Angle dependent stray light measurements of high power laser radiation in natural atmospheric environments

Abstract

Measurements of parameters of the natural atmospheric environment, like aerosol and precipitation distributions as well as the visibility, are simultaneously performed together with the angle dependent scattering of high power laser radiation. These measurements were obtained on the free transmission test range operated by the German Aerospace Center (DLR) in Lampoldshausen. The applied high power disk laser system operates at a wavelength of 1030 nm and all presented measurements are performed at an output power of 3000 W in continuous wave. The laser beam is propagating along the 130 m test range and the focus is ten meters away from the detection setup for the scattered light. Each of the five detection systems consist of a fiber-coupled photoreceiver and all fiber-couplers are positioned on a stage at angles of 30°, 60°, 90°, 120° and 150°, respectively to the direction of the laser beam. The distance between the fiber-couplers and the detection volume is 500 mm and the aperture is about 22 mm. The laser beam is modulated at 10 Hz and the signals of the photoreceivers are transmitted to lock-in amplifiers. The transportable setup is protected by a weatherproofed box and is operated under various conditions and precipitations, like rain and snow. In order to obtain absolute values the detection systems are calibrated using an integrating sphere. The experimental setup of the calibration system is introduced and measurements of angle dependent absolute scattering powers in dependence on the power transmission loss, the geometric scattering coefficient and the visibility are shown.