Effect Of Laser Frequency Research Articles

Fabricating plasma bonded microfluidic chips by CO2 laser machining of PDMS by the application of viscoelastic particle focusing and droplet generation

In this study, direct CO2 laser machining of microchannels onto PDMS slabs and plasma bonding for sealing have been shown to provide the fastest method to fabricate PDMS microfluidic chips. Due to resolidification, the ashes and dust remains that cover the PDMS slab surface following this ablation process change the surface chemistry and prevent plasma bonding. Removing these remnants on the surface has been shown to be only possible via attaching and detaching a tape to the surface. The effect of laser frequency, speed and power settings has been investigated over the entire possible range with regards to channel geometry. The best laser settings were determined and the resulting output channels were examined under SEM and optical microscopes. PDMS spin coating after laser machining has been proposed as a pre-treatment process to improve the geometrical features of the channel. Water-in-oil droplet generation in the T-junction, as well as microparticle focusing in viscoelastic fluid – used to sample enrichment– have been shown as examples of applications that benefit from precise direct laser machined microchannels.

Polaron and bipolaron possibility in graphene nanoribons via laser

In this paper, we investigated the possible formation of polarons and bipolarons in graphene under a laser field. The LLP framework is used to solve the stated problem. We see that the laser greatly affects the properties of the polaron in graphene. We show that the laser also increases the first energy level of the polaron in the structure. It is shown that the laser can be used to modulate the band gap of the graphene. We have observed that the laser frequency enhances the polaron-polaron interaction and promotes the formation of bipolarons. Compared to the polaron, the effects of laser frequency and laser amplitude are opposite. Thus, the laser amplitude tends to reduce the energy of the bipolaron in the graphene. It is also observed that the laser amplitude increases the oscillation period of the polaron. Our results show that the bipolaron depends on an appropriate balance between the laser amplitude and frequency. Similarly, we found that the frequency at which the bipolaron is dynamically stable is the frequency at which the laser intensity increases.

The effect of laser frequency on roughness, microstructure, cell viability and attachment of Ti6Al4V alloy.

Titanium alloys are commonly used in orthopedic devices due to their good corrosion resistance, high specific strength and excellent biological response. The direct contact between the implant surface and the host tissue results in notable effect of surface properties such as surface topography on the biological responses. The aim of this study is to investigate the effect of frequency of pulsed Nd-YAG laser on Ti6Al4V alloy surface topography and its influence on the improvement of biocompatibility while other laser parameters kept constant. The range of applied frequency values were selected from 1 to 20Hz. The range of surface roughness was found between 452nm and 3.37μm. The untreated sample and also samples with the highest and the lowest average surface roughness parameter were subjected to the further analyses. Characterization of the samples was performed with surface roughness tester, Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM). The high rate of melt and solidification during the laser treatment led to the martensite formation and consequently an increase about 12-25% in hardness. Furthermore, in vitro study was carried out using MG-63 osteoblast like cells. The analyses of cell viability for 3 culture times, cell morphology and cell spreading area revealed that sample with the highest average surface roughness parameter is more biocompatible. 10Hz frequency was found as the optimum parameter which led to the highest surface roughness and thus the biocompatibility enhancement. In conclusion, the pulsed Nd-YAG laser with an optimum value of applied frequency can be utilized as an effective technique to improve the biological characteristics.

Wake field excitation and electron acceleration by triangular and sawtooth laser pulses in a plasma: an analytical approach

The amplitude of wake fields generated by the finite-width laser pulse propagating in an underdense plasma are determined using weakly nonlinear equations (n′e≪n0) for triangular (TR) and two types of sawtooth (SD and SI, defined in section 2) pulses by making the pulse duration the same as the electron plasma period. In addition to density perturbations ne′, the potential ϕ and the wake field Ez behind the laser pulses, the expression for the change in relativistic factor γ or energy gain for an electron is obtained and discussed for all these types of laser pulses under the effect of laser frequency f, pulse duration τ (corresponding to plasma density n0) and laser intensity I0. The TR pulse is found to be most significant as in this case the electrons can be accelerated up to hundreds of MeV (471.6 MeV) when τ = 6 ps, I0 = 1.0×1012 W m−2 and f = 282 THz (corresponding to Nd:YAG laser of wavelength 1.064 μm); even more acceleration is possible with prudently selected parameters.

Isotopic Effects in the Laser Control of Dissociative Ionization at High Intensities: Role of Permanent Dipole Moments†

Exact (non-Born-Oppenheimer) numerical solutions of the time-dependent Schrodinger equation for a 1-D model of the one-electron isotopomer systems H 2 +, HD + , and HT + have been obtained in a two-color laser control scheme, ω + 2w, of dissociation and dissociative ionization in the high-intensity (I ≥ 10 1 3 W/cm 2 ), nonlinear, nonperturbative regime of laser-molecule interaction. Calculations have been performed at the fundamental wavelengths λ C O 2 = 10.3 μm and λ Y A G = 1.064 μm in combination with their second harmonics in order to study the effect of laser frequency and permanent dipole moments on the electron-nuclear dynamics in the presence of periodic asymmetric fields. It is found that asymmetries occur in both the ionization and the dissociation. The phase sensitivity is shown to be quite different in the two wavelength regimes. Adiabatic and nonadiabatic quasistatic models of the dissociation and ionization processes are shown to offer simple interpretation of the calculated asymmetries in terms of tunneling ionization and barrier suppression dissociation.

Separation of tritium from deuterium by pulsed NH3 laser-selective multiple photon dissociation of CTCl3

The multiple photon dissociation of ppm level CTCl3 in CDCl3 and the selectivity of T/D separation were investigated using a pulsed ammonia laser. The effect of laser frequency, fluence and buffer gas pressure on the dissociation rate and isotopic selectivity were studied. The depletion of CDCl3 was not observed within experimental errors. A lower limit of single step selectivity factor was found to be >5000 at 133 Pa substrate pressure.

Behavior of phosphine in a focused CO2 laser beam

The energy absorption and decomposition of PH3 in a focused CO2 laser beam exhibit a threshold nature. The effect of laser frequency, pulse energy, pressure of PH3, and the presence of a foreign gas (neon) on the energy absorption and decomposition threshold were studied. The absorption of radiation increases sharply at threshold and is always accompanied by a visible luminescence. All the experimental facts can be explained in terms of an electron avalanche process, driven by inverse bremsstrahlung absorption of energy from the field of a focused IR laser beam. The simplified phenomenological theory of the dielectric breakdown of gases was applied to the explanation of the threshold phenomena. The decomposition of phosphine was studied as a function of laser frequency, pressure of PH3, and in the presence of foreign gases. The only products of the decomposition found were H2 in the gas phase and a solid deposit PHx. The partition of hydrogen between the gas and solid phases depends on the experimental conditions. A reaction scheme is presented which accounts satisfactorily for the experimental facts.

Quantum mechanical study of multiphoton excitation of the nonrotating OCS molecule

A quantum mechanical approach based upon Floquet theory is used to study IR multiphoton excitation of the nonrotating OCS molecule within the frequency and power range of the cw CO2 laser. Using a classical field interacting with a quantum molecule in the dipole approximation, the effects of laser frequency and power are investigated by computing long-time average transition probabilities, total energy absorption, and time-dependent probabilities. While multiphoton excitation is found to occur at the most intense CO2 laser line [P(24)], high-order excitation dominates near the weaker P(16) line, some 10 cm−1 higher in photon energy. Also, various types of time averaging and approximate dipole interactions are investigated.

Laser frequency dependent kinetics of cw laser induced reactions

CF2ClCF2Cl and ethyl acetate have absorption bands of similar width centered at the same frequency. Kinetics of the decompositions of these compounds by a cw CO2 laser have been studied over a range of laser frequencies extending to 25 cm−1 below band center. At constant translational temperature and pressure, the CF2ClCF2Cl rate constant changes by more than 200 with frequency, while the corresponding change for ethyl acetate is at most 3. The effect of laser frequency increases with increasing CF2ClCF2Cl pressure, while the reverse is true in ethyl acetate. Arrhenius plots show activation energies independent of both frequency and pressure.

Tritium isotope separation by CO 2 laser-induced multiphoton dissociation of CTF 3

Isotope separation of tritium at ppm concentration level was achieved by CO 2 laser-induced multiphoton dissociation of CTF 3 in CHF 3 with single-step separation factors exceeding 500. The effects of laser frequency, pulse energy, pulse duration, irradiation geometry, tritium concentration, sample pressure, and buffer gas were investigated.