Proceedings Article | 1 August 2003
Patrick Mercier, Jacqueline Veaux, Jacky Benier, Manuel Vincent, Severine Basseuil
KEYWORDS: Optical fibers, Doppler effect, Interferometers, Cameras, Laser interferometry, Velocity measurements, Streak cameras, Optical amplifiers, YAG lasers, Objectives
For more than 30 years now, Doppler Laser Interferometry has been used in detonics to measure velocity versus time accurately. The means is composed of: a laser source, an optical fiber bringing light to the moving target, another which collects back-reflected light, a device built around a Fabry-Perot interferometer to create the rings pattern, a streak camera. In the beginning, the source was a CW singlemode argon laser with a 7 W output power. Later, it was replaced by a wide spectrum rhodamine dye laser requiring two twin Fabry-Perot interferometers, the first one modulating the spectrum and the second analyzing the Doppler shifted light; the available power was 1 kW for a 40 μs pulse. Recently, we have improved the means by increasing the channel number with sufficient output power, replacing the dye with a solid amplifier, increasing pulse width, decreasing the velocity and time uncertainties and reducing the volume and the cost of the equipment. To achieve this quality we acquired a long-pulse singlemode Yag laser. It has 15 channels, each providing 1 kW with a 70 μs rectangular pulse at 532 nm. The analysis bench uses only 1 Fabry-Perot interferometer for 5 channels. The laser, target and analysis bench are connected through a 3 optical fibers bundle; one for lighting, one to measure velocity and a third one to record the photometric curve and determine shock breakout time accurately. To improve accuracy, we worked on two areas: (1) the equipment with the anamorphic optical device, the value of the fringe constant and the number of rings lit on the camera slit, (2) the building of a chart where we write all influent parameters in order of importance: in order to decrease the uncertainty of velocities less than 1000 m/s, we need to evaluate the influence of electronic streak camera distortion.
