<p>We present the temporally resolved measurements of electron number density and temperature over timescales on the order of 1 ns to 10 ns in a femtosecond (fs) laser-induced plasma (LIP). Additionally, we also report on the neutral gas number density and rotational temperature over timescales on the order of 1 ns to 1000 ns. The fs LIP was generated in ambient air and investigated using laser Thomson and rotational Raman scattering. Electron number densities were observed to decrease from <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\sim 4\times 10^{21}\)</EquationSource> </InlineEquation> <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\hbox {m}^{-3}\)</EquationSource> </InlineEquation> at early times to <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\sim 7\times 10^{20}\)</EquationSource> </InlineEquation> <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(\hbox {m}^{-3}\)</EquationSource> </InlineEquation> at later times, while the electron temperature remained within <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(0.5-1\)</EquationSource> </InlineEquation> eV throughout the probed range. The neutral gas number density remained nearly constant at <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(\sim 2\times 10^{25}\)</EquationSource> </InlineEquation> <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(\hbox {m}^{-3}\)</EquationSource> </InlineEquation> for the first 50 ns before declining to <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(\sim 1.1\times 10^{25}\)</EquationSource> </InlineEquation> <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(\hbox {m}^{-3}\)</EquationSource> </InlineEquation> after 500 ns. The rotational temperature initially decreased from <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(\sim 700\)</EquationSource> </InlineEquation> K within the first 30 ns to <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(\sim 500\)</EquationSource> </InlineEquation> K at 100 ns, before rising back to <InlineEquation ID="IEq12"> <EquationSource Format="TEX">\(\sim 700\)</EquationSource> </InlineEquation> K. Finally, the experimental results were compared with simulations, showing good agreement.</p>

Temporally resolved properties of femtosecond laser-induced plasmas in air

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2026年1月5日

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Gerardo Urdaneta Rincon,
Junhwi Bak,
Sagar Pokharel,
Albina Tropina,
Richard Miles,
Arthur Dogariu

摘要

We present the temporally resolved measurements of electron number density and temperature over timescales on the order of 1 ns to 10 ns in a femtosecond (fs) laser-induced plasma (LIP). Additionally, we also report on the neutral gas number density and rotational temperature over timescales on the order of 1 ns to 1000 ns. The fs LIP was generated in ambient air and investigated using laser Thomson and rotational Raman scattering. Electron number densities were observed to decrease from \(\sim 4\times 10^{21}\) \(\hbox {m}^{-3}\) at early times to \(\sim 7\times 10^{20}\) \(\hbox {m}^{-3}\) at later times, while the electron temperature remained within \(0.5-1\) eV throughout the probed range. The neutral gas number density remained nearly constant at \(\sim 2\times 10^{25}\) \(\hbox {m}^{-3}\) for the first 50 ns before declining to \(\sim 1.1\times 10^{25}\) \(\hbox {m}^{-3}\) after 500 ns. The rotational temperature initially decreased from \(\sim 700\) K within the first 30 ns to \(\sim 500\) K at 100 ns, before rising back to \(\sim 700\) K. Finally, the experimental results were compared with simulations, showing good agreement.