Dynamics Of Optical Response Research Articles

Electrostatic fence induced assembly of low-concentration colloidal nanospheres to form liquid photonic crystals

Liquid photonic crystals (LPCs) have great application potential in sensors, anti-counterfeiting materials and detection due to their sensitive dynamic responsiveness. Currently, the preparation of LPCs mainly relies on the supersaturation of colloidal nanospheres. However, the supersaturation method usually fails to obtain LPCs based on low-concentration colloidal nanospheres. In turn, the use of high-concentration colloidal nanospheres results in poor mobility of LPCs, which makes them inappropriate for subsequent utilization in responsive systems. In this study, self-assembly of LPCs with vibrant structural colors is achieved through the electrostatic fence effect by introducing an anionic carboxylate-containing polymer as an inducer into the system of low-concentration negatively charged colloidal nanospheres (≥1.25 wt%). It is shown that the anionic carboxylate groups on the inducer molecules and the appropriate molecular chain length are the decisive factors for the inducing effect. The obtained LPCs exhibit a typical non-close-packed structure with a face-centered cubic arrangement of nanospheres. The nearest inter-nanosphere surface distance is 12.10 nm, and the farthest one is as long as 40.30 nm. The LPCs possess good dynamic recovery performance and sensitive optical response characteristics, which are conducive to application in responsive optical sensors directly or after filling.

Triggering dual-mode dynamic optical responses by anchoring carbon dots on MnO2 hollow spheres

Multi-mode responsive optical materials with versatile application prospects for optical sensing, optoelectrical devices, and information encryption are highly desired. Here we integrate fluorescent carbon dots onto the hollow MnO2 spheres, and modulate the interaction between them to achieve a water-stimulated responsive system with dual-mode dynamic signals in both fluorescence and structural color. The composite film shows a structural color shifting from blue to green as well as displays a fluorescence “on” in the presence of trace water, with both changes capable of being reversibly switched up to 10 times. The amide bond between the two components enables the controllable dispersion and aggregation of the carbon dots which is essential to the reversibility. Fabrication of several security labels with separate information in structural color and fluorescence channels demonstrates the application potential of the composite. This work provides a concise route to develop new multi-mode responsive optical materials for applications in anti-counterfeiting, sensing, and coding.

On-Substrate Fabrication of CsPbBr3 Single-Crystal Microstructures via Nanoparticle Self-Assembly-Assisted Low-Temperature Sintering.

The growth of all-inorganic perovskite single-crystal microstructures on substrates is a promising approach for constructing photonic and electronic microdevices. However, current preparation methods typically involve direct control of ions or atoms, which often depends on specific lattice-matched substrates for epitaxial growth and other stringent conditions that limit the mild preparation and flexibility of device integration. Herein, we present the on-substrate fabrication of CsPbBr3 single-crystal microstructures obtained via a nanoparticle self-assembly assisted low-temperature sintering (NSALS) method. Sintering guided by self-assembled atomically oriented superlattice embryos facilitated the formation of single-crystal microstructures under mild conditions without substrate dependence. The as-prepared on-substrate microstructures exhibited a consistent out-of-plane orientation with a carrier lifetime of up to 82.7 ns. Photodetectors fabricated by using these microstructures exhibited an excellent photoresponse of 9.15 A/W, and the dynamic optical response had a relative standard deviation as low as 0.1831%. The discrete photosensor microarray chip with 174000 pixels in a 100 mm2 area showed a response difference of less than 6%. This method of nanoscale particle-controlled single crystal growth on a substrate offers a perspective for mild-condition preparation and in situ repair of crystals of various types. This advancement can propel the flexible integration and widespread application of perovskite devices.

Photoswitching the fluorescence of nanoparticles for advanced optical applications.

The dynamic optical response properties and the distinct features of nanomaterials make photoswitchable fluorescent nanoparticles (PF NPs) attractive candidates for advanced optical applications. Over the past few decades, the design of PF NPs by coupling photochromic and fluorescent motifs at the nanoscale has been actively pursued, and substantial efforts have been made to exploit their potential applications. In this perspective, we critically summarize various design principles for fabricating these PF NPs. Then, we discuss their distinct optical properties from different aspects by highlighting the capability of NPs in fabricating new, robust photoswitch systems. Afterwards, we introduce the pivotal role of PF NPs in advanced optical applications, including sensing, anti-counterfeiting and imaging. Finally, current challenges and future development of PF NPs are briefly discussed.

Dynamic optical response of solids following 1-fs-scale photoinjection

Photoinjection of charge carriers profoundly changes the properties of a solid. This manipulation enables ultrafast measurements, such as electric-field sampling1,2, advanced recently to petahertz frequencies3–7, and the real-time study of many-body physics8–13. Nonlinear photoexcitation by a few-cycle laser pulse can be confined to its strongest half-cycle14–16. Describing the associated subcycle optical response, vital for attosecond-scale optoelectronics, is elusive when studied with traditional pump-probe metrology as the dynamics distort any probing field on the timescale of the carrier, rather than that of the envelope. Here we apply field-resolved optical metrology to these dynamics and report the direct observation of the evolving optical properties of silicon and silica during the first few femtoseconds following a near-1-fs carrier injection. We observe that the Drude–Lorentz response forms within several femtoseconds—a time interval much shorter than the inverse plasma frequency. This is in contrast to previous measurements in the terahertz domain8,9 and central to the quest to speed up electron-based signal processing.

Unfolding the Origin of the Ultrafast Optical Response of Titanium Nitride

AbstractUltrafast plasmonics is driving growing interest for the search of novel plasmonic materials, overcoming the main limitations of noble metals. In this framework, titanium nitride (TiN) is brought in the spotlight for its refractory properties combined with an extremely fast electron‐lattice cooling time (<100 fs) compared to gold (≈ 1 ps). Despite the results reported in literature, a clear‐cut explanation of the origin of the ultrafast and giant optical response of TiN‐based materials upon excitation with femtosecond laser pulses is still missing. To address this issue, an original model is introduced, capable of unfolding the modulation of TiN optical properties on a broad bandwidth, starting from the variations of electronic and lattice temperatures following ultrafast photoexcitation. The numerical analysis is validated on ultrafast pump–probe spectroscopy experiments on a simple structure, a TiN film on glass. This approach enables a complete disentanglement of the interband and intraband contributions to the permittivity modulation. Moreover, it is also shown that, varying the synthesis conditions of the TiN film, not only the static, but also the dynamical optical response can be efficiently tuned. These findings pave the way for a breakthrough in the field: the design of TiN‐based ultrafast nanodevices for all‐optical modulation of light.

Recent Advances in Electro-Optic Response of Polymer-Stabilized Cholesteric Liquid Crystals

Cholesteric liquid crystals (CLC) are molecules that can self-assemble into helicoidal superstructures exhibiting circularly polarized reflection. The facile self-assembly and resulting optical properties makes CLCs a promising technology for an array of industrial applications, including reflective displays, tunable mirror-less lasers, optical storage, tunable color filters, and smart windows. The helicoidal structure of CLC can be stabilized via in situ photopolymerization of liquid crystal monomers in a CLC mixture, resulting in polymer-stabilized CLCs (PSCLCs). PSCLCs exhibit a dynamic optical response that can be induced by external stimuli, including electric fields, heat, and light. In this review, we discuss the electro-optic response and potential mechanism of PSCLCs reported over the past decade. Multiple electro-optic responses in PSCLCs with negative or positive dielectric anisotropy have been identified, including bandwidth broadening, red and blue tuning, and switching the reflection notch when an electric field is applied. The reconfigurable optical response of PSCLCs with positive dielectric anisotropy is also discussed. That is, red tuning (or broadening) by applying a DC field and switching by applying an AC field were both observed for the first time in a PSCLC sample. Finally, we discuss the potential mechanism for the dynamic response in PSCLCs.

Dynamic Chiral Metasurfaces for Broadband Phase‐Gradient Holographic Displays

AbstractNext‐generation holographic displays have promising applications in medical science, augmented/virtual reality, smart security, data encryption, etc. Although metasurfaces emerged as the suitable choice to provide compact holographic displays, multifunctionality in metasurfaces at broadband optical wavelengths is inevitable for the abovementioned applications. Here, a metasurface is demonstrated based on chiral structures to introduce multifunctionality in terms of multiple wavefront information depending upon the polarization of incident light. The proposed metasurface integrated with a liquid crystal (LC) provides fast switching and dynamic optical response at broadband visible wavelengths in transmission mode. To avoid the phase distortion in multiple wavefront information embedded into a single planar metasurface, chiral z‐shaped meta‐atoms are used to provide high diffraction efficiency and phase chirality response for circularly polarized (CP) light illuminations. The phase mask of holographic information is encoded into the metasurface using a combination of dynamic and geometric phase modulation techniques. The experimental validation of the designed metasurface is performed to reproduce the spin‐dependent‐specific information at broadband visible wavelengths for changing the polarization of incident light. This research may pave the way toward designing highly efficient multifunctional metadevices to produce next‐generation holographic displays for promising applications in healthcare, media, smart security, and data encryption.

Simulation of the nonlinear Kerr and Raman effect with a parallel local time-stepping DGTD solver.

In this paper, an efficient discontinuous Galerkin time-domain (DGTD) method is proposed to solve Maxwell's equations for nonlinear Kerr or Raman media. Based on our previous work, an arbitrary high-order derivatives DGTD method with a local time-stepping scheme is introduced for simulating dynamic optical responses in nonlinear dispersive media such that the nonlinear effects do not impose constraints on the stability conditions for linear subdomains. Therefore, the scheme enables the simulations in the nonlinear and linear media regions with independent time-stepping increments, which greatly improves the efficiency of the time-domain analysis. Moreover, by applying an iteration solution scheme, the proposed method preserves the intrinsic local features, which is favorable for the realization of highly parallelized algorithms. Numerical examples demonstrate the accuracy and the efficiency of our proposed method. We believe the proposed method provides an effective tool for numerical analysis of nonlinear optical phenomena.

Static, dynamic nonlinear optical (NLO) response and electride characteristics of superalkalis doped star like C6S6Li6

In search of excellent nonlinear optical (NLO) materials, new type of M3O@C6S6Li6 (M = K, Na, Li) electrides are set forth herein. The geometric, electronic and nonlinear optical properties of these electrides are evaluated by using density functional theory calculations. All the considered complexes have interaction energies in the range of -42.86 to -45.56 kcal/mol that validate their thermodynamically stability. The NBO charge analysis is performed to confirm the charge transfer between M3O and C6S6Li6. The highest amount of electronic charge transfer (0.92 |e|) is seen in K3O@C6S6Li6 electride. The frontier molecular orbitals (FMOs) and density of states (DoS) analyses are implemented to further rationalize the electronic properties. The remarkable polarizability (αo) and static first hyperpolarizability (βo) observed for these complexes validate their excellent nonlinear optical response. The highest βo (2.98×105 au) is obtained for Li3O@C6S6Li6 electride. The frequency-dependent first and second hyperpolarizability coefficients along with dipole dependent hyperpolarizability are also analyzed to get insight of NLO response under variational frequencies. Furthermore, the Hyper-Rayleigh Scattering coefficient (βHRS) of these complexes is investigated to provide information required for experimental point of view of NLO response. This study will contribute towards the development of more stable superalkalis doped electrides having pronounced NLO response.

Superalkali (Li2F, Li3F) doped Al12N12 electrides with enhanced static, dynamic nonlinear optical responses and refractive indices

In the present work, superalkalis (Li2F and Li3F) doped Al12N12 nanocages have been designed and investigated theoretically to elucidate the correlations between geometric, electronic and nonlinear optical properties. All complexes (A-E) are stable inorganic electrides as indicated by their interaction energies (−52.97 to −87.58 kcal/mol). The decrease in HOMO-LUMO energy gaps (5.44–5.87 eV) has caused a remarkable increase in the nonlinear optical response of A-E complexes. The maximum values of first hyperpolarizability (1.20 × 104 a.u.) and second hyperpolarizability (1.65 × 107 a.u.) have been achieved for complex A. The highest dynamic hyperpolarizability coefficients including second harmonic generation (9.08 × 105 a.u.) and electro-optic Pockel's effect (9.56 × 105 a.u.) are obtained for complex A at 532 nm. The electric field-induced second harmonic generation (up to 3.52 × 108 a.u.) and dc-Kerr effect (up to 8.13 ×108 a.u.) along with a large quadratic nonlinear refractive index (up to 5.41 × 10−11 a.u.) of the designed electrides reflected their large NLO response.

Controllable nonreciprocal optical response and handedness-switching in magnetized spin-orbit coupled graphene

Starting from a low-energy effective Hamiltonian model, we theoretically calculate the dynamical optical conductivity and permittivity tensor of a magnetized graphene layer with Rashba spin orbit coupling (SOC). Our results reveal a transverse Hall conductivity correlated with the usual nonreciprocal longitudinal conductivity. Further analysis illustrates that for intermediate magnetization strengths, the relative magnitudes of the magnetization and SOC can be identified experimentally by two well-separated peaks in the dynamical optical response (both the longitudinal and transverse components) as a function of photon frequency. Moreover, the frequency dependent permittivity tensor is obtained for a wide range of chemical potentials and magnetization strengths. Employing experimentally realistic parameter values, we calculate the circular dichroism of a representative device consisting of magnetized spin orbit coupled graphene and a dielectric insulator layer, backed by a metallic plate. The results reveal that this device has different relative absorptivities for right-handed and left-handed circularly polarized electromagnetic waves. It is found that the magnetized spin orbit coupled graphene supports strong handedness-switchings, effectively controlled by varying the chemical potential and magnetization strength with respect to the SOC strength.

Silicene dynamic optical response in the presence of external electric and exchange fields

We investigate the dynamic optical transition of monolayer silicene in the presence of external electric and exchange fields within the low-energy tight-binding model. Applying external electric and exchange fields breaks the silicene band structure spin and valley degeneracies. Three phases of silicene corresponding to different strengths of perpendicular electric field with respect to the spin–orbit coupling (Δ z < Δso, Δ z = Δso and Δ z > Δso) are considered. We obtain the spin-valley-dependent optical responses to the incoming circularly polarized light using the Kubo formula. We show and discuss how the magnitude and direction of the transverse and longitudinal optical responses of such a system change with the electric and exchange fields. Our calculations suggest that the intraband part of the longitudinal optical response as well as the initial point of the interband part have strong dependencies on the exchange field. Furthermore, we show that one of the spin subbands plays a dominant role in the response to polarized light. Depending on the type of incident light polarization, the dominant subband may change. Our results shed light on the relation between silicene dynamic optical responses and externally applied fields.

Cholesteric Cellulose Liquid Crystals with Multifunctional Structural Colors

AbstractStructural coloration is an intriguing phenomenon that exists widely in living creatures. A genuine bionic design of artificial structural colors requires accommodating of molecular interactions that contribute to dynamic optical responses over various external stimuli. Novel composite cellulose cholesteric liquid crystals are reported with additional molecular interactions and dynamic regulations as a bionic prototype for biological structural coloration. It is found that the incorporation of polymer monomers increases the amount of hydrogen bonds, leading to a broader range of color tunability. In addition, the crosslinking of the polymer is accompanied by a time‐dependent structure alternation of the cellulose cholesteric liquid crystals, which offers a duration control of irradiation over the color. Based on these phenomena, a series of structural color materials is developed with dynamic photonic responsiveness and high‐resolution patterns; their utility in wearable sensors, graphic displays, and information encryption is demonstrated. It is believed that this study presents a next‐generation biomimetic photonic material design and applications for different areas.

Extremely large static and dynamic nonlinear optical response of small superalkali clusters NM3M’ (M, M’=Li, Na, K)

Exploring novel nonlinear optical (NLO) materials with excess electron properties is essential for advancing the use of excess electron compounds in optics. The studied superalkali clusters NM3M’ (M, M′ = Li, Na, K) are thermodynamically stable and their binding energies range from −27.10 to −53.84 kcal mol−1. The observed significant values for VIPs suggest their electronic stabilities. Being excess electron candidate these clusters show significant βo value (3.9 × 107 au), which nicely correlates the hyperpolarizability reported by a two-level model (βtl). Furthermore, these clusters exhibit a remarkable static second hyperpolarizability (γo) value of 1.1 × 1010 au for the NK4 superalkali cluster. The hyper Rayleigh scattering (βHRS) is also computed where the highest value of 2.9 × 107 is recorded for NNa3K superalkali. The obtained values of βvec values (projection of hyperpolarizability on dipole moment vector) also signify the excellent nonlinearity of clusters. Besides, the calculated electro-optica pockel's effect β(-ω; ω,0) and second harmonic generation β(-2ω; ω, ω) values are much pronounced at larger dispersion frequency ω = 1064 nm. Moreover, the frequency-dependent second hyperpolarizability γ(ω) with dc-Kerr effect γ(-ω; ω,0,0) and electric field induced second harmonic generation γ(-2ω; ω,ω,0) show larger values at ω = 1064 nm. Thus the highest value of the dc-Kerr constant increases up to 1.0 × 1011 au which also signifies the larger nonlinear refractive index of the studied cluster. We hope this work could open up new possibilities using superalkali clusters as NLO materials for optoelectronics, laser, second harmonic generation and as frequency doubler.

Theoretical investigation of superalkali clusters M2OCN and M2NCO (where M=Li, Na, K) as excess electron system with significant static and dynamic nonlinear optical response

Confining excess electrons in a specific space is an effective strategy to design high-performance nonlinear optical (NLO) materials. Herein, with the aid of density functional theory (DFT) calculations, we investigated the nonlinear optical (NLO) properties of excess electron superalkali/supermetals M2OCN and M2NCO (where M = Li, Na, K) clusters. The electronic and optoelectronic properties of these superalkali clusters are studied at CAM-B3LYP/6−311+G(d,p) level of theory. The studied clusters possess significant thermal stability and their binding energies per atom are in the range of -120.98 to -128.04 kcal mol−1. Furthermore, the analyzed superalkali clusters show excellent electronic properties. Being excess electron candidate, these supermetals clusters show significant reduced HOMO-LUMO gaps (-4.40 ∼ 2.79 eV). The HOMO-LUMO gaps are further reduced for M2NCO configuration that reveals excellent conductive properties. The further comprehensive piture of electronic properties is obtained from the plotted density of states (DOS) analysis spectra. With the justified excess electron character, the static hyperpolarizability (βo) response increases up to 1.4 × 104 au. The strong resemblance of total hyperplarizability with βvec provides evidence for practical design of NLO materials. Moreover, the hyperpolarizability from the two-level βtl model nicely correlates with βo. Besides, static nonlinearity, frequency-dependent hyperpolarizability (β(ω)) shows remarkable values for electro-optical pockel’s effect β(-ω;ω,0) at dispersion frequency of 532 nm whereas, the second harmonic generation (SGH) phenomena is much pronounced at higher frequency (ω = 1064 nm). The obtained second hyperpolarizability (γ(ω)) response increase up to 2.1 × 108 au. The dc-Kerr effect (nonlinear refractive index) γ(-ω;ω,0,0) shows a remarkable response (2.1 × 1010 au) at ω = 532 nm.

Optical and magnetic excitations in the underscreened quasiquartet Kondo lattice

The underscreened Kondo lattice consisting of a single twofold degenerate conduction band and a CEF split 4f-electron quasi-quartet has non-conventional quasiparticle dispersions obtained from the constrained mean-field theory. An additional genuinely heavy band is found in the main hybridization band gap of the upper and lower hybridzed bands whose heavy effective mass is controlled by the CEF splitting. Its presence should profoundly influence the dynamical optical and magnetic response functions. In the former, the onset of the optical conductivity is not the main hybridisation energy but the much lower Kondo energy scale which appears in the direct transitions to the additional heavy band. The dynamical magnetic response is also strongly modified by the in-gap heavy band which can lead to unconventional resonant excitations that may be interpreted as coherent CEF-Kondo lattice magnetic exciton bands. Their instability at low temperature signifies the onset of induced excitonic magnetism in the underscreened Kondo lattice.

Thermometric Calibration of the Ultrafast Relaxation Dynamics in Plasmonic Au Nanoparticles

The excitation of plasmonic nanoparticles by ultrashort laser pulses sets in motion a complex ultrafast relaxation process involving the gradual re-equilibration of the system's electron gas, lattice and environment. One of the major hurdles in studying these processes is the lack of direct measurements of the dynamic temperature evolution of the system subcomponents. We measured the dynamic optical response of ensembles of plasmonic Au nanoparticles following ultrashort-pulse excitation and we compared it with the corresponding static optical response as a function of the increasing temperature of the thermodynamic bath. Evaluating the two sets of data, the optical fingerprints of equilibrium or off-equilibrium responses could be clearly identified, allowing us to extract a dynamic thermometric calibration scale of the relaxation process, yielding the experimental ultrafast temperature evolution of the plasmonic particles as a function of time.

Photocontrol of CRISPR/Cas9 function by site-specific chemical modification of guide RNA.

The function of CRISPR/Cas9 can be conditionally controlled by the rational engineering of guide RNA (gRNA) to target the gene of choice for precise manipulation of the genome. Particularly, chemically modified gRNA that can be activated by using specific stimuli provides a unique tool to expand the versatility of conditional control. Herein, unlike previous engineering of gRNA that generally focused on the RNA part only but neglected RNA–protein interactions, we aimed at the interactive sites between 2′-OH of ribose in the seed region of gRNA and the Cas9 protein and identified that chemical modifications at specific sites could be utilized to regulate the Cas9 activity. By introducing a photolabile group at these specific sites, we achieved optical control of Cas9 activity without disrupting the Watson–Crick base pairing. We further examined our design through CRISPR-mediated gene activation and nuclease cleavage in living cells and successfully manipulated the gene expression by using light irradiation. Our site-specific modification strategy exhibited a highly efficient and dynamic optical response and presented a new perspective for manipulating gRNA based on the RNA–protein interaction rather than the structure of RNA itself. In addition, these specific sites could also be potentially utilized for modification of other stimuli-responsive groups, which would further enrich the toolbox for conditional control of CRISPR/Cas9 function.

Polariton-Assisted Cooperativity of Molecules in Microcavities Monitored by Two-Dimensional Infrared Spectroscopy.

Molecular polaritons created by the strong coupling between matter and field in microcavities enable the control of molecular dynamical processes and optical response. Multidimensional infrared spectroscopy is proposed for monitoring the polariton-assisted cooperative properties. The response of molecules to local fluctuations is incorporated and the full dynamics is monitored through the time- and frequency-resolved multidimensional signal. The cooperativity against solvent-induced disorder and its connection to the localization of the vibrational excitations are predicted. New insights are provided for recent 2DIR experiments on vibrational polaritons.