Laser stimulated piezoelectricity in Er3+ doped GeO2–Bi2O3 glasses containing silicon nanocrystals

We report the first observation of the laser stimulated piezoelectricity in Er³⁺ doped GeO₂–Bi₂O₃ glasses containing silicon nanocrystals, prepared using the simple well known melt quenching technique. Two split beams originated from the same nanosecond lasers were used for the performance of the bicolor laser treatment.The fundamental (λ = 1064 nm) and the doubled frequency (λ = 532 nm) signal of a pulsed nanosecond Nd:YAG laser, as the fundamental (λ = 1540 nm) and the doubled frequency (λ = 770 nm) signal of an Er:glass laser were used.The ratio of power densities between the fundamental and the doubled frequency beams has been varied from 4:1 to 8:1. This value was chosen to achieve the maximum output photoinduced piezoelectric response. The present photoinduced piezoelectricity effect opens a new road for obtaining optically operated piezoelectric devices in germanate composites doped with rare-earth ions.     

Biomolecular urease thin films grown by laser techniques for blood diagnostic applications

Matrix assisted pulsed laser evaporation (MAPLE) was used for growing urease thin films designed for bio-sensor applications in clinical diagnostics. The targets exposed to laser radiation were made from a frozen composite manufactured by dissolving biomaterials in distilled water. We used a UV KrF* (λ = 248 nm, τ_FWHM ? 30 ns, ν = 10 Hz) excimer source for multipulse laser irradiation of the frozen targets cooled with Peltier elements. The laser source was operated at an incident fluence of 0.4 J/cm². Urease activity and kinetics were assayed by the Worthington method that monitors urea hydrolysis by coupling ammonia production to a glutamate dehydrogenase reaction. A decrease in absorbance was measured at 340 nm and correlated with the enzymatic activity of urease. We show that the urease films obtained by MAPLE techniques remain active up to three months after deposition.     

Experimental study on the CO2 laser cutting of carbon fiber reinforced plastic composite

Promotion of massive application of carbon fiber reinforced plastics (CFRPs) in the industry can be accomplished by using faster and more flexible technologies such as laser cutting. The anisotropic and heterogeneous features of the CFRP make laser processing very challenging.A comprehensive study on the cut performance of a CO₂ laser to process sheets (3 mm thick) of a CFRP composite is presented. A high-beam quality CO₂ laser has been used in order to ascertain the capabilities of CO₂ laser cutting machines, widely used in metalworking applications, on the machining of this material. On the other hand, the influence of processing parameters, in both CW and pulsed mode, on the cut quality was studied.Cuts with a minimum heat affected zone, about 540 μm, were achieved using a high-beam quality CO₂ laser working in pulsed mode. In consequence, the CFRP strength remains practically unaffected compared to more conventional mechanical machining.     

Effect of solidification parameters on the microstructure of Sn-3.7Ag-0.9Zn solder

In this work, Sn–Ag–Zn alloy of eutectic composition (Sn-3.7wt.%Ag-0.9wt.%Zn) was directionally solidified upward at a constant temperature gradient (G = 4.33 K/mm) in a wide range of growth rates (V = 3.38–220.12 μm/s) and a constant growth rate (V = 11.52 μm/s) with different temperature gradients (G = 4.33–12.41 K/mm) using a Bridgman type directional solidification furnace. The microstructure was observed to be a rod Ag₃Sn structure in the matrix of β–Sn from the directionally solidified Sn-3.7wt.%Ag-0.9wt.%Zn samples. The values of eutectic spacing (λ) were measured from transverse section of samples. The dependency of eutectic spacing on the growth rate (V) and temperature gradient (G) were determined with linear regression analysis. The dependency of λ on the values of V and G were found to be λ = 10.42V ^? 0.53 and λ = 0.27G ^? 0.48, respectively. The values of bulk growth were also determined to be λ²V = 86.39 μm³/s by using the measured values of λ and V. The results obtained in present work were compared with the previous similar experimental results obtained for binary and ternary alloys.     

Compositional variation of photoluminescence from Mn doped MgAl2O4 spinel

Spinel (MgAl₂O₄) crystals doped with 1.0% Mn have been grown by floating zone (FZ) technique with various Mg compositions, x = MgO/Al₂O₃, from 0.2 to 1.0. Compositional variations of photoluminescence are evaluated for a fluorescence thermometer application using crystals grown. Strong photoluminescence (PL) peak is observed at λ from 512 to 520 nm from the crystals grown from compositions, x, from 0.3 to 1.0. Peak wavelength of PL increases linearly from 512 to 520 nm with x. Weak PL peaking at λ = 750 nm is also observed from the specimens. Compositional variations of PL are considered to be due to the variation of crystal field surrounding the Mn²⁺ ions. The variation of crystal field strength agrees with the compositional variation of lattice constant.     

Effect of growth rate on microstructure parameters and microhardness in directionally solidified Ti–49Al alloy

Intermetallics Ti–49Al (at.%) alloy was directionally solidified with different growth rates (V = 5 μm/s–30 μm/s) at a constant temperature gradient (G = 12.1 K/mm) by using a Bridgman type directional solidification furnace. The primary dendritic spacing (λ), interlamellar spacing (λ_L), and microhardness (HV) were measured. Effect of V on HV, λ and λ_L was experimental investigated. The dependencies of λ, λ_L and HV on the growth rate were determined by using linear regressing analysis. According to the result, the values of λ and λ_L decrease with the increasing of V, and the values of HV increase with the increasing of V and with the decreasing of λ and λ_L. The results were compared with previous similar experimental results for TiAl-based alloys.     

Optical constants and crystal chemical parameters of Sc2W3O12

The refractive indices of Sc₂W₃O₁₂, measured at wavelengths of 435.8–643.8 nm, were used to calculate n_a = 1.7331, n_b = 1.7510, n_c = 1.7586 at λ = 589.3 nm and n_∞ values at λ = ∞ from a one-term Sellmeier equation. Mean refractive indices, 〈n_D〉, and mean dispersion values, 〈A〉, are, respectively, 1.7475 and 110 × 10^?16 m². Total electronic polarizabilities, α_obs, were calculated from n_∞ and the Lorenz–Lorentz equation. The unusually large difference between the observed polarizability of 28.415 Å³ and the calculated total polarizability α_T of 26.74 Å³ (Δ = +6.3%) is attributed to (1) a large M–O–W angle, and (2) a high degree of W 5d–O 2p and Sc nd–O 2p hybridization, where n signifies unspecified Sc d orbitals.     

In-vivo study of adhesion and bone growth around implanted laser groove/RGD-functionalized Ti-6Al-4V pins in rabbit femurs

Titanium surfaces were designed, produced, and evaluated for levels of osseointegration into the femurs of rabbits. A total of 36 Ti-6Al-4V pins (15 mm length, 1.64 mm diameter) were prepared into three experimental groups. These were designed to test the effects of osseointegration on laser grooved, RGD coated, and polished control surfaces, as well as combined effects. Circumferential laser grooves were introduced onto pin surfaces (40 μm spacing) using a UV laser (λ = 355 nm). The tripeptide sequence, Arginine-Glycine-Aspartic acid (RGD), was functionalized onto laser grooved surfaces. Of the prepared samples, surface morphology and chemistry were analyzed using scanning electron microscopy (SEM) and Immunoflourescence (IF) spectroscopy, respectively. The experimental pin surfaces were surgically implanted into rabbit femurs. The samples were then harvested and evaluated histologically. Sections of the sample were preserved in a methylmethacralate mold, sliced via a hard microtome, and polished systematically. In the case of the RGD coated and laser grooved surfaces, histological results showed accelerated bone growth into the implant, pull-out tests were also used to compare the adhesion between bone and the titanium pins with/without laser textures and/or RGD coatings.     

UV-laser-assisted fluorination of polymers

PMMA (Polymethylmethacrylate) substrate was covered with 1,2,3,5-tetrafluorobenzene by spin-coating. Then the sample was irradiated by a KrF-excimer laser (λ = 248 nm). After drying out the polymeric substrate, the sample surface was investigated by SEM and EDX indicating some fluorine content at the top of the sample layer. A UV-photochemical fluorination mechanism is proposed.     

Defect detection in CFRP by infrared thermography with CO2 Laser excitation compared to conventional lock-in infrared thermography

This paper presents a NDT by a CO₂ Laser infrared thermography applied to defect detection in CFRP. The CO₂ Laser is an infrared laser with the wavelength of 10.6 μm. This excitation has a controllable heating beam by a geometric relation D = 0.01575·d, which allows to heat the samples at a specific position (placed at the distance “d”) and area (of a diameter “D”). The PPT interpretation principle was used to reduce the non-uniformity’s effect of the excitation causing inhomogeneous heat. The test with this excitation is much faster than the tests with conventional lock-in thermography method.     

Characterization of bromocresol green and resin as holographic film

We present a film composed by bromocresol green (BCG) dye and resin mixed with isopropyl alcohol as photosensitive emulsion. In this film, we have recorded phase gratings with the emission line λ = 457 nm of an argon laser. The characterization of this film indicates us a diffraction efficiency of 2.27%; and its simple fabrication and low cost make this film an attractive option for holographic elements.     

Synthesis and optical properties of photochromic perinaphthothioindigo

(1,2-naphtho)(1,8-naphtho)thioindigo (PNT) has been synthesized following a simple Friedel–Crafts route and its photochemical properties in toluene and polymethylmethacrylate (PMMA) have been characterized. PNT is a photochromic molecule capable of reversible photoisomerization between a yellow form (cis-PNT, λ_max = 484 nm) and a purple form (trans-PNT, λ_max = 595 nm). The stable purple form converts to the yellow form with a trans-PNT to cis-PNT conversion quantum yield of 0.027 in toluene and 0.062 in PMMA. The unstable yellow form exhibits a cis-PNT to trans-PNT quantum efficiency of conversion of 0.27–0.85 in toluene and 0.17–0.68 PMMA, with highest conversion efficiency occurring in the vicinity of its λ_max of 484 nm. trans-PNT has a strong fluorescence quantum yield, 0.14 (toluene) and 0.16 (PMMA). For samples prepared photochemically in the cis-PNT form, slow thermal relaxation to the trans form occurs in the dark, with a half life of about 17 h in toluene (25 °C) and even slower, 168 h, in PMMA. The property of photoswitching between fluorescent and non-fluorescent forms makes this material a candidate for many applications in imaging and data storage.     

Analysis of a diode-pumped passively Q-switched Nd:GdVO4 self-stimulating Raman laser

This paper presents the theoretical and experimental results of a laser diode-pumped passively Q-switched Nd:GdVO₄ self-Raman laser in detail. In the experiment, by using two Cr⁴⁺:YAG crystals with different initial transmissions as the saturable absorber, using Nd:GdVO₄ as the gain medium and Raman medium simultaneously, the passively Q-switched operation of the Nd:GdVO₄ self-Raman laser at 1176 nm was investigated. The average power, pulse energy, pulse width and pulse repetition rate with respect to the incident pump power were measured. The obtained maximum output average power is 244.6 mW with respect to incident power of 5.7 W and the corresponding conversion efficiency is 4.3%. In the theoretical part, we used the rate equations to obtain the theoretical results. In the rate equations, the Gaussian distributions of the intracavity photon densities of the fundamental and Raman lasers and the initial population-inversion density were taken into account, and the ground-state population density of the saturable absorber at t = 0 is assumed to be uniform. The obtained theoretical results were in agreement with the experimental results on the whole.     

Spectroscopic properties of Sm3+-doped oxy-fluoride powders with various Sm3+ concentration and sintering temperature

Sm³⁺-doped oxy-fluoride (OFSm) powders are prepared by the melt quenching technique and characterized using FE-SEM, optical absorption and emission techniques. Spectroscopic properties of Sm³⁺-doped oxy-fluoride powders with different Sm³⁺ concentration and sintering temperature are presented and discussed by using the absorption, emission measurements. The Judd–Ofelt intensity (J–O) parameters (Ω_λ, where λ = 2, 4 and 6), measured from the experimental oscillator strengths of the absorption spectra, are used to evaluate the radiative parameters of the fluorescence transitions. Intense orange emission can be obtained when excited with 325 nm wavelength by increasing the sintering temperature to 1400 °C. Ratio of fluorescence intensities arising from the two closing lying ⁴F_3/2 and ⁴G_5/2 levels is studied, concentration quenching has been noticed beyond 2 mol% of Sm³⁺ ions concentration. The excellent spectroscopic properties along with the outstanding thermal stability suggest that the OFSm03 powders may become an attractive laser material to exhibit efficient visible lasing emission in the orange spectral region.     

The luminescent properties of Er3+–Yb3+-doped fluorophosphate fiber glass preforms at high temperatures

Optical properties of fluorophosphate Er³⁺–Yb³⁺ fiber preforms with different concentrations of ErF₃ and YbF₃ are investigated in the temperature interval 25–300 °C. The temperature-dependent absorption spectra and luminescence at 1535 nm (under the λ = 970 nm excitation) spectra as well as the ⁴I_13/2 → ⁴I_15/2 luminescence decay times are used to compute the luminescence cross-section σ_e(λ). Our results show that in the range of the temperature investigated the quenching effect due to the temperature increase weakly affects the luminescence cross-section and decay time, which make these materials promising for fiber-optics applications.     

Investigation of laser pulse fatigue effect on unpainted and painted CFRP structures

Laser ultrasonic based nondestructive evaluation (NDE) techniques are being increasingly used in aerospace industries. Generally, the service lifetime for an aircraft could be more than 25 years. Thus, the composite structures of the aircraft could be susceptible to laser pulse fatigue damage caused by the laser pulse energy in the long-term repetitive maintenance inspection. In this paper, the effect of repeat laser pulse scanning on the mechanical characteristics of unpainted and painted CFRP specimens (USN175BX Carbon UD prepreg, Bisphenol A epoxy resin) is investigated to verify the reliability regarding the use of laser ultrasonic scanning based NDE techniques on the inspection of the CFRP structure. A high-speed laser ultrasonic scanning system is setup to perform repeat scanning of 1300 times on both CFRP specimens at the five laser pulse energy levels using the 532-nm and 1064-nm Q-switched continuous wave lasers. Elastic modulus assessment based on the ultrasonic Lamb wave pitch–catch method is used and the surface condition of the scanned area is investigated by a microscope. As a result, the laser pulse fluences that is shown in this paper are suitable for the long-term repetitive maintenance inspection in unpainted and painted CFRP structure even if it demonstrates an embrittlement phenomenon similar to the modulus measurement resolution in the unpainted CFRP specimen. In addition, the laser pulse fluence for maximum signal-to-noise ratio without any damage is investigated in both unpainted and painted CFRP specimens. As a result, both 102.45 mJ/cm² in unpainted CFRP specimen and 51 mJ/cm² in painted CFRP specimen can be the laser pulse energy for the maximum signal-to-noise ratio without any damage.     

Investigation of CFRP laser milling using a 30 W Q-switched Yb:YAG fiber laser: Effect of process parameters on removal mechanisms and HAZ formation

A study on laser machining of Carbon Fibre Reinforced Polymer (CFRP) is presented. Experimental tests were carried out on a 4 mm thick CFRP sheet, using a Q-switched 30 W Yb:YAG fiber laser. The aim of the paper is to detect which process parameters and how they affect the laser beam–material interaction, and to explain the effect of the process parameters on the removal mechanisms and HAZ formation. The process parameters examined were: the laser beam scan speed, the pulse frequency, the number of repetitions of the geometric pattern, the distance between two consecutive scan lines and the scanning strategy. The ANalysis Of VAriance (ANOVA) was applied to a two-level factorial design, specifically developed for this aim. Experimental results showed the presence of different interaction mechanisms such as: ablation, matrix burning and mechanical effect. The damage mechanisms and the influence of the process parameters on the HAZ extent are discussed too.     

Efficient laser operation at 1.06 μm in co-doped Lu3+, Nd3+:GdCa4O(BO3)3 single crystal

Efficient laser emission at 1.06 μm was obtained from a diode-laser quasi-continuous wave pumped Nd_0.04Gd_0.86Lu_0.10Ca₄O(BO₃)₃ (Nd:GdLuCOB) single crystal. An uncoated, 6.0-mm long, ZX-cut Nd:GdLuCOB medium yielded laser pulses with 1.76 W peak power for absorbed pump pulses of 5.49 W peak power, corresponding to an overall optical-to-optical efficiency η_oa = 0.32; the slope efficiency was η_sa = 0.44. Comparison is made with an uncoated XY-cut Nd:GdCOB medium (4.0-at.% Nd doping and 6.8-mm length) from which laser pulses with 1.74 W peak power (at optical efficiency η_oa = 0.25) and 0.31 slope efficiency were obtained. The improvements in laser emission of Nd:GdLuCOB at the fundamental wavelength are important for future self-frequency doubling in ZX principal plane of this crystal.     

Polarized spectral properties of Sm3+:LiLuF4 crystal for visible laser application

A Sm³⁺-doped LiLuF₄ single crystal was grown by the vertical Bridgman–Stockbarge technique. Polarized absorption spectra, polarized fluorescence spectra, and fluorescence lifetime of the Sm³⁺:LiLuF₄ crystal were recorded at room temperature. Based on the Judd–Ofelt theory, spectral parameters of the Sm³⁺:LiLuF₄ crystal were calculated. Emission cross sections for the ⁴G_5/2 → ⁶H_J (J = 5/2, 7/2, 9/2, and 11/2) transitions with special interest for visible laser application were obtained by the Füchtbauer–Ladenburg formula. The results indicate that the Sm³⁺:LiLuF₄ crystal may be a potential laser gain medium operating in visible region pumped by diode lasers around 401 nm.     

Threshold crack growth behavior of shear and tensile cracks

Crack-face interference-free mode I and mode II crack-growth data was combined with smooth axial (λ = ε_xy/ε_xx = 0) and torsional (λ = ∞) endurance limit data to develop unified crack growth models that incorporate both shear and tensile cracking. The crack growth models incorporated growth from a slip band (including short crack behavior) size crack until the final failure of a long crack, and the ability to switch between crack growth on shear planes to growth on tensile planes. The models successfully predicted smooth specimen crack-face interference-free fatigue lives and gave reasonable estimates of the smooth specimen endurance limits of crack-face interference free tubular tests run at intermediate strain ratios (λ = 3/4, 3/2, and 3). The series of Kitigawa–Takahashi (threshold fatigue) diagrams developed from the models help illustrate the competition between shear and tensile cracking at the fatigue limit under crack-face interference-free crack growth.