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Self-mixing-based photoacoustic sensing

Tecla Gabbrielli, Jacopo Pelini, Chenhong Zhang, Francesco Cappelli, Mario Siciliani de Cumis, Stefano Dello Russo, Maria Concetta Canino, Alberto Roncaglia, Paolo De Natale, Simone Borri

TL;DR

The work addresses the demand for compact, high-sensitivity trace-gas sensors suitable for in situ applications by integrating a self-mixing interferometric readout with photoacoustic spectroscopy. It demonstrates that a self-mixing readout on a MEMS-based photoacoustic sensor can achieve performance comparable to a bulkier Michelson interferometer, with similar SNR and MDL. The reported results show an MDL of about 90 ppb at integration times of 20–40 s and NEC around 427–428 ppb, while offering a lower baseline and a more compact, potentially chip-scale implementation. The approach leverages the wavelength independence of both PA and SM techniques, enabling flexible tailoring to different spectral regions and paving the way for portable, integrated trace-gas sensing solutions.

Abstract

Versatile, ultracompact, easy-to-handle, high-sensitivity sensors are compelling tools for in situ pivotal applications, such as medical diagnostics, security and safety assessments, and environmental control. In this work, we combine photoacoustic spectroscopy and feedback interferometry, proposing a novel trace-gas sensor equipped with a self-mixing readout. This scheme demonstrates a readout sensitivity comparable to that of bulkier state-of-the-art balanced Michelson-interferometric schemes, achieving the same spectroscopic performance in terms of signal-to-noise ratio (SNR) and minimum detection limit (MDL). At the same time, the self-mixing readout benefits from a reduced size and a lower baseline, paving the way for future system downsizing and integration while offering a higher detectability for lower gas concentrations. Moreover, the intrinsic wavelength independence of both self-mixing and photoacoustic techniques allows the applicability and tailorability of the sensor to any desired spectral range.

Self-mixing-based photoacoustic sensing

TL;DR

The work addresses the demand for compact, high-sensitivity trace-gas sensors suitable for in situ applications by integrating a self-mixing interferometric readout with photoacoustic spectroscopy. It demonstrates that a self-mixing readout on a MEMS-based photoacoustic sensor can achieve performance comparable to a bulkier Michelson interferometer, with similar SNR and MDL. The reported results show an MDL of about 90 ppb at integration times of 20–40 s and NEC around 427–428 ppb, while offering a lower baseline and a more compact, potentially chip-scale implementation. The approach leverages the wavelength independence of both PA and SM techniques, enabling flexible tailoring to different spectral regions and paving the way for portable, integrated trace-gas sensing solutions.

Abstract

Versatile, ultracompact, easy-to-handle, high-sensitivity sensors are compelling tools for in situ pivotal applications, such as medical diagnostics, security and safety assessments, and environmental control. In this work, we combine photoacoustic spectroscopy and feedback interferometry, proposing a novel trace-gas sensor equipped with a self-mixing readout. This scheme demonstrates a readout sensitivity comparable to that of bulkier state-of-the-art balanced Michelson-interferometric schemes, achieving the same spectroscopic performance in terms of signal-to-noise ratio (SNR) and minimum detection limit (MDL). At the same time, the self-mixing readout benefits from a reduced size and a lower baseline, paving the way for future system downsizing and integration while offering a higher detectability for lower gas concentrations. Moreover, the intrinsic wavelength independence of both self-mixing and photoacoustic techniques allows the applicability and tailorability of the sensor to any desired spectral range.

Paper Structure

This paper contains 1 section, 2 figures.

Table of Contents

  1. Data Availability Statement

Figures (2)

  • Figure 1: Sketch of the self-mixing-based photoacoustic setup. In the figure, W1, W2 and W3 are ZnSe windows; PM is a power meter; M1, M2 and M3 are gold-coated mirrors. The piezo-electric transducer (PZT) mounted on the M2 mirror is used to optimize the phase match condition and, therefore, the amplitude of the self-mixing readout signal. Inset: Zoom of the 3-armed spring MEMS.
  • Figure 2: Comparison between the self-mixing and the Michelson-interferometric readouts. (a) photoacoustic peak signal as a function of the sample pressure, (c) PA signal at the best working pressure, and (e) Allan-Werle deviation analysis for the self-mixing-based readout. (b) photoacoustic peak signal as a function of the sample pressure, (d) PA signal at the best working pressure, and (f) Allan-Werle deviation analysis for the Michelson-interferometric-based readout. The y-axis of the Allan-Werle plots is converted from mV to gas noise equivalent concentration (i.e., ppb) via the relation $c/SNR$, where $c$ is the fixed trace-gas concentration within the sample, and SNR is the ratio between the PA peak signal and the noise level.