Coherent laser radar for vibrometry: Robust design and adaptive signal processing

1 ABSTRACT A coherent laser radar system based on semiconductor laser technology has been designed and built. The compact design and the absence of adjustments makes the system mechanically robust and easy to use. The present system has an output power of 50 mW and a line width of 280 kHz (HWHM). The laser radar system has been used in vibrometry measurements. For vibrometry of moving objects, adaptive signal processing is required in order to obtain the vibration signature. Especially for unresolved objects, interference between diierent vibrating parts will complicate the analysis. Modelbased estimation techniques are used to obtain the parameters which determine the dynamics of the reeecting object. 2 INTRODUCTION Coherent laser radar (CLR) systems have been investigated over several decades primarily for military applications. In order to receive a more general industrial acceptance, compact, robust, cost-eeective systems and more general signal processing tools must be developed. Semiconductor laser technology can achieve both high power and narrow line width without using external cavity designs. This allows the design of very compact systems without any movable parts such as pzt-elements. A critical feature is the tolerance designing, allowing for laser welding of the interferometric block. The design is also compatible with distributed ber sensor systems. The compact design and the absence of adjustments makes the system mechanically robust and easy to use. Semiconductor lasers can easily be broadband frequency modulated, and various applications can be addressed by making use of this property. For range/Doppler measurements, chirping or frequency shift keying can be applied. If necessary, a frequency shifted signal can, be obtained by using ,