A Temperature-Tunable Thiophene Polymer Laser

TD-DFT Simulation and Experimental Studies of a Mirrorless Lasing of Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-diphenylene-vinylene-2-methoxy-5-{2-ethylhexyloxy}-benzene)]

In this work, we investigate the TD-DFT simulation, optical, and mirrorless laser properties of conjugated polymer (CP) Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-diphenylene-vinylene-2-methoxy-5-{2-ethylhexyloxy}-benzene)], also known as (PFO-co-PPV-MEHB) or ADS125GE. TD-DFT calculations were performed for three monomer units with truncated tails using time-dependent density functional theory (TD-DFT) calculations. The calculations showed a highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) structure and a very high oscillator strength of 6.434 for the singlet-singlet transition at 374.43 nm. Experimentally, the absorption and fluorescence spectra were examined at various concentrations in verity of solvents, such as benzene, toluene, and hexane. The experimental results obtained in hexane were comparable with theoretical UV-VIS spectra calculated under vacuum. Amplified spontaneous emission (ASE) spectra peaked at approximately 509 nm for CO PFO-co-PPV-MEHB in solution and were obtained at suitable concentrations and pump energies. Additionally, the photochemical stability of this CP and coumarin (C510) were compared. Time-resolved spectroscopy (TRS) studies with a sub-nanosecond resolution were performed for the CO under various pump energies. These results showed the excited state dynamics and single-pass optical gain of CO PFO-co-PPV-MEHB.

Narrowband Spontaneous Emission Amplification from a Conjugated Oligomer Thin Film

In this paper, we studied the laser and optical properties of conjugated oligomer (CO) 1,4-bis(9-ethyl-3-carbazo-vinylene)-9,9-dihexyl-fluorene (BECV-DHF) thin films, which were cast onto a quartz substrate using a spin coating technique. BECV-DHF was dissolved in chloroform at different concentrations to produce thin films with various thicknesses. The obtained results from the absorption spectrum revealed one sharp peak at 403 nm and two broads at 375 and 428 nm. The photoluminescence (PL) spectra were recorded for different thin films made from different concentrations of the oligomer solution. The threshold, laser-induced fluorescence (LIF), and amplified spontaneous emission (ASE) properties of the CO BECV-DHF thin films were studied in detail. The ASE spectrum was achieved at approximately 482.5 nm at a suitable concentration and sufficient pump energy. The time-resolved spectroscopy of the BECV-DHF films was demonstrated at different pump energies.

Gel Trapping Enables Optical Spectroscopy of Single Solvated Conjugated Polymers in Equilibrium

Single-molecule studies have provided a wealth of insight into the photophysics of conjugated polymers in the solid and desolvated state. Desolvating conjugated chains, e.g., by their embedding in inert solid matrices, invariably leads to chain collapse and the formation of intermolecular aggregates, which have a pronounced effect on their properties. By contrast, the luminescent properties of individual semiconducting polymers in their solvated and thermodynamic state remain largely unexplored. In this paper, we demonstrate a versatile gel trapping technique that enables the chemistry-free immobilization and interrogation of individual conjugated macromolecules, which retain a fully equilibrated conformation by contrast to conventional solid-state immobilization methods. We show how the technique can be used to record full luminescence spectra of single chains, to evaluate their time-resolved fluorescence, and to probe their photodynamics. Finally, we explore how the photophysics of different conjugated polymers is strongly affected by desolvation and chain collapse.

Optically Pumped Intensive Light Amplification from a Blue Oligomer

We demonstrated the time-resolved dynamics of laser action from the conductive oligomer (CO) 1,4-Bis(9-ethyl-3-carbazo-vinylene)-9,9-dihexyl-fluorene (BECV-DHF). Absorption and fluorescence spectra were studied for BECV-DHF in different solvents under a wide range of concentrations. The Fourier-transform infrared spectroscopy (FTIR) spectrum was measured using simulation and experiments. The Ultraviolet-Visible (UV-VIS) spectra of the BECV-DHF were simulated in two different solutions. This CO formed a dimer and had two vibration bands in nonpolar solvents, partially dissolved in polar protic solvents, and created an H-type aggregate in polar aprotic solvents. BECV-DHF produced amplified spontaneous emission (ASE) at 464 nm in many solvents. The high efficiency of ASE is due to the waveguiding and self-assembly nature of the oligomer, which is very rare for optically pumped systems. However, BECV-DHF did not produce ASE in polar protic solvents. BECV-DHF produced ASE in both longitudinal and transverse pumping, and the full-width half maximum (FWHM) was 4 nm and 8 nm respectively for different solvents, such as toluene and acetone. The CO had a very low threshold pump energy (~0.5 mJ). The ASE efficiency was approximately 20%. The time-resolved spectroscopy (TRS) studies showed a temporal Gaussian-shaped ASE output from this CO. BECV-DHF shows remarkably high stability compare to the conjugated polymer (CP) PFO-co-pX.

Advances in Conjugated Polymer Lasers

This paper provides a review of advances in conjugated polymer lasers. High photoluminescence efficiencies and large stimulated emission cross-sections coupled with wavelength tunability and low-cost manufacturing processes make conjugated polymers ideal laser gain materials. In recent years, conjugated polymer lasers have become an attractive research direction in the field of organic lasers and numerous breakthroughs based on conjugated polymer lasers have been made in the last decade. This paper summarizes the recent progress of the subject of laser processes employing conjugated polymers, with a focus on the photoluminescence principle and excitation radiation mechanism of conjugated polymers. Furthermore, the effect of conjugated polymer structures on the laser threshold is discussed. The most common polymer laser materials are also introduced in detail. Apart from photo-pumped conjugated polymer lasers, a direction for the future development of electro-pumped conjugated polymer lasers is proposed.

Operating Characteristics of High-Order Distributed Feedback Polymer Lasers

In this study, high-order distributed-feedback (DFB) polymer lasers were comparatively investigated. Their performance relies on multiple lasing directions and their advantages include their high manufacturing tolerances due to the large grating periods. Nine laser cavities were fabricated by spin-coating the gain polymer films onto a grating structure, which was manufactured via interference lithography that operated at the 2nd, 3rd, and 4th DFB orders. Low threshold lasing and high slope efficiency were achieved in high-order DFB polymer lasers due to the large grating groove depth and the large gain layer thickness. A high-order DFB configuration shows possible advantages, including the ability to control the lasing direction and to achieve multiple-wavelength lasers. Furthermore, our investigation demonstrates that the increase in threshold and decrease in slope efficiency with an increase in the feedback order can be limited by controlling the structural parameters.