Spectral, spatial and temporal control of high-power diode lasers through nonlinear optical feedback

A high-power diode laser offers multi-Watt output power from a small and efficient device, which makes them an interesting source for numerous applications. The spatial and spectral output however, are of reduced quality which limits the applicability. This limited quality is connected to the design aiming at high power. The optical power limit achievable by a single-mode element is approximately 100 mW, limited by damage to the end-face of the diode. Scaling to higher power often is usually achieved by increasing the transverse size of the diode laser waveguide. These lasers are called Broad Area diode Lasers (BAL). The broad amplification region supports a number of transverse modes while the broad spectral gain supports oscillation at many longitudinal frequencies. The output therefore consists ofmany modes in space and frequency. These modes compete for gain and connect through nonlinear effects. The exact superposition of modes emitted at any time depends on many parameters such as the precise dimensions of the waveguide, temperature distribution in the gain region, spatial profile of pump current. The output profile is therefore hard to predict, unstable and changes as the diode ages.