Measurement of laser power resistance of fibers for PIV systems

Particle Image Velocimetry (PIV) is a well known measurement protocol for analyzing the dynamic behavior of fluids in liquid or gaseous phases (granulate analysis is also possible). With respect to the demands of the measurement accuracy, a high fluence at the observation zone is required. Presently, this can only be realized by using very precisely aligned equipment and high power laser pulses. For industrial applications a simpler set-up is needed. Thus the research project is aimed at the development of a portable endoscopic-based solution which requires the guidance of laser light through optical fibers. The realization of such an optical fiber system is a technical challenge since the high instantaneous energies, which exist in the laser pulse, can cause irreversible damage to the optical fiber. Consequently, the main goal is the determination of the maximum fluences, that different fiber core bulk materials can tolerate, and the comparison of these results with the maximum achievable fluence when transmitting light through optical fibers. A simple theoretical modeling tool for the approximation of the power handling capability was developed. Based on this theoretical analysis, Laser Zentrum Hannover examined the impacts that laser pulses and fiber materials have on light incoupling and guidance. An experimental set-up was developed to investigate the laser light resistance of different fiber bulk materials as well as the fibers themselves. This paper introduces the measurement set-up and the results of LIDT measurements of several fiber core materials. Furthermore, the fiber measurement set-up, achievable fluences, transmission efficiencies as well as the typical fiber damage behavior are presented.