the treatment of solar lentigines in Asians. Thirty patients with at least 2 solar lentigines on the upper extremities were enrolled. A total of 30 paired lentiginous lesions were randomly treated with a single treatment of either Q-switched KTP 532-nm nanosecond laser vs. KTP 532-nm picosecond laser. In terms of efficacy, mean luminance score was evaluated at baseline, at 6th, and 12th week. Degree of pigment clearance was assessed by a blinded physician and the patients. Satisfaction score was rated by patients using visual analogue scale. Adverse events were also recorded. Twenty-eight patients completed the study. Both lasers showed significant improvement in mean luminance score from baseline (p < 0.05). Likewise, there was no significant difference in pigment clearance between two lasers either assessed by physician or patients. However, patients' satisfaction score was significantly higher with the picosecond laser (p = 0.014). Adverse events and pain were not different between groups. Q-switched KTP 532-nm nanosecond laser and KTP 532-nm picosecond laser are safe and effective for treating solar lentigines in Asians. Based on cost-effectiveness, Q-switched KTP 532-nm nanosecond laser remains the main treatment while KTP 532-nm picosecond laser can be considered as a treatment option.

Ultrasound-assisted water-confined laser micromachining (UWLM) of metals: Experimental study and time-resolved observation

This paper reports the experimental studies and time-resolved observations of the ultrasound-assisted water-confined laser micromachining (UWLM) process on metal workpieces using 532-nm nanosecond laser pulses. UWLM is a new machining process proposed by the corresponding author (Wu, 2014). During UWLM, a laser beam interacts with a workpiece’s front surface location immersed in water to ablate the workpiece, and in-situ ultrasonic waves in water are also applied (for example, from above the front surface using an ultrasonic horn) to the laser ablation site (which energize the water and generate cavitations) to improve the machining process. This paper reports the experimental study of the UWLM process on multiple types of metal workpieces and time-resolved in-situ observations of the process. This kind of study on UWLM has been rarely reported in the literature. Under the studied conditions, it has been found that the ablation depths produced by UWLM at 200 laser pulses are about 2.3–3.8 times the depths by laser ablation in water without ultrasound. Through in-situ time-resolved shadowgraph imaging observations, it has been found that one important likely underlying mechanism for the enhanced material removal rate in the studied UWLM process is that the in-situ ultrasound in UWLM can reduce the material cloud resulted from the previous laser pulse ablation that lingers around laser ablation site, which can enhance the coupling of the subsequent laser pulse(s)’ energy to the workpiece.

Phase-interfacial stimulated Raman scattering generated in strongly pumped water

We have observed unusual blue-shifted radiations in water pumped by a strong 532-nm nanosecond laser. Properties including divergence, polarizations, and pulse shapes of the unusual radiations are measured and compared with those of the regular stimulated Raman scattering (SRS) in water. The unusual radiations are attributed to the parametric anti-Stokes SRS that occurs on the interface of water and ionization plasma (or gas) formed in the laser-induced breakdown of water.

Nonlinear optical properties of multipyrrole dyes

The nonlinear optical properties of a series of pyrrolic compounds consisting of BODIPY and aza-BODIPY systems are investigated using 532nm nanosecond laser and the Z-scan technique. Results show that 3,5-distyryl extension of BODIPY to the red shifted MeO2BODIPY dye has a dramatic impact on its nonlinear absorption properties changing it from a saturable absorber to an efficient reverse saturable absorbing material with a nonlinear absorption coefficient of 4.64×10−10m/W. When plotted on a concentration scale per mole of dye in solution MeO2BODIPY far outperforms the recognized zinc(II) phthalocyanine dye and is comparable to that of zinc(II) tetraphenylporphyrin.

Effects of the ZnSe concentration on the structural and optical properties of ZnSe/PVA nanocomposite thin film

This study investigated the effects of ZnSe nanoparticles (NPs) on the structural and (linear and nonlinear) optical properties of polyvinyl alcohol (PVA) thin film. Three samples of ZnSe NP-doped PVA thin films with different concentrations of ZnSe were produced on a glass substrate. The ZnSe NPs were synthesized by pulsed laser ablation of the ZnSe bulk target immersed in distilled water using a 1064nm wavelength and a high frequency pulsed Nd:YAG laser. The optical bandgap energies of the films were extracted from their UV-Vis-NIR absorption spectra. The corresponding energy bandgaps of the nanocomposite films declined as the ZnSe NPs doping concentration increased. X-ray diffraction analysis was used to characterize the crystalline phases of the ZnSe/PVA nanocomposite films. The concentration-dependent nonlinear optical absorption and nonlinear refraction behaviors of the films after exposure to 532-nm nanosecond laser pulses were investigated using the Z-scan technique. The nonlinear absorption response of the films was positive when measured using an open aperture scheme, which was attributed to the two-photon absorption mechanism. In addition, the nonlinear refraction indices had a negative value and they increased as the concentration of ZnSe NPs in the films increased.

Laser-assisted nanostructuring of metal films by means of a fibre dielectric microprobe

A simple apertureless dielectric microprobe in the form of a section of the tapered optical fibre was proposed for surface laser nanomodification. This probe enables surface λ /2-localisation of laser beam, as demonstrated both numerically and experimentally. The controllable formation of single through nanoholes with the minimum size down to 35 nm (∼ λ /15) in the 50-nm Au/Pd film was shown using this probe and a 532-nm pump nanosecond laser. We also report for the first time on the formation of micro- and nanobumps, jet-like microstructures and microholes on optically thick gold films using single nanosecond laser pulses focused through the fibre dielectric apertureless probe. Both the shape and the sizes of the obtained microstructures were demonstrated to be determined by the pulse energy and film thickness.

Optical Dielectric Apertureless Probe for Surface Laser Modification with λ/15 Lateral Resolution

A simple apertureless dielectric microprobe in the form of a section of the tapered optical fiber was proposed for surface laser nanomodification. This probe enables surface λ/2-localization of laser beam, as shown both numerically and experimentally. The controllable formation of single through nanoholes with the minimum size down to 35 nm (~λ/15) in the 50-nm Au/Pd film was shown using this probe and a 532-nm pump nanosecond laser. We also report for the first time on the formation of micro-and nanobumps, jet-like microstructures and microholes on optically thick gold films by single nanosecond laser pulses focused through the fiber dielectric apertureless probe. The resulting structures were imaged via scanning electron and atomic force microscopy. It was shown that both the shape and sizes of the obtained microstructures are determined by the pulse energy and film thickness.

Sampling considerations when analyzing micrometric-sized particles in a liquid jet using laser induced breakdown spectroscopy

Pollution of water is a matter of concern all over the earth. Particles are known to play an important role in the transportation of pollutants in this medium. In addition, the emergence of new materials such as NOAA (Nano-Objects, their Aggregates and their Agglomerates) emphasizes the need to develop adapted instruments for their detection. Surveillance of pollutants in particulate form in waste waters in industries involved in nanoparticle manufacturing and processing is a telling example of possible applications of such instrumental development. The LIBS (laser-induced breakdown spectroscopy) technique coupled with the liquid jet as sampling mode for suspensions was deemed as a potential candidate for on-line and real time monitoring.With the final aim in view to obtain the best detection limits, the interaction of nanosecond laser pulses with the liquid jet was examined. The evolution of the volume sampled by laser pulses was estimated as a function of the laser energy applying conditional analysis when analyzing a suspension of micrometric-sized particles of borosilicate glass. An estimation of the sampled depth was made. Along with the estimation of the sampled volume, the evolution of the SNR (signal to noise ratio) as a function of the laser energy was investigated as well. Eventually, the laser energy and the corresponding fluence optimizing both the sampling volume and the SNR were determined. The obtained results highlight intrinsic limitations of the liquid jet sampling mode when using 532nm nanosecond laser pulses with suspensions.

Pulsed nanosecond laser ablation of gold in deionized water and aqueous chitosan solution

Gold nanoparticles (AuNP) are produced using a Nd:YAG laser in deionized water and aqueous chitosan solutions via 1064nm nanosecond laser ablation and subsequent 532nm nanosecond laser irradiation. AuNP produced in deionized water under single laser ablation and subsequent irradiation for 20–40min time exhibited coalescence and the formation of nano-chains, with average particle diameters ranging from 34.3 to 18.8nm and 37.2 to 27.3nm, respectively. The introduction of chitosan as a bio-compatible surfactant yielded lesser average diameters and tighter size-distributions with a narrow range of UV-Vis absorption spectra values (514–525nm). For instance, at 20 and 40min, the single laser ablation and subsequent irradiation produced the average diameters of 12.3 and 5.3nm and 5.7 and 4.3nm, respectively. Increases in ablation and irradiation time decrease AuNP size. As time increased, the size-distributions of the AuNP produced in chitosan solution narrowed and the particle size monotonically decreased. Chitosan functionalized the AuNP surface, promoting hydrophobicity, preventing electrostatic attraction of the Au nanoparticles, thus inhibiting coalescence and agglomeration. UV-Vis absorption spectra, TEM and HR-TEM images are used to verify AuNP size distributions. X-ray diffraction measurements of AuNP produced in chitosan confirmed crystallite size and the absence of gold-oxide despite the high-energy laser ablation. Furthermore, samples prepared in chitosan solution showed minimal agglomeration after 24months.

Surface morphology and photoelectric properties of fluorine-doped tin oxide thin films irradiated with 532nm nanosecond laser

In order to improve the transparency and conductivity of the commercial fluorine-doped tin oxide (FTO) films deposited on glass substrates, a nanosecond pulsed laser with a wavelength of 532 nm was used to irradiate the surfaces of the films. The effects of laser fluence and scanning speed on the surface morphology, photoelectric property and overall quality of the FTO films were investigated. The FTO films which were subjected to lower laser fluences or higher scanning speeds achieved gentle laser annealing effects, resulting in unapparent changes in surface morphology. These changes caused enhancements in optical transmittance and decrease in sheet resistance. The FTO films irradiated with higher laser fluences or lower scanning speeds melted and ablated, causing the optical transmittance and the electrical conductivity of the films to drop significantly. Experimental results indicated that the optimum irradiation fluence and scanning speed for 532 nm nanosecond laser annealing of FTO films were 1.02 J/ cm2 and 10 mm/ s, respectively. The corresponding film had an obvious increase in crystallite size. The RMS roughness, the average optical transmittance in the waveband of 380–780 nm and the figure of merit were increased from 100.5 nm, 75.4% and 5.82×10−3 Ω−1 to 113.0 nm, 82.7% and 17.00×10−3 Ω−1 respectively, while the sheet resistance was reduced from 10.2 Ω/□ to 8.8 Ω/□.

Optical apertureless fiber microprobe for surface laser modification of metal films with sub-100 nm resolution

A simple apertureless dielectric microprobe in the form of a section of the tapered optical fiber was proposed for surface laser nanomodification. This probe enables surface λ/2-localization of laser beam, as shown both numerically and experimentally. Single nanoholes with the minimum size down to 90nm (∼λ/6) were fabricated in the 25-nm Au/Pd film, using this probe and a 532-nm pump nanosecond laser.

Photomechanical Wave-Driven Delivery of siRNAs Targeting Intermediate Filament Proteins Promotes Functional Recovery after Spinal Cord Injury in Rats

The formation of glial scars after spinal cord injury (SCI) is one of the factors inhibiting axonal regeneration. Glial scars are mainly composed of reactive astrocytes overexpressing intermediate filament (IF) proteins such as glial fibrillary acidic protein (GFAP) and vimentin. In the current study, we delivered small interfering RNAs (siRNAs) targeting these IF proteins to SCI model rats using photomechanical waves (PMWs), and examined the restoration of motor function in the rats. PMWs are generated by irradiating a light-absorbing material with 532-nm nanosecond laser pulses from a Q-switched Nd:YAG laser. PMWs can site-selectively increase the permeability of the cell membrane for molecular delivery. Rat spinal cord was injured using a weight-drop device and the siRNA(s) solutions were intrathecally injected into the vicinity of the exposed SCI, to which PMWs were applied. We first confirmed the substantial uptake of fluorescence-labeled siRNA by deep glial cells; then we delivered siRNAs targeting GFAP and vimentin into the lesion. The treatment led to a significant improvement in locomotive function from five days post-injury in rats that underwent PMW-mediated siRNA delivery. This was attributable to the moderate silencing of the IF proteins and the subsequent decrease in the cavity area in the injured spinal tissue.

Photoacoustic monitoring of granulation tissue grown in a grafted artificial dermis on rat skin

In this study, we investigated the validity of photoacoustic (PA) measurement for monitoring granulation tissue and hence adhesion of grafted artificial dermis (AD). A 2.5 cm x 2.5 cm, 3-mm-thick AD composed of an atelocollagen sponge sheet and a silicone film was grafted on a full-thickness open wound in rat dorsal skin. The grafted AD was irradiated with low-energy, 532-nm nanosecond laser pulses to photoacoustically excite blood in neovascularities, and the PA signals induced were measured using a piezoelectric transducer as a function of postgrafting time. The PA signals were compared with results of laser Doppler imaging and histological analysis. We found a significant correlation between the depths of the first or shallowest PA signal peaks and the depths of granulation tissues estimated from histology with hematoxylin & eosin staining (R=0.951, p<0.05). There was also a significant correlation between the amplitudes of the first PA signal peaks and densities of CD31-positive cells evaluated from histology with immunohistochemical staining (R=0.859, p<0.05). With laser Doppler imaging, no clear perfusion signals were observed, which is attributable to a high light scattering loss in ADs. These findings suggest the validity of PA measurement for monitoring the adhesion of grafted ADs.

Pulmonary blast injury in mice: A novel model for studying blast injury in the laboratory using laser‐induced stress waves

Primary blast injury is produced by shock waves. Blast injuries to lungs are extremely critical threats to survival, but their etiology is largely undefined. The majority of animal models for these injuries use explosive or complex experimental settings, limiting the laboratory study of blast injury. The aim of this study was to establish a small-animal model for blast injuries, using laser-induced stress waves (LISWs) with high controllability, high reproducibility, and easy experimental settings. LISWs were used to produce isolated pulmonary blast effects in mice. An LISW was generated by the irradiation of an elastic laser target with 532-nm nanosecond laser pulses of a Q-switched Nd:YAG laser. Histopathological evaluations of damage to lung tissue were conducted to estimate the relevance between peak pressure and trauma intensity. Blood pressure, heart rate, and percutaneous oxygen saturation were monitored for 60 minutes. We could flexibly control the peak pressure of the shock wave by varying the laser energy. Non-lethal doses of LISWs caused pulmonary contusions with alveolar hemorrhages depending on peak pressure. Pulmonary contusion was observed only in areas that were exposed to LISWs, allowing study of isolated injuries without concomitant ones. These injuries caused decreased blood pressure, heart rate, and percutaneous oxygen saturation, immediately after LISW exposure. Mice exposed to thoracic LISWs showed pathologic and physiologic changes similar to those seen in other studies in this area, and in clinical practice. Our newly developed model allows fine management of trauma intensity, and concomitant injuries of the exposed animals were limited. This novel mouse model of blast injury using LISWs is suitable for detailed studies of blast lung contusion and other blast injuries in the laboratory.

Fe_3O_4-Ag nanocomposites for optical limiting: broad temporal response and low threshold

We report the observation of optical limiting in Fe(3)O(4)-Ag nanocomposites in solution. With these nanocomposites, we demonstrate that broad temporal optical limiting can be accomplished with low limiting threshold. Due to the presence of Ag nanoparticles, nonlinear scattering gives rise to enhanced optical limiting responses to 532-nm nanosecond laser pulses, with a limiting threshold comparable to carbon nanotubes. As exposed to 780-nm femtosecond laser pulses, the largest value (approximately 10(-44) cm(4)s photon(-1) or 10(6) GM) for two-photon absorption cross-sections reported to date results in superior limiting responses with a limiting threshold as low as 0.04 J/cm(2) or 100 GW/cm(2) for Fe(3)O(4)-Ag (7nm) solution in 1 cm quartz cell. The limiting threshold can be further reduced by increasing Ag particle size through plasmon enhancement or taking advantage of self-defocusing.

Cleaning of artificially soiled paper with 532-nm nanosecond laser radiation

Cleaning of paper is a challenging task due to the fact that a contamination should be removed and a fragile organic original material has to be preserved. Pulsed laser cleaning of artificially soiled Whatman© filter paper samples serving as models for historical paper was performed. Different cleaning strategies employing 8-ns laser pulses at 532 nm wavelength were applied to clean paper avoiding undesired effects like discoloration (yellowing) and mechanical deterioration of the substrate. Multi shot experiments with low-energy pulses were compared with single pulse investigations utilizing high pulse energies achieving a constant energy load incident on the samples in both cases. The cleaning efficiency and possible yellowing effects were evaluated by means of a multi spectral imaging system. An extensive microscopic analysis of the cleaned parts of the samples provided insight into the remaining soiling on the surface and in the bulk of the paper material after laser treatment. As a reference, a hard and a soft eraser were used to clean the samples.

Formation mechanisms of small fragment ions in nanosecond laser induced fragmentation of C60

The time of flight mass spectrometric technique was used to determine the initial mean kinetic energy of small fragment ions C+n (n≤11) produced from C60 excited by 532nm nanosecond laser pulses. The measured kinetic energy shows little variation with the fragment mass and the laser fluence in a broad range. Based on the assumption that C+30 is produced predominantly by a single electron emission followed by successive C2 evaporation from hot C60 in the nanosecond laser field，the formation of small fragments is interpreted as the complete breakup of the unstable C+30 cage structure. The interpretation is consistent with the previously observed results.

Photoacoustic monitoring of neovascularities in grafted skin

In skin grafting, evaluation of graft adhesion to the recipient site in the early postgrafting period is important. However, conventional diagnoses such as visual observation and thermography required about 1 week to obtain results and these methods cannot give quantitative information on the adhesion of a skin graft. We proposed a new method for monitoring adhesion of grafted skin that is based on measurement of photoacoustic signals. To investigate the validity of the method, we performed experiments using rat autografts models. Grafted skin in a rat was irradiated with 200 microJ, 532-nm nanosecond laser pulses, and photoacoustic signals were detected with a piezoelectric transducer placed on the skin at various postgrafting time. Temporal profiles of the signals were converted to depth profiles using an assumed sound velocity of 1,500 m/second. Histological analysis was performed to observe neovascularities formed in the grafts. At 6 hours postgrafting, a photoacoustic signal peak appeared in the depth region corresponding to the graft. The results of histological analysis also showed formation of neovascularities in the graft after 6 hours postgrafting, indicating that photoacoustic signal peaks observed in the graft originated from the neovascularities, which are an indication of graft adhesion. For up to 24 hours postgrafting, no significant difference was observed between the results of visual observation and laser Doppler imaging of the same grafted skins. We have demonstrated that photoacoustic signals originating from neovascularities in grafts can be sensitively detected in the early postgrafting period, suggesting the validity of photoacoustic measurement for adhesion monitoring of skin grafts.

Femtosecond laser induced photochemical reaction and configuration change of silver nanorod clusters in aqueous solution

The photochemical reaction processes and configuration change of the silver nanorod clusters in aqueous medium exposed by an 800-nm femtosecond laser and a 532-nm nanosecond laser were studied by surface plasma absorption spectra and transmission electron microscopy. The results indicate that the clusters were quickly fragmented into small nanospheres through the ejection of electrons. Then, the size of the nanospheres decreased gradually due to a series of photochemistry reactions in the surface of Ag nanospheres. Femtosecond laser has better ability to change the size and shape of the material than nanosecond laser.