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A refined theoretical model predicts the modal content in the plane perpendicular to the junction for heterojunction injection lasers. It gives good agreement with observed far-field patterns. Because high-order modes are favored, lasers with a wide optical cavity sandwiched between two heterojunctions have a beam width at least double that of single-heterojunction lasers. In a thin cavity which supports but one mode, the increased confinement of the double heterojunction broadens the beam to about 40° at half-power.
Butler et al. (1970) studied this question.