Even if a single transverse mode is achieved from the output of the laser diode, the divergence of this mode is significantly larger than nearly any other type of lasers. This divergence is the result of diffraction (since the cross-section of the active region is on the order of λ

_{0}) and a short cavity length, which prevents the high degree of collimation typically enjoyed by other laser systems. The angular divergence of the beam is proportional to the ratio of λ

_{0} to the dimension of the active region (l). Given the small values of l, this can easily give rise to divergence angles exceeding 25° in the direction perpendicular to the junction (most solid-state lasers have angles much less than 1°). Since w is typically several times larger than l, the divergence in the direction parallel to the junction plane is significantly lower. This unequal divergence in orthogonal directions is called astigmatism and can make collimating such a beam quite difficult. However, optical systems have been developed to compensate for this astigmatic behavior.
The spectral distribution from an LED is centered at the transition wavelength (λ

_{g}) associated with E

_{g} (see

Laser Diode and LED Physics). For a laser diode, the center wavelength (λ

_{0}) typically occurs at λ

_{g} as well since the gain bandwidth follows the spontaneous emission distribution. However, if a frequency-selective approach is used to isolate a single longitudinal mode (see below), continuous tuning of λ

_{0} under the gain bandwidth is possible. Finally, the carrier concentrations in the valence and conduction bands are dependent on the temperature of the semiconductor and the injection current. Since the carrier concentration plays a role in determining the effective value of E

_{g} and therefore λ

_{g}, the emission wavelength can be shifted with either drive current or junction temperature.