Enhancement of the Absorption of Intense Visible Femtosecond Laser Pulses in a Silver Film

JETP Letters - The transmission coefficient of a 30-nm-thick silver film for single visible laser pulses with a wavelength of 515 nm and a duration of 300 fs decreases steadily with an increase in...     

Thermal melting and ablation of silicon by femtosecond laser radiation

The space-time dynamics of thermal melting, subsurface cavitation, spallative ablation, and fragmentation ablation of the silicon surface excited by single IR femtosecond laser pulses is studied by timeresolved optical reflection microscopy. This dynamics is revealed by monitoring picosecond and (sub)nanosecond oscillations of probe pulse reflection, which is modulated by picosecond acoustic reverberations in the dynamically growing surface melt subjected to ablation and having another acoustic impedance, and by optical interference between the probe pulse replicas reflected by the spalled layer surface and the layer retained on the target surface. The acoustic reverberation periods change during the growth and ablation of the surface melt film, which makes it possible to quantitatively estimate the contributions of these processes to the thermal dynamics of the material surface. The results on the thermal dynamics of laser excitation are supported by dynamic measurements of the ablation parameters using noncontact ultrasonic diagnostics, scanning electron microscopy, atomic force microscopy, and optical interference microscopy of the modified regions appearing on the silicon surface after ablation.     

Topological evolution of self-induced silicon nanogratings during prolonged femtosecond laser irradiation

Gradual evolution of self-induced silicon surface topology from one-dimensional ridge-like to two-dimensional spike-like nanogratings and then to isotropic sets of micro-columns was observed by evenly increasing IR and UV femtosecond laser irradiation dose. This topological evolution exhibits clear indications of consequent melting and vaporization processes being set up during the prolonged laser irradiation. Monotonously decreasing cumulative IR and UV femtosecond laser-nanostructuring thresholds may indicate an increase of optical absorbance of the laser-nanostructured silicon surfaces versus the increasing laser dose, consistent with the consequent onset of the abovementioned thermal modification processes.     

Erratum to: Several Articles in JETP Letters

JETP Letters - An Erratum to this paper has been published: https://doi.org/10.1134/S0021364022390011     

Femtosecond laser color marking of metal and semiconductor surfaces

Color marking of rough or smooth metal (Al, Cu, Ti) and semiconductor (Si) surfaces was realized via femtosecond laser fabrication of periodic surface nanorelief, representing one-dimensional diffraction gratings. Bright colors of the surface nanorelief, especially for longer electromagnetic wavelengths, were provided during marking through pre-determined variation of the laser incidence angle and the resulting change of the diffraction grating period. This coloration technique was demonstrated for the case of silicon and various metals to mark surfaces in any individual color with a controllable brightness level and almost without their accompanying chemical surface modification.     

Master Oscillator-Power Amplifier carbon monoxide laser system emitting nanosecond pulses

To increase a peak power of carbon monoxide laser emitting nanosecond pulses a Master Oscillator-Power Amplifier (MOPA) laser system was developed. The MOPA CO-laser system employed one and the same gain medium of wide-aperture pulsed electron-beam-sustained-discharge CO-laser facility. Amplification parameters include gain and saturation intensity of amplifying media. The MOPA CO-laser system emitted a train of nanosecond pulses with peak power up to ~ 0.1 MW on a single spectral line and up to ~ 0.4 MW with multiline spectrum.     

Tunneling ionization of air in the strong field of femtosecond laser pulses

The effect of the tunneling ionization of air excited by individual intense femtosecond pulses with subcritical peak powers has been investigated by the optoacoustic method. With an increase in the laser radiation intensity in the range of 0.5–20 PW/cm², the saturation of the amplitude of acoustic pressure with the corresponding decrease in the nonlinearity index of this dependence is observed. The analysis of the ionization of air molecules in the Ammosov-Delone-Krainov model of tunneling ionization predicts a weakly nonlinear increase and saturation of the yield of singly charged ions at an air ionization degree close to 50% under these conditions of the effect of femtosecond laser radiation.     

Ultrafast Broadband Diagnostics of the Filling of the s Band at the Two-Photon Femtosecond Laser Excitation of a Gold Film

JETP Letters - The transmission of near infrared femtosecond laser pulses (wavelength of 800 nm) and supercontinuum radiation (300–750 nm) generated by them through a 50-nm gold film immersed...     

Acceleration of the Decay of Excitons in an Organometallic Perovskite Film on the Crystalline Silicon Surface

JETP Letters - It has been found that the optical properties and characteristics of exciton photoluminescence in thin organometallic perovskite layers, which are promising for application in...     

Silicon Ablation by Single Ultrashort Laser Pulses of Variable Width in Air and Water

The ablation of silicon by single laser pulses of variable width (0.3–9.5 ps) with a wavelength of 515 nm has been comparatively studied in air and water. A nonmonotonic behavior of ablation thresholds with a minimum at 1.6 ps, which is due to achieving the thermalization time of the electron and ion subsystems in silicon, has been revealed. It has been shown that, with an increase in the pulse width in the considered width range, the efficiency of the ablation of silicon decreases by a factor of 2.5 in air and increases by a factor of 2 in water. This behavior of ablation in air is attributed to a partial transition from phase explosion to surface evaporation, which is suppressed in water.