Organic Gain Materials Research Articles

Dual-state emission and two-wavelength amplified spontaneous emission behaviors observed from symmetric dyes based on functionalized fluorene and benzotriazole units.

Structurally symmetric dyes using functionalized fluorenes and benzotriazole as the main building moieties have been synthesized and found to exhibit efficient dual-state emission (DSE) and interesting two-wavelength or dual amplified spontaneous emission (dual-ASE) behaviors in the solution phase, which may benefit the development of organic gain materials with dual-wavelength amplification.

Design, Fabrication and Validation of Mixed Order Distributed Feed-Back Organic Diode Laser Cavity

In the context of the quest for the organic laser diode, we address a key challenge to design and fabricate high-quality factor cavities compatible with electrical excitation of organic semiconductors. More precisely, we present the design of DFB micro-cavities for integration in organic laser diodes and their validation under optical pumping. To design high-quality factor mixed-order DFB micro-cavities, we consider the half- and quarter-wavelength multilayered system and use the optical waveguide analysis to quantify the effective indices of the high and low indices, and the matrix transfer method to calculate the reflectances. Matrices of DFB micro-cavities made from different doses and different grating periods were fabricated. We then identified those showing laser emission under optical pumping as an indication of optimal matching of their resonance wavelength with respect to the electroluminescence peak of the organic gain material. Potential applications of organic laser diodes deal with light communication, spectroscopy, sensors, and other applications where heterogenous integration is important.

Optical gain and photo-bleaching of organic dyes, quantum dots, perovskite nanoplatelets and nanodiamonds

ABSTRACT Optical gain and resistance against photo-bleaching are key material parameters for practical applications in microlasers and microphotonics. Here, we present studies of optical amplification and photo-bleaching in a wide range of optical gain materials, including fluorescent dyes, quantum dots and rods, organic and inorganic room temperature polaritons, and nanodiamonds with emission range from 430 to 680 nm. We used amplified spontaneous emission (ASE) for each material to measure the optical gain. Robustness against photo-bleaching was determined by measuring the intensity of spontaneous emission of the material as a function of the number of excitation femtosecond pulses (106–1010) at various excitation energy densities. We show that pyrromethene laser dyes are the best organic emitters in terms of low excitation energy and good optical gain, whereas solid-state polariton materials are better in terms of high optical gain and stability. We found that all organic and inorganic optical gain materials bleach completely after 106–109 illumination pulses with typical 0.1–0.6 GW/cm2 peak power density, with an exception of nanodiamonds. We show that nanodiamonds are the only optical gain material that shows no photo-bleaching beyond the 1010 excitation pulses of 300 fs pulse duration and with 0.16 GW/cm2 peak power density.

Amplified Spontaneous Emission from Organic Phosphorescence Emitters.

Organic gain materials (OGMs) currently used in organic lasers and optical amplifiers are focused on singlet-fluorescence materials, while triplet-phosphorescence-based OGMs have hardly been developed yet. Herein, we report a novel pure organic phosphorescence gain molecule (SBP) for optical amplification by stimulated emission from triplet states. The introduction of the benzophenone carbonyl group and sulfur atoms increases the spin orbit coupling constant of SBP, which accelerates the intersystem crossing (ISC) and phosphorescence processes. Experimental and theoretical results verify that the formation of the H-type dimer aggregate decreases the fluorescence radiation rate while accelerating the ISC rate, also enhancing the phosphorescence emission of SBP. Doping SBP molecules into a PMMA matrix can stabilize triplet excitons, yielding the maximum phosphorescence quantum yield of 18.9%. We realized triplet phosphorescent amplified spontaneous emission (ASE) at 557 nm from 30.0 wt % SBP@PMMA samples. Our results provide a novel strategy to develop triplet phosphor OGMs.

Microlasers from AIE-Active BODIPY Derivative.

Organic microlasers have attracted much attention due to their unique features such as high mechanical flexibility, facile doping of gain materials, high optical quality, simplicity and low-cost fabrication. However, organic gain materials usually suffer from aggregation-caused quenching (ACQ), preventing further advances of organic microlasers. Here, a new type of microlaser from aggregation-induced emission (AIE) material is successfully demonstrated. By introducing a typical noncrystalline AIE material, a high quality microlaser is obtained via a surface tension-induced self-assembly approach. Distinct from conventional organic microlasers, the organic luminescent material used here is initially nonluminescent but can shine after aggregation under optical pumping. Further investigations demonstrate that AIE-based microlasers exhibit advantages to enable much higher doping concentrations, which provides an alternative way to improved lasing performance including dramatically reduced threshold and favorable lasing stability. It is believed that these results could provide a promising way to extend the content of microlasers and open a new avenue to enable applications ranging from chemical sensing to biology.

A spirofluorene-end-capped bis-stilbene derivative with a low amplified spontaneous emission threshold and balanced hole and electron mobilities

To realize high performance in electrically pumped organic semiconductor laser diodes, organic-gain materials with low thresholds of amplified spontaneous emission and laser and balanced hole and electron mobilities are required. However, it is still very difficult to find such well-balanced organic materials. In this study, we show that a spirofluorene-end-capped bis-stilbene derivative of 4-((E)-2-(9,9′-spirobi[fluoren]-3-yl)vinyl)-4'-((E)-2-(9,9′-spirobi[fluoren]-6-yl)vinyl)-1,1′-biphenyl (BSBSF) is an excellent gain medium with a low amplified spontaneous emission threshold of 0.66 μJ cm−2 even in neat films. Additionally, the hole and electron mobilities of BSBSF films are very similar over a wide voltage range. Taking advantage of the balanced mobilities, we were able to obtain suppressed efficiency roll-off in BSBSF-based organic light-emitting diodes. These results will contribute toward fabrication of optically and electrically pumped organic semiconductor laser diodes with high performance.

Functionalized polymer waveguide optical switching devices integrated with visible optical amplifiers based on an organic gain material

In this work, polymer waveguide based optical switching devices integrated with visible optical amplifying waveguides based on an organic gain material are designed and fabricated. The gain compound is a red emissive oligomer, with good dispersibility in organic polymer matrices. Optical characteristics and thermal stabilities of the active polymer waveguide core and cladding materials are analyzed. Optical gain of the amplifier operating at 650 nm red signal wavelength with 0.1 mW input power is found to be over 3.5 dB under only 1.6 mW pumping power with 532 nm green excitation light. The on-off response time of the integrated thermo-optic switch applied is measured to be 600 μs, with switching extinction ratio of 20 dB and electric switching power of 18.5 mW. The integrated switching device capable of optical gain will be suitable for applications to optical communications at the visible wavelength range involving plastic optical fiber systems.

Lasing in Ni Nanodisk Arrays.

We report on lasing at visible wavelengths in arrays of ferromagnetic Ni nanodisks overlaid with an organic gain medium. We demonstrate that by placing an organic gain material within the mode volume of the plasmonic nanoparticles both the radiative and, in particular, the high ohmic losses of Ni nanodisk resonances can be compensated. Under increasing pump fluence, the systems exhibit a transition from lattice-modified spontaneous emission to lasing, the latter being characterized by highly directional and sub-nanometer line width emission. By breaking the symmetry of the array, we observe tunable multimode lasing at two wavelengths corresponding to the particle periodicity along the two principal directions of the lattice. Our results are relevant for loss-compensated magnetoplasmonic devices and topological photonics.

Ultrafast Pulse Generation in an Organic Nanoparticle-Array Laser.

Nanoscale coherent light sources offer potentially ultrafast modulation speeds, which could be utilized for novel sensors and optical switches. Plasmonic periodic structures combined with organic gain materials have emerged as promising candidates for such nanolasers. Their plasmonic component provides high intensity and ultrafast nanoscale-confined electric fields, while organic gain materials offer fabrication flexibility and a low acquisition cost. Despite reports on lasing in plasmonic arrays, lasing dynamics in these structures have not been experimentally studied yet. Here we demonstrate, for the first time, an organic dye nanoparticle-array laser with more than a 100 GHz modulation bandwidth. We show that the lasing modulation speed can be tuned by the array parameters. Accelerated dynamics is observed for plasmonic lasing modes at the blue side of the dye emission.

Theoretical evidence of low-threshold amplified spontaneous emission in organic emitters: transition density and intramolecular vibrational mode analysis.

Organic gain materials are highly attractive for lasing due to their chemical tunability and large stimulated emission cross sections. In previous reports, the radiative decay rate kr was considered as an important factor to determine outstanding amplified spontaneous emission (ASE) performance of organic molecules. In this study, we use quantum mechanics to reveal the influential factors on photophysical properties of organic emitters, and give insight into the effect of kr on ASE performance. Based on the theoretical analysis of three molecules with similar structure, calculated results show that large kr derives from enhanced transition density ρ between the electronic wave functions of the ground-state and the lowest excited singlet state as well as a handful of low-frequency torsional modes with small Huang-Rhys factor S, further, kr values are calculated depending on molecular vibration terms. In addition, through the analysis of non-radiative decay rate knr considering vibration terms (vibronic coupling constants), the comparison of kr and knr shows that the radiative decay process is promoted in the three molecules. The two aspects are desired for outstanding ASE performance. Our work shows that the roles of transition density and vibrational modes are crucial to clarify the photophysical properties, which govern the ASE performance in organic light emitters.

Organic Lasers: Recent Developments on Materials, Device Geometries, and Fabrication Techniques.

Organic dyes have been used as gain medium for lasers since the 1960s, long before the advent of today's organic electronic devices. Organic gain materials are highly attractive for lasing due to their chemical tunability and large stimulated emission cross section. While the traditional dye laser has been largely replaced by solid-state lasers, a number of new and miniaturized organic lasers have emerged that hold great potential for lab-on-chip applications, biointegration, low-cost sensing and related areas, which benefit from the unique properties of organic gain materials. On the fundamental level, these include high exciton binding energy, low refractive index (compared to inorganic semiconductors), and ease of spectral and chemical tuning. On a technological level, mechanical flexibility and compatibility with simple processing techniques such as printing, roll-to-roll, self-assembly, and soft-lithography are most relevant. Here, the authors provide a comprehensive review of the developments in the field over the past decade, discussing recent advances in organic gain materials, which are today often based on solid-state organic semiconductors, as well as optical feedback structures, and device fabrication. Recent efforts toward continuous wave operation and electrical pumping of solid-state organic lasers are reviewed, and new device concepts and emerging applications are summarized.

Efficient amplified spontaneous emission from oligofluorene-pyrene starbursts with improved electron affinity property.

A series of monodisperse starburst molecules as optical gain media have been investigated in detail. The starburst molecules were composed of a pyrene core with four short oligofluorene arms capped by cyanophenyl moieties. The compounds exhibited low amplified spontaneous emission (ASE) thresholds of 30 nJ pulse-1 and high maximum net gain coefficient of 55 cm-1 under optically pump. Our study demonstrates that the introducing of electron-withdrawing cyanophenyl end-capper onto pyrene centered starburst molecules does not disadvantage their optical gain properties while leading to reduced LUMO level, therefore, improved electron affinity. This study suggested a promising approach for organic gain material synthesis to address the challenge of electrically pumped organic laser.

The molecular picture of amplified spontaneous emission of star-shaped functionalized-truxene derivatives

Organic optical gain materials are the basis for organic solid-state lasers.

Pump spot size dependent lasing threshold in organic semiconductor DFB lasers fabricated via nanograting transfer

Optically excited organic semiconductor distributed feedback (DFB) lasers enable efficient lasing in the visible spectrum. Here, we report on the rapid and parallel fabrication of DFB lasers via transferring a nanograting structure from a flexible mold onto an unstructured film of the organic gain material. This geometrically well-defined structure allows for a systematic investigation of the laser threshold behavior. The laser thresholds for these devices show a strong dependence on the pump spot diameter. This experimental finding is in good qualitative agreement with calculations based on coupled-wave theory. With further investigations on various DFB laser geometries prepared by different routes and based on different organic gain materials, we found that these findings are quite general. This is important for the comparison of threshold values of various devices characterized under different excitation areas.

Plasmonic Bowtie Nanolaser Arrays

Plasmonic lasers exploit strong electromagnetic field confinement at dimensions well below the diffraction limit. However, lasing from an electromagnetic hot spot supported by discrete, coupled metal nanoparticles (NPs) has not been explicitly demonstrated to date. We present a new design for a room-temperature nanolaser based on three-dimensional (3D) Au bowtie NPs supported by an organic gain material. The extreme field compression, and thus ultrasmall mode volume, within the bowtie gaps produced laser oscillations at the localized plasmon resonance gap mode of the 3D bowties. Transient absorption measurements confirmed ultrafast resonant energy transfer between photoexcited dye molecules and gap plasmons on the picosecond time scale. These plasmonic nanolasers are anticipated to be readily integrated into Si-based photonic devices, all-optical circuits, and nanoscale biosensors.

Design and optical characterization of photonic crystal lasers with organic gainmaterial

We present a design concept for an optimized surface-emitting laserwith two-dimensional feedback structure and organic gain material. Thebasic laser structure consists of an array of holes within a thin film ofTa2O5. The optical properties of such feedback structures are investigated theoretically andexperimentally. Combining first-order with second-order photonic structures leads to ahigher quality factor of the feedback structure, resulting in a lower laser threshold and/or amuch smaller footprint of the laser.

Organic mixed-order photonic crystal lasers with ultrasmall footprint

The lasing properties of an optimized two-dimensional photonic crystal structure with an organic gain material are investigated. The feedback structure which is fabricated in a thin film of Ta2O5 increases both the index contrast from the gain material as well as the optical confinement. By combining first-order and second-order photonic crystal structures, losses occuring at the edge of the second order structure are dramatically reduced leading to a lower laser threshold and/or to a much smaller footprint of the laser.

Enhanced backscattering from organic laser gain media bounded with rough gold films

The enhanced backscattering from organic laser gain media that are bounded with one-dimensional (1-D) and two-dimensional (2-D) rough metal films was investigated. We prepared several organic optical gain materials by doping laser-active dyes in matrices of acrylic polymers. These materials produced efficient and broadband fluorescence emission in the visible wavelengths during the pumping of a pulsed YAG or cw argon laser. These gain materials were sliced and coupled with 1-D or 2-D randomly rough gold films with large slopes. An experimental investigation was carried out with a He-Ne laser as the scattering source and the optical gain provided by a cw argon laser. The enhanced backscattering and the satellite peaks located about the enhanced-backscattering peak were obviously amplified, with their widths narrowed. These experimental results agree well with previous theoretical predictions.

Distributed feedback ridge waveguide lasers fabricated by nanoscale printing and molding on nonplanar substrates

This letter describes the use of printing and molding techniques to fabricate plastic photopumped laser that use distributed feedback resonators on ridge waveguides. The results indicate (i) potential optoelectronic applications of a set of emerging low cost lithographic techniques that can pattern a range of materials with submicron resolution on nonplanar substrates, (ii) a new type of plastic laser based on molded organic gain materials, and (iii) that thresholds of plastic distributed feedback ridge waveguide lasers are similar to their planar counterparts.