Realization of high performance LDA-systems using optical amplifiers, high power semiconductor lasers and optical fiber lasers

Abstract

Advanced novel techniques for sophisticated LDA applications are presented in this paper.By applying laser sources with high output powers like MOPA-lasers (master oscillator power amplifier), fiber lasers and booster fiber amplifiers to increase the laser power in the measuring volume and by amplifying the scattered light power with optical fiber preamplifiers to increase the sensitivity of the receiving units, the signal-to-noise-ratio of laser Doppler signals is drastically improved and the overall performance of a laser Doppler anemometer is significantly enhanced.

Optical fibre laser velocimetry: a review

“…Optical fibre amplifiers have been used to improve the SNR in LDV systems [117][118][119][120], by either amplifying the laser source, therefore increasing the power in the measurement volume, or by amplifying the received light prior to detection by a photodetector. Detailed descriptions of fibre amplifier technology can be found elsewhere [121].…”

“…Here the subscripted symbol P indicates the optical power in the various components and where amplification occurs. Dopheide et al [117] describe a concept dual-fibre amplifier LDV system, as shown in figure 32. A fibre amplifier is positioned after the laser source, a distributed Bragg reflector laser diode.…”

“…It is also possible to construct an LDV system using an optical fibre laser as the light source [117,119,121]. Optical fibre lasers have several advantages for LDV-they are highly efficient, simple, compact and reliable.…”

“…However, the higher wavelengths of these devices (∼1060 nm) compared to those typically used for LDV (488/514 nm) result in reduced scattering and decreased detector efficiency. Also, as the emission spectrum of high power fibre lasers has a bandwidth of up to 10 nm, conventional beam splitters will produce measurement volume fringes with poor visibility due to chromatic aberration [117]. Czarske et al [119] proposed using a diffraction grating as a beam splitter.…”