Simple relations for the phase distribution of the fundamental mode of gain-guided lasers are derived, yielding simple, approximate analytic expressions for the far-field distribution parallel to the junction in the case of strong astigmatism. It is shown that the shape of the far-field distribution is essentially determined solely by the distribution of the effective refractive index parallel to the active layer. The relations may be used for any shape of the effective refractive index distribution to yield simple arguments as to why there are lasers which exhibit far-field distributions with double as well as triple maxima. Because of the simplicity of the expressions for the far-field distribution it is also possible to make an estimate of the shape of the carrier profile, once the near-field and far-field intensity distributions are known. In addition, a general relation between the normalized fundamental mode gain and the shape of the far-field distribution is given.
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