Ionization rate vs. laser intensity determined from ion count vs. peak intensity due to neutral gas exposure to an 800 nm ultrashort pulsed laser

TL;DR

This study determines the ionization rates of Ar, O$_{2}$, and N$_{2}$ under intense 800 nm laser pulses by analyzing ion count data, providing calibrated efficiencies and reevaluating O$_{2}$ ionization cross sections.

Contribution

It introduces a method to extract ionization rates from ion count data and recalibrates detection efficiencies, improving accuracy in ionization measurements.

Findings

Ionization rates for Ar, O$_{2}$, and N$_{2}$ were determined up to 300 TW/cm$^{2}$.

The MCP collection efficiency was recalibrated using high intensity data.

Results for O$_{2}$ support a reevaluation of its multiphoton ionization cross section.

Abstract

The optical cycle-averaged ionization rate of Ar, O$_{2}$, and N$_{2}$ vs. local instantaneous laser intensity $I$ for linear polarized $800$ nm light is determined up to approx. $300$ TW/cm$^{2}$ by numerically inverting published time-of-flight ion spectrometer data. The published Ar$^{+}$ collection efficiency of the microchannel plate (MCP) at the end of the spectrometer and its $I_{0}$ scale are recalibrated by fitting it to its high $I_{0}$ solution. The relative collection efficiencies of the other species are determined by published MCP cathode data. Results for O$_2$ are consistent with a reevaluation of published data used to determine its cross section $\sigma_8$ in the multiphoton (low $I$) regime.