Systematic studies were conducted to elucidate the mechanism of splitting and polarization of the Pb Fraunhofer-type absorption (FTA) lines at 363.95 nm and 283.3 nm. These two lines share the same upper absorption level. It was found that the line splittings ΔUobs, expressed in wavenumber units, are proportional to the square root of the second laser pulse intensity.The two lines show similar splittings in wavenumber units, approximately 26.4 and 24.9 cm−1, and the wavelength separation Δλ differs, as expected, proportionally to the square of the central wavelength of the line (Δλ ∝ λ₀2). These results are characteristic of the Autler–Townes (AT) dressed-state mechanism, indicating that this mechanism is responsible for the FTA line splitting and polarization. A simplified AT model is presented. Based on this model, the effective dipole moment of the dressing transition, deff, was estimated. The polarization of the split lines is explained by considering magnetic sublevels m, selection rules, and pump-induced alignment of these sublevels. A strongly polarized absorption line at 285.57 nm, proportional to the second-laser intensity, was also observed. The 285.57 nm line is not listed in spectral databases. We propose that this line may appear due to the resonantly enhanced two-photon absorption (TPA) in Pb I atoms. This transition may be driven coherently by one UV continuum photon and one 1064-nm pump photon in DP LIP. Transitions are driven coherently by one continuum UV photon and one 1064 nm pump photon in Double-Pulse Laser–Induced Plasma (DP LIP). This hypothesis needs additional experimental and theoretical investigations.

LAMIS is a known technique for isotopic shift analysis of light elements, such as B, C, etc. Its application for heavy molecules has been studied less. We proved that vibrational and rotational transitions A(1 - 0), A(1 - 2), and A(2 - 1) of GdO in Laser-Induced Plasma exhibit apparent differences between natural GdO, 156 GdO, and 158 GdO emissions. The absolute values are in the 0.4 - 0.5 cm-1 range. Besides its adequate spectral resolution, the Demon HR Double Echelle Monochromator proved its sensitivity for isotopic analysis of Rare Earth Elements.

Polarization, broadening, and splitting in Fraunhofer-type absorption (FTA) spectra are observed in colinear Double-Pulse Lase-Induced Breakdown Spectroscopy (DP LIBS). Effects are attributable to the Optical Stark Effect (OSE) induced by the electric field of the second laser pulse within the first pulse-created plasma. This effect manifests exclusively in back-directed Laser-Induced Plasma (LIP) emission and during the presence of the second laser pulse. Notably, the OSE is absent in LIBS observations orthogonal to the direction of the laser beams.

Systematic studies have been conducted on the polarization characteristics of Laser-Induced Plasma Lasers (LIPL) that utilize the quasi-three-level generation scheme. The Degree of Polarization for generation lines is found to alter its sign with a change in the total angular momentum by one, either for the level from which pumping begins or for the lower generation level. While this behavior echoes the Hanle effect, our findings recommend an extension of its theoretical framework to scenarios involving resonantly pumped stimulated emission. Additionally, Cu LIPLs represent the inaugural observation of a level-crossing effect in LIPLs. While this manuscript focuses on the underlying physical effects, it is important to note that LIPLs have potential applications in various domains, including developing quantum devices, coherent lighting systems, and remote magnetometers.

The non-resonant Be I line at 457.27 nm is proposed for Be quantitative analysis by LIBS method in samples such as Cu-Be bronze in the concentration range of about 0.1-5 wt%. This makes it possible to overcome the self-absorption effect in resonant the ion's Be II doublet 313.04-313.11 nm used for trace Be concentrations. This atomic/ionic plasma emission may complement molecular BeO LIBS, which does not suffer from the self-absorption effect in the concentration range of about 0.1-5 wt%. Both atom and molecular LIBS methods are unsatisfactory when Be atoms and molecular emissions overlap with emissions from other species in Laser -Induced Plasma (LIP), such as Al-Be bronze. The molecular laser-induced fluorescence of the BeO diatomic molecules was investigated and found that this method is very suitable for complicated cases.

This chapter provides information about the nonlinear effects of optically pumped laser-induced plasmas (LIP). It may be treated as part of the laser-induced breakdown spectroscopy (LIBS). The chapter discusses lasing effects in LIP on a variety of elements. Stimulated emission (SE) is achieved by pumping the LIP with an optic parametric oscillator tuned in resonance with a strong atomic transition. Placing the plasma within an optical resonator enhances the lasing effect. The chapter presents the generation properties of laser-induced plasma lasers (LIPL). The best one investigated is the generation of the 13th group (Al, Ga, In, and Tl) LIPLs, pumped by resonant, linearly polarized light pulses. The generation of elements from the 14th group (Ge, Sn Pb) occurs, mostly according to the direct generation scheme from the pumped to the intermediate levels. The chapter discusses the generation of the Ge LIPL as an example.

We accomplished the high-resolution study by LIBS and LIBS-MLIF techniques of molecular emission of REE in LIP to evaluate its suitability for the isotopic shift analysis. The GdO molecular is the best choice for natural isotope analysis by combining its molecular weight and emission spectra. The isotopic shifts depend on the specific vibrational transition and are in the range from tenths to several cm−1. For the artificially induced isotopes, the lightest REE (Sc and Y) may be the optimal candidates.

Concrete structures experience severe damage during service, for example due to pitting corrosion of rebars caused by the ingress of chlorine (Cl) into the porous concrete structure. The ingress can be monitored using laser-induced breakdown spectroscopy (LIBS), a recently introduced civil engineering technique used to detect Cl in concrete structures in addition to conventional wet chemistry methods. The key advantages of LIBS are high spatial resolution, which is important when analyzing heterogeneous concrete samples, as well as the almost complete absence of sample preparation. To assess LIBS as a reliable analytical method, its accuracy and robustness must be carefully tested. This paper presents the results of an interlaboratory comparison on the analysis of Cl in cement paste samples conducted by 12 laboratories in 10 countries. Two sets of samples were prepared with Cl content ranging from 0.06 to 1.95 wt% in the training set and 0.23-1.51 wt% in the test set, with additional variations in the type of cement and Cl source (salt type). The overall result shows that LIBS is suitable for the quantification of the studied samples: the average relative error was generally below 15%. The results demonstrate the true status quo of the LIBS method for this type of analysis, given that the laboratories were not instructed on how to perform the analysis or how to process the data.

A natural grossular garnet was found to have a luminescence spectrum with a narrow vibrational structure and short decay time that is unusual for minerals. We propose that such emission is generated by Mn2+ accompanied by defect F-centers which both enhance the transition probability and give rise to sensitivity to optical bleaching and reconstitution via irradiation. The elevated Mn concentration in comparison with other potential luminescent impurities was confirmed by LIBS analysis. Such interpretation contradicts the traditional opinion that Mn2+ centers in minerals are characterized only by broadband emission with very long decay times typical of d-d transitions.

The detection of Rare-Earth-Elements by LIBS by their atomic and ionic emission in many cases is difficult due to significant spectral interferences from other members of this group and accompanying elements. Another potential detection mode is to use molecular emission. It was previously considered that only La, Y, and Sc form analytically useful molecules in Laser-Induced Plasma. We proved that the molecules of other rare-earth elements (Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Y, and Lu) with oxygen appear effective for analytical purposes. The type of the emission spectrum depends on specific element molecular weight and differs for Light and Heavy REE sub-groups. This approach is demonstrated for Gd analysis in ceria (CeO2) and in permanent B-Fe-Nd and Sm-Co-Ni magnets. The presence of molecular emission of Rare-Earth-Elements opens an opportunity to apply Laser Ablation Molecular Isotopic Spectrometry and Molecular Laser-Induced Fluorescence - LIBS combination for their isotopes analysis.

The systematic studies of Ti Laser-Induced Plasma Lasers (LIPL) are presented. Many generation lines in the blue–green spectral range are found. Ti LIPLs are generated according to the quasi-three-level (direct lasing) scheme where generation transitions occur from the pumped to the intermediate level. Most Ti LIPL generation lines are strongly linearly polarized with polarization vector Eg normal or parallel to the pumping polarization vector Ep depending on energy states involved in the generation cycle. External magnetic fields directed parallel to the generation direction strongly reduce the generation lines polarization and reduce line intensity. It is proposed that generation lines polarization at zero magnetic fields, and their depolarization in the external magnetic field may be explained by Hanle zero-field level-crossing effect, which needs to be modified for a direct generation scheme.

Laser-Induced Breakdown Spectroscopy (LIBS) and Laser-Induced Plasma Lasers (LIPL) in elongated Laser-Induced Plasma (LIP) are investigated. It is shown that LIBS and LIPL behavior versus ablation laser pulses are about the same, though LIBS emission is proportional to the atoms in excited states, but LIPL generation is proportional to the atoms in the ground state. Furthermore, two peaks are found in LIBS/LIPL intensities dependencies on laser pulses. The first peak is well-known in LIBS. The second, observed at large ablation pulses number (≥104 pulses in our experimental conditions), may be attributed to the sample's thermal properties, especially thermal capacity and thermal diffusivity.

This work addresses the need to spectrally analyze of the absorption of middle-infrared (mid-IR) radiation in single living cells, with subwavelength spatial resolution, to identify molecular groups in them. The challenge is considerable, no lens can be used, so to realize such a device, a near-field probe was developed, from an optical fiber that is transparent in the mid-IR, non soluble in water, non-toxic and mechanically suitable. Incorporation of this probe in a scanning microscope, and use on a specially contained single living cell in water, allowed to achieve subwavelength imaging. Our fiber-material of choice is silver halides, i.e. AgClxBr1-x made in the Applied Phyics Group of Tel-Aviv University. In spite of being bulky they were mechanically adapted to scanning microscopy. Theoretical and experimental investigations into the dampening of the motion of the probe in water were performed. A grid-like holder for containing living-cells for near-field microscopy has been introduced. The operating principle of this grid is based on sinking the cells inside the holes of the grid and letting them only negligibly protrude out of the holes (compared to the height-range of motion of the tip), in air and water. The result is a demonstration of the operation of the SNIM on different types of objects, including yeast cells, in water.

Strong ionic Be II emission doublet at 313.01 and 313.04 nm in Laser-Induced Plasma (LIP) is well known for trace beryllium quantities analysis. Still, being a resonance line, it suffers from strong self-absorption (SA) starting from very low concentration levels, approximately at 0.005% (50 ppm). It makes this doublet unsuitable for Be evaluation at higher concentrations, typical for minor (0.1-1.0%) or major (>= 1.0%) levels, such as in Be bearing minerals and alloys. Quantitative analysis of Be at elevated concentrations may be accomplished using BeO molecular emission previously not used for analytical purposes in LIP. These molecules are characterized by very intensive blue-green emission series located mainly in the 470-480 nm spectral range. In our experimental setup, molecular BeO emission demonstrates a Limit of Detection (LoD) near 0.05% of BeO at Single Pulse (SP) and 0.01% at Double Pulse (DP) modes. The absence of SA for BeO molecular emission is presently proved in the 0.05-5.0% range, which is quite suitable for minerals and alloys analysis.

We propose a model explaining polarization effects in laser-induced plasma lasers (LIPLs) of the 13th group elements, pumped by a linearly polarized laser beam. The model is based on considering optical transitions between magnetic sublevels involved in the pumping–generation cycle. The model reproduces experimentally observed LIPL polarization features under the np 2P1/2, 3/2 → n′s 2S1/2 pumping. On the other hand, polarization-resolved collisional-radiative modeling appears to be required for a quantitative explanation of the LIPL polarization when the np 2P1/2, 3/2 → n′d 2D1/2 pumping is used.

Our recent study was focused on the emission from Laser Induced Plasma (LIP) at the delay times of tenths of microseconds after the laser pulse. At these long delays, the spectrum is dominated by the broadband molecular emission and plasma induced luminescence (PIL) produced by a luminescent matrix; only solitary atomic emission lines can be seen. Barium fluoride BaF2 activated by thulium (Tm) is a famous scintillator that presents the promising object for LIP in terms of both the potential for BaF molecular emission and Tm3+ PIL. The detection of molecular and PIL bands presents a new opportunity for analysis of halogens and rare-earth elements, which are the difficult objects for LIBS. In this paper, we show that the UV, Green, Extreme Red, and Infrared molecular bands from BaF and blue luminescence from Tm3+ are present in the LIP emission spectra while the detection of atomic emission from F I and Tm I was impossible with the same experimental setup. Thus, the detection of molecular emission and PIL can be more sensitive than the traditional detection of emission from atoms and ions.

The review mainly deals with two topics that became important in applications of laser-induced breakdown spectroscopy (LIBS) in recent years: the emission of halogenand rare-earth-containing molecules and selective excitation of molecules by molecular laser-induced fluorescence (MLIF). The first topic is related to the emission of alkaline-earth diatomic halides MX, M = Ca, Mg, Ba, Sr and X = F, Cl, Br, and I and rare-earth element (REE) oxides LaO, YO, and ScO. These molecules form in laser-induced plasma (LIP) soon after its ignition and persist for a long time, emitting broad bands in a visible part of the spectrum. They are best detected after relatively long delay times when emission from interfering plasma species (atoms and ions) has already been quenched. Such behavior of molecular spectra allows of using, for their detection, inexpensive CCD detectors equipped with simple electronic or mechanical shutters and low-resolution spectrometers. A main target for analysis by molecular spectroscopy is halogens; these elements are difficult to detect by atomic spectroscopy because their most intense atomic lines lie in the vacuum UV. Therefore, in many situations, emission from CaF and CaCl may provide a substantially more sensitive detection of F and Cl than emission from elemental F and Cl and their ions. This proved to be important in mining and concrete industries and even Mars exploration. A similar situation is observed for REEs; their detection by atomic spectroscopy sometimes fails even despite the abundance of atomic and ionic REEs' lines in the UV-VIS. For example, in minerals and rocks with low concentrations of REEs, emission from major and minor mineral elements hinders the weak emission from REEs. Many REEs do not form molecules that show strong emission bands in LIP but can still be detected with the aid of LIP. All REEs except La, Y, and Sc exhibit long-lived luminescence in solid matrices that is easily excited by LIP. The luminescence can be detected simultaneously with molecular emission of species in LIP within the same time and spectral window. The second topic is related to the combination of MLIF and LIBS, which is a technique that was proved to be efficient for analysis of isotopic molecules in LIP. For example, the characteristic spectral signals from isotopic molecules containing B-10 and B-11 are easier to detect with MLIF-LIBS than with laser ablation molecular isotopic spectrometry (LAMIS) because MLIF provides strong resonance excitation of only targeted isotopes. The technique is also very efficient in detection of halogen molecules although it requires an additional tunable laser that makes the experimental setup bulky and more expensive.

Natural radiation-induced red fluorescence of fluorite consists of two broad bands at 750 and 635 nm with very short decay times of 20.3 and less than 5 ns, respectively. The first one is connected to an M center compensated by Na, while the second is connected to an M + center, possibly formed as result of the M center’s destruction by UV irradiation. The optically active centers in naturally irradiated fluorite responsible for red luminescence and purple color are different from one another. The most probable reason for the purple color is colloidal calcium and not the M Na center.

The detection of low halogen concentrations by atomic Laser Induced Breakdown Spectroscopy (LIBS) is usually difficult due to low intensity lines, which overlaps with matrix and due to an uncomfortable spectral region. Molecular LIBS (MLIBS) based on diatomic molecules of halogens with alkali earth element emission substantially increases sensitivity for halogen detection. We demonstrate that the Molecular Laser Induced Fluorescence (MLIF) method allows one to further increase the halogen detection approach. Practical application of the LIBS-MLIF method is demonstrated on Cl atom detection in concrete samples.