Optical Conversion Efficiency Research Articles

Carbon nanodot with highly localized excitonic emission for efficient luminescent solar concentrator

Abstract Luminescent solar concentrators (LSCs) are attractive for the easy operation and high compatibility with building integrated photovoltaics due to their low cost, large-scale and applicability. However, underutilized sunlight in visible wavelengths often impedes the advance of LSCs. Here, we demonstrate an orange-emitting carbon nanodots-based LSC (O-CDs) with excitation concentrated in the visible wavelengths. The orange-emitting carbon nanodots (O-CDs) with highly localized excitonic emission are prepared via atomic condensation of doped pyrrolic nitrogen, delivering a high photoluminescence quantum yield of 80 % and a suitable Stokes shift with absorption spectrum situated in the visible region. The O-CDs are embedded in polyvinylpyrrolidone to obtain a highly transparent, stable and environmentally friendly O-CDs-based LSC. Thanks to efficient utilization of solar radiation in visible areas and well match between the emission of O-CDs and the response bands of photovoltaic cells, the O-CDs-based LSC reveals an optical conversion efficiency of 5.17 %, superior to that of most carbon nanodots-based LSCs. These results provide an effective strategy to develop carbon-based luminescent concentrated materials for architectural integrated photovoltaic technology.

High-power and efficient vortex Nd:YVO4 laser using annular pumping

Optical vortex lasers that carry orbital angular momentum are of great significance for many applications. A high-power and efficient continuous-wave vortex Nd:YVO4 laser at 1064 nm was demonstrated with annular pumping based on an axicon. The high-quality LG01 vortex beams with maximum output power up to 6.25 W was achieved under the absorbed pump power of 14.4 W, corresponding to an optical conversion efficiency of 43.4% and a slope efficiency of 44.8%, respectively. Controlling the wavefront handedness of the LG01 beam was simply achieved by carefully adjusting the output coupler and the window inserted in the resonator. This study shows that annular pumping based on an axicon would have great potential in the development of high-power vortex solid-state lasers with simple and compact resonator structure.

Electronic structure and optical absorption property of BaTiO3/BiCoO3

In this paper, we calculated the different forms of BaTiO3/BiCoO3 composite structure, predicting their visible light absorption performance based on the electronic structure using the first principles calculations. Firstly, six possible compounds that come from BaTiO3 and BiCoO3 were constructed. By calculating the different antiferromagnetic (AFM) structures of strip, columnar, and layered composite structures, it is found that the ground state of the composite structure changes to G‐type AFM structure from C‐type AFM structure of pure BiCoO3 under the influence of BaTiO3. Energy band calculations show that band gaps of three composite structures are smaller than those of pure BaTiO3 and pure BiCoO3. Furthermore, density of states analysis shows that the conduction band minimum (CBM) and valence band maximum (VBM) of three composite structures are mainly from the contribution of Co 3d and O 2p. For the characteristic that CBM and VBM of materials come from different atoms, it would reduce the recombination opportunities of electrons and holes and is conducive to the increase of photoelectric conversion efficiency under visible light irradiation. The calculation of optical properties shows that optical absorption coefficients of three composite structures are much larger than that of BaTiO3, especially the layered composite structure. There is a high absorption peak near 500 nm of the solar spectral irradiation maximum, which is significantly important to improve the optical energy conversion efficiency of the composite materials. The work provides an effective way for the application of wide band gap ferroelectric materials in ferroelectric photovoltaic.

Actively Q-switched self-frequency-doubled Yb:YCOB green laser with output power of a dozen watts.

A diode laser (LD) end-pumped acousto-optic Q-switched self-frequency-doubled (SFD) Yb:YCa4O(BO3)3 (Yb:YCOB) pulsed green laser was realized for the first time (to our knowledge), with a maximum average output power of 11.6 W and an optical conversion efficiency of 30.0% from the LD to SFD lasers. The wavelength of the SFD lasers was controlled to be 507 nm for improving quantum efficiency up to 96% and reducing thermal effects. The repetition rates ranged from 20 to 500 kHz, and the maximum pulse energy was 312.0 µJ with a peak power of 4.78 kW at a repetition rate of 20 kHz. This work represents the highest output power in the SFD pulsed lasers and provides an efficient and compact way to generate high-power pulsed green lasers that should have important applications in many aspects, such as ultraviolet (UV) laser generation, laser display, and medical, military, and scientific research.

A high-energy Ho: YLF MOPA system pumped by Tm: YAP lasers

This paper introduces a high-energy Q-switched Ho: YLF master oscillator power amplifier (MOPA) system pumped using linearly polarized Tm: YAP lasers. In this system, the pulse repetition frequency was 100 Hz, and an 84.7 mJ Ho laser was generated with a total pump power of 102.3 W, corresponding to a total optical conversion efficiency of 8.3%. The oscillator yielded a maximum output energy of 20.0 mJ and pulse width of 19.0 ns, corresponding to a peak power of 1.05 MW. Moreover, the amplifier delivered a maximum output energy of 84.7 mJ and pulse width of 18.0 ns, corresponding to a peak power of 4.70 MW. In addition, the system exhibited an excellent beam quality in both directions, with the M2 factors better than 1.1 and 1.3 at the oscillator and amplifier, respectively.

Multimodal Optically Nonlinear Nanoparticles Exhibiting Simultaneous Higher Harmonics Generation and Upconversion Luminescence for Anticounterfeiting and 8‐bit Optical Coding

AbstractNonlinear optical materials are essential in areas such as nanophotonics, optical information processing, and biomedical imaging. However, nanomaterials employed for these diverse applications to date are efficient only for one type of nonlinear optical activity. Herein, the first multimodal nonlinear optically active class of nanomaterials based on lanthanide‐doped lithium niobate nanoparticles, which simultaneously exhibit unprecedentedly efficient second and third harmonic generation, as well as up‐conversion photoluminescence, is reported. These dielectric nanoparticles retain their high nonlinear optical conversion efficiency both as powder and as aqueous colloidal solution. The high stability also allows for the fabrication of optically active biocompatible micron‐sized fibers and polymer‐based 3D‐printable objects, as well as for fingerprint detection. Finally, the first 8‐bit coding platform purely based on multimodal nonlinear optical activity originating from different parametric and nonparametric processes is demonstrated, showcasing the technological potential of these materials for both anti‐counterfeiting and advanced optical information processing.

High repetition rate π-polarized 1084 nm passively Q-switched Nd:MgO:LiNbO3 laser based on 888 nm thermally boosted pumping

We report a high-repetition-rate π-polarized 1084 nm passively Q-switched (PQS) Nd:MgO:LiNbO3 (Nd:MgO:LN) laser under 888 nm thermally boosted pumping. The 888 nm pumping is selected based on Nd:MgO:LN crystal absorption and energy level properties. Under 813 nm pumping, the continuous wave (CW) 1084 nm average output power (AOP) increased to 2.85 W. After that, 1084 nm is suppressed and gradually disappears as the pump power increases. At the same time, the 1093 nm AOP increases, and 4.4 W of 1093 nm laser is obtained. In contrast, under 888 nm pumping, the CW 1084 nm laser AOP of 5.16 W is obtained. The thermally boosted pumping can eliminate quantum defects caused by conventional 813 nm pumping non-radiative transitions and suppress unmatched σ-polarized 1093 nm output. Moreover, the Cr4+: YAG is replaced into the resonant cavity as the output mirror to obtain 1084 nm pulsed laser output. AOP with different initial transmission (T0) on laser output characteristics is measured under the compact resonant cavity structure. Finally, an AOP of 3.52 W pulsed laser with a repetition rate of 24.43 kHz and the highest peak power of 5.26 kW is obtained when T0 = 87 %, and the absorbed pump power is 20.87 W. The optical conversion efficiency is 16.87 %, and the slope efficiency is about 29.38 %.

Optically pumped Milliwatt Whispering-Gallery microcavity laser

Whispering-gallery-mode microcavity lasers possess remarkable characteristics such as high Q factors and compact geometries, making them an essential element in the evolution of microlasers. However, solid-state whispering-gallery-mode lasers have previously suffered from low output power and limited optical conversion efficiency, hindering their applications. Here, we present the achievement of milliwatt laser emissions at a wavelength of 1.06 µm from a solid-state whispering-gallery-mode laser. To accomplish this, we construct a whispering-gallery-mode microcavity (with a diameter of 30 µm) using a crystalline Nd: YAG thin film obtained through carbon-implantation enhanced etching of a Nd: YAG crystal. This microcavity laser demonstrates a maximum output power of 1.12 mW and an optical conversion efficiency of 12.4%. Moreover, our unique eccentric microcavity design enables efficient coupling of free-space pump light, facilitating integration with a waveguide. This integration allowed for single-wavelength laser emission from the waveguide, achieving an output power of 0.5 mW and an optical conversion efficiency of 6.18%. Our work opens up new possibilities for advancing solid-state whispering-gallery-mode lasers, providing a viable option for compact photonic sources.

Broadband self-pulsed Yb:YAG/YVO4 Raman laser

High repetition rate self-pulsed lasers operating at broadband Stokes wavelengths converted with stimulated Raman scattering effect in a compact Raman solid-state laser dramatically extend potential applications on laser ranging, material processing, optical communication. Here, we report broadband self-pulsed laser oscillation in a continuous-wave (CW) laser diode pumped Yb:YAG/YVO4 Raman laser by slightly tilting YVO4 crystal. Stable self-pulsed laser oscillation is obtained in a pump power regime from 2 W to 2.6 W, and the repetition rate increases from 46.5 kHz to 62 kHz. Self-pulsed Raman laser oscillates in multi-longitudinal-mode, the broadband spectral range covers from 1081.5 nm to 1094.3 nm with a bandwidth of 12.8 nm. At input pump power of 2.6 W, average output power up to 140 mW is obtained for stable self-pulsed Raman laser, the optical conversion efficiency is 5.4%. Self-pulsed Raman laser pulses with pulse energy of 2.3 μJ and pulse width of 3.9 μs are obtained. The peak power is 590 mW. This work provides a new route for developing compact self-pulsed Raman lasers for optical communications, material processing.

High-efficiency 261-nm continuous-wave laser by single-blue-laser-diode-pumped Pr3+:LiYF4 crystal

High-power continuous-wave (CW) deep ultraviolet lasers attract growing research interest in the field of optoelectronics. Herein, we perform a CW deep ultraviolet laser at 261 nm by the intracavity frequency doubling of a single-blue-laser-diode-pumped Pr3+:LiYF4 (Pr:YLF) laser. The excellent mode matching between the pump and fundamental-frequency laser beams is realized by optimizing the pump focusing and laser resonator systems. On that basis, the maximum CW fundamental-frequency laser obtained is 1.41 W at 522 nm, corresponding to a slope efficiency of 59.12%. Moreover, a deep ultraviolet laser is further demonstrated at 261 nm using a β-BaB2O4 (BBO) frequency-doubling crystal, yielding a maximum output power of 1.17 W and an optical–optical conversion efficiency of 33.4% with respect to the pump power. Such a result is the highest optical–optical conversion efficiency of the CW DUV lasers from Pr3+-doped crystals, to the best of our knowledge. The finding in this work manifests the development potential of all-solid-state deep ultraviolet lasers and provides a feasible avenue for achieving high-efficiency deep ultraviolet laser output.

Tailoring the bound states in the multi-channel nonlinear plasmonic metasurfaces

Metasurfaces offer a paradigm shift in the nonlinear optics, controlling and enhancing of nonlinear effects at the nanoscale, and offering new opportunities for applications in nonlinear optics, plasmonics and electromagnetics. Particularly, nonlinear optical conversion efficiency is limited due to the inherent losses in metallic materials. Nonlinear metasurfaces based on bound states in the continuum(BIC) can effectively increase the Q value and are expected to further enhance the nonlinear efficiency. In this paper, a tri-capacitance-like metasurface supporting both Friedrich–Wintgen quasi-BIC and symmetry-protected quasi-BIC is proposed to generates multiple high-Q resonances in the spectrum. The coupling between perfect BIC and quasi-BIC mode in the multi-channel optical system corresponds to the storage and release of electromagnetic waves, respectively. At the same time, the electromagnetic field is further enhanced at the resonant frequency, which can significantly improve the second order nonlinear efficiency. In addition, due to the different generation mechanism, the frequency and amplitude of the two resonances are easy to tune independently, which facilitates the sum and difference frequency generation (SFG and DFG). Therefore, the proposed nonlinear metasurfaces in this paper are of wide research value in the fields of nonlinear optics, multi-channel communication and memory.

High-performance passively Q-switched fiber laser based on CuFeO2/SiO2 as saturable absorber

In this paper, we report the optical properties and applications of the CuFeO2 (CFO)/SiO2 novel saturable absorber (SA) by the sol–gel method. The measured results show that our SA’s modulation depth, unsaturated loss and damage threshold are 10.9%, 10.1% and 5121 mJ/cm 2, respectively. High-quality passively Q-switched fiber laser output at 1.5μm was successfully achieved using CFO/SiO2 SA. Due to the high damage threshold and low insertion loss of the SA, the maximum output power of the laser are 59.6 mW, the optical conversion efficiency is 6.4%, much higher than other reports, corresponding to an output pulse’ peak power and single pulse energy of up to 723.98 mW and 307.7 nJ, and the signal-to-noise ratio of 74 dB indicating its stability. The results indicate that the CFO/SiO2 SA prepared by the sol–gel method provides a new opportunity to develop high-performance SA and high-power passive Q-switched fiber lasers.

High Average Power Green Laser Based on LED-Side-Pumped Q-Switched Nd:YAG Laser

In this paper, we demonstrated a watt-level acousto-optic (A-O) Q-switched intracavity frequency-doubled green laser with high average power and beam quality operation based on an efficient LED-pumped Nd:YAG laser module. For the quasi-continuous wave (QCW) running operation, the average output power of fundamental laser at 1064 nm was as high as 10.3 W at a repetition rate of 100 Hz, corresponding to the highest optical conversion efficiency of 25.4% and a slope efficiency of 31.3%, and the maximum energy of single pulse was up to 100mJ. By optimizing the incidence angle of the KTP crystal to meet the non-critical phase matching condition, greater than 3.8 W of 532 nm average power at a repetition rate of 10 kHz was generated with duration of 192 ns and a beam quality factor of M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 1.6 and M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 1.7, corresponding to a frequency doubling conversion efficiency of 45.5%. To the best of our ability, this is the highest average power and high beam quality of an LED-pumped A-O Q-switched intracavity frequency-doubled green laser with watt-level output reported so far.

High-brightness green laser diode that uses a multi-order half-wave plate to realize twice-combined polarized beams

In this paper, we describe a method for realizing twice-combined polarized beams by selectively changing the polarization state of lasers with different wavelengths. This improves the output power and brightness of a green laser diode system. A multi-order half-wave plate plays a significant part in combining the polarization states of the first-combined polarized beam by changing the polarization state from orthogonal to approximately parallel. We obtained a maximum output power of 2.85 W and a laser brightness of 25.36 MW/cm2·sr with an optical–optical conversion efficiency of 82.85% and a spectral width of 15.48 nm. Compared with traditional methods for combining polarized beams, the output power is improved by 22.85% and the brightness by 8.65%. This structure provides a new technology for achieving high output power and high brightness from a green laser diode system, and it breaks through the limit of the number of laser units that can be used in combining polarized beams.

Hybrid Resonator 1319 nm Nd:YAG InnoSlab Laser

The InnoSlab laser has the advantages of excellent thermal management and high overlapping efficiency. In this work, we report an InnoSlab laser with high efficiency at 1319 nm end-pumped 0.6at.% Nd:YAG by 808 nm. The hybrid stable–unstable resonator was adopted. For a cavity length of 17.9 mm and absorbed pumped power of 423.5 W, the output power of 81 W was obtained at T = 5%, exhibiting an optical conversion efficiency of 19.13% and a slope efficiency of 29.80%.

Research on output spot evolution of multi-pass gain Tm:YLF slab laser based on multi-transverse mode competition

In this paper, the multi-transverse mode competition rate equation model of the Tm:YLF slab laser is established based on the cavity structure of multi-pass gain. As the pump power increased, the changing trend of the number of particles in each mode is analyzed. The direction of beam quality change is also mastered, verified by the three-pass gain laser with the evolution of pump power. Due to the limited compression capacity of the x-axial output spot of the three-pass gain laser, the output spot changes significantly under different cavity lengths and output mirror curvatures. By discussing the output spot evolution, it is known that the large curvature output mirror and the appropriate cavity length can optimize the output spot. Finally, under the pump power of 72 W, the four-pass gain laser obtains a laser output of 1.8 W. It’s beam quality is MX2 = 1.77;MY2 = 1.99, the optical–optical conversion efficiency is 2.5 %, and the slope efficiency is 15 %. The beam quality of a three-pass gain laser is MX2 = 2.67; MY2 = 1.70, the optical–optical conversion efficiency is 3.2 %, and the slope efficiency is 11 %. It is verified that the compression of the four-pass gain laser is stronger than that of the three-pass gain laser on the x-axis, laying the foundation for developing a compact multi-pass gain laser.

Formula omitted] optical parametric oscillator with wide temperature tuning

This paper investigated the output characteristics of ZGP optical parametric oscillator (OPO) with tuning over a wide temperature range. The temperature-dependent Sellmeier equation of the ZGP crystal was obtained, and the temperature-tuned curves of ZGP OPO at different phase matching angles were calculated. For temperatures ranging from 25 °C to 200 °C, a tunable long-wave laser at 7.08–7.50 μm, 7.40–7.95 μm, and 7.79–8.47 μm was obtained when the phase matching angles were 51.3°, 50.95°, and 50.6°, respectively. The total tuning range was 1.39 μm. When the idler wavelength was 8.348 μm, the output energy was 0.520 mJ with a pulse width of 15.5 ns, the corresponding slope efficiency and optical conversion efficiency were 10.22% and 8.15%, respectively. The laser has advantages of a wide tunable range and compact mechanical configuration, extending the tuning method of ZGP OPO, which is important in promoting the development of long-wave lasers with a wide tuning range.

Optical manipulation and conversion in whispering gallery mode resonators with pump depletion

In this work, we study optical manipulation and conversion in the high-power regime, and thus the unavoidable intrinsic coupling between the pump light and the signal light, i.e. pump depletion, needs to be included. Compared with the transmission properties that are insensitive to the power of the signal light in the low-power regime with pump non-depletion, our results in the high-power regime with pump depletion show that the resonant transmission coefficients of the nonlinearity can be manipulated from 0 to non-zero by adjusting the intensities of the signal light, and thus it behaves as an intensity-dependent all-optical switch. Although the resonant conversion efficiencies from four-wave mixing of the nonlinearity are generally suppressed by power-dependent frequency shifts as a result of self-phase modulation (SPM) and cross-phase modulation (XPM) in the high-pump regime, the conversion efficiencies can be amplified by tuning the frequency detuning of the signal and pump lights. The optical transmission coefficients and conversion efficiencies can also be enhanced by utilizing the interplay between and nonlinearities in the high-pump regime. The mechanism of enhancing the conversion efficiencies to overcome the suppression from SPM and XPM provides a new way to convert frequency with high efficiencies.

Carbon dots-mediated synthesis of gold nanodendrites with extended absorption into NIR-II window for in vivo photothermal therapy

BackgroundPhotothermal therapy (PTT) in the second near-infrared (NIR-II) window has attracted extensive attention due to the benefits in high maximum permissible exposure and penetration depth. Current photothermal agents generally show a broadband absorption accompanied by a gradual attenuation of absorption in the NIR-II window, leading to poor effect of PTT. It remains a great challenge to gain photothermal agents with strong and characteristic absorption in NIR-II regions. To overcome this problem, based on carbon dots (CDs)-mediated growth strategy, we proposed a simple and feasible approach to prepare plasmonic gold nanodendrites (AuNDs) with NIR-II absorption to enhance the therapeutic effect of PTT.ResultsBy rationally regulating the size and branch length of AuNDs, the AuNDs exhibited a broadband absorption from 300 to 1350 nm, with two characteristic absorption peaks located at 1077 and 1265 nm. The AuNDs demonstrated desired optical photothermal conversion efficiency (38.0%), which was further applied in NIR-II photoacoustic imaging (PAI) and PTT in human colon cancer cells (HCT 116)-tumor-bearing mice model. The tumor cells could be effectively eliminated in vivo under 1064 nm laser irradiation by the guidance of PAI.ConclusionsWe reported a simple but powerful synthetic method to obtain the unique AuNDs with strong and characteristic absorption peaks in the NIR-II window. This study provides a promising solution to tuning the growth of nanoparticles for bioimaging and phototherapy in the NIR-II window.Graphical

Parasitic Heating of Perovskite‐ and Silicon‐Based Photovoltaics

AbstractThe origins of parasitic heating for photovoltaic (PV) technologies based on silicon, perovskites, and their combination in monolithic tandems are investigated. To quantify heating losses, the cooling score (CS) as a new simple metric, representing the percentage of incident solar irradiance not contributing to module heating is introduced. This is a function of both the optical structure and power conversion efficiency (PCE) of the PV modules and allows a fair comparison between different technologies under identical performance‐evaluation scenarios. Silicon single‐junction devices have the lowest CS due to their low bandgap (causing significant carrier thermalization losses) and their use of light‐trapping structures to increase their PCE which also undesirably increases parasitic absorption of sub‐bandgap photons. Conversely, perovskite single‐junction devices show the highest CS in all studied performance‐evaluation scenarios thanks to their wider bandgap and high absorption coefficient, enabling absorption of all solar photons that may contribute to the photocurrent without requiring light‐trapping structures. While perovskite/silicon tandems minimize thermalization losses, they also usually employ light‐trapping structures in their bottom cell to increase their PCE, which lowers their CS. Through simulation and outdoor experiments, it is demonstrated that an efficient module‐cooling environment may significantly suppress the detrimental effects associated with a low CS.