Subnanosecond high-power laser pulses for time-of-flight laser distance meters

TLDR: In this paper, it was found that the rise time of the light pulse varied according to the measurement angle of the received light and the temperature of the laser, and the shape of the optical pulse between different items of the same laser type.

Abstract: Practical, compact time-of-flight (TOF) laser distance meters have been constructed for many industrial applications using a semiconductor laser as the light source. The optical pulse power of such devices has varied in the range of 1 to 30 W, rise times between 1 and 3 ns and pulse widths between 5 and 10 ns. The lasers have usually been DH lasers at low pulse powers (< 5 W) and SH lasers with 1 to 3 stripes at higher powers (5 - 30 W). A capacitor discharged by an avalanche transistor has been widely accepted as the pulser circuit for producing fast electric current pulses for lasers. Improvement of the timing resolution of the measurement result requires an increase in the slew-rate of the received light pulse or a decrease in the noise level. Use of a commercial non-pigtailed 1-stripe SH laser and a commercial power transistor in the avalanche operation mode yielded an optical pulse, the rise time of which was clearly less than 1 ns (rise time of the electric pulse was 3.5 ns). It was noticed in the tests that the rise time of the light pulse varied according to the measurement angle of the received light and the temperature of the laser. In order to obtain fast laser pulses it is necessary to control the temperature and the space angle in which the radiation is collected. There are also big differences in the shape of the optical pulse between different items of the same laser type and for this reason selection of the laser items is needed.