Development of Wavelength-Tunable Solid-State Lasers with Low Thresholds Comprising Nano-Wires of Thiophene/Phenylene Co-Oligmers

（一）有机激光材料的发展我们新开发了各种噻吩/苯基共低聚物，其分子两端都被烷基、甲氧基、氰基、三氟甲基等化学基团修饰。这些共低聚物包括噻吩和苯（苯），并且作为有机激光材料具有潜在的用途。它们的电子态和载流子（空穴和电子）的极性可以通过适当选择取代基来控制。（二）激光振荡的观察我们利用上述共聚物材料制成了高纯度的单晶和纳米线。激光振荡已被明确地观察到。我们特别选择了2,5-双（4-联苯基）噻吩（BP1T）和5,5'''''-二苯基-2,2':5',2':5',2':5',2 '''':5'''',2'''''-六噻吩（P6T）作为模型材料，仔细观察了在不同激发条件下激光激发材料产生的纳米线的发射特性。结果，我们发现BP1T和P6T分别在466 nm和688 nm附近引起激光振荡。在任何一种情况下，晶体的任一边缘平面形成法布里-佩罗谐振器。因此，我们首次观察到有机晶体的激光振荡。这一结果很重要，因为它为宽光谱的波长可调激光器开辟了一条道路。（iii）激光振荡特性的评价我们研究了BP1T纳米线激光振荡的尺寸依赖特征。在相关测量的基础上，我们证实了激光振荡的阈值随着纳米线尺寸的增大而减小。聚焦光束宽度为20 μm的条形激发对激光振荡的重现性特别有效。条纹激发被认为有利于光约束。

(i) Development of Organic Laser MaterialsWe have newly developed various thiophene/phenylene co-oligomers whose molecular terminals of either side are modified with chemical groups such as alkyls, methoxy, cyano, and trifluoromethyl. Those co-oligomers comprise thiophenes and phenylenes (benzenes) and are potentially useful as organic laser materials. Their electronic states and polarity of carriers (holes and electrons) can appropriately be controlled by suitably choosing the chemical groups as substituents.(ii) Observation of Laser OscillationWe have made single crystals and nano-wires of high purity using the above-mentioned co-oligomer materials. The laser oscillation has definitively been observed from them. In particular, we chose as model materials 2,5-bis(4-biphenylyl)thiophene (BP1T) and 5,5'''''-diphenyl-2,2':5',2'':5'',2''':5''',2'''':5'''',2'''''-sexithiophene (P6T) and closely inspected the emission characteristics of the nano-wires that resulted from the laser excitation of the materials under various excitation conditions. As the result, we found BP1T and P6T to cause the laser oscillation around 466 and 688 nm, respectively. In either case either edge plane of the crystals forms the Fabri-Perot resonator. Thus we have observed for the first time the laser oscillation from the organic crystals. The results are important as opening up a route to wavelength-tunable lasers of wide spectra.(iii) Evaluation of Laser Oscillation CharacteristicsWe have investigated the size dependent features of the laser oscillation from the nano-wires of BP1T. We confirmed on the basis of the relevant measurements that the thresholds of the laser oscillation decrease with increasing the size of the nano-wires. The stripe excitation with a focused beam of 20 μm in width is particularly effective in reproducibly causing the laser oscillation. The stripe excitation is thought advantageous to the optical confinement.