Design And Improvement Of The Fiber Raman Spectrometer

The laser raman spectrometers is a large instrument in common use of the material detecting.However,the Raman spectrocopy is very weak,so the Raman spectrometer have complex optics system and its price is very expensive.The JPI-I raman spectrometers which is designed by ourselves is different from the common spectrometer because we adopt the liquid-core optical fiber technology. The intensity of Raman spectrum in liquid-core optical fiber was enhanced 102~104 times, the resonance Raman spectrum enhanced the intensity of Raman spectrum 10E6 times, thus, the resonance Raman spectrum in liquid-core optical fiber can enhanced the intensity of Raman spectrum about 10E9~10E10 times. we designed a sensitive raman spectrometers by using liquid-core optical fiber and Photon counting technology.At the same the cost of the spectrometer is very cheap We know the design is not difficult if the Ramman spectrocopy is strong.。we must enchance the intensity of the spectrocopy and the sensitivity of the photon counter circuit by any ways Detectting photon signal is the difficulty and emphasis in the spectrocopy test .Ramman spectrocopy is weak , we have to adopt the sensitivest means.the weak photon signal is inundated by the noise uaually.Generally the noise is stochastic,we can use the LOCK-IN technology to condense the frequency of the circuit, in this way we can collect the useful ptoton signal from the noise, but when the power of the signal is 10E-13W,the photon is 100/sec , it will be lower than the niose of PMT ,As a result, The photon counting is one of the important means study on collecting photon signal. The nucleus problem is amplifying and distinguishing the photon signal in the photon counter ,which require this circuit with low noise and high gain. TO keep the pulse wave not distort, the circuit must have enough wide bandwidth. As a result, the signal-noise rate and the gain-bandwidth amass of the signal circuit is the focal point in the entire design We adopt the C3355 transistor which has characteristic frequency 6.5GHz and very low noise coefficient.. In the first stage,we use the share E-share B circult, which have excellent frequency characterand low noise. the circuit designed by ourselves can gain the signal 500 multiple and its bandwidth is 150 MHz with 33.5uV equivalen input noise .We can obtain 934uV on the PMT load ,Obviously, the signal-noise rate is 28.9dB .In our experiment we find the photon counter can work regularly when the signal-noise rate is above 15dB. So the circuit conform to our requirement At the same time we take the semiconductor refrigerate technology on the PMT,in this way we can enhance the signal-noise rate 10 time. OK, in the end of the paper let me introduce the character of the Photo counting card 1) PREAMPLIFIER The preamplifier is mounted on the photomultiplier(P.M.T) box,so as to make the connexion between the P.M.T anode and the input as short as possible. Input impedance is 75Ωand output 50ΩPreamplifier Characteristics: -The gain is adjusted with the P.M.T ,about 500 -The bandwidth is 150MHZ...