Performance loss and recovery of virtually imaged phased arrays with imperfect mirror parallelism

Practical defects in parallel-plate interferometers reduce instrument finesse, compromising spectral resolution, and can distort measured spectral lineshapes. The effect of imperfect mirror parallelism is usually described by a single broadened instrument response function and diminished finesse value. However, such a characterization fails to capture spatial field effects from dispersive interferometers, such as the virtually imaged phased array (VIPA). To explore these effects, a model is developed to compute fringe patterns formed by VIPAs with nonparallel mirrors and imaged along planes at specifiable distances from the paired imaging lens. Following validation against an established VIPA model and standard etalon theory with ideal parallel-plate configurations, the new model is used to examine the effects of mirror nonparallelism. While it captures the general loss of instrument performance in spectral resolution and finesse, it also reveals fringe lineshape distortions and nonuniformity of resolution and intensity scaling across the measurement field. Furthermore, when the measurement plane is decoupled from the back focal plane of the lens, there is an evolution of field behavior, and near-ideal instrument performance is recovered within a limited region of the measurement field. Results compare favorably to Zemax simulations and experimental data. This work identifies and characterizes nonideal optical behavior arising from practical defects in mirror parallelism, thereby enabling recognition of measurement artifacts, and imparts remedial measures for selective recovery of instrument finesse.