BEAM QUALITY OF INGAAS RIDGE LASERS AT HIGH-OUTPUT POWER

The nonlinear behavior of the light-current characteristic of single q uantum 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 degr adation under the transient condition suggests that the temperature pr ofile 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 prof ile is computed. There is excellent agreement between the time require d to reach a steady index profile and that required to degrade the bea m. The small beam astigmatism (typically 2 mu m) measured under CW ope rating conditions in the linear regime indicates that the mode is esse ntially index guided, which permits simple quantitative modeling of th e waveguide.