In this paper, the Power Build-Up cavity enhanced Raman spectroscopy is introduced and the matching mode between the cavity length and wavelength is improved simultaneously. At the same time, the laser diode optical frequency modulation circuit is designed. Cavity length control system is built up to enhance the cavity power and experiments are also set up. The 532nm laser is coupled into an external linear optical cavity composed of two highly reflective mirrors. Since the light source is a solid laser, center light wavelength is a constant and line width is also known. Considered the distance between concave mirrors, the cavity length is squirmed slightly by the piezoelectric transducer. The light intensity measurement method is designed to record and analyze the performance of the cavity beam power and figure out the non-linear characteristic of system. In the premise of stable initial condition of enhanced system, the operating point is searched firstly which based on feedback control until the beam power is enhanced ultimately. The final experiment illustrates the feasibility of enhanced Raman effects with controlling cavity length and obtaining build-up optical power. The Power Build-Up cavity enhanced Raman spectroscopy has the potential to become a standard method for sensitive gas phase Raman spectroscopy.
During the design of the photonic crystal fiber Raman gas detection device and taking the cost and practicability in to consideration, we choose to use a stainless steel tube as a connector for the connecting of the HCPCF and SMF to replace the fiber fusing splice. Basis on the measurement to reduce coupling loss, we calculated the optimum fiber gap for maximum light coupling and to reduce Fresnel loss. Using the stainless steel tube not only result in low loss but also benefit input of the sample gas and recycling of the fiber which is very expensive. By adjusting the central alignment of the stainless steel tube we can easily control the fiber deviation loss for specific type of SMF and HCPCF. The mode mismatch is also demonstrated.