Wave CO2 Laser Research Articles

Study on the Quality of Quasi-Isotropic Composite Laminates Containing a Circular Hole

Composite structures used in modern engineering applications are often subjected to circular holes in order to join with metal components via riveting, bolting or pinning joints. These design based holes will interrupt the force flux in the direction of the fibers and create high stress concentrations near the notched area. Objective of the project is to understand the quality of the quasi-isotropic composite laminates ([45°, -45°, 0°, 90°]S) containing circular hole. To achieve this objective, a 3-phase portal milling machine and a 5kW continuous wave (cw) CO2 laser system were used to produce the circular holes in the composite laminates. The processing parameters for both the processes are varied to understand its influence. The quality of the circular hole produced by these methods are further investigated and compared in order to arrive at the optimum processing parameters for the given quasi-isotropic composite laminates.The hole qualities were evaluated by means of delamination factor caused by milling; cone angle, matrix evaporation for cw-CO2 laser system. For further comparisons, the optimal parameter combinations of both methods were selected for a tensile test according to the standard ASTM D5766-2002.

STUDY ON PERFORMANCE OF CO2 LASER IN PAINT REMOVAL OVER SELECTED NATIONAL CAR MODEL

A technique to determine the optimum parameters of 30 Watt Continuous Wave (CW) CO2 laser paint removal has been developed on national car coated substrate. This paper reports on the results of studies carried out on two different coating thicknesses; 196 µm and 201 µm using CW CO2 lasers operating at 10, 600 nm wavelength and relatively high beam power from 40%, 50%, 60%, 70%, 80% and 90% out of 30 Watt. Empirical data were presented to demonstrate the optimum power required for paint stripping process. Macro analysis was done to prove the stripping process was in line with the increase of power percentage applied, whereas microanalysis using EDX and SEM revealed the atomic composition and surface roughness of the crater.

Mid-IR fiber optic light source around 6 µm through parametric wavelength translation

We report a numerically designed highly nonlinear all-glass chalcogenide microstructured optical fiber (MOF) for the efficient generation of light around 6 µm through degenerate four-wave mixing by considering a continuous wave CO laser of 5–10 W power emitting at 5.6 µm as the pump. By tuning the pump wavelength, pump power, fiber dispersion and nonlinear properties, a narrow (N)- and/or broad (B)- band mid-IR all-fiber light source could be realized. Parametric amplification of more than 20 dB is achievable for the N-band source at 6.46 µm with a maximum power conversion efficiency (Cm) ~ 33%, while a amplification ~22 ± 2 dB is achievable for a B-band source over the wavelength range of 5–6.3 µm with a Cm > 40%.

Laser Surface Cladding of Plastic-Molded Steel 718H by CoCrMo Alloy

With the purpose of enhancing the surface properties of plastic-molded steel 718H, in this study, a wear-resistant CoMoCr alloy cladding layer was obtained using laser surface cladding technology. Laser surface cladding was carried out by melting the CoMoCr alloy powder (particle size 15-45 μm) supplied through a pneumatically driven powder delivery system with a 5-kW continuous wave (CW) CO2 laser with the wavelength 10.6 μm. The microstructure, chemical composition, and wear resistance of the cladding coating were revealed by optical microscope (OM), scanning electron microscope(SEM), energy-dispersive x-ray analysis (EDX) and sliding wear machine. The microstructure of the cladding layer was found to consist of three zones: a top cladding zone mainly comprising CoMoCr; an internal zone comprising a cellular microstructure; and the interface zone which was a mixture of CoMoCr and 718H substrate. Compared to the 718H steel substrate with a microhardness of 345 Hv, the microhardness of the cladding coating showed a significant improvement, with its value increasing to 794 Hv. The wear results confirmed that the wear resistance was enhanced after laser cladding CoMoCr alloy powder.

Temper and Wear Resistance of Wide-Band Laser Cladded WC Coating

High power continuous wave (CW) CO2 laser cladding was performed on H13 steel, pre-coated by superfine WC. After laser cladding, the materials were tempered for 6 hours. Scanning electronic microscopy (SEM) was used to observe the morphologies of the cladding layer. X-ray diffraction (XRD) was employed to analyze the microstructure of the cladding layer. The changes of microhardness, temper resistance and wear resistance were tested. The microhardness of cladding layer before tempering was 1.4 times of that of base metal and 1.9 times after tempering at 500°C. The wear resistance and tempering resistance were improved.

ChemInform Abstract: Dynamics of the Thermal Decomposition of 2,3-Diazabicyclo(2.2.1)hept-2- ene.

The dynamics of the thermal decomposition of 2,3-diazabicyclo [2.2.1] hept-2-ene (DBH) have been investigated over the temperature range 900-1400 K. A tunable continuous wave CO laser was used to follow the vibrational energy content of the coupled CO−N 2 system from the initial to the equilibrium conditions. It has been shown that the N 2 is born with very little vibrational energy, while the bicyclo [2.1.0] pentane is born with an excess over the equilibrium distribution. These results provide clear evidence against the concerted decomposition mechanism

Radio frequency energy coupling to high-pressure optically pumped nonequilibrium plasmas

This article presents an experimental demonstration of a high-pressure unconditionally stable nonequilibrium molecular plasma sustained by a combination of a continuous wave CO laser and a sub-breakdown radio frequency (rf) electric field. The plasma is sustained in a CO/N2 mixture containing trace amounts of NO or O2 at pressures of P=0.4–1.2 atm. The initial ionization of the gases is produced by an associative ionization mechanism in collisions of two CO molecules excited to high vibrational levels by resonance absorption of the CO laser radiation with subsequent vibration-vibration (V-V) pumping. Further vibrational excitation of both CO and N2 is produced by free electrons heated by the applied rf field, which in turn produces additional ionization of these species by the associative ionization mechanism. In the present experiments, the reduced electric field, E/N, is sufficiently low to preclude field-induced electron impact ionization. Unconditional stability of the resultant cold molecular plasma is enabled by the negative feedback between gas heating and the associative ionization rate. Trace amounts of nitric oxide or oxygen added to the baseline CO/N2 gas mixture considerably reduce the electron–ion dissociative recombination rate and thereby significantly increase the initial electron density. This allows triggering of the rf power coupling to the vibrational energy modes of the gas mixture. Vibrational level populations of CO and N2 are monitored by infrared emission spectroscopy and spontaneous Raman spectroscopy. The experiments demonstrate that the use of a sub-breakdown rf field in addition to the CO laser allows an increase of the plasma volume by about an order of magnitude. Also, CO infrared emission spectra show that with the rf voltage turned on the number of vibrationally excited CO molecules along the line of sight increase by a factor of 3–7. Finally, spontaneous Raman spectra of N2 show that with the rf voltage the vibrational temperature of nitrogen increases by up to 30%. This novel energy efficient approach allows sustaining large-volume high-pressure molecular plasmas without the use of a high-power CO laser. This opens a possibility of using the present technique for high-yield plasma chemical synthesis and plasma material processing.

Vibrational energy storage in high pressure mixtures of diatomic molecules

CO/N 2, CO/Ar/O 2, and CO/N 2/O 2 gas mixtures are optically pumped using a continuous wave CO laser. Carbon monoxide molecules absorb the laser radiation and transfer energy to nitrogen and oxygen by vibration–vibration energy exchange. Infrared emission and spontaneous Raman spectroscopy are used for diagnostics of optically pumped gases. The experiments demonstrate that strong vibrational disequilibrium can be sustained in diatomic gas mixtures at pressures up to 1 atm, with only a few Watts laser power available. At these conditions, measured first level vibrational temperatures of diatomic species are in the range T V=1900–2300 K for N 2, T V=2600–3800 K for CO, and T V=2200–2800 K for O 2. The translational–rotational temperature of the gases does not exceed T=700 K. Line-of-sight averaged CO vibrational level populations up to v=40 are inferred from infrared emission spectra. Vibrational level populations of CO ( v=0–8), N 2 ( v=0–4), and O 2 ( v=0–8) near the axis of the focused CO laser beam are inferred from the Raman spectra of these species. The results demonstrate a possibility of sustaining stable nonequilibrium plasmas in atmospheric pressure air seeded with a few percent of carbon monoxide. The obtained experimental data are compared with modeling calculations that incorporate both major processes of molecular energy transfer and diffusion of vibrationally excited species across the spatially nonuniform excitation region, showing reasonably good agreement.

Synthesis of metastable silver-nickel alloys by a novel laser-liquid-solid interaction technique

Metastable silver-nickel alloys have been synthesized by chemical wetness and laser-liquid-solid interaction techniques from nitrate and acetate precursors of silver and nickel. Ethylene glycol and 2-ethoxyethanol were used as reductants in the synthesis reactions. Rotating niobium substrates immersed in the liquid precursor were irradiated by a continuos wave CO2 and Nd-YAG laser (λ = 1064 nm). The powders were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and high-resolution transmission electron microscopy (HRTEM). Two-phase alloys containing silver, nickel, and oxygen were fabricated, and the shape of the particles was found to be dependent on laser parameters and the chemical composition of the precursor solution. The synthesis mechanism of non-equilibrium Ag-Ni alloy nanoparticles has been proposed to occur primarily at the laser-liquid-solid interface by a nucleation and growth mechanism.

Laser Processing of Thermal Sprayed Beryllium

The feasibility of using laser processing techniques to consolidate thermal sprayed beryllium deposits has been investigated. During these experiments both continuous wave CO2 and pulsed Nd-YAG lasers have been used to consolidate inert plasma sprayed and vacuum plasma sprayed beryllium deposits. Density of as-sprayed beryllium has been increased from <90% of theoretical to 100% through laser consolidation. Also, critical issues such as depth of consolidation and key processing parameters have been identified. A metallurgical analysis of these results is presented.

Rotationally resolved spectroscopy of the ([Ctilde]-[Xtilde] band of 15NH3 by infrared-ultraviolet double resonance

Double resonance measurements on 15NH3 in a free expansion jet are reported. These were carried out using a continuous wave (CW) CO2 laser and a pulsed ultraviolet (UV) laser system. Infrared radiation was used to prepare molecules in individual rotational levels of the v2=1 vibrational state of the electronic ground state of [15N]ammonia. These molecules were the photoionized via transitions of the [Ctilde]-[Xtilde] band in a (2+1) process using the doubled output of a pulsed dye laser. The ion signal was detected using a time of flight mass spectrometer. Two known coincidences between CO2 laser lines and individual rovibrational transitions of 15NH3 were used to populate the (J, K)=(5, 4) and (3, 0) symmetric levels of v2=1. Double resonance signals corresponding to O, P, Q, R, and S branch two photon transitions in the [Ctilde]-[Xtilde] band were observed and measured accurately. These data were augmented by conventional (2+1) REMPI measurements on the 20/0, 20/1, and 20/2 sub-bands of 15NH3: A complet...

Dynamics of the thermal decomposition of 2,3-diazabicyclo[2.2.1]hept-2-ene

The dynamics of the thermal decomposition of 2,3-diazabicyclo [2.2.1] hept-2-ene (DBH) have been investigated over the temperature range 900-1400 K. A tunable continuous wave CO laser was used to follow the vibrational energy content of the coupled CO−N 2 system from the initial to the equilibrium conditions. It has been shown that the N 2 is born with very little vibrational energy, while the bicyclo [2.1.0] pentane is born with an excess over the equilibrium distribution. These results provide clear evidence against the concerted decomposition mechanism

Laser Chemical Vapor Deposition Of Tin Films

AbstractWe have investigated the pyrolytic deposition of TiN thin films on molybdenum and 304 stainless steel substrates by continuous wave (CW) and pulsed CO2 (λ=10.6 μm) laser radiation. A flow rate of NH3: TiCl4 of 5:1 was maintained during the deposition process. The substrate temperature was controlled by varying the intensity of the incident laser irradiation. The TiN films were characterized by Transmission Electron Microscopy (TEM), Auger Electron Spectroscopy (AES) and Rutherford Backscattering Spectrometry (RBS). TEM results showed that the films were polycrystalline of equiaxed nature with diffraction patterns containing the characteristic TiN rings. The films had a lattice parameter of 4.24Å. AES results showed a slight incorporation of oxygen.

Switching of optically bistable devices by incoherent illuminations

We report the first observation of the external switching of an intrinsic optically bistable device by incoherent radiation. The device, consisting of an InSb etalon held at 85 K and optically biased by a continuous wave CO laser operating at 5.5 pm, was switched both from off to on resonance and from on to off resonance by using a photographic flashlamp. Results presented indicate that the required switching energy per unit area can be of the order of 100 fJ pm -2 .

Saturation of band-tail optical absorption in InSb

The optical absorption in InSb at 5 K, in the region just below the band-gap energy, is investigated as a function of the incident intensity by using a continuous wave CO laser. The linear spectrum agrees with previous measurements but saturation is seen at intensities more than about 1W/cm 2 . In the region where the linear absorption has been ascribed to acceptor-to-conduction-band transitions, the detailed variation of absorption with intensity agrees well with a saturation model developed in this paper. Nearer to the band-gap, the absorption shows some saturation at much lower intensities, and a non-saturating absorption tail is also resolved; the implications for possible absorption mechanisms are discussed.

A Simple Power Meter for Measuring Outputs from a High Power Continuous Wave (CW) CO2 Laser

The design of a power meter for measuring continuous wave (CW) outputs is presented. The principle of the operation is to measure the temperature rise at the surface of an aluminum slab that absorbs the energy of the incident 10.6 micron radiation. In order to make effective absorption, the surface is covered with a layer of Al203 of a few microns in thickness. Linear response to the incident power up to 200 W and allowable power density of more than 500 W/cm2 are attained.