Calculations and experimental demonstration of multi-photon absorption governing fs laser-induced damage in titania

Abstract

Laser damage phenomena are governed by a number of different effects for the respective operation modes and pulse durations. In the ultra short pulse regime the electronic structure in the dielectric coating and the substrate material set the prerequisite for the achieved laser damage threshold of an optical component. Theoretical considerations have been done to assess the impact of contributing ionization phenomena in order to find a valid description for laser-induced damage in the femtosecond (fs) domain. Subsequently, a special set of sample has been designed to verify these considerations via ISO certified laser damage testing. Examining the theoretical and experimental data reveals the importance of multi-photon absorption for the optical breakdown. For titania, the influence of multi-photon absorption has been clearly shown by a quantized wavelength characteristic of the laser damage threshold.

Electronic quantization in dielectric nanolaminates

“…In this model, damage in the dielectric material is linked to a critical level ρ crit of electrons in the conduction band as a starting condition for irreversible damage. The level ρ crit is given by [11] Here m eff refers to the effective mass of an electron, e to the elementary charge, ω 0 to the angular frequency, c to the speed of light, ε 0 to the vacuum permittivity, and λ to the wavelength, respectively.…”

Determination of ultra-short laser induced damage threshold of KH2PO4 crystal: Numerical calculation and experimental verification

“…1,2, 12,20,21 When the electron density in CB reaches the critical density n cr , where the respective plasma waves are resonant with incident laser wave, the excited material would strongly absorb the laser energy via inverse bremsstrahlung, eventually resulting in permanent structural changes (regarded as damage). The generation of free-electron excited from VB to CB can be described by the following rate equation:…”

Simulation in thin film technology

“…For the theoretical modeling, rate equation models are applied to investigate the interaction of high power laser irradiation with dielectric materials. In the framework of thin film technology adapted rate equations are used to calculate the free electron density during irradiation with short laser pulses to model for example the laser induced damage threshold [30] and the linear as well as the nonlinear material absorption [31]. Since the optical and electronic properties in terms of the band gap and the refractive index represent an essential part of the needed input parameters for the rate equation calculations, it is quite desirable to use the concept of the virtual coater in order to calculate these values.…”