Title: Threshold characteristics of ultraviolet and near infrared nanosecond laser induced plasmas

Abstract

The present contribution compares the energy absorption, optical emission, temperature, and fluid dynamics of ultraviolet (UV) λ = 266 nm and near infrared (NIR) λ = 1064 nm nanosecond laser induced plasmas in ambient air. For UV pulses at the conditions studied, energy absorption by the plasmas increases relatively gradually with laser pulse energy starting at delivered energy of E~ 8 mJ. Corresponding measurements of plasma luminosity show that the absorption of UV radiation does not necessarily result in visible plasma emission. For the NIR induced plasmas, the energy absorption profile is far more abrupt and begins at ~55 mJ. In contrast with UV, the absorption of NIR radiation is always accompanied by intense optical emission. The temperatures of both types of plasma have been measured with Rayleigh scattering thermometry (at times after the Thomson signal sufficiently diminishes). The UV plasmas can attain a wider range of temperatures, including lower temperatures, depending on the pulse energy (e.g., T~400–2000 K for E~7–35 mJ at Δt = 10 μs after the pulse) while the NIR plasmas show only hotter temperatures (e.g., T~12 000 K for E = 75 mJ at Δt = 10 μs after the pulse) as is consistent with themore » literature. Differences in the fluid dynamics for UV versus NIR pulses are shown with Schlieren imaging. Finally, the contrast in the UV and NIR plasma threshold behavior is attributed to differing roles of avalanche ionization and multiphoton ionization as is also illustrated by a simple numerical model.« less

Authors:

Dumitrache, Ciprian ^[1]; Limbach, Christopher M.  ^[1];

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• Search DOE PAGES for ORCID "0000-0003-0447-672X"

Yalin, Azer P. ^[1]

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+ Show Author Affiliations

1. Colorado State Univ., Fort Collins, CO (United States). Mechanical Engineering

Publication Date:

Thu Sep 01 00:00:00 EDT 2016

Research Org.:

Colorado State Univ., Fort Collins, CO (United States). Mechanical Engineering

Sponsoring Org.:

USDOE; National Science Foundation (NSF)

OSTI Identifier:

1468934

Alternate Identifier(s):

OSTI ID: 1328457

Grant/Contract Number:  

SC0012454

Resource Type:

Accepted Manuscript

Journal Name:

Physics of Plasmas

Additional Journal Information:

Journal Volume: 23; Journal Issue: 9; Journal ID: ISSN 1070-664X

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY