Spontaneous power and the coherent state of injection lasers

Abstract

A comprehensive model of the injection laser: Formulation and test of the current dependence of spontaneous and coherent emission A proposed relation between spontaneous and coherent properties of injection lasers is applied to several published results. On experimental and theoretical grounds it is shown that the parameter 1 + X, the ratio of conventional gain coefficient to prorated loss for the strongest cavity mode, can be determined from the spontaneous emission. Over a limited range above unity, 1 + X is the ratio of spontaneous intensity at the operating point to its value at threshold. This supplies a needed experimental connection between spontaneous studies at frequencies higher than the lasing band and the coherent properties. Published data of the current dependence of spontaneous emission are discussed in this framework, and the information needed to intercompare their internal state is pointed out. In general, fundamental differences in laser dynamics should be evidenced by radically different values of the critical parameter P * of the nonlinearity associated with the power dependence of X. All published values of p* are of order 5 mW per cavity mode, as predicted, indicating a similarity in the nonlinearity for quite different types of material. The recent observation that P * is independent of facet area gives strong support to the idea that the source of the nonlinearity is saturable optical absorption in a strongly interacting system.

Spectral coherence, Part I: Passive-resonator linewidth, fundamental laser linewidth, and Schawlow-Townes approximation

“…Ref. [76][77][78][79], and this explanation has also been accepted in quantum optics. It becomes clear from those investigations that the gain is not only smaller than the losses in a narrow power region close to the laser threshold, but this situation continues until the lasing mode reaches infinite output power.…”

“…Model (iv) has been exploited to derive the Kramers-Kronig relations [74,75] between susceptibility and absorption. In a simple rate-equation approach equivalent to Einstein 0 s [59] without phase considerations, i.e., in line with model (iii,b), the power behavior of semiconductor lasers around the laser threshold has been explained [76][77][78][79]. A combination of models (iii) and (i) has been applied to calculate quantum-mechanically the fundamental laser linewidth and its reduction compared to the Schawlow-Townes linewidth [10] by an additional factor of two around laser threshold [25,26,[65][66][67].…”