Thermal self-focusing of a laser in collisional plasma: beyond the near axis approximation

Amrita, .; Sharma, Anamika

doi:10.1088/0031-8949/74/1/017

Cited by 7 publications

(3 citation statements)

References 14 publications

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“…Hence diffraction divergence diminishes the signal. We solve equation (12) taking the above parameters at z s = 82 km. We get A s0 = 28.77 × 10 2 and A s = 28.8 × 10 2 .…”

Section: Effect Of Self-focusing On Downward Transmissionmentioning

confidence: 99%

Effect of self-focusing on millimetre wave communication with re-entry space vehicles

Sharma¹,

Amrita²

2008

J. Phys. D: Appl. Phys.

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A high power millimetre wave, employed for communication with a re-entry space vehicle surrounded by a high-density plasma sheath, is affected by linear and nonlinear effects. A signal originating from the ground suffers diffraction divergence through space, prior to entering the fast evolving plasma sheath surrounding the vehicle, and undergoes time dependent absorption inside the sheath. The net signal loss due to diffraction and absorption varies as the spacecraft approaches the ground. The wave launched from the spacecraft for downward communication has a large amplitude in the plasma sheath and gives rise to nonlinear effects. The millimetre wave heats the electrons more strongly in the region where the wave intensity is maximum, causing ambipolar diffusion of the plasma leading to an increase in the refractive index at the axis, thus self-focusing the millimetre wave signal. In free space, after passing through the plasma sheath, the beam suffers defocusing.

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“…Hence diffraction divergence diminishes the signal. We solve equation (12) taking the above parameters at z s = 82 km. We get A s0 = 28.77 × 10 2 and A s = 28.8 × 10 2 .…”

Section: Effect Of Self-focusing On Downward Transmissionmentioning

confidence: 99%

Effect of self-focusing on millimetre wave communication with re-entry space vehicles

Sharma¹,

Amrita²

2008

J. Phys. D: Appl. Phys.

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“…Recently, Ma [22] investigated electromagnetic wave propagation in an inhomogeneous highly collisional plasma. Amrita and Sharma [23] applied an off-axis approximation and analyzed the thermal self-focusing of a laser in a collisonal plasma. In experimental studies of collisional plasmas, the dynamics of a dense laboratory plasma jet [24] and the stimulated Brillouin and Raman scattering from a randomized laser beam [25] have been reported.…”

Section: Introductionmentioning

confidence: 99%

Dielectric constant and laser beam propagation in an underdense collisional plasma: effects of electron temperature

Xia

Qin

et al. 2011

Phys. Scr.

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Dielectric constant and laser beam propagation in an underdense collisional plasma are investigated, using the wave and dielectric function equations, for their dependence on the electron temperature. Simulation results show that, due to the influence of the ponderomotive force there is a nonlinear variation of electron temperature in an underdense collisional plasma, and this leads to a complicated and interesting nonlinear variation of dielectric constant; this nonlinear variation of dielectric constant directly affects the beam propagation and gives rise to laser beam self-focusing in some spatial-temporal regions; in particular, the beam width and the beam intensity present an oscillatory variation in the self-focusing region. The influence of several parameters on the dielectric function and beam self-focusing is discussed.

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“…Semak et al 15 used a finite difference method, whereas Zeng et al 16 presented an analytic model to calculate the temperature field during laser drilling by considering convective heat transfer due to the liquid metal flow induced by the recoil pressure of the outgoing metal vapor. [17][18][19] Strombeck and Kar 20 studied the self-focusing effect in laser welding where convex surfaces are formed by the molten material due to the surface tension between the melt and substrate. 2 Self-defocusing of the laser beam is another effect that can be important in laser drilling of semitransparent materials.…”

Section: Introductionmentioning

confidence: 99%

A model for self-defocusing in laser drilling of polymeric materials

Zhang

Quick

Kar

2008

Journal of Applied Physics

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A numerical thermal model is presented for laser microvias drilling in multilayer electronic substrates with Nd:YAG ͑YAG denotes yttrium aluminum garnet͒ and CO 2 lasers. Such substrates have different optical properties such as the refractive index and absorption coefficient at these two laser wavelengths, resulting in different drilling mechanisms. Since the skin depth of the polymer is large for both the lasers, volumetric heating is considered in the model. As soon as a small cavity is formed during the drilling process, the concave curvature of the drilling front acts as a concave lens that diverges the incident laser beam. This self-defocusing effect can greatly reduce the drilling speed as predicted by the model. This effect makes the refractive index of the substrate at different wavelengths an important parameter for laser drilling. The model was used to calculate the laser ablation thresholds which were found to be 8 and 56 J / cm 2 for the CO 2 and Nd:YAG lasers respectively. Due to the expulsion of materials because of high internal pressures in the case of Nd:YAG laser microvia drilling, the ablation threshold may be far below the calculated value. A particular laser beam shape, such as pitch fork, was found to drill better holes than the Gaussian beam.

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Thermal self-focusing of a laser in collisional plasma: beyond the near axis approximation

Cited by 7 publications

References 14 publications

Effect of self-focusing on millimetre wave communication with re-entry space vehicles

Effect of self-focusing on millimetre wave communication with re-entry space vehicles

Dielectric constant and laser beam propagation in an underdense collisional plasma: effects of electron temperature

A model for self-defocusing in laser drilling of polymeric materials

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