Research On The Key Technologies Of Pulsed Cavity Ringdown Spectroscopy Signal Acquisition

In the 21 st century, the world sets off a boom in the development of marine areas,many countries cares more about the ocean. Seawater contains rich natural resources, it has important implications for studies of gas dissolved in water concentration detection. Laser cavity ring-down spectroscopy with spectral selectivity, high sensitivity and the ability to detect quantitative research, there is likely to be one of the effective means of detecting gas hydrates.In this paper, the pulse wave cavity ring down spectroscopy (Cavity Ringdown Spectroscopy, CRDS) technology as the basis to design a miniaturized, integrated pulse wave cavity ringdown spectroscopy signal acquisition system with high-speed data acquisition.The whole electronic control part of the data acquisition system includes high-speed data acquisition card ART, Taiwan’s Advantech PC 104 and synchronous trigger signal generating circuit. Because the ring-down signal duration is very short, so choosing the trigger mode is a critical issue. In this paper, there is a beam of light from the pattern matching mirror before the chamber, the GT101 photodiode detector gets the signal to trigger data acquisition card.The system control the data acquisition card by using C# programming. To ensure the collection of the ring-down signal, selecting the Intermediate trigger mode completes the acquisition of cavity ringdown signal. For pulse-wave cavity ring-down signal characteristics, the collected data is dealed with Origin software by waveform reduction and exponential fitting.The basis of effective data for evaluation is the correlation coefficient,the final calculation of decay swing time rely on it.This paper consists of the following contents.l)Building electronic control system module with the PC 104 IPC and ART-speed data acquisition card. Designing the C# programming in Microsoft Visual Studio 2010 to complete the function control of data acquisition card. The function generator produces signal, the signal is similar to pulse wave cavity ring-down signal.The electronic control module uses different trigger modes for signal acquisition, the function generator sigal is consistent to the acquisition signal. The function of the signal acquisition system is normal.2) Intruducing the details of the pulse wave cavity ring down spectroscopy principle and main equipment optical system parameter models. Building the optical system modules,using MPL-Ⅲ-532 pulsed laser emitting laser,the laser cross through pattern matching mirror into the ring-down cavity.Ring-down cavity outputs signal. The signal is the pulse wave cavity ring-down signal. The oscilloscope displays waveform ring-down signal, the system verifies the optical ring-down signal. So the optical system’s function is normal.3) Debugging the joint electronic control system module with optical system module, achieving cavity ring-down signal and high-speed data acquisition, the collected data is stored in the computer. Using origin software for data reduction and exponential waveform fitting, completing the calculation of the ring-down time by comparing the correlation coefficient.Through experimental tests, the electronic control system module and the optical system module work properly, the joint commissioning of two modules get a good result. In this paper, the optical system ring-down cavity length is 0.5m with high mirror reflectivity of 99.6%, the theoretical pulse ring-down time is 417ns. Signal acquisition system gets ring-down signal acquisition successfully and achieve high-speed data acquisition functions. Equipment of the whole system is small, stable performance, ease of integration, miniaturization of the system to solve the problem. The system failes due to time constraints.The system need to try samples testing and underwater testing.There are many work to be done.