BEAM QUALITY OF INGAAS RIDGE LASERS AT HIGH-OUTPUT POWER

The nonlinear behavior of the light-current characteristic of single quantum well, graded-index-separate-heterostructure ridge laser diodes emitting at 980 nm is investigated. We have measured the beam-quality factor \M\(2) as a function of the output power, under continuous-wave and transient conditions. The time constant associated with beam degradation under the transient condition suggests that the temperature profile in the cavity plays a significant role in the lateral guiding of the lasing modes. The two-dimensional heat equation is solved for the device, and the time-resolved thermally induced refractive-index profile is computed. There is excellent agreement between the time required to reach a steady index profile and that required to degrade the beam. The small beam astigmatism (typically 2 mu m) measured under CW operating conditions in the linear regime indicates that the mode is essentially index guided, which permits simple quantitative modeling of the waveguide.