Temperature distribution in optical trepanning

Effects of high power ultrasonic vibration on temperature distribution of workpiece in dry creep feed up grinding

An experimental study was performed to explore the effect of gas-density gradient in laser propagation direction on high-harmonic generation from neon-filled cells using a 50 fs annular and Gaussian Ti:sapphire laser beam. It was observed that, despite 20% lower power, the photon flux of the high-harmonics generated using an annular beam under optimum parameter conditions (∼2.5 × 1010 photons/sec for the 37th order in a 5 mm long cell) is on par with the maximum photon flux generated using a full Gaussian beam (∼2 × 1010 photons/sec for the 37th order in a 15 mm long cell). To elucidate the underlying mechanism for the experimental observation, a numerical simulation of the propagation of both the annular and Gaussian laser beams inside the cell was performed. The simulation was extended to estimate the high-harmonic intensity, after incorporating the effect of laser defocusing, the electron trajectory resolved phase-matching, and gas-density gradient. The dominant role of short electron trajectories was observed in the case of the annular beam, whereas, in the case of the Gaussian beam, a contribution of both short and long trajectories was found. Our analysis shows that, in neon-filled cells, the gas-density gradient present at the laser exit end of the cell plays a dominant role in achieving a high photon flux using an annular laser beam. Further, the annular beam not only provides a higher flux but also has lower divergence and higher coherence. This study will be useful in attosecond pulse metrology as well as in imaging applications viz coherent diffractive imaging.

A comparative investigation on temperature distribution in electric discharge machining process through analytical, numerical and experimental methods

The self-action of high-power femtosecond laser beams with a radiation wavelength of 800 nm (formed by superposition of Gaussian and annular beams) in air is theoretically modelled. A detailed analysis of self-focusing and filamentation of this radiation is performed based on the numerical solution of the spectral equation of the unidirectional propagation of a wave packet with allowance for the nonlinearity of the medium, and by tracing averaged diffraction-optical rays. It is shown that, in terms of the diffraction-beam optics, the outer annulus forms a waveguide, which facilitates self-trapping of the central part of the combined beam, supplying the light energy to the filament. The spatial stability of this waveguide depends on the energy stored in the annulus and on the distance from the latter to the beam axis.

The paper proposes an analytical method which enables to predict the temperature distribution in three dimensional metal cutting with single point tool, based only upon orthogonal cutting data. By using the three dimensional cutting model and the energy method presented in the previous paper, it is possible to obtain cutting force and chip formation such as chip flow direction, shear angle and chip shape for the tool of arbitrary shape. An assumption made on the frictional stress distribution on rake face together with the results through the energy method determines the strength of heat sources in the cutting model. The temperature distribution in workpiece, chip and tool is thus obtained through a numerical analysis of the equation involving heat conduction, transfer and generation. The predicted distribution of the temperature on rake face is found to be in good agreement with the distribution measured with a fine, insulated platinum wire embedded in the tool, of which end is exposed on the rake face and makes a thermo-couple with the chip produced.

We report here on a two-dimensional analytical calculation of an upper bound on the space-charge limiting current for a relativistic electron beam in cylindrical geometry. Voronin and co-workers have previously obtained an analytical estimate for the maximum steady-state current that can be propagated in a solid, unneutralized electron beam which completely fills a drift tube immersed in an infinite magnetic guide field. We generalize their method to include annular beams of arbitrary thickness and length, specifying a rigorous upper bound on the limiting current in terms of an eigenvalue of Bessel' s differential equation and separated, homogeneous boundary conditions of the most general form. For the special cases of a thin solid beam in a drift tube of infinite length and a thin annular beam in a drift tube of finite length, we find closed-form analytical expressions for the upper bound which are in good agreement with numerical solutions for the actual space-charge limiting current.

When the near-infrared femtosecond Bessel laser beam (fs-BLB) is obliquely incident on the silica glass, annular beams (ABs) with bandwidths of several tens of nanometers and different peak wavelengths discretely distributed in a visible and near-infrared range are generated simultaneously. It is considered that four-wave mixing (FWM) and the corresponding cascaded parametric processes are responsible for the generation of multi-wavelength ABs. It is also found that the broken symmetry of the optical setup due to the obliquely oriented silica glass and the absorption band of the sample significantly enhance the generation efficiency of ABs. Since the diffraction angles of these colorful ABs mainly depend on their wavelengths and are insensitive to the input laser energy, this technique may find important applications where multi-wavelength ultrashort pulses are needed. For example, these multi-wavelength ABs can be used as light sources in nonlinear dark-field microscopy and multiphoton imaging to further suppress the background noise and improve resolution. They can also be used in multidimensional multiplexing optical communications.

In this work, we report an annular beam confocal laser-induced fluorescence (LIF) configuration, which allows for high spatial resolution measurements of plasma properties in plasma setups and sources with limited optical access. The proposed LIF configuration utilizes the annular laser beam generated by a pair of diffractive axicons. The LIF signal is collected along the main optical axis within the ring region. It is shown experimentally that at a focal distance of 300 mm, a spatial resolution of ∼5.3 mm can be achieved. Using geometric optics estimations, we showed that ∼1 mm resolution at the same focal distance could potentially be achieved by modifying laser beam parameters. This approaches the localization accuracy of conventional LIF collection methods (with crossing laser beam injection and fluorescence collection optical paths). Measurements of the ion velocity distribution function in an argon plasma using both the confocal LIF with an annular laser beam and conventional LIF demonstrate a satisfactory agreement. The proposed LIF setup has potential applications for diagnostics in various plasma processing equipment and plasma sources, such as hollow cathodes, microplasmas, electric propulsion, etc.

Creep feed grinding

High Speed EDM and Laser Drilling of Aerospace Alloys

Drilling time and hole quality in a laser drilling process depend greatly upon the selection of the type and pressure of the process gas. Process gas is commonly used for melt ejection, protection of optics and removal of plasma/vapor. This paper presents a detailed analysis of the gas type and gas pressure effects on the drilling speed and hole quality. O2, N2, Ar and compressed air were used in this investigation for Nd:YAG laser drilling of In718 alloy. It is shown that despite the lower penetration rate, the total volume of material removed is higher with oxygen assist gas due to oxide layer formation and plasma formation within the holes which increases the hole wall ablation, although drilling time with oxygen is longer than with other gases. Hole quality variations for holes under different gas type and pressure conditions are evaluated. One very interesting and significant findings was that the hole quality that achieved by laser drilling without assisting gas is better than that obtained when using argon, nitrogen or compressed air.Drilling time and hole quality in a laser drilling process depend greatly upon the selection of the type and pressure of the process gas. Process gas is commonly used for melt ejection, protection of optics and removal of plasma/vapor. This paper presents a detailed analysis of the gas type and gas pressure effects on the drilling speed and hole quality. O2, N2, Ar and compressed air were used in this investigation for Nd:YAG laser drilling of In718 alloy. It is shown that despite the lower penetration rate, the total volume of material removed is higher with oxygen assist gas due to oxide layer formation and plasma formation within the holes which increases the hole wall ablation, although drilling time with oxygen is longer than with other gases. Hole quality variations for holes under different gas type and pressure conditions are evaluated. One very interesting and significant findings was that the hole quality that achieved by laser drilling without assisting gas is better than that obtained when usi...

In this work, we develop a fluidic laser beam shaper based on the thermal lens effect in MoS2 suspensions. It is demonstrated that another weak unfocused Gaussian beam (probe beam) is transformed into an annular beam due to the thermal lens effect resulting from a strong focused Gaussian beam (pump beam). The time evolution of the generated annular beam is studied, and the result shows that the annular beam exhibits asymmetric caused by heat convection with the high pump beam power. In addition, the tunability of the generated annular beam is investigated. Furthermore, the optical trapping of micro-sized particles in air using the annular beam is researched. It is found that this method exhibits stable performance capture for 3 h. The advantages of adjustable size, flexible setup and low cost of annular beam generated method are significant for lots of laser applications, such as optical trapping, optical imaging and laser machining.

Propagation characteristics of annular laser beams passing through the reflection Bragg grating with deformation

Multi-wavelength annular optical pulses generated by double interferent femtosecond Bessel laser beams in silica glass

The temperature distribution characteristics of a moving annular hollow laser beam irradiated on the substrate are studied in this paper. First, through the linear superposition property of potential function, we derive the analytical solution of temperature distribution and the cooling rate of the moving ideal annular hollow heat source. The entransy dissipation rate per unit volume of the annular hollow laser beam is more uniform than that of the Gaussian laser beam. The “ω”-shaped profile of the cross-sectional melt temperature is predicted. Second, we set up an actual annular hollow heat source expression, and two parameters (hollow ratio and heat source hollow area) are defined to describe the heat transfer characteristics of the actual annular hollow heat source. Experiments are carried out to validate transient numerical results. The maximum relative error between the experiments and the simulations is 6.39%, and the average relative error is 3.16%. In the simulation, we compare the profile temperature field of the annular hollow heat source with that of the Gaussian heat source. The profile temperature field in simulation for the actual annular hollow heat source is in agreement with that predicted in the analytical solution for the ideal annular hollow heat source. The effects of scanning speed, power intensity, hollow ratio, and heat source hollow area on the temperature field are demonstrated. The obtained characteristics provide theoretical support for laser materials engineering applications.