High-peak-power fiber coupled super-pulsed diode lasers

Abstract

Diode lasers are frequently used for numerous applications demanding high cw average power in the kW region and comparably low brightness. These applications include polymer welding, transformation hardening of metals and medical applications. Compared to solid state lasers, diode lasers can not be efficiently q-switched due to their low upper state life time. Therefore diode lasers are usually not suited for applications requiring high peak power like marking and coating removal. To overcome this problem, we have developed a novel electrically pulsed diode laser source. If the pulses are comparably short in the region of a few hundred nanoseconds, diode lasers can be operated with a current five to ten times higher than the maximum cw current. This so called super-pulse mode of operation broadens the field of applications of high power diode lasers towards applications usually reserved for q-switched solid state lasers. To benefit from the improved brightness delivered by the super-pulsed diode lasers for materials processing, a state of the art beam forming optics is required. In this paper, we will demonstrate the design of a super-pulsed diode laser source consisting of four diode laser bars coupled into a 100 µm NA=0.2 optical fiber. This module is designed for an output power of 500 W. To select diode laser bars appropriate for the super-pulse mode of operation, different diode laser bars have been tested with peak currents up to ten times higher than the rated cw current. Material processing results with super-pulsed diode lasers will be presented.

940-nm Broad Area Diode Lasers Optimized for High Pulse-Power Fiber Coupled Applications

“…Hence, it should be possible to couple more than 5 kW (τ = 1ms, f = 10 Hz) or 18 kW (τ = 300 ns, f = 1 kHz) into the fiber. More complex coupling schemes could potentially further increase power density in fiber [3].…”

“….500 ns would also potentially find application in direct material processing, as a direct replacement for YAG or fiber laser sources for cases where beam quality is not critical, such as cleaning, structuring and marking [3]. For example, diode laser modules have recently demonstrated peak Manuscript [3].…”