Measurements and analysis of spectrally resolved spot profile of diffuse reflection micro spectrometers using knife-edge white reference

Abstract

Diffused reflectance infrared spectroscopy is well known as a compact, low-cost, and efficient handheld spectrometers. One of the spectrometer’s most important optical parameters is the effective collected spot profile from diffuse reflection samples not the simple illumination spot which determines the analyzed sample portion defining the spatial resolution. In this work, we present a novel method for characterizing the spot size based on the Knife-Edge technique. A sharp high scattering material such as PTFE is displaced into the spectrometer optical interface on a 1-dimensional moving stage while capturing the power at each step. Then by differentiating this cumulative power, the intensity spot profile is obtained and fitted to a Gaussian profile where the spot size is defined as the diameter that contains 90% of the reflected power. MEMS FT-IR spectrometers with different spot sizes measured as a demonstration of the technique. Moreover, this method quantifies different other parameters such as Goodness of Fit, spot lateral shift in addition to spot shape wavelength dependence that may occurs due to any non-ideality in the spectrometer system.