High Gain Coefficient Research Articles

Spontaneous Raman spectra analysis and efficient nanosecond pulse Raman laser of a BaTeW2O9 crystal.

In this Letter, the spontaneous Raman spectra of a novel, to the best of our knowledge, crystal α-BaTeW2O9 (α-BTW) are characterized and analyzed. The relative Raman gain coefficient of the α-BTW crystal is calculated to be 0.84 times that of YVO4. With a 35-mm-long crystal, the first-order Raman laser of α-BTW operating at 1178 nm is realized. The simple external resonator setup is employed in the first-order Raman laser of α-BTW. The pump source is a lamp-pumped electric-optical Q switched Nd:YAG laser amplifier system operating at 1064 nm with a pulse width of 10 ns. The Raman laser exhibits a threshold of 14.7 MW/cm2. In our experiments, a maximum pulse energy of 21.5 mJ is obtained with an optical-to-optical conversion efficiency and slope efficiency of 43.6%, 57.9%, respectively. Due to its high laser damage threshold, relative high Raman gain coefficient, and excellent thermal properties, the α-BTW crystal is a potential Raman material.

Two-Photon Lasing from Two-Dimensional Homologous Ruddlesden-Popper Perovskite with Giant Nonlinear Absorption and Natural Microcavities.

Two-dimensional Ruddlesden-Popper perovskites (RPPs) with multiple quantum well-like structures, strong excitonic quantum confinement, and high stability are promising optical gain media. However, the lasing from such material with a small number of inorganic well layers is difficult to achieve. Herein, we demonstrate the low-threshold upconversion lasing from the homologous RPP (PEA)2(MA)n-1PbnI3n+1 (n = 2 and 3) microflakes with wavelength varies from 598 to 637 nm under 800 nm laser excitation at low temperature (≤153 K). Using the micro Z-scan technique, we discovered that the RPP flakes have a giant two-photon absorption coefficient β as high as 3.6 × 103 cm GW-1, resulting in the effective upconversion transition under two-photon excitation. Furthermore, the self-formation of Fabry-Pérot microcavities provides the support for lasing emission from the n ≥ 2 RPP flakes. Calculation results and microscopic transient absorption measurements reveal that low-threshold lasing is due to the high differential gain coefficient and the suppressed nonradiative Auger recombination rate inside the quantum confinement structures. These properties enable RPPs as potential gain media for developing upconversion microcavity lasers.

Effect of structural modifications on the spectral and lasing characteristics of truxene-cored starbursts with/without diphenylamine end-cappers

This study examined the effect of chemical modifications on the spectral and lasing characteristics of truxene-cored starbursts as gain media for organic lasers. A series of conjugated starburst materials, consisting of a truxene core and oligofluorene bridges with and without diphenylamine (DPA), namely, TrXD and TrX, were assessed as model molecules to investigate the influence of DPA on the photophysical characteristics and organic lasing behaviors. TrXD with DPA could effectively restrain the aggregation and greatly suppress the aggregation-induced emission quenching, yielding high photoluminescence efficiency. A higher radiative decay rate kr was observed for TrXD than for TrX, suggesting that DPA is beneficial for enhancing the radiative decay process. TrXD showed low amplified spontaneous emission thresholds of 2.1–4.3 μJ cm−2 with high net gain coefficients of 80–101 cm−1, rather low loss coefficients of 2.6–4.4 cm−1, compared with TrX. The best performance with a lasing threshold of 0.31 kW cm−2 was obtained for Tr3D, which was superior to that of Tr3 (0.86 kW cm−2). The molecular systems with DPA have a large potential as attractive molecules for organic lasers because of the superior lasing properties induced by kr.

Cascade Brillouin Lasing in a Tellurite-Glass Microsphere Resonator with Whispering Gallery Modes.

Brillouin microlasers based on microresonators with whispering gallery modes (WGMs) are in high demand for different applications including sensing and biosensing. We fabricated a microsphere resonator with WGMs from a synthesized high-quality tellurite glass with record high Q-factors for tellurite microresonators (Q ≥ 2.5 × 107), a high Brillouin gain coefficient (compared to standard materials, e.g., silica glasses), and a Brillouin frequency shift of 9 ± 0.5 GHz. The high density of excited resonance modes and high loaded Q-factors allowed us to achieve experimentally cascade Stokes-Brillouin lasing up to the 4th order inclusive. The experimental results are supported by the results of the theoretical analysis. We also theoretically obtained the dependences of the output Brillouin powers on the pump power and found the pump-power thresholds for the first five Brillouin orders at different values of pump frequency detuning and Q-factors, and showed a significant effect of these parameters on the processes under consideration.

Quarter acoustic period pulse compression using stimulated Brillouin scattering in PF-5060.

The pulse duration of the near quarter-acoustic period (τa) is demonstrated in transient stimulated Brillouin scattering (SBS) pulse compression by the suppressing Stokes trailing-edge broadening at high intensities. A theoretical analysis reveals that the difficulty in attaining the transient compression limit is caused by the broadening of the Stokes trailing edge owing to insufficient pump depletion, and this undesirable phenomenon can be significantly suppressed by a high SBS gain coefficient. An average pulse duration of ∼1.05 τa was experimentally achieved in transient compression with a high-energy efficiency of over 30%. Benefiting from energy back conversion, compression below the transient SBS limit (< τa) also occurred when the pump peak power was increased to 150 MW.

Optimized Super-Wideband MIMO Antenna with High Isolation for IoT Applications.

A compact, low profile, multiple-input–multiple-output (MIMO) diversity antenna with super-wideband (SWB) characteristics has been proposed. The proposed antenna comprises four symmetric monopole-radiating elements printed on low-cost FR4 substrate with the slotted ground plane. The single antenna of a monopole structure and a quad-port MIMO antenna, with the dimensions of 30 × 20 mm2 and 60 × 55 mm2, respectively, are ideal for IoT and high-speed data applications. The proposed MIMO antenna has a high diversity gain and low envelope correlation coefficient (ECC) within the frequency range. Simulated results demonstrate the performance of the MIMO-SWB antenna, which operates from 2.3 to 23 GHz, with a high isolation level over 20 dB in the achieved frequency band. Moreover, the proposed MIMO antenna has been investigated with mirror fashion and orthogonal structure. Both structures provide similar results except for mutual coupling performance. The orthogonal adjustment for high isolation achieves better results with the proposed model. Further, the prototype of the proposed antenna is fabricated and measured effectively. Simulated and measured results show good agreement for super-wideband applications.

Amplified Spontaneous Emission from Perovskite Quantum Dots Inside a Transparent Glass

AbstractThe diverse optoelectronics systems can provide interesting design inspiration for photonics devices, ranging from optical modulators to light‐emitting displays. With the increasing applications and requirements of optical interconnect in complex environments, an essential operation is increasingly being pursued to exploit the consolidation of various merits of basic components. Here, an optical gain from monodisperse CsPbBr3 quantum dots crystallized in a selected transparent glass is revealed. The threshold of amplified spontaneous emission increases from 7.4 to 100.4 µJ cm−2 with the temperature from 78 K to room temperature, accompanied with a high gain coefficient of 627.9 cm−1. A small fluctuation of the lifetime (≈10.5%) with temperature and the photostability (&gt;12 h) with the excitation of femtosecond laser indicates the robustness of the crystallized CsPbBr3 quantum dots in the transparent glass. These demonstrations present a deep understanding of the optical gain in the composite of metal halide perovskites and transparent glass and pave a path for the potential applications of CsPbBr3‐based glass–ceramics as a gain medium for coherent light sources including laser/incoherent diode, fiber laser as well as optical amplifier chips.

Design of photonic crystal fiber amplifier based on stimulated Brillouin amplification for orbital angular momentum

A probe made of amino acids is arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues. The sequence of amino acids in a protein is determined by a gene and encoded in the genetic code. This can happen either before the protein is used in the cell, or as part of control mechanisms. In order to transmit and amplify high-purity orbital angular momentum mode, a photonic crystal fiber amplifier based on stimulated Brillouin amplification is proposed and designed in this paper. The transmission properties of the photonic crystal fiber amplifier are systematically analyzed by using the finite element method in the C-band. The results show that this photonic crystal fiber amplifier can support the transmission and amplification of 66 orbital angular momentum modes, and all values of the purity of the orbital angular momentum modes supported by this amplifier are higher than 99.4%. By systematically analyzing the Brillouin gain spectra of orbital angular momentum modes with different topological charges, it is found that they have all high Brillouin gain coefficients (&gt; 7 × 10&lt;sup&gt;–9&lt;/sup&gt; m/W) which are 4–5 orders of magnitude higher than the existing OAM amplifiers with the best performance, thus higher signal gain can be obtained. The comprehensive performance of the proposed photonic crystal fiber amplifier is superior to that of the existing optical fiber amplifiers based on stimulated Brillouin amplification and the optical fiber amplifiers doped with rare-earth ions. This makes the amplification and long-distance transmission of OAM mode stable and accurate and provides a possibility for designing the orbital angular momentum mode laser system.

Compact 2*1 Reader Array Antenna Operating in ISM Band for RFID Applications

This paper proposes a compact 2*1 reader array antenna for RFID system having high directivity, good gain, and good reflection coefficient. The structure consists of two main radiating rectangular patch antennas connected in parallel with a common impedance of (50 Ω). These patches are printed on an RT/duroid 5880 substrate possessing a dielectric constant εr equal to 2.2 and 0.0009 as a loss tangent. It operates in ISM (Industrial, Scientific and Medical) band with a resonant frequency of 5.8 GHz. The structure is implemented on a compact size of 38.77× 59.44× 1.6 mm3 equivalent to an electrical size of 0.74λ0× 1.14λ0× 0.03λ0, where λ0 is the free-space wavelength at the resonant frequency. The gain achieved by the final design of the proposed antenna is equal to 9.83 dB, the directivity is around 9.99 dB and the coefficient of reflection (S11) is equal to -49.48 dB. The proposed antenna design is optimized and simulated using Computer Simulation Technology software (CST Microwave Studio).

HVAC electricity and natural gas saving potential of a novel switchable window compared to conventional glazing systems: A Canadian house case study in city of Toronto

This paper investigates performance of a novel switchable window to reduce HVAC energy consumption of a typical Canadian house located in city of Toronto. Energy saving potential of the proposed glazing system is compared with highly efficient low emissivity coated double and triple pane static windows with low, medium, and high solar heat gain coefficients. Glazing systems material properties are chosen from LBNL experimentally validated international glazing system data base, (IGDB). EnergyPlus software is used to simulate and predict heating and cooling loads of the house with natural gas furnace and electric coils as the building HVAC system. Considering windows orientation, two operation strategies are developed to enhance performance of the switchable window inter-pane coatings and adjust desired solar heat gain and thermal resistance in winter and summer. Medium and high window to wall ratio effects on glazing systems performance are investigated and the result shows that proposed system significantly reduce building heating and cooling energy consumption. Considering window to wall ratio of 90%, compared to conventional clear single and double pane windows, energy analysis shows that switchable glazing system decreases HVAC annual energy bill by 47% and 33%, respectively.

Parametric study of plasma active medium and gain saturation region in a Ne‐like soft X‐ray laser

AbstractPlasmas created by the interaction of high power optical laser with a target surface can be used as a source of soft X‐ray lasers. Plasma and pump laser characteristics play significant role in achieving high gain coefficient for such plasma based on soft X‐ray lasers. In the present work, the plasma active medium parameters for germanium element at a wavelength of 19.6 nm irradiated by a double‐pulse pump laser have been studied using MED103 hydrodynamic code. For this purpose, first, the effects of laser intensity, pulse width and delay time of two pulses on the gain coefficient have been investigated and the optimum conditions for the maximum gain extent of Ne‐like germanium soft X‐ray laser are obtained. Then, in order to calculate the intensity of such high gain lasers in which Linford equation is invalid, we have adopted the general formula of amplified spontaneous emission intensity, which is valid in all range of intensities even at much higher intensities than saturation intensity. Finally, the soft X‐ray laser intensities in the saturated areas for different plasma lengths have been calculated. The results show that the output of soft X‐ray laser intensity with 294 cm−1 gain coefficient can reach to about several times saturated intensity by applying a 1–2 mm plasma length as the active medium.

Orthogonal mode dual band MIMO antenna system for 5G smartphone applications using characteristic mode analysis

PurposeThe purpose of this paper is to provide a miniaturized antenna design for a mobile phone. The second design is 2 × 4 elements multiple-input multiple-output (MIMO) antenna with 8 port having a substrate size is 20 × 40 mm2 which fits easier within smartphone handset devices for fifth generation technology.Design/methodology/approachIn this work, the first design is a conventional patch antenna, and its dual-band characteristics are obtained by characteristic mode analysis. In this method, orthogonal modes are carried out for 28 GHz and 38 GHz, and further, both orthogonal modes are excited by finite integration technique full-wave method with 50 Ohm single port coaxial feed line.FindingsIn this configuration, better return loss, high gain, larger bandwidths and low envelope correlation coefficient (ECC) are evaluated by the full-wave simulation computer simulation technology (CST) studio suite.Originality/valueIn this arrangement, the performance metrics of the antenna are analyzed using electromagnetic simulator CST Studio suite.

Preparation of Er:YAG Crystal-Derived All-Glass Silica Fibers For a 1550-nm Single-Frequency Laser

YAG crystal-derived all-glass silica fibers (YDSFs) with different doping concentrations of Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> were fabricated using the molten-core method. A maximum gain coefficient of 1.46 dB/cm was obtained when an Er:YAG rod at a doping concentration of 5 at.% was used as the precursor material. To the best of our knowledge, this is the highest gain coefficient at the 1.5-μm band in similar YDSFs. The diffusion between the Er:YAG core and silica cladding was investigated during the whole preparation process. Based on the homemade Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> -doped YDSF, a 1.55-μm pulsed single-frequency YDSF laser was demonstrated for the first time, delivering an output power of 24.2 mW when the absorbed pump power was 174 mW. The corresponding slope efficiency was 15.1%. A single-pulse energy of ~32.7 nJ was obtained with a pulse duration of 78 ns and a repetition rate of 739 kHz. The signal-to-noise ratio was higher than 75 dB.

Advances in metal halide perovskite lasers: synthetic strategies, morphology control, and lasing emission

In the past decade, lead halide perovskites have emerged as potential optoelectronic materials in the fields of light-emitting diode, solar cell, photodetector, and laser, due to their low-cost synthesis method, tunable bandgap, high quantum yield, large absorption, gain coefficient, and low trap-state densities. In this review, we present a comprehensive discussion of lead halide perovskite applications, with an emphasis on recent advances in synthetic strategies, morphology control, and lasing performance. In particular, the synthetic strategies of solution and vapor progress and the morphology control of perovskite nanocrystals are reviewed. Furthermore, we systematically discuss the latest development of perovskite laser with various fundamental performances, which are highly dependent on the dimension and size of nanocrystals. Finally, considering current challenges and perspectives on the development of lead halide perovskite nanocrystals, we provide an outlook on achieving high-quality lead perovskite lasers and expanding their practical applications.

Structural evolution, crystallization behaviour and mid-infrared emission properties in Yb/Ho codoped oxyfluoride germanosilicate glass ceramics with varied Si/Ge ratio

Changes in glass structure and crystallization behaviour from oxyfluoride silicate glass to oxyfluoride germanate glass were studied by modifying the ratio of Si/Ge in oxyfluoride germanosilicate glass ceramics, and transparent glass ceramic with low light scattering and efficient mid-infrared emissions were obtained. The NaYF4 nanocrystals crystallization ability of oxyfluoride glass was decreased with the increase in Ge content, which can be attributed to the weakened oxide and fluoride phase separation in GeO2-rich glass. Upconversion and down-conversion emission spectra together with Ho3+: 5I6 energy level fluorescent decay curves have been discussed for SiO2-rich glass ceramics and GeO2-rich glass ceramics, in which the fluoride crystallization induced the decrease of multi-phonon non-radiative decay rates plays the main role in the energy transfer processes. The influence of Si/Ge ratio on 2 μm and 3 μm fluorescent emissions in glasses and glass ceramics, and its link with glass network structural changes were discussed. The optimized Yb/Ho codoped oxyfluoride germanosilicate glass ceramic with low light scattering, high peak emission cross section(11.18 × 10−21cm2) and maximum gain coefficient (1.387 cm−1) at 2888 nm provides a potential application in the development of new 3 μm laser devices based on transparent oxyfluoride glass ceramic materials.

5.1 kW Tandem-Pumped Fiber Amplifier Seeded by Random Fiber Laser With High Suppression of Stimulated Raman Scattering

In this work, high-power tandem-pumped random fiber lasers are investigated in detail. A 6.5 W random fiber laser seed centered at 1070 nm with a half-open cavity structure was built. Boosted by two amplifier stages, the random fiber laser achieved a power of several kilowatts. Stimulated Raman scattering (SRS) mitigation is challenging in tandem-pumped fiber lasers. To suppress SRS, several methods were applied, including avoiding external feedback in the oscillator stage, incorporating a high core/cladding diameter ratio gain fiber, and using a band pass filter (BPF) to mitigate Raman noise. The latter proved to be the most effective method; therefore, SRS mitigation without and with a BPF was investigated at 3.5 kW, leading to suppression ratios rising from 14 to 30 dB. By increasing the pump power continuously to 5.6 kW, we realized a record output power of 5.1 kW, corresponding to an SRS suppression ratio of 27 dB. Owing to the high-brightness 1018 nm fiber lasers serving as the pump sources and the high gain coefficient in the second amplifier stage, the entire system demonstrated high efficiency and stability. At the maximum power level, the total optical-to-optical efficiency reached 89.0%. This work offers an economic and practical technique for realizing high-power and high-efficiency random fiber lasers with effective SRS mitigation, while the experimental results suggest the potential for further power scaling.

Tuning stimulated emission properties of oligofluorene-based gain media via non-conjugation strategy

To uncover spiro-substitution effect in gain media, four types of spiro-terfluorene derivatives, in which two individual conjugation chains with different conjugation length were connected via spirofluorene-9,9′-xanthene (SFX) and spirobifluorene (SBF) units, have been designed and synthesized. All spiro-terfluorene derivatives display high photoluminescent quantum yield (PLQY) and radiative transition rate (Kr) in solution. The PLQY and Kr gradually increase in the spin-coating films of 2SFX-SBF, 3SFX-SBF and 4SFX-SBF, clearly indicating that the lateral spiro-substitution can effectively suppress aggregation-induced exciton quenching. As a result, 4SFX-SBF with two identical conjugation chains possesses the best amplified spontaneous emission (ASE) performance with a low threshold of 0.28 μJ/cm2 and high gain coefficient of 159 cm−1. In addition, the spiro-terfluorenes display outstanding thermal stability, and the ASE threshold only doubles after 150 °C annealing. Hence, the lateral spiro-substituted strategy would be an intriguing strategy to design high-gain and low-threshold media for organic lasers.

Gain dynamics in a CO2 active medium optically pumped at 4.3 μm

A pulsed ∼2 mJ Fe:ZnSe laser tunable around ∼4.3 μm is used to optically pump mixtures of CO2 and He to create gain at 10 μm. A conventional low-pressure CO2 laser operating on both regular (001-100) and sequence (002-101) bands is used to study the gain dynamics of the optically pumped CO2 amplifier. Time-resolved measurements of the CO2 asymmetric stretching mode vibrational temperature, T3, as well as the translational temperature, T, are made. The measured T3 value of ∼2500 K is much higher than that typically measured in discharge pumped CO2 lasers. High gain coefficients ∼30%/cm in the optically pumped active medium are attributed to the efficient storage of energy in the asymmetric stretching mode and the selective population of the upper laser level. The measured optical-to-optical energy conversion efficiency of ∼30% for 10 μm lasing at sub-atmospheric pressures is close to the theoretical quantum limit of 40% and, thus, supports our claim of gain dynamics optimization. It is concluded that a joule-class 4.3 μm pump laser will be required for the amplification of sub-picosecond 10 μm pulses in a multi-atmosphere optically pumped CO2 active medium.

(Invited) Semiconductor Nanocrystal Optoelectronics of Colloidal Quantum Wells

Solution-processed semiconductor nanocrystals have been attracting increasingly greater interest in photonics including spectrally pure color conversion and enrichment in quality lighting and display backlighting [1,2]. These nanocrystals span different types and structures of semiconductors in the form of colloidal quantum dots and rods to a more recently developing class of colloidal quantum wells. In this talk, we will introduce the emergent field of nanocrystal optoelectronics using solution-processed quantum dots and wells. In particular, we will present a new concept of all-colloidal lasers developed by incorporating nanocrystal emitters as the optical gain media, intimately integrated into fully colloidal cavities [3]. In the talk, we will then focus on our recent work on the latest rising star of tightly-confined atomically flat nanocrystals, the quasi-2D colloidal quantum wells (CQWs), also popularly nick-named ‘nanoplatelets’. Among various extraordinary features of these CQWs, we will present our most recent discovery that the CQWs uniquely enable record high optical gain coefficients among all colloids [4]. In addition, we will show the controlled stacking and assemblies of these nanoplatelets, which provides us with the ability to tune and master their excitonic properties [5], and present the first accounts of doping them for high-flux solar concentration [6] and precise wavefunction-engineered magnetic properties [7]. Given their current accelerating progress, these solution-processed quantum materials hold great promise to challenge their epitaxial thin-film counterparts in semiconductor optoelectronics in the near future.[1] H. V. Demir et al., Nano Today 6, 632 (2011).[2] E. Mutlugün et al., Nano Letters 12, 3986 (2012); T. Özel et al., Nano Letters 13, 3065 (2013); X. Yang et al., ACS Nano 8, 8224 (2014).[3] B. Güzeltürk et al., Advanced Materials 27, 2741 (2015); and ACS Nano 8, 6599 (2014).[4] B. Güzeltürk et al., Nano Letters 19, 277 (2019).[5] O. Erdem et al., Nano Letters 19, 4297 (2019); N. Taghipour et al., ACS Nano 12, 8547 (2018).[6] M. Sharma et al., Advanced Materials 29, 1700821 (2017); M. Sharma et al., Chemistry of Materials 30, 3265 (2018).[7] F. Muckel et al., Nano Letters 18, 2047 (2018). Figure 1

Simultaneously Enhancing Photoluminescence Quantum Efficiency and Optical Gain of Polyfluorene via Backbone Intercalation of 2,5‐Dimethyl‐1,4‐Phenylene

AbstractSimultaneous enhancement of photoluminescence quantum efficiency (PLQE) and optical gain in semiconducting polymer films is desirable for optically‐ or electrically‐pumped organic solid‐state lasers. In this work, a simple self‐dilution effect is achieved by introducing a small amount (≈10% by weight) of 2,5‐dimethyl‐1,4‐phenylene (DP) units in the backbone of poly(9,9‐dioctylfluorene) (PFO). The resulting copolymers, compared with PFO (PLQE 39%), exhibit a significantly increased PLQE (66%) while keeping similar absorption and photoluminescence profile, concomitant with an enhancement in optical gain properties. The radiative decay rate increases sharply along with a sustaining reduction in the non‐radiative decay rate in these copolymers, following similar principle of physical dilution of a luminescent compound in solution or in a polymer matrix. Among all the copolymers, the one containing 10% DP units exhibits the lowest amplified spontaneous emission/distributed feedback laser threshold (10.9 nJ/1.4 nJ, eightfold reduction), and the highest gain coefficient (54.4 cm−1). The results demonstrate that a moderate DP/fluorene ratio can maximize the beneficial self‐dilution effects. These investigations shed light on new design strategies to achieve conjugated polymers with concurrent high PLQE and large optical gain properties.