Real-time assessment of spectrometer alignment using modulation transfer function (MTF) measurement

Abstract

The effective spectral resolution of a spectrometer that utilizes dispersive optics is normally limited by either the size of the sensor pixels or the optical resolution of the focusing optics. Therefore, achieving optimal optical alignment is crucial to maximize the spectrometer's effective spectral resolution. In this paper, we introduce a laboratory method for real-time assessment of spectrometer alignment by measuring the modulation transfer function (MTF). The modulation on spectral signal is generated using an interferometer, allowing control of the modulation frequency by adjusting the optical path difference. The results show that the proposed technique can provide useful information about the alignment of the spectrometer, which can be used to obtain the optimum alignment of the spectrometer. The accuracy of the proposed method was confirmed by comparing the MTF measurement, and hence the resolution evaluation, with the specifications of a commercial spectrometer. In addition, we demonstrate the use case of the proposed method by performing a through-focus MTF measurement on a custom-built spectrometer with known misalignments.