Ultrafast Laser Material Damage Simulation—A New Look at an Old Problem

Abstract

The chirped pulse amplification technique has enabled the generation of pulses of a few femtosecond duration with peak powers multi-Tera and Peta–Watt in the near infrared. Its implementation to realize even shorter pulse duration, higher energy, and higher repetition rate laser systems relies on overcoming the limitations imposed by laser damage of critical components. In particular, the laser damage of coatings in the amplifiers and in post-compression optics have become a bottleneck. The robustness of optical coatings is typically evaluated numerically through steady-state simulations of electric field enhancement in multilayer stacks. However, this approach cannot capture crucial characteristics of femtosecond laser induced damage (LID), as it only considers the geometry of the multilayer stack and the optical properties of the materials composing the stack. This approach neglects that in the interaction of an ultrashort pulse and the materials there is plasma generation and associated material modifications. Here, we present a numerical approach to estimate the LID threshold of dielectric multilayer coatings based on strong field electronic dynamics. In this dynamic scheme, the electric field propagation, photoionization, impact ionization, and electron heating are incorporated through a finite-difference time-domain algorithm. We applied our method to simulate the LID threshold of bulk fused silica, and of multilayer dielectric mirrors and gratings. The results are then compared with experimental measurements. The salient aspects of our model, such as the implementation of the Keldysh photoionization model, the impact ionization model, the electron collision model for ‘low’-temperature, dense plasma, and the LID threshold criterion for few-cycle pulses are discussed.

Preparation of High Damage Threshold Device Based on Bi2Se3 Film and Its Application in Fiber Lasers

“…According to the research results of Zhang et al, we know that the damage of photoelectric thin films often comes from the photoionization effect after absorbing too much energy. The effect describes a mechanism of material damage caused by excessive thermal energy generated by electron–hole pair recombination through nonradiative transition.…”

Nanoscale reshaping of resonant dielectric microstructures by light-driven explosions

“…Much higher laser intensities would be required for near-IR laser pulses to impart the same kinetic energy to the tunneled electrons. Third, because mid-IR photons with energies much smaller than the bandgap (ℏ𝜔 𝐿 ≪ 𝐸 𝑔 ) satisfy the Keldysh adiabatic tunneling condition [39][40][41] 𝛾 K < 1 (where 𝛾 K = 𝜔 𝐿 √ 𝑚 eff 𝐸 𝑔 /𝑞 𝑒 𝐸 hs is the Keldysh adiabaticity parameter and 𝐸 hs ∝ √𝐼 hs is the peak optical field at the hot spot), the volume of the high-density hot plasma produced by the laser pulse is much smaller than that of the optical energy itselfhence the cascading of the localization scales from hundreds of nanometers (the size of the photonic hot spot) to tens of nanometers (the size of the ablated region).…”

“…The above scaling offers further justification for using a longer-wavelength laser for FLANEM, while the numerical estimate is fully consistent with our experimentally measured ablation rate of 𝑣 abl ≈ 30 nm per pulse. A 3D simulation based on the EPOCH (Extendable PIC Open Collaboration) code 42 incorporated with the home-built refractive index and dynamic Keldysh photoionization modules [39][40][41] was performed to elucidate the nano-trenching process.…”

Laser-induced damage of dielectric-enhanced surface-modified single-point-diamond-turned Al-6061 multiband mirrors

“…The results suggest that the FDTD simulation is a powerful tool to predicat defect-initated laser-induced damage. In addition, the FDTD simulation technique has been applied to dielctric mirrors with random-shaped seeds [11], defects on the femtosecond laser damage resistance of multilayer dielectric mirrors and gratings [12,13], and nanosecond laser-induced surface damage of CaF2 optics at 248 nm [14], precipitates for the mechanical strengthening of the alloy. In addition, there are other inclusions.…”