Nanomechanics Group, Biotechnology Center, TU Dresden, Tatzberg 47-51, 01307 Dresden, Germany.
Phys Rev Lett. 2011 Nov 25;107(22):228301. doi: 10.1103/PhysRevLett.107.228301. Epub 2011 Nov 21.
The random thermal force acting on Brownian particles is often approximated in Langevin models by a "white-noise" process. However, fluid entrainment results in a frequency dependence of this thermal force giving it a "color." While theoretically well understood, direct experimental evidence for this colored nature of the noise term and how it is influenced by a nearby wall is lacking. Here, we directly measured the color of the thermal noise intensity by tracking a particle strongly confined in an ultrastable optical trap. All our measurements are in quantitative agreement with the theoretical predictions. Since Brownian motion is important for microscopic, in particular, biological systems, the colored nature of the noise and its distance dependence to nearby objects need to be accounted for and may even be utilized for advanced sensor applications.
布朗运动粒子所受的随机热作用力在朗之万模型中通常用“白噪声”过程来近似。然而，流体夹带会导致热作用力的频率依赖性，从而使其具有“颜色”。尽管从理论上很好理解，但缺乏对噪声项的这种有色性质以及它如何受到附近壁面影响的直接实验证据。在这里，我们通过跟踪一个被强约束在超稳定光阱中的粒子，直接测量了热噪声强度的颜色。我们所有的测量结果都与理论预测定量一致。由于布朗运动对于微观，特别是生物系统很重要，因此需要考虑噪声的有色性质及其与附近物体的距离依赖性，甚至可以将其用于先进的传感器应用。
