2013 Progress Report: Compact Multi-Pollutant Mid-Infrared Laser Spectroscopic Trace-Gas Sensor

EPA Grant Number: R835137
Title: Compact Multi-Pollutant Mid-Infrared Laser Spectroscopic Trace-Gas Sensor
Investigators: Wysocki, Gerard
Institution: Princeton University
EPA Project Officer: Hunt, Sherri
Project Period: February 1, 2012 through January 31, 2016
Project Period Covered by this Report: February 1, 2013 through January 31,2014
Project Amount: $250,000
RFA: Developing the Next Generation of Air Quality Measurement Technology (2011) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Air


This project will focus on development of a compact, cryogen-free trace gas sensor node targeting the spectral range containing the absorption band of benzene, which is a highly toxic atmospheric pollutant. The proposed proof-of-concept instrumentation will also provide multi-species sensing capabilities. Two major innovations will be addressed: Multi-component chemical analysis will be enabled thorough application of novel broadband mid-IR lasers, and an ultra-compact sensor system will be developed to address deployments in wireless sensor networks. 

Progress Summary:

In this project, we focus on development of a compact spectroscopic sensor node for quantitative measurements of multiple chemical compounds simultaneously. We proposed application of broadly tunable mid-IR semiconductor lasers (with a particular focus on quantum cascade lasers, QCLs) to meet the requirements for wide electromagnetic frequency coverage required for multi-species detection, as well as we plan to develop an ultra-compact sensor system with a dedicated control and data acquisition electronics for applications in wireless sensor network (WSN) configurations.
The project is carried out accordingly to the originally proposed research plan that is divided into four major research tasks: (1) design and build a laboratory breadboard prototype of an EC-QCL based sensor system operating at 9.6μm, (2) laboratory tests and calibration of the breadboard prototype, (3) develop EC-QCL based sensor node with WSN capabilities, and (4) field test and instrument inter-comparison. In addition to the main goals indicated in the original research proposal, we are continuously developing and testing new laser technologies that are potentially more suited to the proposed research.
Year 2 efforts were focused on the tasks #2 and #3 as indicated in the original plan. The only departure from the original plan was the change of laser wavelength planned for the external cavity (EC) laser under development. We have utilized the newest Interband Cascade Laser (ICL) technology that can target the absorption band of Benzene (C6H6) at 3.3 μm. The band strength at 3.3 μm is ~2x the originally planned C6H6 band at 9.6 μm, which is expected to improve the sensitivity of the instrument. A prototype of a compact EC-ICL source has been developed and tested including preliminary C6H6 detection. As a continuation of task #2, we have carried out theoretical and experimental research on calibration of direct laser absorption spectroscopy system based on EC-ICL. 
Within task #2, a new calibration technology for high accuracy WSN nodes with short optical pathlengths has been fully developed and characterized. The technique has been proven extremely efficient in eliminating long-term drifts in QCL-based spectrometers, which results in technology that can provide reliable and accurate trace-gas sensing. The results have been published in [1]. Currently, a further development of this technology is pursued with a focus on spectroscopic systems that require long optical paths for sensitivity enhancement (that includes sensors for C6H6 in this project). 
The main limitation of EC laser technology is its opto-mechanical stability that can strongly restrict field applications. We have continued to study other laser sources and spectroscopic measurement techniques that could allow for wide electromagnetic frequency coverage required for multi-species detection, and high spectral resolution for selectivity and sensitivity, while providing all-solid-state/nomoving-parts laser systems for reliable field deployments. Last year, we have demonstrated a new method of performing broadband mid-infrared spectroscopy with conventional, free-running, continuous wave Fabry-Perot quantum cascade lasers (FP-QCLs). The measurement method is based on multiheterodyne down-conversion of optical signals. The sample transmission spectrum probed by one multimode FP-QCL is down-converted to the radio-frequency domain through an optical multi-heterodyne process using a second FP-QCL as the local oscillator. Both a broadband multi-mode spectral measurement as well as high-resolution (~15 MHz) spectroscopy of molecular absorption are demonstrated and show great potential for development of high performance FP-laser-based spectrometers for chemical sensing. Two different species ammonia (NH3) and nitrous oxide (N2O) have been demonstrated with the FP-QCL multi-heterodyne spectrometer. The results have been recently published in Applied Physics Letters [2].
The main goals of the project that include development of a broadband mid-infrared sensor node with WSN capabilities and instrument field test and inter-comparison with other established technologies have not changed from the original grant application. 

Future Activities:

In the next reporting period, we plan to continue work on task #2 (Laboratory tests and calibration of the breadboard prototype) using the EC‐ICL based spectrometer developed last year. We will also continue efforts within the task #3 (Develop EC‐QCL based sensor node with WSN capabilities) with a focus on development of mobile WSN node for trace‐gas sensing. Based on the performance tests, either EC‐ICL technology or multi‐heterodyne FP‐QCL spectrometer will be implemented into the field deployable WSN node. We will also start logistical planning for the field deployment anticipated in year 4 of the project (2015) within task #4 (Field test and instrument inter‐comparison). 

Journal Articles on this Report : 2 Displayed | Download in RIS Format

Other project views: All 21 publications 5 publications in selected types All 5 journal articles
Type Citation Project Document Sources
Journal Article Smith CJ, Wang W, Wysocki G. Real‐time calibration of laser absorption spectrometer using spectral correlation performed with an in‐line gas cell. Optics Express 2013;21(19):22488‐22503. R835137 (2013)
R835137 (Final)
  • Abstract from PubMed
  • Full-text: OSA-Full Text HTML
  • Abstract: OSA-Abstract
  • Other: OSA-Full Text PDF
  • Journal Article Wang Y, Soskind MG, Wang W, Wysocki G. High‐resolution multi‐heterodyne spectroscopy based on Fabry‐Perot quantum cascade lasers. Applied Physics Letters 2014;104(3):031114. R835137 (2013)
    R835137 (2014)
    R835137 (Final)
  • Abstract: AIP-Abstract
  • Supplemental Keywords:

    Laser spectroscopy, multi-species detection, trace-gas sensor networks, gas sensors

    Progress and Final Reports:

    Original Abstract
    2012 Progress Report
    2014 Progress Report
    Final Report