Probe Absorption Research Articles

Full spectrum 2D IR spectroscopy reveals below-gap absorption and phonon dynamics in the mid-IR bandgap semiconductor InAs.

While the mid-infrared spectral region spans more than 3000cm-1, ultrafast mid-IR spectroscopies are normally limited to the spectral bandwidth that can be generated in optical parametric amplifiers-typically a few hundred cm-1. As such, the spectral coverage in conventional two dimensional infrared (2D IR) spectroscopy captures only about 1% of the full potential 2D mid-IR spectrum. Here, we present 2D IR spectra using a continuum source as both the excitation and probe pulses, thus capturing close to the full 2D IR spectrum. While the continuum pulses span the entire mid-IR range, they are currently too weak to efficiently excite molecular vibrational modes but strong enough to induce electronic responses and excite phonons in semiconductors. We demonstrate the full spectrum 2D IR spectroscopy of the mid-IR bandgap semiconductor indium arsenide with a bandgap at 2855cm-1. The measured response extends far below the bandgap and is due to field-induced band-shifting, causing probe absorption below the bandgap. While the band-shifting induces an instantaneous response that exists only during pulse overlap, the 2D IR spectra reveal additional off-diagonal features that decay on longer timescales. These longer-lived off-diagonal features result from coherent phonons excited via a Raman-like process at specific excitation frequencies. This study illustrates that the full spectrum 2D IR spectroscopy of electronic states in the mid-IR is possible with current continuum pulse technology and is effective in characterizing semiconductor properties.

Two-color, intracavity pump-probe, cavity ringdown spectroscopy.

We report a proof-of-principle demonstration of intracavity pump-probe, cavity ringdown (CRD) detection in a three-mirror, traveling-wave cavity. With cavity-enhanced pump power and probe absorption path length, the technique is a generally applicable, high-sensitivity, high-selectivity detection method. In our experiments, the pump radiation is switched off during every other probe ringdown, which allows uncorrelated measurements of analyte and background cavity decay rates. The net, two-color signal from the difference between the pump-on and pump-off decay rates is immune to empty-CRD drifts and spectral overlaps from non-target molecular transitions. The immunity to the ringdown drifts allows longer signal-averaging and, thus, higher detection sensitivity. The ability to compensate for the background absorption enhances the detection selectivity in spectrally congested regions. Our technique is well-suited for trace-detection in the mid-IR region, where pump-probe schemes based on strong rovibrational transitions can be applied. In this work, two-color CRD detection is implemented on a ladder-type, three-level system based on the N2O, ν3 = 1 ← 0, P(19) (pump) and ν3 = 2 ← 1, R(18) (probe), rovibrational transitions. By frequency-locking two-quantum cascade lasers to the p-polarization (pump, Finesse = 5280) and s-polarization (probe, Finesse = 67700) cavity modes, we achieve high intracavity pump power (36W) and high probe ringdown rates (>2 kHz). The observed two-color spectra are simulated by a density-matrix, three-level system model that is solved under the constraints of the cavity resonance conditions. In addition to its background compensation capability, experimental flexibility in the selection of pump-probe schemes and signal insensitivity to intracavity laser power are further features that enhance the utility of our technique for mid-IR trace-detection.

Radial spatiotemporal evolution of rf magnetic field and plasma current in a very-high-frequency plasma source over a wide range of plasma density and pressure.

We present detailed spatiotemporal measurements of rf magnetic fields and plasma conduction current as well as the corresponding plasma density profiles when very-high-frequency 100-MHz waves are introduced to a parallel plate plasma. The magnetic probe, optical emission, and plasma absorption probe measurements support a model in which the interaction of high-frequency waves with the moving plasma sheath at specific phases of the very high frequencies (VHF) period leads to local reversals in the vertical rf electric field which can lead to conduction current reversals and circulations. The presence of current reversals and circulation correlate with measured plasma uniformity. In particular, measured electric field and current reversals coincide with the strongly center-peaked plasma density profiles frequently observed in VHF plasma. The magnitude of the center peak increases with the number and magnitude of the current reversal cells. The scale length of the current reversal cells is on the order of what is expected for plasma surface waves. Measurements indicate that plasma conductivity is the common scaling factor for both plasma uniformity and the circulation. The propagation of high-frequency waves and the generation of rf current reversal in one phase of the rf cycle rather than another results in the appearance of harmonics in Fourier decomposed magnetic probe wave forms. These harmonics turn out not to be actual waves or evidence of standing waves at these frequencies but rather consequences of packets of wave propagation that occur periodically.

Doppler-free spectroscopy of the lowest triplet states of helium using double optical resonance

Optical pumping on the 2 $$^3$$ S–2 $$^3$$ P transition (1083 nm) of metastable $$^3$$ He or $$^4$$ He atoms is used for fundamental science and applications. We report on its combination with an optical probe on the 2 $$^3$$ P–3 $$^3$$ S transition (706.5 nm) in a ladder-type double optical resonance scheme, with CW single-frequency pump and probe diode lasers. Theoretical expectations for level structure and absorption spectra were computed for both isotopes. Narrow Doppler-free absorption lines were experimentally obtained in low-pressure gas samples. The line weights and Zeeman structure in weak magnetic field agreed with expectations. The precision of the line positions and line splittings was limited by generic errors of our commercial Fizeau wavemeter, which were independently characterised. The potential of this double resonance scheme for spectroscopic measurements on the three lowest triplet states of He was evaluated. The relevance of velocity- and sublevel-selective pumping combined with polarisation spectroscopy of probe absorption for a study of pressure-dependent population transfers in the 2 $$^3$$ P state was established.

Investigation of Ultrafast Carrier Dynamics in InGaN/GaN‐Based Nanostructures Using Femtosecond Pump–Probe Absorption Spectroscopy

GaN‐based optoelectronic devices including light‐emitting diodes and lasers realized with quantum‐confined nanostructures, revolutionized the solid‐state lighting. Excited‐state ultrafast nonlinear dynamics of these nanostructures are crucial in determining the device performance in terms of luminescence efficacy, emission spectra, wall‐plug efficiency, turn‐on delay, lasing threshold current, and modulation bandwidth. Therefore, understanding the carrier and photon dynamics of these nanostructures is of utmost importance. A comparative investigation of ultrafast nonlinear carrier‐photon dynamics of 2D, 1D, and 0D InGaN/GaN nanostructures is carried out. Femtosecond pump–probe absorption spectroscopy is used uniformly herein to obtain the wavelength‐dependent ultrafast kinetics of these nanostructures, with a temporal resolution of ≈50 fs. Carrier thermalization and relaxation processes of all the samples are studied both experimentally and theoretically. Distinguished phenomena, such as fast carrier trapping and subsequent detrapping of the carriers from sub‐bandgap defect states are observed. Real‐time monitoring of quantum confined Stark effect, enhanced radiative recombination, and diffusion‐limited carrier kinetics are manifested. Carrier capture and recombination time constants are calculated theoretically, considering quantum properties. Theoretical values are in good agreement with the experimental observations. In addition, transient absorption spectroscopy is used to investigate and decouple the surface and the bulk properties of GaN surfaces.

Cross-Investigation on Copper Nitroprusside: Combining XRD and XAS for In-Depth Structural Insights

The emerging energy demand and need to develop sustainable energy storage systems have drawn extensive attention to fundamental and applied research. Anion redox processes were proposed in cathodic materials in addition to traditional transition metal redox to boost the specific capacity and the electrochemical performance. Alternatively, copper nitroprusside (CuNP) features an electroactive nitrosyl ligand alongside the two structural metals (Fe, Cu), representing an alternative to anion redox in layered oxides. Here, a deep structural investigation is carried out on CuNP by complementing the long-range order sensitivity of X-ray diffraction (XRD) and the local atomic probe of X-ray absorption (XAS). Two different CuNP materials are studied, the hydrated and dehydrated forms. A new phase for hydrated CuNP not reported in the literature is solved, and Rietveld refined. The XAS spectra of the two materials at the Cu and Fe K-edges show a similar yet different atomic environment. The extended XAS spectra (EXAFS) analysis is accomplished by considering three- and four-body terms due to the high collinearity of the atomic chains and gives accurate insight into the first-, second-, and third-shell interatomic distances. Both materials are mounted in Li-ion and Na-ion cells to explore the link between structure and electrochemical performance. As revealed by the charge/discharge cycles, the cyclability in Na-ion cells is negatively affected by interstitial water. The similarity in the local environment and the electrochemical differences suggest a long-range structural dependence on the electrochemical performance.

Probing large-scale UV background inhomogeneity associated with quasars using metal absorption

ABSTRACT We study large-scale UV background inhomogeneity in three-dimensions associated with the observed quasar populations at high redshift. We do this by measuring metal absorption through quasar absorption spectrum stacking as a function distance to closest quasar in SDSS-IV/eBOSS on 10 s of comoving megaparsec scales. We study both intergalactic medium absorbers and mixed circumgalactic medium absorbers and probe absorption in O vi, C iv, and Si iv, and Si iii. Overall, stronger high ionization species absorption is seen closer to quasars at 2.4 < z < 3.1. O vi absorption shows a particularly strong change, with effects in C iv evident in some cases, and more marginal effects in Si iii and Si iv. We further study 2.05 < z < 2.4 (with weak signs of increasing homogeneity with time) and explore the study of metal absorption as a function of integrated SDSS-r band flux quasar flux (yielding consistent but less significant results). While the metal absorption does show sensitivity to large-scale 3D quasar proximity, the current incomplete quasar samples limit detailed interpretation. This work does, however, demonstrate that UV background inhomogeneities exist on scales of several 10 s of comoving megaparsecs associated with quasars and that they can be measured with precision by examining metal absorption in the intergalactic medium.

Effective Control of the Optical Bistability of a Three-Level Quantum Emitter near a Nanostructured Plasmonic Metasurface

We study, theoretically, the phenomena optical bistability and multistability of a hybrid quantum-plasmonic system immersed within an optical ring cavity. The hybrid quantum-plasmonic system consists of a three-level V-type quantum emitter and a two-dimensional plasmonic metasurface of gold nanoshells. The quantum emitter and the plasmonic metasurface are placed in close proximity to each other so that a strong quantum interference of spontaneous emission occurs, which enables the strong modification of optical-bistability/ multistability hysteresis curves. Along with this, the strong interaction between the emitter and the plasmonic metasurface allows for active control of the corresponding bistable threshold intensity. Furthermore, we show that by varying the metasurface-emitter separation, a transition from bistability to multistability of the hybrid system is observed. Lastly, by introducing an additional incoherent pumping in the system, we have the emergence of phenomena, such as probe absorption and gain, with or without population inversion. The results may find technological application in on-chip nanoscale photonic devices, optoelectronics and solid-state quantum information science.

Controllable probe absorption spectrum via vortex beams excitation in a cascaded atomic system

Dynamic control of probe absorption spectrum via vortex beams in multilevel systems has attracted much attention because it provides an avenue to observe unique transport properties. In this paper, we employ experimentally accessible parameters to flexibly control the probe absorption spectrum that shows vortex-induced transparency (VIT) and absorption (VIA) phenomena. Specifically, this system can be served as an optical switch while the vortex beams can act as the control knob, which has the ability to switch from a transparency dip to an absorption peak. Differing from a conventional electromagnetically induced transparency technique, our proposed scheme investigates VIT and VIA by tuning the orbital angular momentum of vortex beams in the resonance and non-resonance cases. Moreover, the collective feature caused by constructive or destructive interference is also studied via adjustable frequency detuning. Our results may provide an efficient approach to study similar phenomena in multilevel quantum systems driven by optical vortex beams.

Ultrafast cation doping of perovskite quantum dots in flow

•Ultrafast continuous flow cation doping of metal halide PQDs •Microfluidic mechanistic investigations of the ultrafast cation-doping process •Unveiled a two-stage mechanism of post-synthetic cation doping of PQDs •Precise in-flow tuning of the optical properties of Mn-doped PQDs Among all-inorganic metal halide perovskite quantum dots (PQDs), cesium lead chloride (CsPbCl3) with its large band-gap energy is an excellent candidate for enhancement of PQD radiative pathways through incorporation of additional internal energy transfer within its exciton band gap. In this study, we introduce a post-synthetic chemistry for ultrafast metal cation doping of CsPbCl3 QDs with a high degree of tunability, using a model transition metal impurity dopant, manganese. Due to the fast nature of the post-synthetic metal cation-doping reaction, an engineered time-to-space transformation strategy is employed to unravel the kinetics and fundamental mechanism of the doping process. Using a modular microfluidic platform equipped with a translational in situ absorption and photoluminescence spectroscopy probe, we propose a heterogeneous surface-doping mechanism through a vacancy-assisted metal cation migration. The developed in-flow doping strategy can open new avenues for on-demand optoelectronic properties tuning and scalable precision synthesis of high-quality metal cation-doped PQDs. Among all-inorganic metal halide perovskite quantum dots (PQDs), cesium lead chloride (CsPbCl3) with its large band-gap energy is an excellent candidate for enhancement of PQD radiative pathways through incorporation of additional internal energy transfer within its exciton band gap. In this study, we introduce a post-synthetic chemistry for ultrafast metal cation doping of CsPbCl3 QDs with a high degree of tunability, using a model transition metal impurity dopant, manganese. Due to the fast nature of the post-synthetic metal cation-doping reaction, an engineered time-to-space transformation strategy is employed to unravel the kinetics and fundamental mechanism of the doping process. Using a modular microfluidic platform equipped with a translational in situ absorption and photoluminescence spectroscopy probe, we propose a heterogeneous surface-doping mechanism through a vacancy-assisted metal cation migration. The developed in-flow doping strategy can open new avenues for on-demand optoelectronic properties tuning and scalable precision synthesis of high-quality metal cation-doped PQDs.

Nd(III) hypersensitive peak as an optical absorption probe for determining nitric acid in aqueous solution: An application to aqueous raffinate solutions in nuclear reprocessing

A new method using Nd(III) absorption peak as a probe is described for the measurement of nitric acid concentration in aqueous solution. The hypersensitive peak of Nd(III) at 575.1 nm shows a substantial enhancement in the absorbance in comparison to other absorption peaks with increasing nitric acid concentration. The integrated area and absorbance of this hypersensitive peak show a linear dependency over a large dynamic range of 0.5–15.5 M of nitric acid. A methodology for the correction of spectral interference to the probing absorption peak of Nd(III) is also reported. The method is applied for the measurement of nitric acid in synthetic high level liquid waste solution and shown to be comparable to that obtained by titrimetric method. The present method can be easily adopted for the measurement of nitric acid concentration in aqueous raffinate solutions of nuclear reprocessing streams.

Theoretical study of the control of absorption, transparency, and amplification in a microwave- and RF-driven four-level (Δ + ∇)-type closed-contour interaction system

This paper describes a theoretical study of the optical responses of an atomic medium to the probe field in a four-level (Δ + ∇)-type closed-contour interaction system driven by two pump laser fields (P1, P2), one probe laser field (Pr) and two microwave or radio frequency (RF) coupling fields (L, U). Here, L and U are considered to connect the forbidden electric dipole transitions, i.e. two hyperfine ground states of the Δ subsystem and two hyperfine excited states of the ∇ subsystem, respectively. Since each subsystem is a closed-loop system, relative phases are thought to be present between the optical fields (pump and probe fields), and the microwave or RF fields. The manipulation of the quantum coherence of the system by the strengths of coupling fields along with the relative phases is demonstrated in terms of the changes occurring in the absorption of the probe field by the medium. The probe absorption and dispersion profiles are extracted by numerically solving the optical Bloch equations for the system under steady-state conditions. In this study, we start by illuminating the system with the probe only, and then, by applying the pump fields and the coupling fields one by one, the changes in the absorptive and dispersive probe line profiles are investigated for two distinct cases that depend on the relative strengths of the pump fields, e.g. when P2 is stronger than P1 and vice versa. Furthermore, the individual effects of the strengths and phases of the coupling fields on the probe absorption, transparency and amplification are also explored for both cases. All the changes that appear in the probe signal as a result of the application of different fields are explained by the modified interaction fields or the corresponding effective Rabi frequencies obtained from the partial dressed-state analysis.

Electronic structure modulation of MoS2 by substitutional Se incorporation and interfacial MoO3 hybridization: Implications of Fermi engineering for electrocatalytic hydrogen evolution and oxygen evolution

The design of earth-abundant electrocatalysts that can facilitate water splitting at low overpotentials, provide high current densities, and enable prolonged operational lifetimes is central to the production of sustainable fuels. The distinctive atomistic and electronic structure characteristics of the edges of MoS2 imbue high reactivity toward the hydrogen evolution reaction. MoS2 is nevertheless characterized by significantly high overpotentials as compared to platinum. Here, we demonstrate that modulation of the electronic structure of MoS2 through interfacial hybridization with MoO3 and alloying of selenium on the anion sublattice allows for systematic lowering of the conduction band edge and raising of the valence band edge, respectively. The former promotes enhanced electrocatalytic activity toward hydrogen evolution, whereas the latter promotes enhanced activity toward the oxygen evolution reaction. Such alloyed heterostructures prepared by sol-gel reactions and hydrothermal selenization expose a high density of edge sites. The alloyed heterostructures exhibit low overpotential, high current density, high turnover frequency, and prolonged operational lifetime. The mechanistic origins of catalytic activity have been established based on electronic structure calculations and x-ray absorption and emission spectroscopy probes of electronic structure, which suggest that interfacial hybridization at the MoO3 interface yields low-lying conduction band states that facilitate hydrogen adsorption. In contrast, shallow Se 4p-derived states give rise to a raised effective valence band maximum, which facilitates adsorption of oxygen intermediates and engenders a low overpotential for the oxygen evolution reaction. The findings illustrate the use of electronic structure modulation through interfacial hybridization and alloying to systematically improve electrocatalytic activity.

1-Oxo-1H-phenalene-2,3-dicarbonitrile Based Sensor for Selective Detection of Cyanide ions in Industrial Waste

A phenalenedicarbonitrile (1-oxo-1H-phenalene-2,3-dicarbonitrile) based probe 3 has been synthesized by following oxidative nucleophilic substitution of aromatic hydrogen reaction (SNArH) also called green reaction. Probe 3 is found to be selective towards detection of cyanide (CN−) ions even in the presence of other anions. It originally gives pink color in H2O-CH3CN (1:9, v/v) and is found to be non-emissive when observed under Ultraviolet (UV) lamp. Upon adding of CN− ions to solution of probe 3 (20 µM, H2O-CH3CN (1:9, v/v)) the pink color of probe 3 is bleached out and bright yellow emission is attained when observed under UV-lamp. The colorimetric changes are also accompanied by spectral changes. The absorption and low-intensity emission maximum of probe 3 have been observed at 527 nm and 567 nm, respectively but upon adding CN−, the absorption at 527 nm is quenched with formation of new band at 454 nm whereas enhancement in emission band at 567 nm is observed. Probe 3 shows strong binding for CN− ions and binding constant is calculated to be 1.1 × 104 M−1 through fluorescence titration profile and can detect CN− as low as 5.5 × 10−8 M. Binding mechanism of CN− with probe 3 is analyzed through infra-red spectroscopy and proton NMR titration, which reveals that CN− ions attack chemodosimetrically on -C=O of probe 3 to form cyanohydrin. Probe 3 is also used for detection of CN− in industrial waste water. The spectral changes of probe 3 in presence of a specific ion have been used to design a 1-to-2 decoder.

Loop-mediated fluorescent probes for selective discrimination of parallel and antiparallel G-Quadruplexes

Herein we report simple pyridinium (1–3) and quinolinium (4) salts for the selective recognition of G-quadruplexes (G4s). Among them, the probe 1, interestingly, selectively discriminated parallel (c-KIT-1, c-KIT-2, c-MYC) G4s from anti-parallel/hybrid (22AG, HRAS-1, BOM-17, TBA) G4s at pH 7.2, through a switch on response in the far-red window. Significant changes in the absorption (broad 575 nm → sharp 505 nm) and emission of probe 1 at 620 nm, attributed to selective interaction with parallel G4s, resulted in complete disaggregation-induced monomer emission. Symmetrical push/pull molecular confinements across the styryl units in probe 1 enhanced the intramolecular charge transfer (ICT) by restricting the free rotation of CC units in the presence of sterically less hindered and highly accessible G4 surface/bottom tetrads in the parallel G4s, which is relatively lower extent in antiparallel/hybrid G4s. We confirm that the disaggregation of probe 1 was very effective in the presence of parallel G4–forming ODNs, due to the presence of highly available free surface area, resulting in additional π-stacking interactions. The selective sensing capabilities of probe 1 were analyzed using UV–Vis spectroscopy, fluorescence spectroscopy, molecular dynamics (MD)–based simulation studies, and 1H NMR spectroscopy. This study should afford insights for the future design of selective compounds targeting parallel G4s.

Studies of Ultrafast Molecular Dynamics by Femtosecond Extreme Ultraviolet Absorption Spectroscopy

Transient absorption spectroscopy is one of the most widely used experimental techniques for time-resolved studies of ultrafast phenomena. Recent advances in the generation of short-wavelength pulses of ultrashort duration have made transient absorption probing of atomic core level transitions possible. In this Highlight Review, we introduce our recent work on using extreme ultraviolet (XUV) transient absorption spectroscopy to investigate the ultrafast molecular dynamics induced by intense laser fields. While investigations of intense laser-molecule interaction have primarily focused on elucidating electron dynamics, it is important to understand the vibrational dynamics that are triggered by intense laser fields because of their coupling to electron dynamics. Probing the iodine 4d core level, our XUV transient absorption studies of iodoalkanes irradiated by intense laser fields elucidate ultrafast dissociative ionization dynamics and vibrational wave packet dynamics. Time-dependent XUV spectral shifts and global analysis of time-resolved XUV transient absorption spectra can be used to reconstruct C–I dissociation dynamics and identify multiple dissociation channels. In addition, XUV transient absorption spectroscopy also unravels both small- and large-amplitude coherent vibrational motion, whose origin can be identified by analyzing the phase of the oscillatory XUV transition energies. Our studies show that XUV transient absorption spectroscopy is a powerful technique for the study of ultrafast molecular dynamics.

Upconversion Nanoparticles Encapsulated with Amorphous Silica and Their Emission Quenching by FRET: A Nanosensor Excited by NIR for Mercury Detection

Near-infrared (NIR) region has been considered as a diagnostic window since it avoids sample autofluorescence and light scattering. Upconversion nanoparticles (UCNPs) convert NIR light into high energy excitation light, making them a suitable excitation source for nanoprobes with deep penetration depth and high signal-to-noise ratio. The current work reported a rhodamine-derived probe for the detection of Hg(II). Corresponding absorption and emission responses for Hg(II) and detailed recognizing mechanism were discussed. An absorption titration experiment was performed. It was found that Hg(II) directly bonded with probe with chemical stoichiometry of 1:1, its association constant was calculated as 2.59 × 105 M−1. Such a high value indicated a direct coordination affinity between Hg(II) and this rhodamine-derived probe. Most metal cations exerted no increasing effect on the probe emission or absorption, exhibiting good sensing selectivity of probe towards Hg(II). Upconversion nanoparticles (UCNPs) were firstly encapsulated with silica (SiO2) and then bonded with the probe via a covalent bond. Given a near-infrared (NIR) laser excitation with wavelength of 980 nm, this probe, (E)-2-((3′,6′-bis(diethylamino)-2′,7′-dimethyl-3-oxospiro[isoindoline-1,9′-xanthen]-2-yl)imino)acetaldehyde (denoted as RHO), captured the energy of UCNPs via a FRET (fluorescence resonance energy transfer) path, resulting in the emission quenching of UCNPs. This composite system showed linear sensing behavior towards Hg(II) with high selectivity, which was similar to the case of pure probe. No probe emission, however, was observed from the composite system, which was different from the case of most literature reports. The self-quenching between probe molecules was claimed responsible for the probe emission, which was confirmed by experiment result and analysis. To the best of our knowledge, this is the first demonstration of covalently integrating SiO2-coated UCNPs with a rhodamine-derived probe for Hg(II) sensing.

The analysis of coherent phenomena for both linear and non-linear interactions in a four-level ladder (Ξ)-type configuration using density matrix formalism in dressed state representation

In this paper, we present a theoretical study of Autler-Townes (AT) splitting, electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) phenomena in a four-level ladder (Ξ)-type configuration formed by two coupling and one probe laser fields using density matrix formalism in dressed state representation (DSR). The DSR is followed by the analytical solution of the optical Bloch equations (OBEs) under density matrix formalism in bare state representation (BSR). The density matrix elements are presented in both linear and non-linear interaction regimes under DSR. The concept of transfer of population (TOP) mechanism has been shown by calculating the different transition probabilities in DSR. It has been found that the population in a particular dressed state is greatly enhanced by increasing the strength of coupling field and played a key role to manipulate the induced coherence between different energy levels. The present theoretical model of DSR offers an excellent interpretation of the formation of EIT, EIA and conversion from EIT to EIA in both linear and third order non-linear probe absorption profiles. Besides, the dispersion profiles in both linear and non-linear interaction regimes have also been studied and the conversion of normal to anomalous dispersion profile which drastically modifies the optical responses of the medium has been discussed. We have found that the amplitudes of the coherent signals are more sensitive to the third order non-linear interaction compared to first order linear interaction.

Photoluminescence nonlinearity and picosecond transient absorption in an LYSO:Ce scintillator excited by a 266 nm ultraviolet laser.

Lutetium–yttrium oxyorthosilicate doped with cerium (LYSO:Ce) is a widely used scintillator, and the study of its nonlinear behavior under high excitation density is very significant owing to its direct influence on radiation measurements. Using a 266 nm ultraviolet laser to excite an LYSO:Ce crystal, the relationship between the photoluminescence (PL) light yield and excitation density was studied by Z scan experiments. The excitation threshold of the LYSO:Ce was obtained, which is about 2.3 J cm−3. Picosecond transient absorption of LYSO:Ce at 800 nm was obtained and used to analyze the dynamic process of carriers. The physical mechanism behind the nonlinearity was discussed and analyzed using the Förster dipole–dipole interaction model, and the interaction characteristic radius was obtained by fitting. This work can help us understand the nonlinearity phenomenon in scintillators and provide references for related radiation detection applications.

Subwavelength three-dimensional Rydberg atom localization by optical absorption microscopy

We propose a scheme for subwavelength three-dimensional (3D) Rydberg atom localization in a (V + Ξ)-type atomic system by spatial optical absorption microscopy. Position-dependent atom–field interaction allows atom position information to be obtained via measurement of the probe absorption. Some distinctive spatial localization patterns are discovered by adjusting the detuning and Rabi frequency of the laser fields. A 100% probability of finding the Rydberg atom at a specific position in 3D subwavelength space is achieved under appropriate conditions. This scheme may provide a novel approach for realizing high-precision 3D Rydberg atom localization in experiment.