The dependence of the ablation rate of aluminium on the fluence of nanosecond laser pulses with wavelengths of 532 nm and respectively 1064 nm is investigated in atmospheric air. The fluence of the pulses is varied by changing the diameter of the irradiated area at the target surface, and the wavelength is varied by using the fundamental and the second harmonic of a Q-switched Nd-YAG laser system. The results indicate an approximately logarithmic increase of the ablation rate with the fluence for ablation rates smaller than ∼6 μm/pulse at 532 nm, and 0.3 μm/pulse at 1064 nm wavelength. The significantly smaller ablation rate at 1064 nm is due to the small optical absorptivity, the strong oxidation of the aluminium target, and to the strong attenuation of the pulses into the plasma plume at this wavelength. A jump of the ablation rate is observed at the fluence threshold value, which is ∼50 J/cm2 for the second harmonic, and ∼15 J/cm2 for the fundamental pulses. Further increasing the fluence leads to a steep increase of the ablation rate at both wavelengths, the increase of the ablation rate being approximately exponential in the case of visible pulses. The jump of the ablation rate at the threshold fluence value is due to the transition from a normal vaporization regime to a phase explosion regime, and to the change of the dimensionality of the hydrodynamics of the plasma-plume.

Optical hysteresis is a fundamental phenomenon that can lead to optical bistability and high-speed signal processing. Here, we present a theoretical and experimental study of the optical hysteresis phenomenon in amorphous As ₂ S ₃ chalcogenide based waveguide structures under surface plasmon resonance (SPR) conditions. The SPR structure is irradiated with low power CW Ar laser radiation at 514 nm wavelength, with photon energy near the optical band-gap of As ₂ S ₃ , in a Kretschmann–Raether configuration. First, we determined the incidence angle on the SPR structure for resonant coupling of the laser radiation within the waveguide structure. Subsequently, by setting the near resonance incidence angle, we analyzed the variation of the laser power reflected on the SPR structure with incident power. We demonstrated that, by setting the incidence angle at a value slightly smaller than the resonance angle, the increase followed by the decrease of the incident power lead to a wide (up to 60%) hysteresis loop of the reflected power. This behavior is related to the slow and persistent photo-induced modification of the complex refractive index of As ₂ S ₃ under 514 nm laser irradiation. The experimental and theoretical results are in good agreement, demonstrating the validity of the theoretical model presented here.

The paper is a review of surface plasmon resonance (SPR) structures containing amorphous chalcogenide (ChG) films as plasmonic waveguides. The calculation method and specific characteristics obtained for four-layer SPR structures containing films made of amorphous As₂S₃ and As₂Se₃ are presented. The paper is mainly based on our previously obtained and published scattered results, to which a generalized point of view was applied. In our analysis, we demonstrate that, through proper choice of the SPR structure layer parameters, we can control the resonance angle, the sharpness of the SPR resonance curve, the penetration depth, and the sensitivity to changes in the refractive index of the analyte. These results are obtained by operating with the thickness of the ChG film and the parameters of the coupling prism. Aspects regarding the realization of the coupling prism are discussed. Two distinct cases are analyzed: first, when the prism is made of material with a refractive index higher than that of the waveguide material; second, when the prism is made of material with a lower refractive index. We demonstrated experimentally that the change in reflectance self-induced by the modification in As₂S₃ refractive index exhibits a hysteresis loop. We present specific results regarding the identification of alcohols, hydrocarbons, and the marker of E. coli bacteria.