In this work, we present studies on the effect of laser wavelengths on the laser-induced plasma characterization using a femtosecond (fs) ytterbium-doped potassium-gadolinium tungstate (Yb:KGW) ...laser. Plasma plumes of copper, steel, ceramics, and glass samples were induced using a multiple shot of 200 fs laser pulses with 1030 nm and 343 nm wavelengths at fixed laser fluence (
10.5
J
/
cm
2
) and analyzed using the laser-induced breakdown spectroscopy (LIBS) technique. Time-resolved fs-LIBS measurements were performed on the same set of samples and under the same experimental conditions. For the calculation of plasma parameters, the set of spectral lines of Cu(I) (for copper sample), Fe(I) (for steel sample), and Ca(I), K(I) (for glass and ceramics samples) were observed. The plasma electron temperature and density were evaluated from the Boltzmann plots and Stark-broadening profiles of the plasma spectral lines, assuming the local thermodynamic equilibrium condition. Time-resolved plasma temperature and electron density for fs-LIBS using ultraviolet (UV) and infrared (IR) laser wavelengths were analyzed and no significant dependence on fs laser wavelength was observed for any of the samples. However, for all samples the signal-to-noise ratio (SNR) significantly increased using UV laser radiation: copper (
∼
100
%
), steel (
∼
300
%
), glass (
∼
400
%
), and ceramics (
∼
40
%
). Therefore, by using a fs UV laser wavelength for laser-induced breakdown spectroscopy experiments, for certain materials the SNR and at the same time the limit of detection can be significantly enhanced.
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NUK, OILJ, SAZU, UKNU, UL, UM, UPUK
Recent measurements of time delays during tunnelling of cold atoms through an optically created potential barrier have fuelled an ongoing debate about possible time delays during light-induced ...tunnelling of an electron from an atom. Yet, such a delay—whether it is present or not—is only one quantity characterizing the tunnelling wavepacket, whilst the underlying dynamics are richer. Here we show how to complement photo-electron detection in laser-induced tunnelling by measuring the light emitted by the tunnelling electron—the so-called Brunel radiation. Using a combination of single- and two-colour driving fields, we identify the all-optical signatures of the reshaping of the tunnelling wavepacket as it emerges from the tunnelling barrier and moves away from the core. This reshaping includes not only an effective time delay but also the time-reversal asymmetry of the ionization process, which we describe theoretically and observe experimentally. We show how both delay and reshaping are mapped onto the polarization properties of the Brunel radiation, with different harmonics behaving as different hands of a clock moving at different speeds. The all-optical detection may also allow time-resolved measurements of optical tunnelling in condensed matter systems on the attosecond time scale.Whether or not an electron wavepacket accumulates a time delay when tunnelling out of an atom is still under debate. Improved all-optical characterization of the tunnelling dynamics by combining one- and two-colour driving fields may shed light on this question.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Investigations on the ablation of steel and copper with femtosecond laser pulses using single pulses and bursts of infinite sequence of pulses with 1 GHz intraburst repetition rate are presented in ...this paper. The ablation efficiency is compared to the case of single femtosecond laser pulses. Based on the literature a model of the ablation process is presented explaining the behavior of a pulse burst and the good qualitative agreement of the numerical and experimental ablation efficiencies is obtained.
•Laser ablation by femtosecond burst pulses is facilitated by the heat accumulation.•Bursts with a 1 ns period cause lower ablation efficiency than the single pulses.•At 1 GHz intra-burst rate, plasma shielding reduces the amount of absorbed energy.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
Here we present an experimental as well as theoretical study of third-harmonic generation in tightly focused femtosecond filaments in air at the wavelength of
$$1.5 \,\upmu \hbox {m}$$
1.5
μ
...m
. At low intensities, longitudinal phase matching is dominating in the formation of 3rd harmonics, whereas at higher intensities locked X-waves are formed. We provide the arguments that the X-wave formation is governed mainly by the tunnel-like ionization dynamics rather than by the multiphoton one. Despite of this fact, the impact of the ionization-induced nonlinearity is lower than the one from bound–bound transitions at all intensities.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The continuous vacuum ultra-violet (VUV) emission enhancement of argon (Ar2*) and xenon (Xe2*) is reported. In the case of Ar2* the spectral distribution o VUV radiation under the conditions of a ...negative voltage dc discharge with supersonic expansion was obtained. A gain of 2.77 cm−1 of the singlet excimer transition (~ 126nm) was measured in a multi-nozzle setup. In addition, strong emission of the Xe2* singlet state was also observed in a single supersonic nozzle, which was higher than the Ar2* emission, indicating a strong possibility of a laser operation in a novel multi-nozzle setup and a proper evacuating system.
•Narrowband emission of the second continuum of argon dimers.•High gain of argon dimers, in a multi-nozzle setup.•Enhancement of the second continuum of xenon dimers.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
We report pulsed terahertz (THz) emission from solution-processed metal halide perovskite films with electric field 1 order of magnitude lower than p-InAs, an efficient THz emitter. Such emission is ...enabled by a unique combination of efficient charge separation, high carrier mobilities, and more importantly surface defects. The mechanism of generation was identified by investigating the dependence of the THz electric field amplitude on surface defect densities, excess charge carriers, excitation intensity and energy, temperature, and external electric field. We also show for the first time THz emission from a curved surface, which is not possible for any crystalline semiconductor and paves the way to focus high-intensity sources. These results represent a possible new direction for perovskite optoelectronics and for THz emission spectroscopy as a complementary tool in investigating surface defects on metal halide perovskites, of fundamental importance in the optimization of solar cells and light-emitting diodes.
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IJS, KILJ, NUK, PNG, UL, UM
We have studied femtosecond ablation of soda-lime glass sample under thin water film, under KOH and NaCl aqueous solutions films and their influence and benefits compared with ablation in the air ...atmosphere. These have been studied in case of the groove ablation using the infrared (IR) femtosecond laser. KOH aqueous solution film above the glass sample improved the ablation efficiency and led to the formation of the grooves with a higher aspect ratio when multi-scan glass cutting conditions were applied.
We report here the results of comprehensive plasma characterization and diagnostics by analyzing time-resolved absorption spectra of short ultrabroadband (0.1-50 THz) pulses propagated through the ...test plasma. Spectral analysis of plasma-induced absorption of such THz pulses provides very direct, in situ, high dynamical range, potentially single-shot access to the plasma density, plasma decay time, electron temperature, and ballistic dynamics of the plasma expansion. We have demonstrated a proof-of-principle measurement of plasma created by an intense laser beam. In particular, we showed a reliable measurement of plasma densities from around 10^{16} to 10^{20}cm^{-3}. Apart from the plasma parameters, this method allowed us to reconstruct peak intensity inside the plasma spot and to observe a very early stage of plasma evolution after its excitation.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
It is shown, both theoretically and experimentally, that in normally dispersive media under tight-focusing conditions third harmonic is generated by six-wave mixing rather than via common third-order ...frequency tripling. Though far-field pattern of third-harmonic signal was an axially symmetric ring for a wide range of the material wave vector mismatch and laser beam focusing conditions, in some cases the generation of more complex beams has been found possible. Results of simulations of the proposed model qualitatively correspond well with experimental data for the calculated values of third- and fifth-order nonlinear susceptibilities of sodium.
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