Influence of the wavefront curvature on the characteristics of a diode laser with an external cavity

An experimental investigation was made of the influence of the length of an external cavity on the threshold current and on the normal-mode spectrum of gain-guiding diode lasers. The wavefront curvature was taken into account. An analogy between a laser with an external resonator and one with a curved facet was confirmed. This was used to propose a method for simulating the influence of the wavefront curvature on the degree of feedback. A numerical calculation was used to show why the use of an external cavity in which the wavefront is ‘conjugated’ leads to the greatest reduction in the threshold current in such lasers.