Amplified Spontaneous Emission (ASE) threshold represents a crucial parameter often used to establish if a material is a good candidate for applications to lasers. Even if the ASE properties of conjugated polymers have been widely investigated, the specific literature is characterized by several methods to determine the ASE threshold, making comparison among the obtained values impossible. We quantitatively compare 9 different methods employed in literature to determine the ASE threshold, in order to find out the best candidate to determine the most accurate estimate of it. The experiment has been performed on thin films of an homopolymer, a copolymer and a host:guest polymer blend, namely poly(9,9-dioctylfluorene) (PFO), poly(9,9-dioctylfluorene-cobenzothiadiazole) (F8BT) and F8BT:poly(3- hexylthiophene) (F8BT:rrP3HT), applying the Variable Pump Intensity (VPI) and the Variable Stripe Length (VSL) methods. We demonstrate that, among all the spectral features affected by the presence of ASE, the most sensitive is the spectral linewidth and that the best way to estimate the ASE threshold is to determine the excitation density at the beginning of the line narrowing. We also show that the methods most frequently used in literature always overestimate the threshold up to more than one order of magnitude.

中文翻译：

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确定对聚合物有源波导中放大的自发发射阈值进行量化的最佳经验方法

放大自发发射 (ASE) 阈值代表一个关键参数，通常用于确定材料是否适合应用于激光。即使共轭聚合物的 ASE 特性已被广泛研究，具体文献也通过几种方法来确定 ASE 阈值，从而无法在获得的值之间进行比较。我们定量比较了文献中用于确定 ASE 阈值的 9 种不同方法，以找出最佳候选方法来确定其最准确的估计值。该实验是在均聚物、共聚物和主体：客体聚合物共混物的薄膜上进行的，即聚（9,9-二辛基芴）（PFO）、聚（9,9-二辛基芴-共苯并噻二唑）（F8BT）和 F8BT ：聚（3-己基噻吩）（F8BT：rrP3HT），应用可变泵强度 (VPI) 和可变条纹长度 (VSL) 方法。我们证明，在受 ASE 存在影响的所有光谱特征中，最敏感的是光谱线宽，估计 ASE 阈值的最佳方法是确定线变窄开始时的激发密度。我们还表明，文献中最常用的方法总是高估阈值超过一个数量级。