Numerical study of multiline CO laser frequency conversion in a ZnGeP2 crystal to the THz range

A numerical simulation was performed for frequency conversion of multiline CO laser radiation to the THz range by difference frequency generation in a ZnGeP2 crystal. It was shown that the difference frequencies spectrum can be tuned in the wavelength interval of 70–1300 μm by tuning the phase-matching angle in the range of 11° to 55°. The maximal peak power of difference frequencies radiation (integral over the spectrum) was ~0.23 W at 45° phase-matching angle, which corresponds to a peak power conversion efficiency of 6 × 10−5

The morphological and compositional changes of bimetallic Ti/Al thin film induced by ultra-short laser pulses

Results regarding morphological and compositional changes of bimetallic thin film (BMTF), composed of aluminium (Al) and titanium (Ti) nano-layers, by single fs laser pulses, are presented. Laser irradiation was conducted in the air with focused, linearly polarized laser pulses, the duration being 300 fs, wavelength 515 nm, and pulse energy up to 1.2μJ. Effects of the variations of the pulse energy on the changes were studied. In the experiment, single pulse energy values from 0.03 to 0.08 μ J caused ablation–photomechanical spallation of the upper part of BMTF layer from the Si substrate, without ablation of the whole film. Irradiation at higher pulse energies gradually removed the whole BMTF and even a part of the Si substrate. We explained the influence of different electron–phonon dynamics, in the case of multilayered thin films composed of Al and Ti, on BMTF ablation. Damage/ablation threshold, which is minimal pulse energy/fluence sufficient for starting ablation, was calculated. Graphic abstract: [Figure not available: see fulltext.] © 2021, The Author(s), under exclusive licence to EDP Sciences, SIF and Springer-Verlag GmbH Germany, part of Springer Nature

Verification of an integral figure of merit for mid-IR nonlinear crystals

The examination and verification of a simple integral figure of merit for nonlinear crystals, taking into account different crystal properties, was studied. The examination was carried out on the basis of experimental data on the broadband sum frequency generation of CO laser radiation in ZnGeP 2 , BaGa 2 GeSe 6 , AgGaSe 2 , GaSe, and PbIn 6 Te 10 mid-IR nonlinear crystals. Taking into account spectral and angular phase-matching bandwidths, the figure of merit provides the best agreement with the experiment and can be applied for qualitative, and even quantitative, comparison of the nonlinear crystals

Three-stage frequency conversion of sub-microsecond multiline CO laser pulse in a single ZnGeP2 crystal

Broadband three-stage frequency conversion of multiline sub-microsecond CO laser radiation in a single sample of ZnGeP2 crystal was experimentally and numerically studied for the first time, to the best of our knowledge. As a result, the hybrid laser system emitted more than 200 narrow spectral lines within the 2.4–6.2 μm spectral range. The measured conversion efficiencies of the first, second, and third stages were about 4.8%, 0.4%, and 0.05%, respectively. Our numerical simulation demonstrated that the third stage of this frequency conversion can extend the laser system spectrum toward the shorter wavelength of 2.2 μm

Carbon cloth damage induced by various shapes of CO2 laser pulses

A qualitative study of the damages on a carbon cloth induced by various shapes of CO2 laser pulses is presented. Three pulse shapes were used: short (100 ns, 84 MW/cm(2)), tailed (similar to 100-ns spike of 70 MW/cm(2), 2-mu s tail), and extralong (45 mu s, 0.5 MW/cm(2)). Apparently, the energy absorbed by the cloth was mainly converted into thermal energy, causing a range of damages, from instantaneous evaporation to cracking and melting, all of which resulted in the cutting of individual fibers in the yarns of the cloth. The two longer types of pulses allowed sufficient time for the stabilization of the affected zone temperature, thus producing melting and a crater-like burning through of the cloth

Nanosecond-Laser Generation of Nanoparticles in Liquids: From Ablation through Bubble Dynamics to Nanoparticle Yield

A comprehensive picture of the nanosecond-laser generation of colloidal nanoparticles in liquids is nowadays the demand of their high-throughput industrial fabrication for diverse perspective biomedical, material science, and optoelectronic applications. In this study, using silicon as an example, we present a self-consistent experimental visualization and theoretical description of key transient stages during nanosecond-laser generation of colloidal nanoparticles in liquids: plasma-mediated injection of ablated mass into the liquid and driving the vapor bubble, finalized by the colloid appearance in the liquid. The explored fundamental transient stages envision the basic temporal and spatial scales, as well as laser parameter windows, for the demanded high-throughput nanosecond-laser generation of colloidal nanoparticles in liquids

Single-shot selective femtosecond laser ablation of multi-layered Ti/Al and Ni/Ti films: Cascaded heat conduction and interfacial thermal effects

Single-shot femtosecond laser ablation of Ti(Al/Ti)(5) and (Ni/Ti)(5) films on silicon substrates was studied as a function of laser fluence by means of scanning electron microscopy, energy-dispersive x-ray spectroscopy, and optical profilometry. Ablation occurs as gradual threshold-like selective removal of a few top layers at lower fluences and rather continuous removal at higher fluences, exponentially increasing versus ablated depth, with the final complete (through) ablation of the entire films. The observed selective rupture at the different internal interfaces was related to thermomechanically and chemically enhanced (interface-facilitated) explosive boiling, with the corresponding energy deposition provided by cascaded heat transfer in the poorly conducting Ti and Ni, and highly conducting Al layers and the interfacial thermal (Kapitza) resistance effect. Published by AIP Publishing