Grantee Research Project Results

Final Report: 1790nm Tunable Laser for VOC Monitoring

EPA Contract Number: 68HERC22C0009
Title: 1790nm Tunable Laser for VOC Monitoring
Investigators: Morrison, Gordon
Small Business: Freedom Photonics
EPA Contact: Richards, April
Phase: I
Project Period: December 1, 2021 through May 31, 2022
Project Amount: $99,999
RFA: Small Business Innovation Research (SBIR) Phase I (2022) RFA Text |  Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Air

Description:

Air toxics, which include a number of volatile organic compounds (VOCs), have been linked to severe health impacts ranging from asthma exacerbations to cancer and premature deaths.  In many cases, emissions are localized, and are particularly of concern for communities near industrial sites (which tend to be disproportionately low-income, often with predominantly indigenous or minoritized residents).  In order to identify and manage health risks from exposure to air toxics, the EPA has called for high-sensitivity, high-specificity air monitoring technologies to provide real-time, continuous measurements of VOC concentration at the neighborhood level. 

Through this program, Freedom Photonics began developing a widely tunable diode laser source, which is a key component of an ultra-sensitive broadband near-infrared (NIR) spectrometer.  The longer-wavelength tunable laser will cover NIR absorption bands for more VOCs, and instruments incorporating multiple overlapping tunable laser sources will be capable of observing more spectral features simultaneously.  Quantification of more gases in mixtures with improved specificity extends continuous monitoring capabilities to detect leaks of multiple air toxics in real time. 

Relative to current EPA methods for volatile toxic organic compound determination, broadband NIR spectroscopy is better suited to ambient monitoring, has a lower detection limit, and does not require sample conditioning.   Most current EPA toxic organic determination methods require sample preparation in order to prevent chromatography column contamination - this precludes continuous ambient monitoring, and time consuming chromatographic separation limits sample throughput.  Many compounds with similar functional groups may co-elute; fitting multiple peaks introduces more error into quantification by chromatography peak integration.  Co-elution also complicates mass spectrometry interpretation, where fragmentation analysis may be needed to distinguish structural isomers.  These limitations preclude the use of GC-MS or LC-MS methods for ambient monitoring.  Broadband NIR spectroscopy, on the other hand, does not require sample preparation, provides rapid measurements, and is a compact instrument - all features supporting its use in ambient monitoring.  Beyond this tremendous benefit, even in cases where traditional EPA methods must be used, broadband NIR spectroscopy offers complementary characterization, which is very beneficial from an analytical chemistry standpoint in that it can reduce uncertainty when matrix interference is problematic for organic air toxics methods.

Summary/Accomplishments (Outputs/Outcomes):

In collaboration with our commercial partner, we agreed on a set of preliminary specifications for a long-wavelength tunable laser to be used as a key component of a broadband near-infrared spectrometer.

Using a combination of optical modeling, laser simulations, and empirical data from previous tunable lasers at different wavelengths, Freedom Photonics designed an epitaxial platform suitable for 1790 nm tunable lasers.  After wafer growth, we confirmed that the base epitaxy met all of our design specifications and was suitable to begin fabrication. 

We then designed a series of widely tunable lasers for the new platform, using numerical simulations and relevant empirical data.  The designs were arrayed to produce a final design matrix, which arrayed various parameters in an effort to reduce risk and ensure that some devices would meet our design specifications under a range of foreseeable fab outcomes.  The final design matrix was used to produce a set of photolithography masks to be used in wafer fabrication of laser chips.  We have started the fabrication process, which takes several months and will require procurement of additional funding to complete.

Conclusions:

Our successful Phase I effort culminated in the growth of a set of epitaxial wafers consistent with our design, which used specifications derived from our commercial partner's instrument requirements.  Based on the extensive design simulations we conducted, as well as the wafer validation data, we believe our epitaxy and designs will produce tunable lasers that may meet most or all of the specifications for the product line we want to develop.  Once additional funding has been secured, we will be able to complete wafer fabrication, fully characterize the lasers, and once they are packaged, integrate the lasers into the broadband NIR spectrometer.  Subsequently, our customer will be able to continue method development for ambient monitoring of air toxics.  The integration of our 1790 nm tunable lasers alongside the 16xx tunable lasers already in use will facilitate detection of additional absorption bands - enabling determination of a broader range of analytes with higher specificity.

The laser specifications were developed jointly with our commercial partner, who plans to integrate the resulting product into their spectrometer.  Design and fabrication documetation generated during the course of the Phase I program will feed into Freedom Photonics' new product introduction process, along with characterization data we will be able to obtain if follow-on funding to complete the fabrication run can be secured.

The tunable diode laser spectroscopy market was $450M in 2019, and our capabilities with the new 1790 nm tunable laser source will expand relevance to other industries.  Beyond environmental monitoring, industrial hygiene, and public health, which represent global concerns, we foresee applications in chemical process monitoring and oil/gas pipeline monitoring, as well as medical imaging like optical coherence tomography.  Our tunable lasers are also suitable for airborne LIDAR applications such as foliage mapping.