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Materials with significant first hyperpolarizability values are essential for application in second harmonic generation to achieve frequency doubling. Therefore, ideal NLO materials must not only exhibit a substantial NLO response but also maintain transparency when exposed to laser light. In this study, we investigate two series of nanoparticles, namely M@b64Al12N12 and M@b66Al12N12 (M ranges from Sc to Zn). The aim is to evaluate the second and third NLO responses through DFT and TD-DFT calculations. These evaluations are performed using the CAM-B3LYP/6-311+G(d) level of theory and the sum-over-states method in the static and dynamic regime (λ = ∞, 1906, 1341, and 1064 nm). These properties are further explained by considering factors such as molecular topology, delocalization indices, Waber–Cromer radius, excitation energy, oscillator strengths, variations of dipole moment of the excited state, and one/two-photon resonance effects. The results indicate that incorporating transition metals into Al12N12 substantially increases both the first and second hyperpolarizability. The delocalization index values reveal a higher degree of electron delocalization between the transition metal and nitrogen compared to that between the transition metal and aluminum. The QTAIM analysis displays that the presence of a closed quasi-ring structure between the metal and the nanocage, combined with electron delocalization, significantly enhances the first hyperpolarizability. TD-DFT calculations suggest potential application of these compounds in deep ultraviolet laser devices due to their transparency below 200 nm. The SOS approach reveals that the most critical excited states are local excitations, characterized by high Sr, small D, and negative t values. On the other hand, in the dynamic regime, our results indicated that the values of βHRS, βSHG(−2ω; ω, ω) and γESHG(−2ω; ω, ω, 0) are larger than their static counterparts. Additionally, one/two photon resonance energy, along with substantial oscillator strength, plays a pivotal role in enhancing the dynamic hyperpolarizability of the investigated nanoparticles. Our findings suggest that the increase in βλ is primarily linked to two-photon resonance rather than one-photon resonance. Based on our current understanding, this study provides novel evidence that, at λ = ∞, the first hyperpolarizability of M@b64/66Al12N12 is correlated with the Waber–Cromer radius of the transition metal. Additionally, in the dynamic regime, the first hyperpolarizability is correlated with the second hyperpolarizability. [ABSTRACT FROM AUTHOR]

Laser induced damage sites on the surface of a KDP crystal component tend to grow with subsequent laser irradiation, which substantially decrease the lifetime of these optics. The structural investigation suggests that this may be related to the surface damage products of the crystals. In this work, the differences in the crystal structures, electronic properties and optical absorption between the KDP crystal and its surface laser-induced decomposition products K2H2P2O7 and KPO3 are investigated by using first-principles calculations. The theoretical results show that the nonlinear optical active units of KDP crystals are disrupted after irradiation dehydration to K2H2P2O7 and KPO3, which leads to the optical properties at the surface damage being deteriorated. In terms of the electronic structure, the dehydration products K2H2P2O7 and KPO3 have a shorter band gap compared with the KDP crystal. In addition, K2H2P2O7 and KPO3 have a wider optical absorption band than that of the KDP crystal and introduce more ultraviolet absorption in the optical elements. Compared to polycrystalline KDP at the bulk damage sites, the dehydration products at the surface damage increase the ultraviolet absorption of the crystals and cause the surface damage to continually grow under subsequent irradiation, whereas the bulk damage does not continue to increase in subsequent laser irradiation. [ABSTRACT FROM AUTHOR]

Development of novel ultraviolet (UV) upconversion materials has been emerging as a hot research topic for application in tunable UV lasers, photocatalysis, sterilization, tagging, and most recently luminescence thermometry. We readily synthesized a series of Ho3+/Gd3+ co-doped LiYO2 upconversion phosphors by a traditional high-temperature reaction. Under excitation from a blue ∼445 nm laser, LiYO2:Ho3+,Gd3+ polycrystalline powders yield intense sharp ultraviolet B (UVB) upconversion luminescence from Gd3+ 6Pj (j = 7/2, 5/2, 3/2) excited states. By means of steady and dynamic photoluminescence spectra, we systematically investigated the involved two-photon absorption upconversion as well as the accompanying energy transfer processes between Ho3+ and Gd3+ ions in the LiYO2 host lattice. Interestingly, the distinguishable UVB luminescence constituents from Gd3+ 6Pj excited states exhibit sensitive temperature dependence in a 353–673 K range. Shedding light on thermal equilibria between Gd3+ 6Pj UV-emitting levels, their luminescence intensity ratios follow Boltzmann statistics for the application of new luminescence thermometry. For the scheme of 6P7/2–6P3/2 thermally coupled levels, it works over a temperature range of 373–673 K with a maximum relative sensitivity (Sr) of about 1.07% K−1 at 373 K, and its 6P7/2–6P5/2 counterpart works over 353–533 K with a maximum Sr of about 0.83% K−1 at 353 K. Overall, our study provides a new pathway to develop UV upconversion materials, and promotes the application of Gd3+-related UV luminescence constituents in sensitive temperature sensing over a wide temperature range. [ABSTRACT FROM AUTHOR]

Multi-element detectable laser excited atomic fluorescence (LEAF) technique has been regarded as impressive progress in the analytical field because it possesses high sensitivity and overcomes the specific resonant wavelength constraint. However, a limited understanding of the universal signal enhancement mechanism restricts its further development and follow-up studies. In this study, experiments of LEAF are conducted to investigate the details of the ablation process, excitation process, and coupling behavior. Multi-element signals were dramatically enhanced with 1.49 mJ ablation laser energy at tip = 200 ns, and quantitative analysis with minimal destruction was obtained. Compared with the literature, the following new understandings are firstly proposed: (1) the ablated mass from the ablation process was plasma instead of just a plume, which was stimulated by an excitation laser; (2) photoexcitation contributes to the enhanced signal other than the electron thermal excitation supported by the fact that the signal gains its higher intensity when the re-excited plasma was less bright. That is, the multi-element excitation may relate to the atom energy-level distortion by the electric field. With the elucidation of key processes and mechanisms, there would be a much broader application for laser ablation-assisted ultraviolet LEAF due to its distinctive advantages. [ABSTRACT FROM AUTHOR]

Considerable efforts have been devoted to the development of visible light-emitting phosphors for anti-counterfeiting application, but the design of multifunctional near-infrared materials with suitable luminescent properties was lacking. Based on the crystal field theory, a near ultraviolet excitable and near-infrared emitting Ca2Sn2(1−x)Al2(1−x)O9:2xCr3+,2xSi4+ phosphor was designed. On the one hand, the Ca2Sn2(1−x)Al2(1−x)O9:2xCr3+,2xSi4+ phosphor showed great potential for applications including anti-counterfeiting and secret signals under a 405 nm near UV laser. The integrated intensity at 150 °C was 75.9%, implying high thermal stability when irradiated with a high power light source. On the other hand, an unexpected red emission component originating from the Cr3+–Cr3+ dimer was observed and was confirmed by fast luminescence decay and electron spin resonance signals. The different thermal stabilities of Cr3+ near-infrared and Cr3+–Cr3+ red emissions opened up a new opportunity for luminescence ratiometric thermometers. [ABSTRACT FROM AUTHOR]

The separation and detection of isomers remains a challenge for many areas of mass spectrometry. This article highlights laser photodissociation and ion mobility strategies that have been recently deployed to meet this challenge with focus on small molecule isomers including protonation isomers, structural isomers, conformation isomers and new studies emerging on chiral isomers. Laser techniques span UV and visible laser photodissociation, time-resolved pump–probe schemes and application of laser hole-burning arrangements to assign isomers within selected ion populations. Also surveyed are applications of ion mobility strategies to separate isomers followed by laser spectroscopic techniques to assign the separated ions. Ultimately, with ongoing refinement in hardware and methods, there are clear pathways forward for laser and mass spectrometry techniques to make decisive breakthroughs in understanding how isomeric details affect biological processes, physiology and disease. [ABSTRACT FROM AUTHOR]

Extreme ultraviolet laser ablation and ionization time-of-flight mass spectrometry (EUV TOF), using a laser that operates at a wavelength of 46.9 nm (26.4 eV photon energy), is a relatively new analytical technique with many unexplored performance characteristics. In this work, we use the EUV TOF to directly measure the 206Pb/238U and 232Th/238U isotope ratios in different geological materials to investigate if the EUV laser is a good candidate for reducing matrix effects in geological analyses. We use the EUV TOF to analyze synthetic glasses of silicate, basalt, and phosphate as well as mineral samples ranging from iron manganese to zircons and monazites to uraninites and a thorite at a spatial scale of approximately 8 μm and at depths ≤500 nm. The results show that the EUV TOF measures 206Pb/238U ratios that have a systematically low bias in glass, iron manganese, zircon, and monazite matrices. This bias can be calibrated using NIST 610 as a non-matrix matched external calibration sample, resulting in 206Pb/238U ratios that are within analytical uncertainty (±2σ) of the expected values. Unlike 206Pb/238U, the 232Th/238U ratios measured in the glass, zircon, and monazite matrices do not show a systematic bias and are within ±2σ of the expected values from direct measurements. The 206Pb/238U and 232Th/238U ratios measured in the uraninite and thorite samples are not within analytical uncertainty of the expected values. The uncertainty in the uraninite and thorite measurements are likely a result of the high amounts of Pb, Th, and U in these samples relative to the other analyzed samples and their effect on the instrument's performance. Overall, this study shows that the EUV ionization mechanisms for Pb, Th, and U are similar in glass, iron manganese, zircon, and monazite matrices, resulting in inter-element ratios that are within analytical uncertainty. EUV laser ablation and ionization is therefore a good candidate for directly measuring the isotopic content in select geological materials at spatial scales of <10 μm. [ABSTRACT FROM AUTHOR]

Bacillus spores are highly resistant to toxic chemicals and extreme environments. Because some Bacillus species threaten public health, spore inactivation techniques have been intensively investigated. We exposed Bacillus atrophaeus spores to a 266 nm Nd:YVO4 laser at a laser power of 1 W and various numbers of scans. As a result, the UV laser reduced the viability of Bacillus atrophaeus spores. Although the outer coat of spores remained intact after UV laser irradiation of 720 scans, damage inside the spores was observed. Spore proteins were identified by matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry during the course of UV laser irradiation. Photochemical and photothermal processes are believed to be involved in the UV laser sterilization of Bacillus spores. Our findings suggest that a UV laser is capable of sterilizing Bacillus atrophaeus spores. [ABSTRACT FROM AUTHOR]

We document the utility for in situ Rb–Sr dating of a one-of-a-kind tribrid mass spectrometer, 'Proteus', coupled to a UV laser ablation system. Proteus combines quadrupole mass-filter, collision cell and sector magnet with a multicollection inductively-coupled plasma mass spectrometer (CC-MC-ICPMS/MS). Compared to commercial, single collector, tribrid inductively-coupled plasma mass spectrometers (CC-ICPMS/MS) Proteus has enhanced ion transmission and offers simultaneous collection of all Sr isotopes using an array of Faraday cups. These features yield improved precision in measured 87Sr/86Sr ratios, for a given mass of Sr analysed, approximately a factor of 25 in comparison to the Thermo Scientific™ iCAP TQ™ operated under similar conditions. Using SF6 as a reaction gas on Proteus, measurements of Rb-doped NIST SRM (standard reference material) 987 solutions, with Rb/Sr ratios from 0.01–100, yield 87Sr/86Sr that are indistinguishable from un-doped NIST SRM 987, demonstrating quantitative 'chemical resolution' of Rb from Sr. We highlight the importance of mass-filtering before the collision cell for laser ablation 87Sr/86Sr analysis, using an in-house feldspar standard and a range of glass reference materials. By transmitting only those ions with mass-to-charge ratios 82–92 u/e into the collision cell, we achieve accurate 87Sr/86Sr measurements without any corrections for atomic or polyatomic isobaric interferences. Without the pre-cell mass-filtering, measured in situ87Sr/86Sr ratios are inaccurate. Combining in situ measurements of Rb/Sr and radiogenic Sr isotope ratios we obtain mineral isochrons. We utilise a sample from the well-dated Dartmoor granite (285 ± 1 Ma) as a calibrant for our in situ ages and, using the same conditions, produce accurate Rb–Sr isochron ages for samples of the Fish Canyon tuff (28 ± 2 Ma) and Shap granite pluton (397 ± 1 Ma). Analysing the same Dartmoor granite sample using identical laser conditions and number of spot analyses using the Thermo Scientific™ iCAP TQ™ yielded an isochron slope 5× less precise than Proteus. We use an uncertainty model to illustrate the advantage of using Proteus over single collector CC-ICPMS/MS for in situ Rb–Sr dating. The results of this model show that the improvement is most marked for samples that have low Rb/Sr (<10) or are young (<100 Ma). We also report the first example of an in situ, internal Rb–Sr isochron from a single potassium-feldspar grain. Using a sample from the Shap granite, we obtained accurate age and initial 87Sr/86Sr with 95% confidence intervals of ±1.5% and ±0.03% respectively. Such capabilities offer new opportunities in geochronological studies. [ABSTRACT FROM AUTHOR]

We report a new method that enables fabrication of Ag–Cu2O core–shell nanowires (NWs) by using pulsed ultraviolet laser light to irradiate a mixed aqueous copper acetate and Ag NW solution. Multiple experimental characterization techniques indicate that laser irradiation can induce both rapid (0.5–6 min) and controllable growth of Cu2O (20–150 nm) on the Ag NWs. Finite-difference time-domain simulations and mechanism analyses show that the good photocatalytic properties of the Ag–Cu2O core–shell NWs are related to the enhanced visible light absorption caused by localized surface plasmon resonance and the improved electron–hole separation efficiency caused by the Ag–Cu2O Schottky junction. [ABSTRACT FROM AUTHOR]

A fluorophore encapsulated in a metal–organic framework showed photochromic multicolour fluorescence. Irradiation with an ultraviolet laser induced the relocation of the fluorophore from a polar to a nonpolar environment, altering the emission from red to blue. This change in emission color can be repeatably recovered by heating the fluorophore–MOF composite. [ABSTRACT FROM AUTHOR]

The fabrication of crystalline oxide films using excimer laser-assisted metal organic decomposition (ELAMOD) involves deploying pulsed UV laser irradiation to achieve photochemical and photothermal reactions of metal–organic materials or amorphous oxide materials. In this study, ELAMOD was used to fabricate SrFeO3−δ thin films under various atmospheric conditions in order to clarify the effect of such conditions on ELAMOD-produced films. Analysis of lattice constants and work functions of the films revealed that performing ELAMOD in air and vacuum induced reduction while performing it in O2 induced oxidation. The extents of reduction and oxidation were enhanced by increasing the laser fluence. Such an ability to control reduction and oxidation when performing ELAMOD should be helpful for the fabrication of functional oxide films. [ABSTRACT FROM AUTHOR]

Thirteen organochlorine pesticides in a standard sample mixture were measured by gas chromatography combined with mass spectrometry using an ultraviolet femtosecond laser (267 nm) as the ionization source, and the observed mass spectra were compared with the corresponding spectra obtained using an electron ionization source. When an ultrashort optical pulse was used for ionization, molecular ions were typically produced which was preferential for reliably identifying the analytes. The ionization mechanism was studied based on three models constructed for resonance-enhanced two-photon ionization, non-resonant two-photon ionization, and non-resonant three-photon ionization. The optimal conditions for observing a molecular ion were investigated using data obtained for three pulse widths. The results suggest that two-photon ionization with minimum excess energy would be optimal for observing a molecular ion. [ABSTRACT FROM AUTHOR]

Utilizing a customized mass spectrometer, we analyze selective C–C bond and C–N bond activation in neurotransmitters dopamine (DA) and norepinephrine (NE) under deep ultraviolet laser irradiation. [ABSTRACT FROM AUTHOR]

We have developed an in situ method for removing a native silicon oxide layer from an amorphous silicon (a-Si) surface using a UV laser. The a-Si film containing crystalline silicon seeds is used for the subsequent growth of crystalline Si layers by steady-state liquid phase epitaxy (SSLPE). The main goal of this technique is to grow crystalline silicon layers on low-cost glass substrates which can be used as absorber layers for thin film solar cells. We have investigated the interaction between a-Si and laser pulses as well as the growth results by scanning force microscopy (SFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR). The heating of the a-Si surface by a laser pulse is modelled by numerical simulations using a finite element approach in COMSOL-Multiphysics. The simulations verify that the laser pulse heats a-Si to temperatures sufficient for the thermal desorption of the native oxide layer but lower than both the crystallization temperature of a-Si and the glass transition temperature. [ABSTRACT FROM AUTHOR]

We demonstrate a new technique for trace analysis that has nanometer scale resolution imaging capability: Extreme Ultraviolet Time-of-Flight Laser Ablation Mass Spectrometry (EUV TOF). We describe the characterization of this technique and discuss its advantages. Using the well-standardized NIST 61x glasses, the results show the EUV TOF spectra contain well defined signatures of U, Th, and their oxides, with far fewer spectral interferences than observed in Time-of-Flight Secondary Ion Mass Spectrometry (SIMS TOF). We demonstrate that the ratio of U and Th ions to the oxide ion signatures is adjustable with EUV laser pulse energy. Sample utilization efficiency (SUE) which measures the ratio of detected ions to atoms in the ablated volume was used as a measure of trace analysis sensitivity of EUV TOF. For U and Th, SUE is 0.014% and 0.017%, respectively, which is comparable to SIMS TOF in the same mass range. In imaging mode EUV TOF is capable to map variations in composition with a lateral resolution of 80 nm. Such high lateral resolution enabled mapping of the isotope distribution of 238U and 235U in closely spaced micron-size uranium oxide particles from isotope standard materials. Trace elemental sensitivity and nanometer spatial resolution gives EUV TOF great potential to dramatically improve the state-of-the-art laser ablation/ionization mass spectrometry and elemental spectro-microscopy for applications such as geochemical, forensic and environmental analysis. [ABSTRACT FROM AUTHOR]

In this article, the coupling of a UV-fs-LA system with a sector-field ICP-MS for isotopic analysis of individual sub micrometric and micrometric uranium particles, especially for the measurement of minor isotopes (234U and 236U), is discussed. Ablation of uranium particles results in short (a few seconds) and highly noisy signals with sudden and extremely brief (＜1 ms) increases in intensity (referred to as ‘spikes’), making the precise determination of isotope ratios very challenging. Uranium particles were located beforehand by means of suitable techniques. Three isotope ratio calculation methods are evaluated. The influence of signal spikes on the accuracy and precision of the isotope ratios is discussed. Thanks to the implementation of a ‘spike rejection filter’, the measurement of uranium isotope ratios in particles from an isotopically certified reference material (NBS U010) is greatly improved. Measured ratios are in acceptable agreement with the reference values although a systematic bias was observed. Limits of detection of a few tens of attograms for minor isotopes are achieved. Isotopic mapping in the area around the initial ablation crater allows the observation of the deposition of debris. No isotope ratio bias is observed when analyzing uranium particles mixed with lead particles, showing that no significant lead-based polyatomic interference is produced. Results, including minor isotope ratios, obtained with particles of sizes from 0.3 to 1.5 μm sampled in a nuclear facility, are in good agreement with the values obtained by another well-established method for such analysis. [ABSTRACT FROM AUTHOR]

Many organic molecules have strong absorption bands which can be accessed by ultraviolet short pulse lasers to produce efficient ionization. This resonant multiphoton ionization scheme has already been exploited as an ionization source in time-of-flight mass spectrometers used for environmental trace analysis. In the present work we quantify the ultimate potential of this technique by measuring absolute ion yields produced from the interaction of 267 nm femtosecond laser pulses with the organic molecules indole and toluene, and gases Xe, N2 and O2. Using multiphoton ionization cross sections extracted from these results, we show that the laser pulse parameters required for real-time detection of aromatic molecules at concentrations of one part per trillion in air and a limit of detection of a few attomoles are achievable with presently available commercial laser systems. The potential applications for the analysis of human breath, blood and tissue samples are discussed. [ABSTRACT FROM AUTHOR]

The fabrication of thin oxide films at low temperatures using simple processes has been a significant challenge associated with expanding the potential applications of these materials. Recent developments have demonstrated that the photo-assisted chemical solution deposition (PACSD) process offers a promising means of solving these difficulties, allowing high volume, on-demand production of variable sample sizes using an advantageous wet process. A better understanding of the crystal growth phenomena associated with this process, however, is required to enable various oxide thin films to be prepared using this new concept. Under pulsed ultraviolet (UV) laser irradiation, crystal growth has been confirmed to proceed by near-instantaneous photothermal heating and photochemical effects at the reaction interface. Vacuum UV lamp irradiation is also a useful means of generating oxide nuclei, since it results in effective chemical bond cleavage and simultaneously produces reactive oxidant (O3/O(¹D)) species. In this review, the nucleation and growth mechanisms which occur during the PACSD process are introduced and discussed and we examine the future possible applications of this process. [ABSTRACT FROM AUTHOR]

We study the use of an ultraviolet (UV) femtosecond (fs)–nanosecond (ns) double-pulse scheme to improve the analytical capabilities of Laser Induced Breakdown Spectroscopy (LIBS) in the few-micron (＜2 μm) spatial resolution regime. We show that a double-pulse orthogonal configuration can enhance the spectral emission intensity by roughly 360 times as compared to a single-fs laser pulse LIBS of silicon (Si). Although the spectral emission lifetime in single-pulse LIBS is less than 20 ns, the second pulse provides signal enhancement hundreds of nanoseconds later, indicating that a significant number of non-radiative species (neutrals and/or particles) exist in these small length-scale plasmas long after the fs-laser pulse is over. The double-pulse configuration is a practical way to improve the limits of detection of LIBS for micron/submicron spatial resolution. [ABSTRACT FROM AUTHOR]