中文摘要：

针对纳秒量级荧光寿命的测量，提出一种改进的相调制法，提取周期性激发信号和相应的发射波形信号傅立叶级数中的一级项，按照相位法测量荧光寿命的原理求得荧光寿命T值。据此采用易于调制的发光二极管为激发光源，充分利用实验室常用的仪器资源，设计了一种针对单指数衰减的测量系统。该系统主要由激发光源、光谱仪、示波器三部分组成，结构简单灵活、抗噪性好。对测量原理、频率的选择、系统的组成进行了详细讨论。利用该系统测量了乙醇溶液中甲酚紫（0．0033mol／L）的T值为（4．03±0．87）ns，与采用德国PieoQuant公司TCPSC仪器测量的结果4．24ns相当。

英文摘要：

A modified phase demodulation method for measuring nanosecond fluorescence lifetime is introduced in this paper. The method is based on phase modulation technique and Fourier analysis of both the excitation and the emission waveforms. Excitation light is modulated by an arbitrary periodic wave. Emission of the sample follows the excitation light, is also modulated and with a delay because of the fluorescence lifetime. In the modified method, the first harmonics of the Fourier series are figured out from the excitation and the emission waveforms. The lifetime can be obtained by the relationship same as in the ordinary phase modulation method from the phase difference between the first harmonics. A test system, composed of an oscilloscope, a spectroscope and an excitation light source, was designed and developed. An LED light source modulated by a crystal oscillator is built at an acceptable cost for the system. The emission and excitation are detected by a spectroscope, converted to electrical signal by a photomultiplier tube, digitalized by a digital oscilloscope, and then transmitted to a computer. Fluorescence lifetime is then obtained by Fourier analysis of the emission and excitation waveforms. The relationship between the optimized modulation frequency and the range of the measured lifetimes is discussed. The lifetime of cresyl violet ethanol solution （0.003 3 mol/L） measured with this method is （4.03 ± 0.87） ns which is comparable with that by a commercial equipment.