Upconversion Pump Research Articles

Intense emission at 605 nm from Pr3+-doped fluorotellurite glass fibers.

Pr3+-doped fluorotellurite glass fibers (PDFTFs) were fabricated by using a rod-in-tube method. By using a 976/1400 nm dual-wavelength upconversion pump technique, an intense emission at 605 nm was obtained from a 6 cm long PDFTF, which was attributed to the transition 1D2 → 3H4 of Pr3+ ions. With an increase in power of the 1400 nm laser from ∼34 to ∼136 mW, the spectral bandwidth of the 605 nm emission decreased and the intensity of the 605 nm emission increased monotonically, indicating the generation of 605 nm amplified spontaneous emission (ASE). To the best of our knowledge, this is the first report of 605 nm ASE in PDFTFs. Our results showed that PDFTFs had the potential for constructing red fiber lasers and amplifiers.

Dual Emission Bands of a 2D Perovskite Single Crystal with Charge Transfer State Characteristics.

Several hybrid halide 2D-perovskite species emit light with an emergent and controversial broadband emission Stokes-shifted down from the narrow band emission. This paper uncovers the sub- and above-bandgap emission and absorption characteristics of PEA2PbI4 prepared with gap states introduced during single crystal growth. Here, gap states led to coexistent intrinsic and heterostructured electronic frameworks that are selectively accessible with ultraviolet (UV) and infrared (IR) light, respectively, resulting in the phenomenon of photoluminescence (PL) switching from narrowband green to broadband red. Electron-energy dependent cathodoluminescence shows a relative increase in the broadband red PL intensity as the electron penetration depth increases from 30 nm to 2 μm, confirming the heterostructured framework is formed in the bulk of the crystal. Excitation-emission power slope of 2.5 and up-conversion pump transient absorption (TA) spectra suggest that the IR up-conversion excitation with red photoluminescence, peaked at 655 nm, is a multiphoton process occurring in the heterostructured framework through a nonlinear optical response. The energetic pathways toward the dual emission bands are revealed by pump-probe transient absorption spectroscopy, showing energetically broad gap states with high sensitivity to an IR pump are upconverted and subsequently quickly relax from high to low energy levels within 4 ps. Furthermore, the up-conversion red PL demonstrates a linear polarization with magnetic field effects, thus affirming that the band-like heterostructured framework is crystallographically aligned with characteristics of spatially extended charge-transfer states.

2.3 µm lasing in Tm3+ doped fluoroaluminate glass fibers with an upconversion pumping scheme

Tm3+ doped fluoroaluminate glass fibers are fabricated by using a rod-in-tube method based on AlF3-BaF2-YF3-MgF2-PbF2 glasses. By using a 1400/1570 nm dual-wavelength upconversion pump technique, lasing at ∼2.3 µm is obtained from a 2.3 m long Tm3+ doped fluoroaluminate glass fiber. The measured maximum unsaturated output power is ∼111 mW for a pump power of 1.5/0.14 W at 1400/1570 nm, and the corresponding slope efficiency is ∼11%. The effect of the gain fiber length on lasing at ∼2.3 µm is also investigated. Our results indicate that Tm3+ doped fluoroaluminate glass fibers are promising gain media for constructing ∼2.3 µm fiber lasers.

Ultra-low-noise microwave to optics conversion in gallium phosphide

Mechanical resonators can act as excellent intermediaries to interface single photons in the microwave and optical domains due to their high quality factors. Nevertheless, the optical pump required to overcome the large energy difference between the frequencies can add significant noise to the transduced signal. Here we exploit the remarkable properties of thin-film gallium phosphide to demonstrate bi-directional on-chip conversion between microwave and optical frequencies, realized by piezoelectric actuation of a Gigahertz-frequency optomechanical resonator. The large optomechanical coupling and the suppression of two-photon absorption in the material allows us to operate the device at optomechanical cooperativities greatly exceeding one. Alternatively, when using a pulsed upconversion pump, we demonstrate that we induce less than one thermal noise phonon. We include a high-impedance on-chip matching resonator to mediate the mechanical load with the 50-Ω source. Our results establish gallium phosphide as a versatile platform for ultra-low-noise conversion of photons between microwave and optical frequencies.

White upconversion emission and color tunability of Y2O3:R(R=Yb3+, Er3+, Tm3+) nanophosphors

The Y2O3:R(R = Yb3+, Er3+, Tm3+) nanophosphors were synthesized by a solvothermal method and the temperature dependence of the white upconversion emission was studied using a 975 nm LD. The upconversion emission spectra in 1 mol% Er3+/5 mol% Yb3+/xTm3+ tri-doped Y2O3 nanophosphors were sintered at 1000 °C with x from 0 to 0.5 mol%. The blue emission intensity increases increasing Tm3+ concentration from 0 to 0.5 mol%, because the Tm3+ state can be easily reached due to the 2F7/2 → 2F5/2 transition of Yb3+ near 10,000 cm−1. The Y2O3: Er3+/Yb3+/Tm3+ nanophosphors exhibit upconversion emission from white to green with increasing sintering temperature. The calculated CIE coordinates are located in the white region at a pump power of 700 mW at 1000 °C, and the color coordinates were very similar to the standard white light emission. Their upconversion process was described through energy level diagrams and results of upconversion emission spectra and pump power dependence.

Upconversion dark-field imaging with extended field of view at video frame rate.

Dark-field imaging is a well-known optical method for obtaining edge-enhanced images of objects containing steep gradients in either amplitude or phase. Edge enhancement is commonly achieved by using a small physical obstruction in the center of the Fourier plane of a 4f imaging setup. By blocking the low spatial frequencies in the center of the Fourier plane, only the higher spatial frequencies from the object reach the image plane. In this work, simultaneous optical image processing (i.e., dark-field imaging) and sum-frequency generation are performed by placing a periodically poled lithium niobate crystal in the Fourier plane of a 4f setup and using a 1575 nm upconversion pump beam with a dark core. We demonstrate upconversion dark-field (UDF) imaging in which edge-enhanced images are obtained at the upconverted wavelength ($\sim{630}\;{\rm nm}$∼630nm) as a result of infrared object illumination ($\sim 1\;\unicode{x00B5}{\rm m}$∼1µm). Furthermore, we experimentally confirm that UDF imaging can be extended from collinear to noncollinear interactions between the signal and pump. The presented system allows for adjustment of the spatial cutoff frequency while maximizing the power conversion efficiency. Simultaneous collinear and noncollinear upconversion imaging of phase objects is demonstrated using broadband 1 µm illumination with a spectral bandwidth of 6 nm-resulting in a UDF imaging system with an enhanced field of view at video frame rates.

Effect of F/O ratio on up-conversion and down-conversion luminescence properties of Er3+/Yb3+ co-doped SiO2–Al2O3–AlF3-Gd2O3–Na2O glass

Er3+/Yb3+ co-doped SiO2–Al2O3–AlF3-Gd2O3–Na2O glass with different F/O ratios were prepared. The effect of F/O ratio on the structure and optical properties of the glasses was investigated. The amorphous nature of the glasses was determined by XRD, and the glass transition temperature (Tg) and the crystallization peak temperature (Tc) were obtained from the DSC curves. The change in the structure of the glass network was analyzed by infrared spectroscopy. The density and absorption spectra of the bulk glass was also investigated. The excitation spectrum, emission spectrum and 4S3/2 level fluorescence lifetime of Er3+ ions in the glasses were tested by a Xenon lamp with adjustable wavelength. The up-conversion luminescence spectrum of Er3+ ions was measured under excitation of a 980 nm laser. The results show that the green (2H11/2, 4S3/2) and red (4F9/2) up-conversion luminescence intensity is the highest when the F/O ratio is 0.214. According to the variation law of up-conversion luminescence intensity and pump power, it is confirmed that the up-conversion green (2H11/2 → 4I15/2, 4S3/2 → 4I15/2) and red (4F9/2 → 4I15/2) light of Er3+ ions are the three-photon absorption process based on excited state absorption (ESA) and energy transfer up-conversion (ETU) mechanism. Finally, energy transfer transitions between Er3+ and Yb3+ are also analyzed. The CIE chromaticity coordinates were calculated from the emission spectrum obtained at two different excitation wavelengths of 378 nm and 980 nm.

The Dispersion Reduction Frequency Upconversion System at 1550 nm With Tightly Focused Beam

The upconversion detection is a promising method to detect infrared radiation. It is proved that the focused beam makes a contribution to improving the upconversion efficiency. A near-infrared detector at room-temperature based on sum frequency generation(SFG) with focused beams is demonstrated. To enhance the upconversion efficiency, the signal and pump beams are tightly focused by the same focal lens. To reduce that the dispersion of the focal lens has a negative effect on upconversion efficiency in a tightly focusing system, the relation between the upconversion efficiency and the focused beams in our system is investigated. In the setup, the signal and pump beams are combined by a polarization maintaining wavelength division multiplexer (PMWDM) that is connected on a collimator. The mixed beam is focused into a periodically poled lithium niobate (PPLN) bulk by a lens of 35mm focal length. The signal pulse at 1550nm is converted to 863nm with a 172mW continuous-wave pump beam at 1950nm. The converted signal is measured by a photomultiplier tube(PMT) and results shows the maximum upconversion efficiency is 5.23×10-4 while the pump power is 172mW.

Ultrafast Relaxation Dynamics in Zinc Tetraphenylporphyrin Surface-Mounted Metal Organic Framework

Ordered porphyrin-based metal organic frameworks (MOFs) may serve as a model for mimicking the natural photosynthesis with highly ordered chlorophylls, i.e., porphyrin-like chromophores. Study of light harvesting and energy transfer as the primary event of photosynthesis is of great importance leading to improvement of photovoltaics overall performance. Detailed characterization of ultrafast dynamics of zinc tetraphenylporphyrin (ZnTPP) surface mounted metal organic framework (SURMOF) is reported by using various steady-state and time-resolved laser spectroscopic techniques, i.e., time-correlated single photon counting, fluorescence up-conversion and transient absorption pump–probe with 20 fs resolution. Obtained results in these nanoporous materials were compared with corresponding results for ZnTPP in ethanol measured under the same conditions. Dramatic quenching of both upper excited singlet state S2 and first excited state S1 was observed. Subpicosecond and picosecond lifetimes were detected in transi...

Upconversion Luminescence and Energy‐Transfer Mechanism of NaGd(MoO4)2: Yb3+/Er3+ Microcrystals

Uniform and well‐crystallized NaGd(MoO4)2: Yb3+/Er3+ microcrystals with tetragonal plate morphology were synthesized by a facile hydrothermal method. The structure and phase purity of the samples were identified by powder XRD analysis. The steady‐state and transient luminescence spectra were measured and analyzed. Under 980 nm excitation, intense green luminescence at 531 and 553 nm, and red luminescence at 657 and 670 nm were observed. The optimum doping concentrations for Yb3+ and Er3+ are determined to be 20% and 1% in NaGd(MoO4)2 tetragonal plate microcrystals. With increasing Yb3+ doping concentrations, the total integral emission intensities increase first and then decrease. The red/green intensity ratio of NaGd(MoO4)2: Yb3+/Er3+ microcrystals increases from 0.4 to 1.0 with the increase in Yb3+ concentrations. Based on the energy level diagram, the energy‐transfer mechanisms are investigated in detail according to the double logarithmic plot of upconversion intensities versus pump powers. The energy‐transfer mechanisms for green and red upconversion luminescence are ascribed to two‐photon processes at lower Yb3+ concentrations, and involve high‐Yb3+‐induced one‐photon processes at higher Yb3+ concentrations. For the red upconversion luminescence, energy back‐transfer process, that is, 4S3/2 (Er3+) + 2F7/2 (Yb3+) → 4I13/2 (Er3+) + 2F5/2 (Yb3+), is dominant at higher Yb3+ concentrations. Theoretical model of the energy‐transfer mechanisms based on rate equations is established, which agrees well with the experimental results.

Upconversion Luminescence from Ho3+ and Yb3+ Codoped α-NaYF4 Single Crystals

The Ho3+/Yb3+ co-doped α-NaYF4 single crystal was grown successfully for the first time by a modified Bridgman method in which KF was used as assisting flux and a large temperature gradient (70–90 °C/cm) of solid-liquid interface was adopted. Upconversion emissions at green ∼544 nm, red ∼657 and ∼751 nm were obtained under 980 nm laser diode excitation. The intensity at ∼544 nm was much stronger than those of ∼657 and ∼751 nm. The mechanisms of the upconversion emissions were investigated by studying the relationship between the upconversion intensity and pump power. The optimized Yb3+ concentration was about 8.08mol% when Ho3+ concentration was hold at about 1.0mol%. The results showed that Ho3+/Yb3+ doped α-NaYF4 single crystal was a possible candidate upconversion material for the green solid-state laser.

Carbon nanodots: toward a comprehensive understanding of their photoluminescence.

We report the characterization of carbon nanodots (CNDs) synthesized under mild and controlled conditions, that is, in a microwave reactor. The CNDs thus synthesized exhibit homogeneous and narrowly dispersed optical properties. They are thus well suited as a testbed for studies of the photophysics of carbon-based nanoscopic emitters. In addition to steady-state investigations, time-correlated single-photon counting, fluorescence up-conversion, and transient pump probe absorption spectroscopy were used to elucidate the excited-state dynamics. Moreover, quenching the CND-based emission with electron donors or acceptors helped shed light on the nature of individual states. Density functional theory and semiempirical configuration-interaction calculations on model systems helped understand the fundamental structure-property relationships for this novel type of material.

Up-conversion sensitization luminescence in Pr3+and Yb3+ co-doped fluoride glasses

In experiment, Pr3+,Yb3+:ZBLAN glass is chosen as a frequency up-conversion fluorescence material, and detailed reasons for choosing ZBLAN glass as a material are given. In this paper we also analyze the relations between up-conversion fluorescence intensity and pump light intensity and between up-conversion fluorescence intensity and ions doped concentration. Therefore we obtain experimental conditions to realize a clear two-frequency up-conversion 3-D display.

Optical gain by upconversion in Tm–Yb oxyfluoride glass ceramic

Evidence of positive optical gain is observed in Tm3+–Yb3+-codoped oxyfluoride glass ceramic in an upconversion pump and probe experiment. The 1G4 level of the Tm3+ ions is populated by an upconversion mechanism under excitation of the Yb3+ ions at 975 nm with a high-power pulsed laser and give rise to an intense emission from the 1G4 to the 3F4 levels. The 1G4→3F4 electronic transition is stimulated with a low signal at 650 nm as a probe.

Green emission from Eu2+/Dy3+ codoped SrO-Al2O3-B2O3 glass-ceramic by ultraviolet light and femtosecond laser irradiation

A spectroscopic investigation of Eu 2+ /Dy 3+ codoped SrO-Al 2 O 3 -B 2 O 3 glass-ceramic is presented. The sample exhibits green emission excited by ultraviolet (UV) light and near-IR femtosecond (fs) laser. The emission profile obtained by near-IR fs laser irradiation is similar to that by UV excitation, indicating that both of the emissions come from 5d → 4f transition of the Eu 2+ ions. The relationship between the upconversion luminescence (UCL) intensity and pump power reveals a two-photon process in the conversion of near-IR radiation to the green emission. The possible mechanism of UCL from such glass-ceramic is proposed.

Optical amplification by upconversion in Tm–Yb fluoroindate glass

Evidence of a positive optical gain at 650 nm is observed in Tm 3+–Yb 3+ codoped fluoroindate glass in an upconversion pump and probe experiment. The 1G 4 level of the Tm 3+ ions is populated by an upconversion mechanism under excitation of the Yb 3+ ions at 975 nm with high power pulsed laser and give rise to an intense emission from the 1G 4 to the 3F 4 levels. The 1G 4 → 3F 4 electronic transition is stimulated with a low signal at 650 nm as a probe. Under this condition, we reach the population inversion necessary between the Tm 3+ levels of the transition 1G 4 → 3F 4 and we observed an increase of the emission intensity at the signal wavelength due to the stimulated emission. Transient positive optical gain around 3 cm −1 (∼12 dB/cm) has been measured in Tm–Yb codoped fluoroindate glass during the first 400 μs.

1310-nm quantum key distribution system with up-conversion pump wavelength at 1550 nm

We show that the performance of a 1310-nm quantum key distribution (QKD) system with up-conversion detectors pumped at 1550 nm is comparable with or better than that of current 1550-nm QKD systems with a pump at shorter wavelength. The nonlinearly-induced dark counts are reduced when the wavelength of the pump light is longer than that of the quantum signal. We have developed a 1550-nm pump up-conversion detector for a 1310-nm QKD system, and we experimentally study the polarization sensitivity, pump-signal format, and various influences on the dark count rate. Using this detector in a proof-of-principle experiment, we have achieved a secure key rate of 500 kbit/s at 10 km and 9.1 kbit/s at 50 km in a 625-MHz, B92, polarization-coding QKD system, and we expect that the system performance could be improved further.

980-nm diode-pumped Tm^3+?Yb^3+-codoped tellurite fiber for S-band amplification

We report gain measurements in Tm(3+)/Yb(3+)-codoped tellurite glass fibers in the 1460-1530-nm region using a conventional 980-nm pumping scheme. The gain spectrum is dependent on the geometry of the fiber and the length owing to the superfluorescence upconversion pump scheme.

Femtosecond dynamics of active semiconductor waveguides: microscopic analysis and experimental investigations

We present theoretical and experimental results of nonlinear amplification and propagation of short optical pulses in Fabry–Perot semiconductor lasers. The theoretical description is based on spatially resolved Maxwell–Bloch–Langevin equations that take into account the spatially varying light-field dynamics including counterpropagation, diffraction, self-focusing, and the microscopic carrier dynamics including carrier heating and carrier relaxation. Femtosecond pump–probe measurements using upconversion and femtosecond-resolved pump–probe measurements and frequency-resolved optical gating on a Fabry–Perot laser allow a combined analysis of the transmitted pulses in real time and the spectral domain. The experimental results are compared with the microscopically calculated gain and index distributions, pulse shapes, and optical spectra. In order to assess the full potential of semiconductor lasers and amplifiers, a quantitative measurement and understanding of amplitude and phase dynamics is required. The computer simulations of the ultrashort dynamics of semiconductor waveguides with optical injection of light pulses provide insight into the dynamic spectral gain and index changes responsible for frequency drifts and self-phase modulation, visualization of propagation effects, and a time- and frequency-resolved analysis of the amplified light pulses.

Ultrafast Relaxation Processes of Triarylpyrylium Cations

The time evolution of the fluorescence and the photoinduced absorption spectra of four triarylpyrylium cations, differing in the number of dodecyl chains attached to the chromophore, was studied by means of femtosecond fluorescence upconversion and picosecond pump−probe absorption techniques. The dependence on solvent viscosity was also examined. The results are rationalized in terms of excited and ground-state relaxation dynamics and may be differentiated into intramolecular conformational changes and intermolecular solute−solvent contributions. The dynamic fluorescence shift is related to solvent relaxation, whereas the fluorescence intensity decay is attributed to molecular twisting acting in an intricate manner. First, the geometrical relaxation reduces rapidly the fluorescence oscillator strength, but it also greatly enhances the nonradiative S0 ← S1 internal conversion rate. Molecular back-twisting combined with vibrational relaxation in the ground state is shown to be the last and the slowest process of the reaction.