Tanaka Hiroki, Püschel Stefan
Opt Express. 2024 Jan 15;32(2):2306-2320. doi: 10.1364/OE.503250.
We propose an approach to evaluate solid-state media for laser cooling by anti-Stokes fluorescence employing a Monte Carlo-based simulation of fluorescence ray tracing. This approach prompted a revisit of the experimental method, laser-induced thermal modulation spectroscopy (LITMoS), showing that the external quantum efficiency and the background absorption coefficient can be retrieved solely from the two wavelengths where neither cooling nor heating is observed. Our simulation can accurately compute two experimentally inaccessible quantities essential to evaluate laser-cooling media: the mean fluorescence wavelength and the fluorescence escape efficiency. These computed quantities in combination with LITMoS results allow us to retrieve the internal quantum efficiency which is a performance indicator independent of various factors such as the sample size and doping level. Using the proposed approach, we thoroughly investigate the impact of doping level, sample geometry, and refractive index on the fluorescence escape efficiency and reveal its temperature dependency for the example of Yb:YLF. Through comprehensive numerical analysis, we demonstrate that the reduction of sample symmetry is crucial in achieving lower cooling temperatures.
我们提出了一种通过基于蒙特卡罗的荧光射线追踪模拟来评估用于反斯托克斯荧光激光冷却的固态介质的方法。这种方法促使人们重新审视实验方法——激光诱导热调制光谱法（LITMoS），结果表明，仅从未观察到冷却或加热的两个波长就可以获取外部量子效率和背景吸收系数。我们的模拟可以准确计算出评估激光冷却介质必不可少的两个实验上无法获取的量：平均荧光波长和荧光逃逸效率。这些计算出的量与LITMoS结果相结合，使我们能够获取内部量子效率，内部量子效率是一个独立于诸如样品尺寸和掺杂水平等各种因素的性能指标。使用所提出的方法，我们深入研究了掺杂水平、样品几何形状和折射率对荧光逃逸效率的影响，并以Yb:YLF为例揭示了其温度依赖性。通过全面的数值分析，我们证明降低样品对称性对于实现更低的冷却温度至关重要。
