Theory of the natural width of a semiconductor laser emission line

An investigation is made of the dependence of the width of a line emitted by a single-mode semiconductor laser on the intensity of this line. The line width is calculated allowing for the saturation effect. It is shown that saturation results in an additional broadening of the laser line. In a weak field, when the saturation parameter η is small, the product of the line width and the number of photons increases proportionally to the line intensity. In a strong field (η >> 1), this product becomes constant but its value is considerably greater than the value in a weak field.