Transmission of High-power Laser Light through Tapered Dielectric Tubes and Rods

Abstract

THE transmission of high-power laser light was investigated for dielectric tubes and rods of a geometry schematically shown in Fig. 1. The measurements were performed with a Q-switched ruby laser as radiation source and with a calibrated ‘rat's nest’ bolometer (type Westing-house) as energy measuring device. The energy in the laser beam could be varied between 0.07 and 1.0 J. The characteristic values for the laser pulse were 15 nsec rise-time and 30 nsec half-width. For all values of output energy, the beam showed a typical two-mode pattern. The energy distribution in each mode was approximately Gaussian. The beam was focused by a 6.4-cm focal length lens on to the centre of the entrance surface of the light guide. In all experiments the angle between the mode axes and the optical axis of the system was 2°. In the focal plane 99 per cent of the total energy was concen trated within a circular area of 1.5 mm diameter. 75 per cent of the beam energy was within an area of 0.5 mm². The average power density within the 75 per cent limit calculates to about 20 MW/mm² for 0.5 J laser output. The light guides were drawn by glass-blowing techniques from materials with equal optical properties. The measurements are shown in Table 1.