Laser Induced Damage Thresholds and morphologies of damage sites on thin films samples irradiated by sub-ps pulses are studied based on experimental and numerical studies. Experiments are conducted with 500fs pulses at 1030nm and 343nm and the irradiated sites are analyzed with phase imaging, AFM and SEM. The results are compared to simulations of energy deposition in the films based on the Single Rate Equation taking account transient optical properties of the films. Results suggest that a critical absorbed energy as a damage criterion give consistent results both with the measured LIDT and the observed damage morphologies.
We report on the sub-picosecond laser-induced damage of optical thin films of different thickness made by Magnetron sputtering, Ion assisted deposition and Ion plating, and submitted to single irradiation of the first and the third harmonics of an Ytterbium laser (1030 and 343nm). Using a single rate equation approach for free electron excitation coupled with calculation of the spatial and temporal distribution of the electric field, we investigate numerically the spatial density distribution of the absorbed energy and evaluate its capacity to describe damage phenomena especially damage threshold and morphologies (damage diameter, ablation deepness). Laser-induced damage thresholds are compared for different film thicknesses and different irradiation conditions.
Laser-induced damage is defined as any permanent laser-induced change in the characteristics of a sample. This change can be observed by many different inspection techniques, with different sensitivity, depending on the intended objectives and available techniques. The damage threshold definition and measurement are therefore very subjective and related to the detection method. The choice and implementation of a damage test system is then a critical issue on any experiment. In this work we present some implementation of detection techniques for laser damage metrology in the sub-picosecond regime. Different damage testing methods that have been applied will be discussed in view of their potential applications for testing functional optical components or to study physical process in the femtosecond regime, particularly the role of defects: optical microscopy, phase microscopy and time-resolved microscopy.
We investigate quantitative phase imaging as a measurement method for laser damage detection and analysis of laser induced modification of optical materials. Experiments have been conducted with a wavefront sensor based on lateral shearing interferometry technique associated to a high magnification optical microscope. The system has been used for in situ observation of optical thin films and bulk samples irradiated by 500fs pulses. It is shown that the technique realizes high sensitivity, convenient use and can provide quantitative information on the refractive index or surface modification of the samples under test.
We report on the laser-induced damage threshold at 500fs of optical films made by Magnetron Sputtering and
submitted to single and multiple irradiations at different harmonics of an Ytterbium laser (1030nm, 515nm
and 343nm). Single layers of SiO2, HfO2, and Nb2O5 as bare fused silica samples are under investigation.
Optical materials submitted to multiple subpicosecond irradiations are known to exhibit a decrease of the laser-induced damage threshold (LIDT) with the applied number of pulses, an effect referred to as “fatigue” or “incubation.” In this work, we experimentally investigate this effect for the case of optical thin films submitted to multiple exposures with 500 fs pulses at different wavelengths: 1030, 515, and 343 nm. Niobia, hafnia, and silica films made with dense coating techniques (magnetron sputtering, ion-assisted deposition, and reactive low voltage ion plating) are studied, as well as the surface of a fused silica substrate. These samples have been exposed to different pulse numbers (from 1 to 100,000) at a low-frequency repetition rate (less than 1 kHz) and the LIDT has been measured. The results reveal the differences between materials and for the various wavelengths such as the decrease rate of the LIDT or the stabilization level that is reached after multiple exposures. All the results evidence the role of native- and laser-induced defects that we discuss on the basis of published works on the subject.
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