P.G. Bleotu, R. Udrea, A. Dumitru, O. Uteza, M.-D. Mihai, D.Gh. Matei, D. Ursescu, S. Irimiciuc, V. Craciun [ https://https://www.cambridge.org/core/journals/high-power-laser-science-and-engineering/article/exploring-fslaser-irradiation-damage-subthreshold-behavior-of-dielectric-mirrors-via-electrical-measurements/950BD0CAF928541FBBCD38F3E58A52D7 ]
An alternative method for Laser Induced damage threshold (LIDT) estimation is presented based on a combination of an Langmuir probe (LP) and compensation target current (TC) measurement. The method was implemented for understanding the fs irradiation of HfO2 and ZrO2 films produced by pulsed laser deposition in various O2 conditions.
For laser fluences above the LIDT value, the emitted charge from the thin film increases exponentially. The LP-TC method identifies the damage point quickly, and in a similar way as standard scattering, reflectance or transmittance detection methods, but with less experimental complexity. The higher sensitivity for the LIDT values determined by the TC when compared to the LP approach is in line with the fundamental processes describing subthreshold charge dynamics. When comparing with standard LIDT measurements, 1:1 to 1000:1 with the LP-TC measurements, it is shown that the LP-TC measurements provide an indication of damage at fluences below the standard LIDT in the single shot.
The TC measurements indicate electronic processes taking place at even lower fluences, below the 1000:1 standard LIDT. Hence, it is also conjectured here that the TC measurements correspond to the infinity-extrapolated damage threshold. In this way, a conservative LIDT value that predicts the optical component resistance for very long laser exposure can be extracted more quickly and used for the practical implementation of optical components in high-power laser systems.
The implementation of the LP and TC as on-shot diagnostic tools for optical components infinity-extrapolated LIDT determination will improve the reliability of next-generation ultrafast and high-power laser systems as it will make possible laser damage self-diagnosis of critical components.
The work was performed in a joint effort ELI-NP with National Institute for Lasers Plasma and Radiation Physics, Magurele, Romania (INFLPR), using the Optics Lab facility of ELI-NP.
Fig.1 Experimental setup. BS, beam splitter; EM, energy meter; FM, flip mirror; LASER, Ti:sapphire; L1 and L2, focusing lenses; LP, Langmuir probe; M1, high-reflection mirrors; M2, 99 % -reflection mirror; M3, spherical mirror; NDF, neutral density filter; OSC, oscilloscope; POL, polarizer; PD, photodiode; TC, target current; TS, translation stage; RS, rotation stage; VC, vacuum chamber; WP, half-waveplate. The inset illustrates the input beam profile used for A eff calculation.
