Study On The Use Of Ultra-Short Pulse Laser Modulation In The High Time-Resolved Spectrometer

The research direction and content of this article is based on the NSFC project -the development of picosecond time-correlated single photon counting (TCSPC) spectrometer. The item has researched and developed the single photon counting with time resolution. The project has been checked and accepted favorably. This paper analyses the high time-resolved spectrometer request the repeat frequency of the ultra-short pulse laser is variable, and discusses the necessity of the design ultra-short pulse laser modulation system. The design scheme of the modulation system is brought forward. The emphasis is put on the development of picosecond laser cavity dumping driver, and the design of the impedance matching network between the acousto-optic modulation and the driver. The driver operates in the pulse mode, and can generate drive signal whose repeat frequency and pulse interval is tunable. The electronics of the cavity dumper driver consists of a frequency source, a pulse modulator and a power amplifier. In the premise analyzing the principle of the driver circuits, the system developed uses the monolithic integrated phase-locked loop (PLL) and the double balance amplitude modulator, the isolated components are placed, so the difficulty of the RF signal transmission is resolved. And the system uses singlechip to control the output frequency and the mode of the driver. The output pulses repeat frequency of the drive is: 4 M ,800 K ,400 K ,80 K ,40 K ,8 K ,4 K ,800,400Hz . The power of the output signal is wattage level required by the acousto-optic (Bragg) cell. The paper has thoroughly discussed the impedance matching network of the frequency scope that modulation system operates, and definited the type of the matching network, drawn up the whole design scheme. The results of calculation the matching network's rank count and the components parameter are listed concretely. The prime matching value is attained by computing the wastage of energy during the signal transmitting and comparing the results with the net and without the net. In virtue of the theoretic result, the matching circuit has been designed and executed. The ultra-short laser pulse modulator makes the picosecond laser system of the spectrometer perfect, and the modulator can alter the laser pulse's repeated frequency, power of the peak value, and pulse interval, all of which can meet the demand of spectrometer system for time window. According to different experiment objects, the spectrometer can measure accurately the fluorescence attenuation curve and time resolution spectrum in the range of ps, ns and μs by choosing suitable laser pulse interval. According to a great deal of experiment data, we can say that the spectrometer can test the fluorescence longevity curve in quite large time extension, the time resolution of the spectrometer is 8.8ps, the sensitivity is single photon counting.