| Laser Doppler velocimeters have been widely used in variety of fields, thanks to their several advantages: contactless measurements, excellent spatial resolution and fast response. The traditional single-frequency laser Doppler velocimeter has the problem of DC drift, and it is sensitive to the measurement environment, therefore, its application is limited. The heterodyne dual-frequency laser Doppler velcimeter is superior for high signal-to-noise ration with no DC drift. However, its maximum measurable velocity is limited by the frequency difference of the laser, which is generally less than 1000mm/s, so it can not meet the current demands for the velocity measurement of the high-velocity target.In order to solve the problems of traditional laser Doppler velocimeters, this paper presents a novel method for velocity measurement with dual-frequency laser. Different from traditional heterodyne velocimeter, which uses an orthogonally linear-polarized dual-frequency laser as light source and applies only one frequency to sense the velocity, in the novel scheme, a parallelly linear-polarized dual-frequency laser is used and both of the frequencies are used to sense the velocity. The novel method can increase the maximum measurable velocity efficiently.This paper researches a dual-frequency Nd:YVO4 laser according to the demands for the light source of the novel method. The frequency difference of the laser can be adjusted by choosing the cavity length depends on the specific measurement demand, and the range is 500MHz-200GHz.In order to verify the feasibility of the novel method, a velocity measurement system is designed and realized in the lab. The experimental results show that the novel method can measure the velocity of the high-velocity moving target with high precision, the measurement relative error is less than 2%, and it can increase the maximum measurable velocity significantly. Therefore, it must be of great interest for high velocity measurement application. |
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