Effect of refractive-index nonlinearity on the optical quality of high-power laser beams

Both small-scale and large-scale partial self-focusing produce phase distortions which result in loss of optical quality of the beam. Both effects are herein studied and both can result in significant power loss. Incipient fine-scale self-focusing losses can be mitigated by spatial filtering. Nonlinear lensing, i.e., partial large-scale self-focusing, is more or less serious depending on the size of the target onto which the beam is to be focused.     

A novel thermally-stable zirconium amidinate ALD precursor for ZrO2 thin films

ZrO₂ thin films were deposited by the atomic layer deposition process on Si substrates using tetrakis(N,N′-dimethylacetamidinate) zirconium (Zr-AMD) as a Zr precursor and H₂O as an oxidizing agent. Tetrakis (ethylmethylamino) zirconium (TEMA-Zr) was also evaluated for a comparative study. Physical properties of ALD-derived ZrO₂ thin films were studied using ellipsometry, grazing incidence XRD (GI-XRD), high resolution TEM (HRTEM), and atomic force microscopy (AFM). The ZrO₂ deposited using Zr-AMD showed a better thermal stability at high substrate temperature (>300 °C) compared to that using TEMA-Zr. GI-XRD analysis reveals that after 700 °C anneal both ZrO₂ films enter tetragonal phase. The electrical properties of N₂-annealed ZrO₂ film using Zr-AMD exhibit an EOT of 1.2 nm with leakage current density as low as 2 × 10⁻³ A/cm² (@V_fb−1 V). The new Zr amidinate is a promising ALD precursor for high-k dielectric applications.     

Electrical properties of atomic-layer-deposited La2O3 films using a novel La formamidinate precursor and ozone

La₂O₃ films were grown by atomic layer deposition technique using a novel formamidinate precursor, tris(N,N′-diisopropylformamidinato) lanthanum [La(ⁱPrfAMD)₃], with H₂O and O₃ as an oxidant. La₂O₃ films grown with H₂O in the film exhibited a parasitic chemical vapor deposition type growth possibly due to a La(OH)_x component. However, the use of O₃ as the oxidant revealed a stable ALD process window. A post-deposition annealing (PDA) of the deposited La₂O₃ films using O₃ significantly reduces leakage current density by four orders of magnitude relative to as-deposited samples. The dielectric constant of La₂O₃ films with a TaN metal gate is found to be ～29, which is higher than reported values for CVD and ALD La₂O₃ films.     

Self-focusing phenomena in air-glass laser structures

The effect of the air space on self-focusing instability growth rates has been considered for glass laser systems. The situation may be viewed as a min-max problem in which the air space may be adjusted to minimize the fastest growing instability. A solution exists to the min-max problem which reduces the problem to the solution of a single transcendental equation. Solutions to this equation indicate that, at most, a 10-percent reduction in the effective value of the non-linear index of refraction can occur.     

Comments on Shakir's “zero-area optical pulse processing by degenerate four-wave mixing”

We disagree with one of the contentions of Shakir's paper, namely that a zero-area pulse can be generated by an unstable phase conjugator. We find, on the contrary, that any unstable conjugator would, if the pumps were not depleted, generate a conjugate wave of infinite area. We show by counterexample that the response generated by Shakir's technique is noncausal if the conjugator is unstable.     

Self-focusing of very powerful laser beams II

In a recent paper the author proposed a self-focusing theory based on linear stability analysis of the quasi-optical equation [1]. Strictly, the theory applies only to a plane wave of infinite aperture. In this paper the theory is extended to beams of finite aperture, which may be initially convergent or divergent.