Laser Pump Power Research Articles

Tunable Emission and Color Temperature of Yb3+/Er3+/Tm3+-Tridoped Y2O3-ZnO Ceramic Nano-Phosphors Using Er3+ Concentration and Excitation Pump Power.

In this study, a series of well-crystallized Yb3+/Er3+/Tm3+-tridoped Y2O3-ZnO ceramic nano-phosphors were prepared using sol–gel synthesis, and the phosphor structures were studied using X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. The phosphors were well crystallized and exhibited a sharp-edged angular crystal structure and mesoporous structure consisting of 270 nm nano-particles. All phosphors generated blue, green, and red emission bands attributed to Tm: 1G4→3H6, Er: 2H11/2 (4S3/2)→4I15/2, and Er: 4F9/2→4I15/2 radiative transitions, respectively. Increasing in luminescent centers, weakening of lattice symmetry, and releasing of dormant rare earth ions can enhance all emissions. Er3+ can obtain energy from Tm3+ to enhance green and red emission. These colors can be tuned by optimizing the doping concentrations of the Er3+ ion. The color coordinates were adjusted by tuning both the Er3+ concentration and excitation laser pump power to shift the color coordinates and correlated color temperature. The findings of this study will broaden the potential practical applications of phosphors.

Optical Characterization of Bitumen: Inspecting the Quantum Size Effect in the Nanostructured Phase.

Bitumen (BIT) is an oil sub-product with many applications. A variety of literature reports the analysis of its optical properties, as the fluorescence and the Fourier transform infrared (FT-IR) optical transmittance (OT). We have performed photoluminescence (PL) on the visible region of the spectrum and OT on the visible-NIR in solutions of BIT in toluene at different concentrations. The results revealed a nonlinear, concentration-dependent effect attributed to intermolecular solvent-solute interactions. PL analysis of pure BIT as a function of the temperature and the laser pumping power pointed to the existence of nanosized crystalline inclusions on the amorphous BIT matrix with noticeable optical properties. The inference was confronted with the results of X-ray diffraction studies and literature reports. The possibility of the occurrence of a quantum size effect governing the luminescence is considered.

Supercontinuum comb generated by soliton molecule pulse laser injecting into a nonlinear amplifying loop mirror

Very first time, we experimentally demonstrated the generation of supercontinuum (SC) comb by pumping a tunable soliton molecule fiber laser output signal into a nonlinear amplifying loop mirror (NALM). SC signals with different comb-teeth structures were obtained by controlling the pump power and waveplate orientation of the polarization-maintained soliton molecule fiber laser. The maximum achieved output powers of dual SC combs from two ports were 21.95 (output 1) and 3.75 mW (output 2), respectively. The spectral and temporal profiles of the SC comb were compared with the simulation results and the first-order coherence was evaluated. Our experiment provides a novel technique for the generation of SC signal with various comb-teeth structures that can be utilized in broadband spectrometers and full-field 3D metrology.

Dynamics of a Spin-Exchange Relaxation-Free Comagnetometer for Rotation Sensing

We investigate the dynamics of the spin-exchange relaxation-free (SERF) comagnetometer for rotation sensing. The transient and steady-state models of the rotation response are established by solving a set of Bloch equations. The transient responses of the comagnetometer with inertial rotation input and magnetic field input are compared. The effects of the pump-laser power density on the transient response are studied and the results indicate that the transient response reaches the fastest when the pumping rate equals the product of the gyromagnetic ratio and polarization field factor of the electron spins. The measuring range of the comagnetometer is investigated by experiment and simulation, which suggests that the measuring range can be improved by increasing the relaxation rates of the electron spins and nuclear spins and the ratio of the Fermi-contact field of the electron spins to that of the nuclear spins. The theory and method presented here pave the way for the practical application of SERF comagnetometers for rotation sensing.

Spectral and thermal characteristics of energy transferred polymeric solid dye mixtures

We synthesized two solid dye mixtures with Coumarin-545 and Rhodamine-6G without a drying step, but it showed the comparable spectral and material properties with other reported solid dyes, despite a simplified synthesizing process. Coumarin-545 was selected as donor dye, because its fluorescence spectrum was well coincided to the absorption spectrum of Rhodamine-6G, for efficient energy transfer mechanism. We investigated the spectral characteristics with two molarities of 0.1 mM and 0.3 mM of Coumarin-545, at fixed molarity of 0.1 mM of Rhodamine-6G. The fluorescence peak and spectral width of the first one, 0.1 mM molarity for both dyes, appeared at 556 nm and 63 nm, which were 4 nm shorter and 16 nm wider than those of Rhodamine-6G only, respectively. On the other hand, the second one, 0.3 mM molarity for donor, showed 555 nm and 61 nm in their fluorescence peak and spectral width, respectively, which were also 5 nm shorter and 14 nm broader than those of Rhodamine-6G only. The second solid dye mixture showed a little shorter fluorescence peak and a narrower spectral width, compared to the first one. Maximum temperature at the spot where the sample is irradiated by a pumping laser source is investigated. The first one showed the maximum temperature raised from 30°C to 38°C, when a pumping laser power increases from 50 mW to 200 mW. On the other hand, the maximum temperature of the second one raised from 34°C to 53°C, when an output power of the source increases from 50 mW to 200 mW, due to larger absorption of pumping power than the first one.

Study of near-infrared induced color tunability and optical bistability in Ho3+/Yb3+ codoped YV0.75Ta0.25O4 phosphor

This work reports the green to red color tunable upconversion emission in a newly synthesized Ho3+/Yb3+ codoped YV0.75Ta0.25O4 phosphor, prepared by solid-state reaction (SSR) method. The crystal phase formation has been confirmed by X-Ray diffraction analysis. The Fourier transform infrared (FTIR) spectrum show bands at different frequencies due to V-O and Ta-O, and found to play a vital role in relaxation (radiative and non-radiative) processes. The synthesized phosphor sample show intense upconversion (UC) emission in green (∼539 nm), red (∼659 nm) and in near infrared (NIR∼ 754 nm) regions on 980 nm laser excitation. These bands appear as a result of (5F4+5S2→5I8), (5F5→5I8) and (5F4+5S2→5I7) transitions of Ho3+ ion, respectively. The tunability in color from green to orange-red is observed on varying the pump power of NIR laser (980 nm excitation). The intrinsic optical bistability is observed in both, green & red upconversion bands with the increase and decrease in power of NIR source. The Ln I-Ln P plots suggest that green & red UC emissions are due to two photon absorption at low laser power. A decrease in the slope values at higher pump powers confirms the laser induced optical heating (LIOH) in the material. The pump power based color tunable emission and optical bistability can be utilized in security detection, optical memory, optical color coding, color switching and in various advanced applications.

Multistate Tuning of Third Harmonic Generation in Fano‐Resonant Hybrid Dielectric Metasurfaces

AbstractHybrid dielectric metasurfaces have emerged as a promising approach to enhancing near field confinement and thus high optical nonlinearity by utilizing low loss dielectric rather than relatively high loss metallic resonators. A wider range of applications can be realized if more design dimensions can be provided from material and fabrication perspectives to allow dynamic control of light. Here, tunable third harmonic generation (THG) via hybrid metasurfaces with phase change material Ge2Sb2Te5 (GST) deposited on top of amorphous silicon metasurfaces is demonstrated. Fano resonance is excited to confine the incident light inside the hybrid metasurfaces, and an experimental quality factor (Q‐factor ≈ 125) is achieved at the fundamental pump wavelength around 1210 nm. Not only the switching between a turn‐on state of Fano resonance in the amorphous state of GST and a turn‐off state in its crystalline state are demonstrated, but also gradual multistate tuning of THG emission at its intermediate states. A high THG conversion efficiency of η = 2.9 × 10−6% is achieved, which is 32 times more than that of a GST‐based Fabry–Pèrot cavity under a similar pump laser power. Experimental results show the potential of exploring GST‐based hybrid dielectric metasurfaces for tunable nonlinear optical devices.

DFB-FL Applied in the Liquid-Solid Composite Dielectric for Ultra-High Sensitive Partial Discharge Acoustic Emission Detection

The traditional fiber optic acoustic emission (AE) sensor, used to detect the partial discharge (PD) in the liquid-solid composite dielectric such as oil-immersed transformers, is not satisfactory in engineering applications due to the limitation of sensitivity and sensor size. This work proposes that the distributed feedback fiber laser (DFB-FL), benefiting from its tiny size and ultra-high sensitivity, is a better choice for PD AE detection. We build the PD AE detection system using erbium-ytterbium co-doped (Er-Yb-co-doped) DFB-FL, with suitable photoelectric components to design the demodulation system and intensity noise of DFB-FL as an index. Noise analysis shows that the average noise amplitude of the system is reduced by 91.67% after digital filtering technology and pump laser power regulation technology. We also use an 80 kVA oil-immersed transformer winding structure to construct a liquid-solid composite dielectric PD AE detection platform. Moreover, experiment results in different pump power show that the DFB-FL PD AE detection system can effectively detect the PD AE signal in the environment with sizeable acoustic impedance. The peak-to-peak value of its response is 31.36 times larger than the background noise and 637% higher than piezoelectric transducer sensors (PZT).

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.

Controllable Fast and Slow Light in Photonic-Molecule Optomechanics with Phonon Pump.

We theoretically investigate the optical output fields of a photonic-molecule optomechanical system in an optomechanically induced transparency (OMIT) regime, in which the optomechanical cavity is optically driven by a strong pump laser field and a weak probe laser field and the mechanical mode is driven by weak coherent phonon driving. The numerical simulations indicate that when the driven frequency of the phonon pump equals the frequency difference of the two laser fields, we show an enhancement OMIT where the probe transmission can exceed unity via controlling the driving amplitude and pump phase of the phonon driving. In addition, the phase dispersion of the transmitted probe field can be modified for different parametric regimes, which leads to a tunable delayed probe light transmission. We further study the group delay of the output probe field with numerical simulations, which can reach a tunable conversion from slow to fast light with the manipulation of the pump laser power, the ratio parameter of the two cavities, and the driving amplitude and phase of the weak phonon pump.

Optical thermometry based on upconversion luminescence of Ba3Gd2F12: Yb3+/Er3+ nanocrystals embedded in glass ceramics

The traditional melt quenching method was used to successfully prepare transparent glass ceramics (GCs) containing Ba3Gd2F12: Yb3+/Er3+ nanocrystals. The structure and morphology characteristics of the nanocrystals were studied and confirmed by X-ray diffraction, selected-area electron diffraction, and transmission electron microscopy. Under 980 nm excitation, the influence of Er3+ concentration, the heat treatment temperature of the GCs, and the pump power of laser on the upconverted luminescent properties were systematically discussed. GCs have a longer lifetime and higher emission intensity compared to precursor glass. In addition, the temperature dependence of fluorescence intensity ratio based on the thermal coupling energy levels of Er3+ was studied. FIR changes monotonously with temperature, and at 296 K, the relative sensitivity of the GCs sample reaches its maximum value (1.12% K−1). The results show that the GC embedded with Ba3Gd2F12: Yb3+/Er3+ nanocrystals may be a promising candidate for optical temperature sensors.

Spatio-temporal behavior of laser induced plasma shock wave probed by optical beam deflection technique

Spatio-temporal evolution of Nd:YAG laser induced shock wave generated from copper target under various pump laser power densities (0.8–2.38 GW/cm2) at atmospheric pressure is investigated. Using optical beam deflection method, a supersonic shock wave is detected, it propagates in air and progressively decays into an acoustic wave. The results show that neither the point-explosion blast wave model nor the drag force model is able to estimate the temporal evolution of the shock front. A power model considering the background pressure effect was suitable to fit the experimental data. The temporal behavior of the shock waves at different laser power densities is quite similar, but at higher laser power densities, a noticeable presence of reflected shock waves is seen. The effect of laser power density on the shock wave velocity is clearer near the target surface. A cooling wave with estimated velocity of 30 m/s is also detected.

Thermo-optic tuning of a nematic liquid crystal-filled capillary whispering gallery mode resonator.

A novel tunable whispering gallery modes (WGMs) resonator based on a nematic liquid crystal (LC)-filled capillary and magnetic nanoparticles (MNPs)-coated tapered fiber has been proposed and experimentally demonstrated. Thermo-optic tuning of the WGM resonances has been demonstrated by varying optical pump laser power injected into the MNPs-coated fiber half-taper inside the capillary. The tuning mechanism relies on the change of the effective refractive index (RI) of the nematic LC, caused by the photo-thermal effect of MNPs on the surface of the fiber half-taper inducing a temperature change inside the capillary. Tuning of the WGM resonances with sensitivities of 101.5 ± 3.5 pm/mW and 146.5 ± 3.5 pm/mW and tuning ranges of 1.96 nm and 3.28 nm respectively for the two types of liquid crystals (MLC-7012, MDA-05-2782) has been demonstrated. In addition, the relationship between the optical power of the pump laser and the local temperature of the nematic LC was investigated and the heating rate is estimated as 1.49 °C/mW. The proposed thermo-optic tuning scheme has many potential applications in tunable photonic devices and sensors.

Optically tuned dielectric characteristics of SrTiO3/Si thin film in the terahertz range* *Project supported by the National Natural Science Foundation of China (Grant No. 62075248), the National Key R&D Program of China (Grant Nos. 2017YFB0405400 and 2020YFB2009300), and the Program for the Innovation Team of Science and Technology in University of Henan, China (Grant No. 20IRTSTHN014).

Active control of the optical parameters in strontium titanate (SrTiO3, STO) thin films is highly desirable for tunable terahertz (THz) integrated devices such as filters, phase modulators, and electro-optical devices. In this work, optically tuned dielectric parameters of a STO thin film epitaxially grown on a silicon wafer were characterized in the THz region with an 800 nm laser pump-THz detection system. The refractive index, extinction coefficient, and complex dielectric constant of the STO thin film were calculated using thin-film parameter extraction. Owing to carrier transportation and soft-mode oscillation, the above optical parameters changed notably with the pump power of the external laser. This study is of great significance for rapid and non-contact THz phase-modulation technology and may serve as a powerful tool to tune the dielectric properties of the STO thin films.

A whispering-gallery-mode microlaser based on dual erbium-doped microspheres

We demonstrate a low-cost whispering gallery mode tunable microlaser based on dual erbium-doped microspheres, which is created by directly doping erbium ions when melting the tapered fiber tip by electrode discharge of a fusion splicer. The incident light from the tapered fiber is diverged into the microsphere and stimulates whispering gallery mode. The light field of whispering gallery mode interacts with the internal gain material, erbium ions, and ends up with lasing. The quality factor (Q) value of the device is up to 1.4 × 104. When the pumping laser power changes continuously from 4.6 mW to 7.5 mW, the lasing wavelength shifts from 1560.14 nm to 1560.49 nm, the lasing emission power can be tuned from 0.25 µW to 0.41 µW.

Spectral Characteristics and Molecular Structure of (E)-1-(4-Chlorophenyl)-3-(4-(Dimethylamino)Phenyl)Prop-2-en-1-One (DAP).

In this work, a laser dye of (E)-1-(4-chlorophenyl)-3-(4-(dimethylamino)phenyl)prop-2-en-1-one (DAP) was synthesized and examined as a new laser medium. The compound DAP’s photophysical properties were investigated under the influence of solvents, concentrations, and pump power excitations. The absorption spectra showed a single band, and the shape of the spectra remained the same, regardless of the optical density. The fluorescence spectra showed a band around 538 nm; its intensity was inversely proportional to the concentration. DAP exhibits dual amplified spontaneous emission (ASE) bands at 545 and 565 nm under suitable pump power laser excitation and concentration. The results revealed that the ASE band at 565 nm is affected by solvents polarity, concentrations and pump power energies. This band could be attributed to the combination of two excited molecules and the solvent between them (superexciplex). Moreover, the molecular structure, the energy bandgap, and the total energy of DAP was calculated using density functional theory.

Synthesis of Tm2WO6:Er3+ upconversion phosphor for high-contrast imaging of latent-fingerprints

A series of Tm2−xWO6:xEr3+ (where x = 0.02–0.50 mol) phosphors were synthesized successfully by the solid-state reaction method. The powder X-ray diffraction patterns of the Tm2−xWO6:xEr3+ phosphors confirmed that the as-synthesized materials belonged to the monoclinic crystalline structure, which has a P2/c (13) space group. Due to a similar ionic size and valence state of the Er3+ ions, they can easily replace the Tm3+ in the Tm2WO6 crystal lattice. High-resolution X-ray photoelectron spectroscopy was used to explore the photoelectron binding energy and chemical state of all the elements. The XPS results confirmed that the W atom coordinated octahedrally to the oxygen atoms with its highest 6+ state in the Tm2WO6 material. The upconversion luminescence intensity at 657 nm [4F9/2→4I15/2 (Er3+)], when excited at 980 nm, was enhanced with higher magnitude when increasing the doping concentration from 0.02 mol to 0.20 mol of Er3+ ions. The dependence of the laser pump power with respect to the upconversion luminescence intensity depicts that the emission at 657 nm is due to a single-photon absorption process, and the possible reasons for the number of photons involved in the excitation of the emitting state, n ≤ 1 were discussed. The Commission Internationale del'Eclairage chromaticity coordinates and decay time measured for the Tm2WO6:Er3+ phosphors were investigated. Real-time latent-fingerprint detection using Tm2WO6:Er3+ upconversion phosphor without using Yb3+ ion showed an excellent marking agent for applications in forensic science and medical diagnostics.

Upconversion luminescence and optical temperature sensing characteristics of Er3+/Yb3+ codoped Na3Gd(PO4)2 phosphors

A new series of Yb3+/Er3+ ions co-doped Na3Gd (PO4)2 (NGPO) upconversion phosphors were synthesized by the solid-state method. The structural analyses indicate that all phosphors possess a single-phase monoclinic structure. Upon 980 ​nm excitation, with controlling the laser pump power, the emission color is tuned from yellow to greenish-yellow. We have also investigated the UC emissions thermal properties between 300 and 440 ​K, using a dual-mode temperature sensor based on fluorescence intensity ratio of thermally coupled levels (TCL) and non-thermally coupled levels (NTCL). The maximum absolute and relative sensitivities are calculated to be 14.07 10−3 ​K−1 ​at 440 ​K and 1.45% K−1 at 300 ​K respectively. Moreover, the heating effects produced by laser excitation were also measured. These results indicate that NGPO: Er3+/Yb3+ phosphors could be used for temperature sensing and optical heater applications.

Quantum-enhanced two-photon spectroscopy using two-mode squeezed light.

We investigate the prospects of using two-mode intensity squeezed twin beams, generated in Rb vapor, to improve the sensitivity of spectroscopic measurements by engaging two-photon Raman transitions. As a proof-of-principle demonstration, we recorded quantum-enhanced measurements of the Rb 5D3/2 hyperfine structure with reduced requirements for the Raman pump laser power and Rb vapor number density.

Stochastic Analysis of Miniature Optoelectronic Oscillators Based on Whispering-Gallery Mode Electrooptical Modulators

We propose a theoretical analysis of the stochastic dynamics of miniature optoelectronic oscillators (OEOs) based on whispering-gallery mode resonators. The core element in this microwave photonic oscillator is a high-Q whispering-gallery mode resonator with quadratic nonlinearity, which simultaneously performs electrooptical modulation, frequency filtering and energy storage. This multi-task resonator allows the oscillator to feature improved size, weight and power metrics. In this article, we analyze how the various sources of optical and electrical noise in the oscillator are converted to output microwave signal fluctuations. We use an approach based on stochastic differential equations to characterize the dynamics of the microwave signal as a function of radiofrequency gain and laser pump power. This stochastic analysis also allows us to understand how key parameters of the resonator such as its intrinsic and extrinsic Q-factors influence the system's dynamics below and above threshold. The time-domain numerical simulations for miniature OEO stochastic dynamics provides an excellent agreement with the analytical predictions.