Wang Tao, Liu Xiao-Fei, Hu Yunqi, Qin Guoqing, Ruan Dong, Long Gui-Lu
State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China.
State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China; School of Science and the State Key Laboratory of Information photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876, China.
Sci Bull (Beijing). 2018 Mar 15;63(5):287-292. doi: 10.1016/j.scib.2018.02.005. Epub 2018 Feb 5.
Opto-thermal relaxation is one of the most important properties of nonlinear optical materials. Rapid and high precision measurement of this parameter is vital in both fundamental research and applications. Current measurement uses either complicated structure with poor precision or high power heating source with low efficiency. Here, we propose a pump-probe method (PPM) to optically measure the thermal relaxation using whispering gallery mode (WGM) microcavities. When the pump laser shines on a microcavity, the materials absorb the input power resonantly and heat up. Then the heat dissipates from the cavities to the surroundings. The opto-thermal effect induces a refractive index change reflected in the signal light transmission spectra. By analyzing the curve character of the transmission spectra of the signal response in the spontaneous relaxation process, the thermal relaxation time can be rapidly measured with high precision. Additionally, we systematically verify the PPM using microtoroids under various pump powers and at various locking points of the signal laser mode. The small rate of refractive index changes (∼10) can be discerned with an input pump power as low as 11.816 μW. Hence, the PPM can be used to detect refractive index perturbation, like gas or liquid sensing, temperature fluctuations with ultra-high sensitivity and be applied to optical materials analysis efficiently.
光热弛豫是非线性光学材料最重要的特性之一。对该参数进行快速、高精度测量在基础研究和应用中都至关重要。目前的测量方法要么结构复杂且精度差，要么使用效率低的高功率加热源。在此，我们提出一种泵浦 - 探测方法（PPM），利用回音壁模式（WGM）微腔对热弛豫进行光学测量。当泵浦激光照射到微腔上时，材料会共振吸收输入功率并升温。然后热量从微腔散发到周围环境中。光热效应会引起信号光传输光谱中反映出的折射率变化。通过分析自发弛豫过程中信号响应的传输光谱的曲线特征，可以快速、高精度地测量热弛豫时间。此外，我们在各种泵浦功率和信号激光模式的各种锁定点下，使用微环系统地验证了PPM。在低至11.816 μW的输入泵浦功率下，就可以分辨出小的折射率变化率（约为10）。因此，PPM可用于检测折射率扰动，如气体或液体传感、超高灵敏度的温度波动，并能有效地应用于光学材料分析。
