CW Green Laser Research Articles

Energy-efficient microwelding of copper by continuous-wave green laser: Insights into nanoparticle-assisted absorptivity enhancement

As a highly reflective material, copper has been difficult to weld with IR lasers. Short-wavelength (400–600 nm) lasers offer promising solutions to copper welding due to significant increases in absorptivity (to > 50 %). In this work, we present an experimental study on copper welding by CW green laser. We unveil that nanoparticles redeposited on the copper surface from the vaporized plume can strongly modify the surface condition and result in significant enhancement of the surface absorptivity. The absorptivity can be theoretically enhanced by nanoparticles up to 82 % compared to the polished copper surface. Assisted by this absorptivity enhancement, the threshold power density (critical laser intensity) for copper melting is reduced by more than 50 %, so that continuous and smooth conductive welding tracks can be generated in energy-efficient manner. In situ deposition of nanoparticles generated upon cooling and oxidation of the vapor plume in the vicinity of the melt zone has been identified as the key mechanism of absorptivity enhancement. XPS measurements of the nanoparticles indicated that Cu2O is the dominant species in the redeposited nanoparticles. This study provides novel insights into the fundamental mechanisms in highly-reflective material welding by short-wavelength lasers and offers an opportunity for energy-efficient high-quality welding of highly-reflective material thin films, which can find numerous applications in consumer electronics and electric vehicles, as well as battery industries. Moreover, it enables a new process-material-environment design route for laser additive manufacturing of nanoparticle-reinforced metal matrix composites.

One-step metallization of weft-knitted fabrics for wearable biaxial strain sensors

One-step direct patterning of high definition conductive tracks in textiles is realized through laser direct writing in combination with a silver organometallic ink developed in-house. Photoreduction, nano-crystallization, and sintering are accomplished in one pass under the irradiation of a CW green laser light (λ = 532 nm) at moderate intensities (I ≥ 95 mW/mm2). By tailoring the surface tension and viscosity of the ink, high-definition conductive tracks are formed in weft-knitted polyester-Spandex composite fabrics, well-following the laser’s profile with negligible coffee stain effect. Length resistance as low as 4 Ω/cm is measured and anisotropy of the gauge factor as high as 25 is achieved. The metallized fabric exhibits reversible and hysteresis-free electromechanical responses subject to high strains. Durability assessment qualifies that the as-metallized strain sensors are able to sustain their performance for over 5000 stretch/release cycles, demonstrating its potential applications in biaxial strain sensing and interactive smart textiles.

Absorptivity measurements during laser powder bed fusion of pure copper with a 1 kW cw green laser

A 1 kW CW green laser source operating at 515 nm was used to investigate the absorptivity of pure copper powder beds and pure copper substrates. Various interaction regimes were considered, ranging from the solid and/or powder layers, to the liquid state and up to the deep penetration keyhole regime. Reflectance measurements were carried out using an Ulbricht integrating sphere during static tests and single L-PBF tracks. For each experiment, absorptivity values were discussed using the real penetration depth observed on cross-section. Absorptivity values were found to be in relatively good agreement with analytical models of the powder bed and the keyhole regime absorptivity. Such results provide useful insight on the use of green wavelengths for the optimization of the L-PBF process on highly reflective and conductive materials like copper.

A novel chlorocadmate hybrid cocrystal delivering intermolecular charge transfer enhanced nonlinear optical properties and optical limiting

Employing the donor-acceptor configuration of cocrystals, the intermolecular charge transfer enhanced third order nonlinear optical properties and the optical limiting behaviour of a novel chlorocadmate cocrystal Cd 2 Cl 6 OH 2 2 C 4 H 12 N 2 n ( 1 ) are reported. Optimization of crystal growth parameters is discussed to achieve bulk single crystal with reduced crystal defects by slow solvent evaporation technique. The acid hydrolysis of the piperazine molecule during the pH optimization converted it into piperazine-1,4-diium, which is neutralized by Cd 2 Cl 6 OH 2 2 2 - via hydrogen bond interactions. The intermolecular charge transfer responsible for optical nonlinearity in 1 is proved possible by calculating the intermolecular interaction energies at HF/3-21G level of quantum mechanical calculations. The two-photon absorption coefficient measured at different nanosecond pulsed laser intensities is found to vary, which explicitly confirmed sequential 2 PA in 1 . Lower optical limiting threshold of 1 measured under CW and nanosecond pulsed green laser regime ( ( 1.027 ± 0.02 ) × 10 3 Wcm -2 and ( 1.87 ± 0.02 ) × 10 12 Wm -2 respectively) with coherent dielectric, thermal, mechanical, linear absorption and emission properties showed its suitability for an efficient optical limiting device application. • A Novel intermolecular charge transfer cocrystal for NLO applications is reported. • Sequential two-photon absorption was conclusively proved from intensity-dependent β. • Intermolecular charge transfer interactions assisted optical nonlinearity is proved possible in the title material. • Third order nonlinear optical susceptibility (χ (3) ) of title cocrystal is found to be (0.527 ± 0.008) × 10 −6 esu. • Optical limiting threshold of title cocrystal for nano pulsed (100 mJ, 532 nm) and CW (100 mW, 532 nm) laser irradiance are calculated.

Technological and optical methods for increasing the spatial resolution of thermochemical laser writing on thin metal films

Various techniques, effects, and factors are examined that enable one to increase the spatial resolution of thermochemical direct laser writing on thin metal films. A few specific conditions of experimental laser processing with the focused beam of a CW green laser are investigated therewith. One of the goals of this work was to find a suitable metal and its thickness that would make it possible to implement the through-oxidation regime. When properly adjusting a value of laser exposure, this regime was found to be very useful for increasing the spatial resolution of the laser writing. This is due to bleaching of an oxidized film near the peak of a focused laser spot. Apart from the experimental results concerning the technology of laser processing of the metal films, in this work, there are also considered some ways of reducing a focused spot size used for the direct laser writing.

Laser excitation dependent nonlinear absorption of 2-Amino 5-Nitropyridinium dihydrogen phosphate

Laser excitation and intensity-dependent third-order nonlinear optical (NLO) absorption properties of 2-amino 5-nitropyridinium dihydrogen phosphate (2A5NPDP) in both pulsed (532 nm, 5 ns, 100 µJ) and continuous wave (532 nm, 50 mW) regime were studied by Z-scan experiment. Under CW laser excitation, 2A5NPDP exhibits saturable absorption (SA) ascribed to be of thermo-optic origin. Interestingly the sample show reverse saturable absorption (RSA) due to genuine two-photon absorption (2PA) process under nano pulsed laser excitation. Earlier thermodynamic properties such as thermal conductivity (51 W/m.K), specific heat capacity (3894 J/Kg.K) and thermal diffusivity (7.5 × 10−6 m2/s) were estimated theoretically from the DSC curves. Thus 2A5NPDP with excellent thermal stability and high NLO coefficients can be utilized as an energy-absorbing optical limiter and saturable absorber under nano pulsed and CW green laser excitation.

Energy absorbing and energy spreading optical limiting action of 2-amino 5-nitropyridinium derivatives

By Nd:YAG green laser driven Z-scan experiment, nonlinear optical properties of 2-amino 5-nitropyridinium derivatives (2A5NPCl and 2A5NPBr) are studied. Both the samples exhibit genuine 2 PA induced electro-optic based optical limiting action process under pulsed (5 ns, 100 μJ) mode. And they display self-defocusing promoted thermo-optic based optical limiting action under continuous wave (50 mW) mode. NLO coefficients and thermodynamic properties of 2A5NPBr is higher than 2A5NPCl. Results show 2A5NPBr molecular liquids are superior for energy absorbing and energy spreading optical limiting applications to prevent the laser damages from nano pulsed and CW green laser excitation.

Write – Read all-Optical System Based on Diffraction Ring Patterns in Aloe, Cresson and Taramira Vegetable Oils.

Multiple diffraction ring patterns appeared in Aloe , Cresson and Taramira oils under irradiation with cw blue (473 nm ) laser light beam . No ring patterns appeared in these oils using the green cw ( 532 nm) and red cw ( 635nm ) laser light beams . As a result of irradiation of these oils with the blue beam together with the green or with red beam or with both green and red beams together, blue and green , blue and red , and blue , green and red rings appeared respectively at very low input powers of the green and red beams . The number of rings produced by the green and red lights are totally controlled by the blue beam input power and not by their input powers . By this technique .we have established a write ( by the blue beam ) – Read ( by the green and red beams ) all optical system in these three oils

Plasmon-mediated discrete diffraction behaviour of an array of responsive waveguides.

We investigate the discrete diffraction phenomenon in a Polymer-Liquid Crystal-Polymer Slices (POLICRYPS) overlaying a random distribution of gold nanoparticles (AuNPs, plasmonic elements). We study the propagation of a CW green laser beam through the waveguide structure as a function of beam polarization, laser intensity and sample temperature. It turns out that the plasmonic field created at the interface between AuNPs and POLICRYPS waveguides enables and stabilizes the optical field propagation within the responsive nematic liquid crystal channels. The active role of the liquid crystal is pointed out by a polarization, temperature and beam divergence experimental analysis and evidenced by a peculiar trumpet-shaped discrete diffraction pattern. Theoretical simulations confirm that the observed optical behavior is governed by the interaction of the nematic liquid crystal with optical and plasmonic fields.

Experimental investigation of thermal effects in laser-nanofluid interaction by moiré technique

Interaction of a CW laser with a nonlinear medium leads to some thermal phenomena. Thermal lensing, which changes the distribution of the refractive index of the medium in the interacting area, is the most important phenomenon among them. Moiré deflectometry is a known technique for measuring the profile of refractive index. In this work, by using nonscanning moiré deflectometry, the refractive index profile in the interaction region of a graphene oxide nanofluid sample and a green CW laser is measured. Using the thermal diffusion equation, the thermo-optical coefficient is calculated. The obtained thermo-optical coefficient value is in good agreement with value from other methods. Having the thermo-optical coefficient and three-dimensional profile of the refractive index, the three-dimensional distribution of temperature is obtained. Although this method is inexpensive and simple, it is applicable for liquid, solid, and gas samples.

Single-frequency linear orthogonally polarized modes resulting in unidirectional traveling wave cavity green laser

A narrow linewidth (∼ 8 MHz , instrument limited) CW green laser at 532 nm is demonstrated in linear orthogonally polarized modes resulting in an unidirectional travelling wave cavity using intracavity second-harmonic generation technique with 250-mW output power.

Wideband fluorescence-based thermometry by neural network recognition: Photothermal application with 10 ns time resolution

Neural network recognition of features of the fluorescence spectrum of a thermosensitive probe is exploited in order to achieve fluorescence-based thermometry with an accuracy of 200 mK with 100 MHz bandwidth, and with high robustness against fluctuations of the probe laser intensity used. The concept is implemented on a rhodamine B dyed mixture of copper chloride and glycerol, and the temperature dependent fluorescence is investigated in the temperature range between 234 K and 311 K. The spatial dependence of the calibrated amplitude and phase of photothermally induced temperature oscillations along the axis of the excitation laser are determined at different modulation frequencies. The spatial and frequency dependence of the extracted temperature signals is well fitted by a 1D multi-layer thermal diffusion model. In a time domain implementation of the approach, the gradual temperature rise due to the accumulation of the DC component of the heat flux supplied by repetitive laser pulses as well the immediate transient temperature evolution after each single pulse is extracted from acquired temporal sequences of fluorescence spectra induced by a CW green laser. A stroboscopic implementation of fluorescence thermometry, using a pulsed fluorescence evoking probe laser, is shown to achieve remote detection of temperature changes with a time resolution of 10 ns.

Tunable vacuum ultraviolet laser based spectrometer for angle resolved photoemission spectroscopy

We have developed an angle-resolved photoemission spectrometer with tunable vacuum ultraviolet laser as a photon source. The photon source is based on the fourth harmonic generation of a near IR beam from a Ti:sapphire laser pumped by a CW green laser and tunable between 5.3 eV and 7 eV. The most important part of the set-up is a compact, vacuum enclosed fourth harmonic generator based on potassium beryllium fluoroborate crystals, grown hydrothermally in the US. This source can deliver a photon flux of over 10(14) photon/s. We demonstrate that this energy range is sufficient to measure the k(z) dispersion in an iron arsenic high temperature superconductor, which was previously only possible at synchrotron facilities.

Third-order nonlinear optical properties of silver nanoparticles mediated by chitosan

Silver nanoparticles in chitosan medium were prepared by the chemical reduction method. Silver nitrate and hydrazine were used as the precursor and reducing agent in the present of chitosan as a natural host polymer. The samples are characterized by UV–visible spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The measurements of nonlinear optical properties were defined by Z-scan technique using green CW laser beam operated at 532nm wavelengths. Thermal effect has a dominant role in the overall material nonlinearity with CW laser. It is shown that the synthesized samples have a negative nonlinear refractive index.

Size-Dependent Photothermal Conversion Efficiencies of Plasmonically Heated Gold Nanoparticles

We report the light-to-heat energy transfer efficiencies of gold nanoparticles with variable sizes by assessing the temperature profiles of laser-activated particle suspensions in water. Gold nanoparticles with sizes ranging from 5 to 50 nm were synthesized by chemical reduction methods using sodium borohydride, sodium citrate, or hydroquinone as reducing agents. As-synthesized gold nanoparticle solution (1 mL) was loaded into a quartz cuvette and exposed to a CW green laser (532 nm). Heat input into the system by energy transfer from nanoparticles equals heat dissipation at thermal equilibrium. The transducing efficiency was then determined by plotting temperature increase as a function of laser power extinction. The efficiency increases from 0.650 ± 0.012 to 0.803 ± 0.008 as the particle size decreases from 50.09 ± 2.34 to 4.98 ± 0.59 nm, respectively. The results indicate that the photothermal properties of gold nanoparticles are size-tunable, and the variation of efficiency can be correlated to the absorption/extinction ratios calculated by Mie theory for different particle sizes. We further expanded our Mie theory calculations of absorption/extinction ratios to a broader range of diameters and wavelengths. These studies are crucial for practical applications of gold nanoparticles in nanotechnology and bioengineering, such as enhancing the treatment efficiency of laser surgery.

Single-Beam Optical Biosensing Based on Enzyme-Linked Laser Nanopolymerization of o-Phenylenediamine

We report an innovative biosensing technique using a focused laser beam for the fabrication of a polymer nanostructure and the detection of its nanoscale growth. A nanoaggregate structure is formed by focusing a single beam of a continuous-wave (cw) green laser beam on an o-phenylenediamine (o-pD) solution dropped on a glass substrate. The backreflection intensity of the focused laser beam shows a temporal oscillation, whereas the size of the aggregate monotonously increases. Simple calculations based on the Fresnel equation qualitatively reproduce the experimental results, indicating that the backreflected laser oscillation occurs because of the interference between two beams reflected at the front and the back surfaces of the aggregate. Because the growth speed of the aggregate depends on light absorption by the oxidized o-PD, the backreflection oscillation curve can be used to monitor the oxidative reaction in the solution. We apply this phenomena to optical biosensing based on the oxidation of o-PD by the peroxidase enzyme reaction. A reliable quantification of glucose can be achieved by simply focusing a single laser beam and detecting its reflection intensity in a manner similar to the optical pickup unit of optical storage drives.

Generating a 2.4-W cw Green Laser by Intra-Cavity Frequency Doubling of a Diode-Pumped Nd:GdVO4 Laser with a MgO:PPLN Crystal

High-power cw green laser radiation is generated by intra-cavity frequency doubling of a diode-pumped Nd:GdVO4 laser with a MgO-doped periodically-poled LiNbO3 (MgO:PPLN) crystal at room temperature. An average power of 2.4 W at 0.53 μm is obtained under the pump 15 W at 808 nm, corresponding to an overall optical-to-optical conversion efficiency of 16%. The M2 factor of the green beam is 3.90 and 1.34 for the horizontal and vertical direction, respectively. In addition, the power fluctuation is measured to be about ±5%.

Diode-pumped laser and self-frequency-doubling properties of a Nd^3+:Na_3La_9O_3(BO_3)_8 crystal

We report efficient, diode-pumped, self-frequency doubling (SFD) in the newly developed laser crystal Nd3+:Na3La9O3(BO3)8 (Nd:NLBO). More than 730 mW of fundamental output power at 1072 nm was achieved with a slope efficiency of 16.2%. With incident pump power of 8 W, 29 mW of green cw laser emission at 536 nm was observed with proper phase matching. This initial performance and the good optical properties of the crystalline host are encouraging for the development of a high power diode-pumped SFD visible light laser source.

P‐12: Self‐Aligned Bottom Gate LTPS Backplanes without Ion‐Implantation Process

AbstractWe developed and fabricated self‐aligned bottom gate LTPS backplanes without ion‐implantation process. CW green laser is used to fabricate polycrystalline silicon, and self‐alignment photo‐sensitive SiO coating film is used as a channel etch stopper. For high performance TFT backplanes, we developed CMOS process that allows us to operate CMOS circuits. Our developed TFT shows high mobility and high reliability.

15.4: Backplane Process Technology for AMOLEDs with Bottom‐Gate TFTs and Laser Annealing

AbstractTFT backplane process for AM‐OLED was developed by integrating a G8 compatible CW green laser annealing into conventional bottom‐gate TFT process. Novel coating channel‐etching‐stopper (CES) and contact doping processes achieved the same high TFT performance as LTPS without critically increasing extra process steps.