| A new method for measuring nanosecond fluorescence lifetime is introduced in this paper. The method is based on phase-demodulation technique and the first harmonics in the Fourier series of both the excitation and the emission waveforms. A simple test system, composed of an oscilloscope, a spectroscope and an excitation light source, was designed to and proved the method is available. The excitation light source is modulated by a high-frequency electrical signal offered by a crystal oscillator, which is focused on a sample. The spectra of the emission light of sample and the excitation light are detected by spectroscope, and then the light signal is converted to electrical signal by PMT. The waveforms of the excitation and the emission are both analog signals but converted into digital signals by a oscillograph, which transmits the data to a computer. At last, the computer can deal with the data to obtain the fluorescence lifetime.A type of high-frequency modulated light source device is invented at a acceptable cost. The high-frequency varies 10MHz to 50MHz, as well as the wavelength of light changes from 940nm to 380nm.Furthermore, all necessary details were discussed, including the suitable frequency coverage (10-50MHz), the signal transmission, the I/V convection, the A/D convection, the connection of PMT and oscillograph, etc.The result of measuring the fluorescence lifetime of the cresyl violet ethanol solution (0.0033mol/L) is available (4.03±0.87 ns) , compared with a result of a TCPSC equipment (4.24 ns) .
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