Organic Dye Laser Threshold
Organic Dye Laser Threshold
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DOI：
10.1063/1.1660468
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发表时间：
1971-04
影响因子：
3.2
通讯作者：
O. Peterson;J. Webb;W. Mccolgin;J. Eberly
中科院分区：
文献类型：
--
作者：
O. Peterson;J. Webb;W. Mccolgin;J. Eberly
本文介绍了对确定三种有机染料（罗丹明 B、罗丹明 6G 和荧光素）激光阈值的相关物理参数的研究结果。这些染料（特别是罗丹明 6G）不仅是使用最广泛和最重要的激光染料之一，而且从我们对这些特定染料的研究中得出的对阈值条件的见解应该普遍适用于未来的染料激光研究。我们对这些染料阈值的详细表征和我们的新颖见解源于首次以彻底和定量的方式使用三重态光谱数据，再加上三重态种群与单重态激发态种群成比例的物理现实近似。对于激光发射波长自调谐的情况，提出了阈值方程的解，该方程建立了影响激光的所有参数之间的关系：临界反转、发射波长、外在损耗、染料浓度、活性介质长度以及三重态与激发单重态布居比。对于相当高的外在腔损耗，临界反演是外在损耗的简单幂律函数，并且发射波长以外在损耗与内在单线态吸收损耗的比率基本恒定的方式自调谐。存在一个低但物理上可实现的腔损耗区域，其中激光作用完全由染料的固有特性（三线态吸收、单线态发射和吸收）决定。最大发射波长和最小临界反转的渐近限制出现在该区域，超过该限制就没有必要减少外在腔损耗。三重态分子的比例还决定了外部调谐激光器的长波长截止。概述了测量具有已知三重态吸收光谱的染料的三重态与激发单重态群的比率的方法，以及在未知信息的情况下半定量确定染料中的三重态效应的方法。最后一个有趣的结论是，罗丹明 6G 的分子修饰不能将其作为激光染料的阈值特性提高超过 4 倍。
This paper describes the results of an investigation of the interrelated physical parameters that determine laser threshold for three organic dyes: rhodamine B, rhodamine 6G, and fluorescein. Not only are these dyes (rhodamine 6G in particular) among the most widely used and important laser dyes, but insights into the threshold condition derived from our studies of these particular dyes should be generally applicable to future dye laser research. Our detailed characterization of threshold for these dyes and our novel insights result from the use of triplet state spectral data in a thorough and quantitative way for the first time, coupled with the physically realistic approximation that the triplet population is proportional to the singlet excited state population. For the case of self‐tuning of the laser emission wavelength, solutions to the threshold equations are presented that establish relations between all the parameters affecting lasing: critical inversion, emission wavelength, extrinsic losses, dye concentration, length of active medium, and triplet to excited singlet population ratio. For reasonably high extrinsic cavity losses, the critical inversion is a simple power law function of extrinsic loss, and the emission wavelength is self‐tuned in such a manner that the ratio of extrinsic losses to intrinsic singlet absorption losses is substantially constant. There exists a region of low, but still physically realizable, cavity losses, where laser action is determined exclusively by intrinsic characteristics of the dyes (triplet absorption, singlet emission, and absorption). Asymptotic limits on the maximum wavelength of emission and on the minimum critical inversion appear in this region, beyond which there is no point in reducing extrinsic cavity losses. The fraction of triplet state molecules also determines long wavelength cutoffs for an externally tuned laser. Methods are outlined for measuring the ratio of triplet state to excited singlet state populations for dyes with known triplet absorption spectra and for determining semiquantitatively the triplet effects in dyes where this information is not known. A final interesting conclusion is that molecular modifications of rhodamine 6G cannot be expected to improve its threshold characteristics as a laser dye by much more than a factor of 4.