Rough surface absorption of Nd:YAG laser rods

The rough surface of Nd:YAG-laser rods exhibits a broad spectral absorption due to impurities. The optical density of the investigated surfaces was determined up to several percent in the near infrared and visible spectral range. The characteristics of the rough surface absorption was investigated.     

Laser-diode-pumped Nd:YAG active-mirror laser

We describe a simple design, laser-diode-pumped cw Nd:YAG active-mirror laser and present a thermal analysis of the crystal. A cw output power of 2.4 W and an M(2) beam quality value of less than 1.9 at an incident pumping power of 8.9 W were obtained. From the thermal analysis we predict that the output power can be increased by increasing the pump beam diameter and the pump power at a constant excitation density.     

Effect of a pulsed Nd:YAG laser irradiation on multi-walled carbon nanotubes film

Multi-walled carbon nanotubes (MWCNTs) film have been analyzed by Raman spectroscopy to clarify the effect of a pulsed Nd:YAG laser heating. The MWCNTs film surface was flashed with the fundamental harmonic (λ = 1064 nm) or the second harmonic (λ = 532 nm) of a single pulse of Nd:YAG laser in the air. The dynamics of pulsed nanosecond laser heating process was simulated by the solution of the one-dimensional heat conduction equation. At the laser fluence of 500 mJ/cm² with Nd:YAG laser (λ = 1064 nm), the surface reached the maximum temperature 1395 °C at 12 ns. Moreover, the Raman spectroscopy of MWCNTs films before and after irradiation were measured. The intensity of the two characteristic Raman shifts I_D (defect-mode) and I_G (graphite-mode) was measured by the Raman spectroscopy. The maximum surface temperature was calculated and compared with the I_G/I_D ratio of MWCNTs film. The graphitization occurred on the sample after irradiation.     

Segment side-pumped Q-switched Nd:YAG laser

In the design of conduction-cooled lasers, a side-pumped configuration is an attempt to solve the space conflict between pump and heat removal. The pump radiation always competes with the heat removal and mechanical support device for the lateral surface of a laser rod. This space conflict can be addressed by a segment side-pumped configuration in which circular laser diode arrays and heat-conducting rod holders alternate periodically along the length of the laser rod. This scheme permitted 11 Hz operation of a 190 mJ Q-switched laser at the wavelength of 1064 nm without the use of liquid cooling for both the laser rod and laser diode arrays and the corresponding optical-optical conversion efficiency of 23.1%. Thus, it has great potential to be used in compact and miniature laser systems.     

Doubly Q-switched tape casting YAG/Nd:YAG/YAG ceramic laser

A doubly Q-switched 1.06 μm pulsed laser using a novel tape casting YAG/Nd:YAG/YAG composite ceramic with a sandwich structure was demonstrated for the first time. Compared to purely acousto-optical (AO) Q-switching, this laser using an AO Q-switch and Cr⁴⁺:YAG saturable absorber simultaneously can generate shorter pulses. The pulsed laser performance was investigated at two modulated repetition rates of 10 and 20 kHz.     

Diode-laser-pumped Nd:YAG laser injection seeding system

We have designed and tested a compact injection seeding system consisting of a diode-laser-pumped Nd:YAG master oscillator and a permanent-magnet Faraday isolator. With active resonator frequency stabilization, this system permits highly reliable single-axial-mode operation of a Q-switched Nd:YAG laser over a period of hours. The system is capable of injection seeding both stable and unstable resonator designs and is suitable for injection seeding commercial lasers with only minor modifications.     

Crystal growth induced by Nd:YAG laser irradiation in patterning glass ceramic substrates with dots

In this work a glass ceramic substrate was processed by focusing a laser beam inside the said material. The crystal phase within the amorphous matrix provides mechanical properties to the glass ceramic substrate in such a way that dots can be patterned inside the fore-mentioned material without producing any cracks. These marks are made up of crystals, the growth of which has been induced by the laser beam. These inner structures can modify the optical, thermal and mechanical properties of the glass ceramic substrate.A Q-switched Nd:YAG laser at its fundamental wavelength of 1064 nm with pulsewidths in the nanosecond range has been used.Morphology, composition, microstructure, mechanical and thermal properties of the processed material are described.     

Studies of graphite surface after laser irradiation

Graphite was irradiated by CO₂ laser of energy 10J and pulse width 4 μs. SEM and XRD examinations were carried out before and after laser irradiation. It was observed that XRD pattern changed after irradiation and new entities were seen on surface. Amorphous graphite was also irradiated and it was found that it became partly crystalline. The changes were explained on the basis of phase changes induced by high pressures and temperatures during laser irradiation.     

Laser surface hardening of AISI 420 stainless steel treated by pulsed Nd:YAG laser

The AISI 420 martensitic stainless steel was surface-hardened by a pulsed Nd:YAG laser. The influences of process parameters (laser pulse energy, duration time and travel speed) on the depth and hardness of laser treated area and its corrosion behavior were Investigated. In the optimum process parameters, maximum hardness (490 VHN) in the laser surface treated area was achieved. The pitting corrosion behavior was studied by potentiodynamic polarization technique in 3.5% NaCl solution at 25 °C. Metallographical and electrochemical corrosion studies illustrated beneficial effects of laser surface hardening by refining the microstructure and enhancing the pitting corrosion resistance of the martensitic stainless steel. The pitting corrosion resistance of laser surface treated samples in 3.5% NaCl solution depends on the overlap ratio clearly. The pitting potential (E_pp) decreased significantly by increasing the ratio of pulse overlapping.     

Diode-pumped 100-W green Nd:YAG rod laser

We developed a diode-pumped high-average-power Nd:YAG green laser. By use of a monolithic diffusive reflector having three slits and a rod with low doping concentration, uniform distribution of excited Nd ions could be achieved. Uniform distribution in the rod reduced thermal birefringence. We employed a Z-shaped cavity to have a constant beam size at the frequency-doubling crystal independent of thermal lensing in the rod. The pulse width and green power dependence on the pump power were analyzed. A maximum green power of 101 W was obtained when the total pump power was 398 W. The optical-to-optical conversion efficiency was as high as 25.4%.     

Compact scalable diode-pumped Nd:YAG ceramic slab laser

We describe our preliminary studies of the use of neodymium-doped slab-shaped ceramic YAG media in the construction of compact, rugged, high-power diode-pumped solid-state lasers. A maximum extraction of more than 160 W at a 20% slope efficiency level, with a narrow transverse direction beam-parameter product of the order of 4 mm mrad(-1) is experimentally obtained from an extremely simple and compact (overall dimensions 160 mm x 100 mm x 60 mm) laser head in a quasi-continuous-wave regime. Experimental data together with finite-elements method simulations indicate that power extraction can be scaled up at least to 900 W cw with this laser head geometry.     

Characterization of plasma propulsion by Nd:YAG laser

Significant propulsion parameters, specific impulse and coupling coefficient for the different metallic pendulums are presented. 4 N (99.99%) pure, solid targets are in the form of foils of aluminium, copper and gold. The targets are irradiated by Q-switched pulsed Nd:YAG laser (1064 nm, 10 mJ, 1.1 MW, 9-14 ns) under standard conditions of temperature and pressure. Plasma plume of these targets is also observed by employing CCD (BOSCH LTC0510, monochrome camera) based, computer controlled image capturing system and it was seen that expansion of plasma plume for oscillating targets is anisotropic in air. The results reveal that not only very high exhaust velocity of propellant 10⁶ m/s is achieved but also very specific impulse values of Al, Cu and Au targets (3.14 × 10⁶ s, 1.37 × 10⁷ s, 7.16 × 10⁵ s respectively) are obtained. Coupling coefficients are for Al, Cu and Au were 1.54 × 10³ (N-s/J), 1.88 × 10³ (N-s/J), and 1.08 × 10³ (N-s/J) respectively.     

Beam quality after propagation of Nd:YAG laser light through large-core optical fibers

Laser beam characteristics are altered during propagation through large-core optical fibers. The distribution of modes excited by the input laser beam is modified by means of mode coupling on transmission through the fiber, leading to spatial dispersion of the profile and, ultimately and unavoidably, to degradation in the quality of the delivered beam unless the beam is spatially filtered with consequent power loss. Furthermore, a mismatch between the intensity profile of a typical focused high-power laser beam and the profile of the step-index fiber gives rise to additional beam-quality degradation. Modern materials processing applications demand ever higher delivered beam qualities (as measured by a parameter such as M(2)) to achieve greater machining precision and efficiency, a demand that is currently in conflict with the desire to utilize the convenience and flexibility of large-core fiber-optic beam delivery. We present a detailed experimental investigation of the principal beam-quality degradation effects associated with fiber-optic beam delivery and use numerical modeling to aid an initial discussion of the causes of such degradation.     

Nd:YAG laser surface melting of aluminium alloy 6013 for improving pitting corrosion fatigue resistance

Laser surface treatment of aluminium alloy 6013 was conducted with the aim of improving the alloy’s resistance to pitting corrosion fatigue. The study showed that laser melting using a high power Nd:YAG laser increased the resistance of the alloy to pitting corrosion and pitting corrosion fatigue. As corrosion pits are favourable sites for the initiation of fatigue cracks, and the process of crack initiation often takes up most of the fatigue life, especially at low stress levels, a high pitting corrosion resistance resulted from the laser treatment improved fatigue crack initiation resistance. With regard to fatigue crack propagation, although interdendritic boundaries are vulnerable to corrosion attacks due to the presence of second phase particles, nonetheless, due to the nature of the rough and undulating fracture surface, fatigue growth would be retarded. Under the present experimental conditions, the improvement in corrosion resistance brought about by laser surface melting was found to prevail over the adverse effect caused by the residual stresses induced by laser melting.     

Nonlinear optical investigations on Al doping ratio in ZnO thin film under pulsed Nd:YAG laser irradiation

In the present study, it has been reported on the effect of Al doping on linear and nonlinear optical properties of ZnO thin films synthesized by spray pyrolysis method. The structural properties of ZnO thin films with different Al doping levels (0–4 wt%) were analyzed using X-ray diffraction (XRD). The results obtained from XRD analysis indicated that the grain size decreased as the Al doping value increased. The UV–Vis diffused refraction spectroscopy was used for calculation of band gap. The optical band gap of Al-doped ZnO (AZO) thin films is increased from 3.26 to 3.31 eV with increasing the Al content from 0 to 4 wt%. The measurements of nonlinear optical properties of AZO thin films have been performed using a nanosecond Nd:YAG pulse laser at 532 nm by the Z-scan technique. The undoped ZnO thin film exhibits reverse saturation absorption (RSA) whereas the AZO thin films exhibit saturation absorption (SA) that shows RSA to SA process with adding Al to ZnO structure under laser irradiation. On the other hand, all the films showed a self-defocusing phenomenon because the photons of laser stay on below the absorption edge of the ZnO and AZO films. The third-order nonlinear optical susceptibility, χ⁽³⁾, of AZO thin films, was varied from of the order of 10^?5–10^?4 esu. The results suggest that AZO thin films may be promising candidates for nonlinear optical applications.     

Cracking in Be/Al Nd: YAG laser weld

An investigation was conducted to determine the cause of weld cracking in laser Be/Al weldments. In agreement with earlier studies, features consistent with hot shortness cracking on the fracture surfaces were observed. Closer examinations of the fusion zone crack regions reveal that the cracking was a result of thermal stress, shape of weld roots and impurities segregation. The defects are related to the weld parameters. The cracks easily nucleate at conduction mode weld and blowholes easily appear at keyhole mode weld.