激光自混频技术可用于纳米颗粒和纳米流体的探测。在纳米流体自混频信号自相关函数的基础上，理论推导了功率谱函数的表达式。结果表明，纳米流体的激光自混频信号功率谱是洛伦兹线型和高斯线型的卷积，即佛赫特(Voigt)线型。通过数值计算研究了各种典型情况下激光自混频信号功率谱的频谱特征，颗粒定向运动速度决定了多普勒频移和高斯线宽，颗粒粒度决定了洛伦兹线型的宽度，颗粒粒度和速度与功率谱之间的对应关系为纳米流体的测量提供了理论基础。

The laser diode self-mixing interferometry can be employed to measure nano-particles and nano-fluids. The analytical expression of power density of the feedback self-mixing signal from a flowing Brownian motion system is obtained theoretically. It reveals that the power density is of the Voigt profile, which is a convolution of the Lorentzian and Gaussian line profiles. The characteristics of the self-mixing spectrum are studied numerically. It is found that the Doppler shift and the Gaussian term in the power density are determined by flow velocity while the Lorentzian term is determined by the Brownian motion of particles (i.e., the particle size). The study provides fundamentals for the measurement of nano-fluids.