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Accession Number:

AD1112804

Title:

Fundamentals of Femtosecond Laser Induced Damage of Solids: Advancement Through Experimental, Computational and Theoretical Development

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Report Date:

2020-04-01

Abstract:

Femtosecond laser induced damage (fsLID) is an exciting non-perturbative non-linear phenomenon with a wide range of applications. The present effort concentrates on understanding this phenomenon from experimental, theoretical and computational perspectives, with each effort benchmarking and providing feedback for the improvement of the other method. Among its chief achievements, understanding of the wavelength scaling of fsLID in several semiconductors have been well understood, with appropriate theoretical model development, notably the Keldysh-Vinogradov model of field induced free carrier generation and energy absorption. Large scale hybrid PIC computational method has been developed. In the current program, we have significantly extended our understanding of few cycle pulse (2 - 4 cycles, FCP) laser damage and ablation of solids and how it differs from that induced by longer (many cycle, > 10 cycles) pulses. FCPs typically exhibit bandwidth around 25% of the carrier frequency, while 100 fs pulses require ~1.5% bandwidth. It implies that first, the FCPs promote valence electrons to the conduction band at higher rate (due to lower order of multiphoton processes for the high-frequency part of the broad FCP spectrum); second, the FCPs produce free electrons with higher kinetic energy compared to those produced by 100-fs pulses. The higher kinetic energy supports deeper electron penetration into samples and reduced electron-particle collision time. The reduced collision time drives the laser-generated free-carrier plasma faster to quasi-equilibrium and increases the rate of energy transfer to phonons. The increased rate of electron- phonon energy transfer supports reduced temperature of the laser-generated free-carrier plasma.

Pages:

20

File Size:

1.76MB

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Distribution Statement:

Approved For Public Release

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