Electromagnetic analysis of threshold conditions for modes of 1-D microcavity laser with noble metal and distributed Bragg reflectors

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The study considers the threshold conditions for a flat-layered laser model containing a gain-material cavity, sandwiched between a noble metal, namely gold or silver, a superstrate film, and a distributed Bragg Reflector (DBR). We implement the Lasing Eigenvalue Problem approach to study the mode-specific emission frequencies and the threshold gain index values. Therefore, we look for them as two components of eigenvalue pairs of a specific boundary-value problem for the time-harmonic electromagnetic field, where the active region is taken into account and described with the aid of the refractive index imaginary part of the gain material. The results clarify the role played by the noble metal film thickness and DBR parameters in the lasing mode characteristics. Namely, the location of the reflection band of DBR determines the cavity’s lowest-threshold mode. Moreover, its threshold can be progressively lowered by increasing the metal film thickness. Our analysis can be fruitful in the microlaser performance optimization.