Two-photon Process Research Articles

Energy transfer and luminescent properties of Tb3+ and Tb3+, Yb3+ doped CNGG phosphors

In this work, calcium niobium gallium garnet (Ca3Nb1.6875Ga3.1875O12 - CNGG) ceramic samples single-doped with Tb3+ and co-doped with Tb3+ and Yb3+ ions were sintered by the solid-state reaction method. The structural characterization of the samples was carried out by X-ray diffraction measurements. The optimal concentration of Tb3+ ions corresponding to the maximum luminescence in the green spectral range in CNGG:x at% Tb (x = 0.1, 0.5, 1, 2, 3, 4, and 5) was determined to be 4 at%. The time-resolved luminescence of the 5D4 level (Tb3+) in the CNGG:x at% Tb samples was analysed to explore the quenching mechanisms involved in the Tb3+ green emission. Co-doped CNGG:4 at% Tb,y at% Yb (y = 0.5, 2, 4, 6, 8, and 10) ceramics were prepared and investigated. It is shown that CNGG:4 at% Tb,y at% Yb phosphors exhibit intense green luminescence under ultra-violet (UV), visible (VIS), and near-infrared (NIR) excitation, thus demonstrating the presence of simultaneous down-conversion (DC) and up-conversion (UC) processes. The dependence of the UC luminescence intensity on the diode laser pumping power was measured and the results indicate a two-photon process based on cooperative energy transfer (CET). Under UV excitation, the lifetime of the 5D4 (Tb3+) level slowly increases with increase of Yb3+ concentration, suggesting the energy transfer from Yb3+ to Tb3+ ions, while under NIR excitation, the lifetime of the 5D4 (Tb3+) level decreases with increase of Yb3+ ions concentration, indicating the presence of a strong energy transfer from Tb3+ to Yb3+ ions. The highest energy transfer efficiency of ηET ≈42% was determined for the CNGG:4 at% Tb,10 at% Yb sample. The obtained results indicate that CNGG:(Tb3+, Yb3+) could be efficient new yellowish-green-emitting phosphors.

Synthesis and luminescence properties of Er3+ doped and Er3+–Yb3+ codoped phosphovanadate YP0.5V0.5O4 phosphors

A series of Orthovanadate phosphate pure YP0.5V0.5O4, YP0.5V0.5O4 doped Er3+ and codoped Er3+/Yb3+ have been synthesized using a solid-state reaction. The samples were investigated by X-ray diffraction (XRD), infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscopy (SEM) for detailed structural and morphological characterizations. The photoluminescence (PL) spectra were studied as a function of Er3+ concentration. The optimal Er3+ doping concentration in YP0.5V0.5O4 host was determined to be 2 mol%. The extinction phenomenon was correlated to the dipole - dipole (D - D) interactions. In the Er/Yb codoped YP0.5V0.5O4, the Er3+ green-red emission was intensified via the two-photon absorption process. Furthermore, the fluorescence intensity ratio (FIR) method was used to evaluate the optical temperature sensing parameters of the 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 thermally coupled levels (TCL) over the 100–440 K range. The maximum values of Sa absolute and Sr relative sensitivity thermometric parameters were calculated to be 4.10−3 K−1 and 6.58%·K−1 respectively. The effects of the host composition by the presence of the phosphate (PO43−) and the vanadate (VO43−) entities were investigated on the Er3+ emissions and on the Er3+/Yb3+ optical thermometric parameters. YP0.5V0.5O4: Er3+, Er3+/Yb3+ prepared phosphors could be used for display and temperature sensing applications and to optimize the host effects on the luminescence and thermometric properties.

The physical origin of a photon-number parity effect in cavity quantum electrodynamics

The rapidly increasing capability to modulate the physicochemical properties of atomic groups and molecules by means of their coupling to radiation, as well as the revolutionary potential of quantum computing for materials simulation and prediction, fuel the interest for non-classical phenomena produced by atom-radiation interaction in confined space. One of such phenomena is a “parity effect” that arises in the dynamics of an atom coupled to two degenerate cavity field modes by two-photon processes and manifests itself as a strong dependence of the field dynamics on the parity of the initial number of photons. Here we identify the physical origin of this effect in the quantum correlations that produce entanglement among the system components, explaining why the system evolution depends critically on the parity of the total number of photons. Understanding the physical underpinnings of the effect also allows us to characterize it within the framework of quantum information theory and to generalize it. Since a single photon addition/removal has dramatic effects on the system behavior, this effect may be usefully applied, also for amplification purposes, to optoelectronics and quantum information processing.

Nonlinear optical effects in a nucleus

Intense laser technologies generate light with unprecedented and growing intensities. The possibility emerges that a nucleus responds nonlinearly to an intense light field, pointing to an emerging research area of nuclear nonlinear optics. Here we consider two-photon and three-photon absorption (with subsequent disintegration) processes of the deuteron, the simplest and the most fundamental nontrivial nucleus, as prototypes of nuclear nonlinear optical effects. Novel observable effects are predicted. Two-photon and three-photon absorptions are shown to lead to remarkably different angular distributions compared to one-photon absorption. Absorption rates are calculated supporting the feasibility of near-future experimental realization. This work paves a way to the emerging field of nuclear nonlinear optics.

Hyperchaotic and quasiperiodic behaviors of a two-photon laser with multi-intermediate states

In this paper, we discuss a new prospective of chaotic behaviors of a two-photon laser with multi-intermediate states. The generalized density matrix equations of the two-photon process with a cascade configuration are obtained. The nonlinear dynamics of the laser system is investigated using bifurcation diagrams and maximum Lyapunov exponent spectrum in addition to phase portraits. It is shown that the dynamics of the system is highly sensitive to any parameters’ change. Also, the non-symmetric two intermediate levels are investigated. Rich dynamical exhibitions of the system such as periodic, quasiperiodic, chaotic and hyperchaotic behaviors are obtained due to varying pumping parameter. The considered theoretical model illustrates the distinct dynamical regimes at various cases pumping.

Effect of dopants on the nonlinear optical properties of fluorotellurite glasses for optical limiting application

Investigation on non-linear optical property of zinc and barium based fluorotellurite glasses based on open aperture Z-scan technique and its application as an optical limiter is reported. Changes in various parameters like polarizability, refractive index and molar refractivity have been attributed to the presence of barium/ zinc atoms and their impact on modifying the structure. Formation of non-bridging sites owing to fluorine doping have been explored based on Raman measurements. Open aperture data shows reverse saturable absorption behaviour and is attributed to the two-photon absorption process. Non-linear absorption values are found to increase with doping of both barium fluoride and zinc fluoride which has been attributed to the formation of non-bridging fluorine sites alongwith the polarizability of barium atoms. Effect of non-bridging fluorine sites on modifying the optical properties have been justified based on the energy bandgap values. Samples show comparably good optical limiting thresholds with a value of 2.59 × 1012 W m−2 for the sample with highest fluorine concentration, which enables them to be used as limiting devices.

Ultraviolet, blue and singular green upconversion from Gd2Hf2O7 nanocrystals through dopant manipulation

Despite of several advantages of upconversion luminescence (UCL), their full potential is still not completely and commercially harnessed particularly in generating ultraviolet photon and singular visible light. We have taken up this research problem to overcome the global material crisis and tune the color emission in the same materials. Here in this work, we have designed Gd2Hf2O7 nanocrystals (NCs) and co-doped them with Yb3+-Er3+ (GHO-YE) and Yb3+-Tm3+ (GHO-YT) using a molten salt synthesis. Raman spectroscopy data suggest a defect fluorite structure for both GHO-YE and GHO-YT NCs. The GHO-YE NCs display unique UCL phenomenon by converting near infrared (NIR) photon into singular green emission by back transferring host defect and 4F9/2 → 4I15/2 red photon to 4S3/2 → 4I15/2 transition. On the other hand, the GHO-YT NCs show multiple ultraviolet bands and intense blue emission upon NIR irradiation. The UC processes have been further investigated in detail by pump power dependence measurements and confirmed as two-photon absorption process for both samples. This work will not only be boon to the global community working on upconversion phosphors but also highlight the importance of UCL NCs for societal applications towards lighting and imaging technologies.

Luminescence properties related to energy transfer process and cross relaxation process of Y2O3: Yb3+/Er3+ thin films doped with K+ ion

In this paper, K + ion-doped Y 2 O 3 : Yb 3+ /Er 3+ luminescent films were prepared using the sol-gel method. The structures of the films were studied using X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy. A series of high-quality thin films with good crystallization were prepared. The effect of K + ion doping on the light emission of the samples was investigated. With increasing K + doping concentration, initially, the lattice was compressed and then stretched. For the undoped samples, the main light emission bands were green and red emissions attributed to Er 3+ : 2 H 11/2 ( 4 S 3/2 ) → 4 I 15/2 and Er 3+ : 4 F 9/2 → 4 I 15/2 , respectively, both of which are two-photon processes, accompanied by weak purple emission attributed to Er 3+ : 2 G 7/2 → 4 I 15/2 , which is a three-photon process. Compared with the undoped sample, the emission attributed to three-photon process may be eliminated by using K + doping, and the green and red emission intensity may be increased by factors of 2.39 and 2.51 with increasing K + ion doping, respectively. With the increase in K + ion doping, the changes in active luminescent centers and distance between rare earth ions were analyzed, and the effect of the process energy transfer (ET) process and cross relaxation (CR) attributed to those on light emission was discussed. • K + enhanced both green and red luminescence intensity notably. • K + eliminated purple emission, retained green and red emission. • K + reduced lattice's symmetry and changed the distance between rare earth ions. • Cross relaxation played major role in low K + doping concentration. • Energy transfer played major role in high K + doping concentration.

X‐ray Spectrometry Best Referee awards 2021

X‐ray Spectrometry Best Referee awards 2021

Aperiodic bandgap structures for enhanced quantum two-photon sources

In this paper, we propose a novel approach to enhance the efficiency of the two-photon spontaneous emission process that is driven by the multifractal optical mode density of photonic structures based on the aperiodic distributions of Eisenstein and Gaussian primes. In particular, using the accurate Mie–Lorenz multipolar theory in combination with multifractal detrended fluctuation analysis, we compute the local density of states of periodic and aperiodic systems and demonstrate the formation of complete bandgaps with distinctive fractal scaling behavior for scattering arrays of dielectric nanocylinders. Moreover, we systematically study the Purcell enhancement and the most localized optical mode resonances in these novel aperiodic photonic systems and compute their two-photon spontaneous emission rates based on the general Green’s tensor approach. Our results demonstrate that excitation of the highly resonant critical states of Eisenstein and Gaussian photonic arrays across broadband multifractal spectra gives rise to significantly enhanced emission rates compared to what is possible at the band edges of periodic structures with comparable size. Besides defining a novel approach for enhanced quantum two-photon sources on the chip, the engineering of aperiodic bandgap structures with multifractal mode density may provide access to novel electromagnetic resonant phenomena in a multi-scale-invariant vacuum for quantum nanophotonics applications.

Dual-ratiometric thermometry of Erbium(Ⅲ) in electrospun fibers inlaid with BaMgF4 microcrystals

(Ba1−x−yErxYby)MgF4/PAN (BMF-EY/PAN) fibers have been prepared by electrospinning technique, in which composite fibers vested with smooth surface, excellent flexibility and self-calibration temperature sensing function. Under 977 nm laser excitation, the strong green and red up-conversion (UC) emissions produced by the flexible fibers through effective UC luminescence are considered to be a two-photon absorption process, attributing to 2H11/2/4S3/2 → 4I15/2 and 4F9/2 (Ⅰ)/4F9/2 (Ⅱ) → 4I15/2 radiation transitions of Er3+, respectively. Combined utilization of green (523 and 545 nm) and red (656 and 669 nm) emissions endows the composite fibers with the potential in microdomain temperature sensing, realizing the accurate temperature acquisition in complex environment. At a relatively moderate working temperature (363 K), the absolute (SA) and relative (SR) sensitivity values in fibers based on green-emission reach up to 0.351 and 0.824 %K−1 for main sensing, and correspondingly, the values depended on red-emission are 0.342 and 0.302 %K−1 for auxiliary sensing, respectively. Composite fibers inlaid with crystallites have superior performances in luminescence, thermal feedback and flexibility, providing a breakthrough for the development of temperature-sensing materials in biomedical field.

Multiphoton Photoluminescence in Hybrid Plasmon–Fiber Cavities with Au and Au@Pd Nanobipyramids: Two-Photon versus Four-Photon Processes and Rapid Quenching

We investigate the multiphoton photoluminescence (MPPL) characteristics of bare and palladium-capped gold nanobipyramid particles deposited on microfibers with diameters around 1.7 μm. A broad luminescence emission with two evident peaks is detected when the coupled gold nanobipyramid particles are illuminated with a femtosecond laser. By employing multiple peak Lorentz fitting to each PL emission spectrum and performing nonlinear order analysis of the excitation power-dependent measurement, we come to the conclusion that four-photon photoluminescence (4PPL) at around 520 nm and two-photon photoluminescence (2PPL) at longer wavelengths are the main constituents of the broad luminescence emission. Additionally, we observed unexpectedly that those two emission processes have different polarization characteristics. These characteristics can be understood and explained by taking into account the band and crystalline structure of the gold nanobipyramids. Furthermore, the L-band-related 4PPL emission is quenched for Au@Pd nanobipyramids due to the fast transfer of electrons from the gold to the palladium. This provides us with a new way of modifying the photoluminescence in coupled hybrid bimetallic nanostructures. This deeper understanding of MPPL in gold nanoparticles paves the way to precise control of the luminescence emission from plasmonic nanoparticles, which is crucial for further applications in biological imaging and photothermal therapy.

Three-dimensional printing of glass micro-optics

To meet the increasing needs of high-precision glass micro-optics and address the major limitations of current three-dimensional (3D) printing optics, we have developed a liquid, solvent-free, silica precursor and two-photon 3D printing process. The printed optical elements can be fully converted to transparent inorganic glass at temperatures as low as 600 C with a shrinkage rate of 17%. We have demonstrated the whole process, from material development, printing, and performance evaluation of the printed glass micro-optics. 3D printing of glass micro-optics with isotropic shrinkage, micrometer resolution, low peak-to-valley deviation ( < 100 n m ), and low surface roughness ( < 6 n m ) has been achieved. The reported technique will enable the rapid prototyping of complex glass micro-optics previously impossible using conventional glass optics fabrication processes.

Rydberg excitation spectrum ofK40ultracold Fermi gases

We report the measurement of the Rydberg excitation spectrum by two-photon process in ultracold $^{40}\mathrm{K}$ Fermi gases. Two different methods are employed to measure the Rydberg excitation spectrum, depending on the power of the probe laser. One scheme is to reduce atomic losses by means of electromagnetically induced transparency. The other is to enhance the atomic losses by spontaneous avalanche ionization due to the strong Rydberg-Rydberg interactions. We verify the consistency of both of the methods. The highest Rydberg states detectable in our experiment are limited to $n\ensuremath{\le}62$ due to the competition between the long Rydberg blockade effective range and the limited atomic cloud size.

Mutual cooperative effects between the mode components of two-photon and Raman induced cavity lasing processes

The paper proposes to unify the two-photon laser and induced cooperative scattering Raman lasing in which the flying ensemble of two-level excited radiators are coupled with the bimodal cavity field in nonlinear two-photon and scattering interactions. It discusses the situation in which the induced two-quantum lasing takes place together with the cooperative scattering conversion of photons between the pump, Stokes, and anti-Stokes cavity modes. The proposed master equation describes cooperative energy exchanges between Raman and two-photon lasing processes by portions of energies multiple to the energy of the entangled photon pair.The generators of such emission and absorption processes belonging to the symmetries of Raman conversion and two-photon cooperative generation are unified. The first symmetry belongs to su(2) algebra connected to the scattering conversion in the Stokes, pump, and anti-Stokes modes of cavity (Opt. Commun.,285(5) (2012) 686–692). The second one belongs to multi-mode su(1,1) symmetry which quantifies the cooperative process belonging to two-photon emission in cavity/fiber mode components of field (see Opt. Commun. 247(4–6) (2005) 381–392). The bimodal collective photon operators are introduced describing the emission or absorption acts of the fixed portion of energy from the cavity equal to the transition energy between the states of each excited atom. A key impact of the study focuses on the statistical properties of the bimodal field and their detection possibilities are proposed for the description of the time evolution of quantum correlations between the field components of Raman conversion and two-photon emission.

Resonant control of photoelectron directionality by interfering one- and two-photon pathways

Coherent control of interfering one- and two-photon processes has for decades been the subject of research to achieve the redirection of photocurrent. The present study develops two-pathway coherent control of ground state helium atom above-threshold photoionization for energies up to the $N=2$ threshold, based on a multichannel quantum defect and R-matrix calculation. Three parameters are controlled in our treatment: the optical interference phase $\Delta\Phi$, the reduced electric field strength $\chi=\mathcal{E}_{\omega}^2/{\mathcal{E}_{2\omega}}$, and the final state energy $\epsilon$. A small energy change near a resonance is shown to flip the emission direction of photoelectrons with high efficiency, through an example where $90\%$ of photoelectrons whose energy is near the $2p^2\ ^1S^e$ resonance flip their emission direction. However, the large fraction of photoelectrons ionized at the intermediate state energy, which are not influenced by the optical control, make this control scheme challenging to realize experimentally.

Additive manufacturing of highly fluorescent organic 3D-metastructures at sub-wavelength resolution

Functional metastructures exhibiting unique optical properties are desirable for advancements in microfluidics, optoelectronics, nonlinear photonics, biochemical sensing, and metamaterials. Additive manufacturing techniques are expected to enable rapid prototyping of complex 3D architectonics required for such applications. We report the fabrication of highly fluorescent all-organic metastructures via carbon quantum dot assisted in-situ polymerization of acrylate and carbon dot composite resin. The polymerized structures fabricated from acrylate and carbon dot composite resin exhibit excellent linear and nonlinear optical properties due to the presence of two-photon active carbon quantum dots incorporated in the resin. By activating the two-photon process, we eliminated the need for adding two-photon absorbing toxic chemicals for initiating the polymerization process. The fabrication of functional nanostructures using acrylate and carbon dot composite resin opens the door for rapid prototyping of metastructures for various applications such as developing functional metamaterials, solid-state lighting, live monitoring of cells in cultures, fluorescent tagging and detection of counterfeiting among others.

Laser-detected magnetic resonance induced by radio-frequency two-photon processes

We have theoretically and experimentally investigated the laser-detected magnetic resonance induced by radio-frequency two-photon processes in ${F}_{g}=4$ of ${D}_{1}$ line of cesium atoms. The effective Hamiltonian for the interaction between the two radio-frequency magnetic fields and sublevels at the ground state of ${F}_{g}=4$ is derived. By appropriately selecting the frequencies of the two radio-frequency fields, the Raman two-photon process and the cascade two-photon process can occur, which induce the magnetic resonance detected through laser transmission spectra. The theoretical calculation results fit well with the experimental data. Our results maybe apply for measuring the high bandwidth radio-frequency magnetic fields in space and studying the magnetic-induction tomography.

Ultrafast two-photon optical switch using single crystal hybrid halide perovskites

Photoelectronic performance of organic–inorganic hybrid perovskites has been investigated extensively. Advancement in optoelectronic characterization and application of this group of materials in solar cells, light-emitting diodes, and lasers has been pushed forward rapidly. However, nonlinear optical properties for applications in optical logic devices have not been exploited. Moreover, long-lived excitons and charges limit the response speed of such materials and further construction of ultrafast devices. In this work, we make use of the high third-order optical nonlinearity of ( C H 3 N H 3 ) P b B r 3 single crystals and develop a femtosecond optical switch (OS) based on strong two-photon processes through absorbing one pump and one probe photon. The fascinating band structure, with a steep edge at 2.22 eV between the transmission and strong absorption bands, endows single crystals of ( C H 3 N H 3 ) P b B r 3 with perfect characteristics for two-photon optical switching in the near infrared. An on–off ratio of the probe pulses of about 90% and a speed faster than 400 fs have been achieved for this OS device. To the best of our knowledge, such high efficiency has not been realized for an ultrafast OS with any other materials and devices. Moreover, this is a first exploration, to our best knowledge, of the third-order optical nonlinearity of organic–inorganic hybrid halide perovskites for application in ultrafast optical logic devices with high reliability and low threshold in the near infrared.

Nonlinear Optical Studies of Conjugated Organic Dyes for Optical Limiting Applications

D-π-A conjugated organic dyes made of different donor/acceptor moieties namely Hexylcarbazole (HC), 4,7- Dithiophene-2-yl) benzo[c][1,2,5]thiadiazole (DTBT) and Poly-4-(5-(9-Hexyl-9H-carbazol-2-yl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole (PCTB) were prepared by coupling reactions. FTIR, NMR, and mass spectrometry were used to determine the molecular structure of synthesized compounds. Both HC and DTBT show a wide optical transmittance window (400-600 nm) with absorption maxima in the UV region. However, PCTB shows an altered band structure with a broad absorption in the visible domain (448 nm). Density functional theory (DFT) calculations expose that the bandgap between HOMO and LUMO decreases as the conjugation extends, and redshift occurs in UV-Vis absorption spectra. The emission spectrum of PCBT shows strong emission maxima at 541 nm with the corresponding large Stokes shift 3837 cm−1 due to its enhanced charge transfer property in the excited state. Nonlinear optical absorption was studied by open-aperture Z-scan technique using Nd:YAG laser (532 nm, 10 Hz, 9 ns). Here HC, DTBT exhibit a genuine two-photon absorption (TPA) process while PCTB possesses sequential TPA involving excited-state absorption. All dyes exhibit energy-absorbing optical limiting behaviour ascribed due to the two-photon absorption process. Among the investigated dyes, PCTB polymer shows a higher TPA coefficient (1.22 × 10−10 m/W) and a lower onset optical limiting threshold (1.06 × 1012 W/m2). Thus, the tunability of band structure and nonlinearity with a change in the molecular arrangement was successfully demonstrated in thiophene-benzothiadiazole-based organic dyes.