High-energy picosecond pulses with a single spatial mode from a passively mode-locked, broad-area semiconductor laser

TL;DR

This paper demonstrates a passively mode-locked broad-area semiconductor laser that produces high-energy, picosecond pulses with record peak power and near-ideal beam quality, using a novel external cavity and electrical control of the saturable absorber.

Contribution

It introduces a new configuration combining a broad-area diode amplifier with external cavity mode-locking and electrical control of the saturable absorber for high-power, single-mode picosecond pulses.

Findings

Achieved 5-8 ps pulses at 379 MHz repetition rate.

Recorded peak power of 112 W and pulse energy of 0.5 nJ.

Produced near-ideal beam quality with M^2 = 1.3.

Abstract

We present a mode-locked semiconductor laser oscillator that emits few picosecond pulses (5-8ps at 379MHz repetition) with record peak power (112W) and pulse energy (0.5nJ) directly out of the oscillator (with no amplifier). To achieve this high power performance we employ a high-current broad-area, spatially multi-mode diode amplifier (0.3x5mm), placed in an external cavity that enforces oscillation in a single spatial mode. Consequently, the brightness of the beam is near-ideal ($M^2 = 1.3$). Mode locking is achieved by dividing the large diode chip (edge emitter) into two sections with independent electrical control: one large section for gain and another small section for a saturable absorber. Precise tuning of the reverse voltage on the absorber section allows to tune the saturation level and recovery time of the absorber, which provides a convenient control knob to optimize the mode-locking performance for various cavity conditions.