High-Precision Wavelength Modulation Spectroscopy Enabled by a Digital Lock-in Amplifier on a 32-Bit Microcontroller

Abstract This manuscript presents the feasibility of designing a digital Lock-In Amplifier (LIA) for measuring experimental sys-tems through optical measurement techniques, from 32-bit micro-controller platforms, derived from the technology coming from the Internet of Things (IoT). As a proof of concept, the STM32F446RE microcontroller was used, in which the resident program uses the Direct Digital Synthesis (DDS) and synchronous detection tech-nique to promote lock-in processing from harmonic signals gener-ated in 2f. The digital LIA was tested to detect C2H2 (Acetylene) concentrations in a spectrometric cell by Wavelength Modulation Spectroscopy (WMS). The experimental setup also included a DFB laser and other optical components. The comparative analysis with the Signal Recovery® DSP7265 benchtop LIA showed that both systems effectively measured up to 54 ppm of C2H2. A strong Pearson correlation (r>0.8) was observed for all measurements performed. This confirms its potential for applications in situ nonlinear optical spectroscopy, especially WMS.