YAG Laser System Research Articles

Study on laser welding of austenitic stainless steel by varying incident angle of pulsed laser beam

In the present work, AISI 304 stainless steel sheets are laser welded in butt joint configuration using a robotic control 600W pulsed Nd:YAG laser system. The objective of the work is of twofold. Firstly, the study aims to find out the effect of incident angle on the weld pool geometry, microstructure and tensile property of the welded joints. Secondly, a set of experiments are conducted, according to response surface design, to investigate the effects of process parameters, namely, incident angle of laser beam, laser power and welding speed, on ultimate tensile strength by developing a second order polynomial equation. Study with three different incident angle of laser beam 89.7deg, 85.5deg and 83deghas been presented in this work. It is observed that the weld pool geometry has been significantly altered with the deviation in incident angle. The weld pool shape at the top surface has been altered from semispherical or nearly spherical shape to tear drop shape with decrease in incident angle. Simultaneously, planer, fine columnar dendritic and coarse columnar dendritic structures have been observed at 89.7deg, 85.5deg and 83deg incident angle respectively. Weld metals with 85.5deg incident angle has higher fraction of carbide and δ-ferrite precipitation in the austenitic matrix compared to other weld conditions. Hence, weld metal of 85.5deg incident angle achieved higher micro-hardness of ∼280HV and tensile strength of 579.26MPa followed by 89.7deg and 83deg incident angle welds. Furthermore, the predicted maximum value of ultimate tensile strength of 580.50MPahas been achieved for 85.95deg incident angle using the developed equation where other two optimum parameter settings have been obtained as laser power of 455.52W and welding speed of 4.95mm/s. This observation has been satisfactorily validated by three confirmatory tests.

Building and Characterization of Q-Switched Pulsed Nd:YAG Laser Range Finder Transmitter

A passive Q-switched pulsed Nd:YAG laser system was built for TOF (time-of-flight) laser range finder. The main goal is to build a TOF laser rangefinder transmitter operating at 1064 nm with 25 mJ output energy, 22 mm beam diameter, 15 ns pulse width, 0.5 mrad beam divergence. Construction and characterization of the laser cavity components including the function of the component for the laser transmitter and factor affect the performance are presented. In our design it is possible to use the transmitter in other applications using its compact dimension and power supply mobility by using batteries and also exploiting the narrow angle of the output transmitter with power reaches distance up to 15 km.

Opacity effects on soft X-ray spectra from highly charged lanthanide ions in laser-produced plasmas

We have observed soft X-ray spectra from highly charged ions of seven different lanthanide elements with atomic numbers ranging from 60 to 70 in laser-produced plasmas (LPPs) using CO2 and Nd:YAG laser systems, the wavelengths of which are 10.6μm and 1.064μm, respectively. The spectral feature drastically changes between the two types of LPPs due primarily to the difference in opacity. Narrowband quasicontinuum features arising from n=4–4 transitions, the centre wavelength of which systematically moves to shorter wavelength as the atomic number (Z) increases, are observed in the CO2 LPPs, accompanied by sharp peaks coinciding with the strongest resonance lines of Pd-like ions for lower Z elements. In contrast, the quasicontinuum bands are broader and smoother in the Nd:YAG LPPs, appearing with bands of n=4–5 transitions on the shorter wavelength side. The results are also discussed based on comparisons with atomic structure calculations for ions with outermost 4d and 4f subshells.

Laser Melting of High Thermal Conductivity Steel (HTCS) Surface

This paper presents a laser melting of high thermal conductivity steel (HTCS) dies for surface properties modification due to die failures during operations. Sample were cut from as-received die without any defect or crack. Melting process was conducted using Nd:YAG laser system with pulse mode at 50 W average power. The laser beam was defocused to a spot size of 1 mm on the sample surface. Parameters controlled in this study were peak power of 800 and 1200 W, and pulse repetition frequency of 80 and 90 Hz. Metallographic study and chemical composition analysis were conducted using Hitachi TM3030Plus scanning electron microscope (SEM) and energy dispersive x-ray spectrometer (EDXS). Surface roughness was measured using Mitutoyo SURFTEST SJ-410 stylus profilometer. Hardness properties of the modified layer were characterized by Wilson Hardness tester at 100 N force. The metallographic study showed high porosity at partially melted zone (PMZ) area. From overall findings, laser processing parameter affected hardness properties and surface roughness of modified layer. Where the surface roughness value obtained is between 1.49 and 3.15 μm, while the hardness value is between 550.9 and 610.9 HV0.1. These findings are significant to parameters selection for hot stamping die surface repair and prolong its service.

53 W average power CEP-stabilized OPCPA system delivering 5.5 TW few cycle pulses at 1 kHz repetition rate.

We present a high peak and average power optical parametric chirped pulse amplification system driven by diode-pumped Yb:KGW and Nd:YAG lasers running at 1 kHz repetition rate. The advanced architecture of the system allows us to achieve >53 W average power combined with 5.5 TW peak power, along with sub-220 mrad CEP stability and sub-9 fs pulse duration at a center wavelength around 880 nm. Broadband, background-free, passively CEP stabilized seed pulses are produced in a series of cascaded optical parametric amplifiers pumped by the Yb:KGW laser, while a diode-pumped Nd:YAG laser system provides multi-mJ pump pulses for power amplification stages. Excellent stability of output parameters over 16 hours of continuous operation is demonstrated.

High beam quality 5 J, 200 Hz Nd:YAG laser system

High beam quality 5 J, 200 Hz Nd:YAG laser system

Shot-noise-limited laser power stabilization for the AEI 10 m Prototype interferometer.

The AEI 10 m Prototype interferometer is an experiment to investigate the standard quantum limit of interferometry and, in particular, its relevance in gravitational-wave detection. As such it has stringent requirements on the power stability of its high-power light source. In this Letter we present the power stabilization concept of the 35 W Nd:YAG laser system used in the AEI 10 m Prototype. With a shot-noise-limited multiphotodetector sensing scheme we achieved a relative power noise level of 1.8×10-9 Hz-1/2 in a frequency band of 100 Hz to 1 kHz. The limiting noise sources at lower and higher frequencies are analyzed, and possible improvements on the power noise sensing are discussed.

Micro-Bulges Investigation on Laser Modified Tool Steel Surface

This paper presents micro-bulges investigation on laser modified tool steel. The aim of this study is to understand the effect of laser irradiance and interaction time on surface morphology configuration. An Nd:YAG laser system with TEM00 pulse processing mode was used to modify the samples. Metallographic study shows samples were analyzed for focal position effect on melted pool size, angle of peaks geometry and laser modified layer depth. Surface morphology were analyzed for surface roughness. Laser modified layer shows depth ranged between 42.22 and 420.12 μm. Angle of peak bulge was found to be increase with increasing peak power. The maximum roughness, Ra, achieved in modified H13 was 21.10 μm. These findings are significant to enhance surface properties of laser modified steel and cast iron for dies and high wear resistance applications.

Nonlinear Mechanooptical Transmittance Controlled by a Rotating TiO2 Thin Solid Film with Embedded Bimetallic Au-Pt Nanoparticles

The modification in the third-order nonlinear optical behavior exhibited by a titanium dioxide thin solid film with embedded Gold-Platinum nanoparticles was induced by nanosecond optical pulses. A Nd:YAG laser system was employed for the experiments explored by a vectorial two-wave mixing method with the sample in rotation. The nanostructures were prepared by a sol-gel technique. Transmission Electron Microscopy studies and ultraviolet-optical spectroscopy measurements were undertaken. The evolution of the optical transmittance exhibited by the sample in rotation controlled by a servomechanism was observed. Potential applications for developing mechanooptical functions based on third-order optical nonlinearities were contemplated.

Stone Retropulsion with Ho: YAG and Tm: YAG Lasers: A Clinical Practice-Oriented Experimental Study.

To compare the retropulsion of stones with the use of holmium: yttrium aluminum garnet (Ho: YAG) laser and thulium: yttrium aluminum garnet (Tm: YAG) laser in settings that could be used in clinical practice. The experimental configuration included a glass tube set in a water bath filled with physiologic saline. Plaster of Paris stones were inserted in the tube. Tm: YAG and Ho: YAG laser systems were used along with a high-speed slow-motion camera. The lasers were activated with different settings. The displacement of the stone was measured according to a custom-made algorithm. Ho: YAG: the retropulsion of stones was the lowest with the energy setting of 0.5 J and the frequency of 20 Hz with long pulse duration. The highest retropulsion was observed in the case of 3 J, 5 Hz, and short pulse. Tm: YAG: the retropulsion of stones was the lowest with the energy setting of 1 J and the frequency of 10 Hz with either long or short pulse duration. Practically, there was no retropulsion at all. The highest retropulsion was observed in the case of 8 J, 5 Hz, and short pulse. Ho: YAG laser has a linear increase in stone retropulsion with increased pulse energy. On the other hand, the retropulsion rate was kept to the minimum with Tm: YAG as much as the energy level of 8 J. The activation of lasers with short pulse resulted in further displacement of the stone. Lower frequency with the same power setting seemed to result in further stone retropulsion. Higher power with the same frequency setting resulted in further displacement of the stone.

Droplet-based, high-brightness extreme ultraviolet laser plasma source for metrology

We report on the development of a high brightness source of extreme ultraviolet radiation (EUV) with a working wavelength of 13.5 nm. The source is based on a laser-produced plasma driven by pulsed radiation of a Nd:YAG laser system. Liquid droplets of Sn-In eutectic alloy were used as the source fuel. The droplets were created by a droplet generator operating in the jet break-up regime. The EUV emission properties of the plasma, including the emission spectrum, time profile, and conversion efficiency of laser radiation into useful 13.5 nm photons, have been characterized. Using the shadowgraphy technique, we demonstrated the production of corpuscular debris by the plasma source and the influence of the plasma on the neighboring droplet targets. The high-frequency laser operation was simulated by usage of the dual pulse regime. Based on the experimental results, we discuss the physical phenomena that could affect the source operation at high repetition rates. Finally, we estimate that an average source br...

The effect of NiB additive on surface morphology and microstructure of 316L stainless steel single tracks and layers obtained by SLM

Abstract Stainless steel (316L) powder and mixed 316L-1wt.%NiB powders were melted by laser irradiation. Laser employed was pulsed, millisecond Nd:YAG laser system. The relationship between major process variables – average laser power, laser scan speed, number of spots, pulse energy, pulse duration, pulse frequency – of selective laser melting, and their effect on the structure of single tracks and single layers in case of 316L and 316L-NiB alloys has been investigated. The morphology, macro- and microstructure of laser melted samples were characterized by digital camera and by scanning electron microscope with an energy dispersive X-ray spectrometer. Surface roughness of the layers was measured using optical profilometer. It was determined that the addition of NiB to 316L stainless steel powder provides much better surface quality and wider set of parameters for successful melting.

Studies on the growth aspects, structural, thermal, dielectric and third order nonlinear optical properties of solution grown 4-methylpyridinium p-nitrophenolate single crystal

An ionic organic optical crystal of 4-methylpyridinium p-nitrophenolate was grown from methanol by slow evaporation method at ambient temperature. Powder and single crystal X-ray diffraction studies revealed the crystal system and its crystalline perfection. The rocking curve recorded from HRXRD study confirmed the crystal quality. FTIR spectral analysis confirmed the functional groups present in the title compound. UV–visible spectral study revealed the optical window and band gap of grown crystal. The thermal, electrical and surface laser damage threshold properties of harvested crystal were examined by using TGA/DTA, LCR/Impedance Analyzer and Nd:YAG laser system respectively. The third order nonlinear optical property of grown crystal was elucidated by Z-scan technique.

Quantitative picosecond laser-induced fluorescence measurements of nitric oxide in flames

Quantitative concentrations measurements using time-resolved laser-induced fluorescence have been demonstrated for nitric oxide (NO) in flame. Fluorescence lifetimes measured using a picosecond Nd:YAG laser and optical parametric amplifier system have been used to directly compensate the measured signal for collisional quenching and evaluate NO concentration. The full evaluation also includes the spectral overlap between the ∼15cm−1 broad laser pulse and multiple NO absorption lines as well as the populations of the probed energy levels. Effective fluorescence lifetimes of 1.2 and 1.5ns were measured in prepared NO/N2/O2 mixtures at ambient pressure and temperature and in a premixed NH3-seeded CH4/N2/O2 flame, respectively. Concentrations evaluated from measurements in NO/N2/O2 mixtures with NO concentrations of 100–600ppm were in agreement with set values within 3% at higher concentrations. An accuracy of 13% was estimated by analysis of experimental uncertainties. An NO profile measured in the flame showed concentrations of ∼1000ppm in the post-flame region and is in good agreement with NO concentrations predicted by a chemical mechanism for NH3 combustion. An accuracy of 16% was estimated for the flame measurements. The direct concentration evaluation from time-resolved fluorescence allows for quantitative measurements in flames where the composition of major species and their collisional quenching on the probed species is unknown. In particular, this is valid for non-stationary turbulent combustion and implementation of the presented approach for measurements under such conditions is discussed.

Two-beam combined 3.36 J, 100 Hz diode-pumped high beam quality Nd:YAG laser system.

In this paper, we develop a diode-pumped all-solid-state high-energy and high beam quality Nd:YAG laser system. A master oscillator power amplifier structure is used to provide a high pulse energy laser output with a high repetition rate. In order to decrease the amplifier working current so as to reduce the impact of the thermal effect on the beam quality, a beam splitting-amplifying-combining scheme is adopted. The energy extraction efficiency of the laser system is 50.68%. We achieve 3.36 J pulse energy at a 100 Hz repetition rate with a pulse duration of 7.1 ns, a far-field beam spot 1.71 times the diffraction limit, and 1.07% energy stability (RMS).

Bond strengths of brackets bonded to enamel surfaces conditioned with femtosecond and Er:YAG laser systems.

The aim of this study was to compare femtosecond and Er:YAG laser systems with regard to enamel demineralization and bracket bond strength. Human-extracted premolars were randomized to three groups (n = 17) depending on the conditioning treatment used for the buccal surfaces: 37% orthophosphoric acid, Er:YAG laser etching (MSP mode 120mJ, 10Hz, 1.2W), and femtosecond laser etching (0.4W, 800nm, 90fs/pulse, 1kHz). Metal brackets were bonded with Transbond XT to the conditioned surfaces and light cured for 20s. The samples were thermocycled (5000cycles, 5-55°C) and subjected to shear bond strength (SBS) testing using a universal testing machine. Failure types were analyzed under an optical stereomicroscope and SEM. The adhesive remnant index (ARI) was evaluated to assess residual adhesive on the enamel surface. The results revealed no significant differences in SBS between the Er:YAG laser (7.2 ± 3.3MPa) and acid etching groups (7.3 ± 2.7MPa; p < 0.05), whereas a significant difference was observed between the femtosecond laser etching group (3.3 ± 1.2MPa) and the other two groups (p < 0.01). ARI scores were significantly different among the three groups. The results of our study suggest that laser conditioning with an Er:YAG system results in successful etching, similar to that obtained with acid. The sole use of a femtosecond laser system may not provide an adequate bond strength at the bracket-enamel interface.

Evaluation of temperature rises during the application of different power levels of potassium titanyl phosphate and neodymium-doped:yttrium aluminum garnet lasers to external primary root canals

Background/purposeNowadays, laser systems play crucial roles in endodontic treatments. Therefore, these systems should be investigated in terms of parameters that may prevent periodontal tissues damages during laser irradiation. In this context, the purpose of this study was to evaluate temperature rises during the application of different power levels of potassium titanyl phosphate (KTP) and neodymium-doped:yttrium aluminum garnet (Nd:YAG) lasers to external primary root canals. Materials and methodsSixty primary mandibular molars were selected and chemomechanical preparation was performed. KTP laser treatment was applied to 30 of these 60 samples and the remaining 30 received Nd:YAG laser treatment. The teeth samples received laser application (KTP or Nd:YAG) at three different power levels (1 W, 1.5 W, and 2 W, respectively, applied to 10 samples from each group). Nine holes were drilled (1 mm in diameter) through the level of the coronal, middle, and apical third of each tooth canal to provide entry for a Type L thermocouple wire, which was used to measure temperature changes. Data were assessed with two-way analysis of variance and the Tukey test. ResultsAll power levels indicated statistically significant differences between Nd:YAG and KTP laser systems (P < 0.05). Moreover, the same regional (apical, middle, and coronal) comparisons performed between Nd:YAG and KTP laser systems showed statistically significant differences (P < 0.05). ConclusionAll parameters of KTP laser indicated lower temperature rises than Nd:YAG laser. Therefore, KTP laser may be preferable to protect the periodontal tissues from harmful thermal effects during the endodontic treatment of primary root canals.

In vivo optical monitoring of transcutaneous delivery of calcium carbonate microcontainers.

We have developed a method for delivery of biocompatible CaCO3 microcontainers (4.0 ± 0.8 µm) containing Fe3O4 nanoparticles (14 ± 5 nm) into skin in vivo using fractional laser microablation (FLMA) provided by a pulsed Er:YAG laser system. Six laboratory rats have been used for the microcontainer delivery and weekly monitoring implemented using an optical coherence tomography and a standard histological analysis. The use of FLMA allowed for delivery of the microcontainers to the depth about 300 μm and creation of a depot in dermis. On the seventh day we have observed the dissolving of the microcontainers and the release of nanoparticles into dermis.

High efficiency Tm:YAG slab laser with hundred-watts-level output power

We report on a hundred-watts-level high power Tm:YAG slab laser system operating at room temperature. The laser has a threshold pump power of 46.7 W, benefiting from the good mode matching of an end-pumping scheme and the excellent heat-dissipation capability of our cooling system. At 350 W of incident pump power, 100 W of output power at ∼2015 nm has been generated, corresponding to a slope efficiency of 33.6% with respect to the incident pump power and an optical-to-optical conversion efficiency of 28.6%. As far as we know, this is the highest optical-to-optical conversion efficiency so far achieved in a high power Tm:YAG laser system operating at a hundred-watts level.

Quantitative fuel vapor/air mixing imaging in droplet/gas regions of an evaporating spray flow using filtered Rayleigh scattering.

This Letter demonstrates the application of filtered Rayleigh scattering (FRS) for quantitative two-dimensional fuel vapor/air mixing measurements in an evaporating hydrocarbon fuel spray flow. Using the FRS approach, gas-phase measurements are made in the presence of liquid-phase droplets without interference. Effective suppression of the liquid-phase droplet scattering using FRS is enabled by the high spectral purity of the current Nd:YAG laser system. Simultaneous Mie-scattering imaging is used to visualize the droplet field and illustrate the droplet loading under which the FRS imaging is applied in the current spray flows. The initial quantification of the FRS imaging is based on calibration measurements from a flow cell of known fuel vapor/air mixtures, while future work targets the utilization of a Rayleigh-Brillouin spectral model for quantification of the FRS signals.