Quantum-Noise-Limited Cavity Ring-Down Spectroscopy in the Mid-Infrared Adam J. Fleisher,* David A. Long, Qingnan Liu, and Joseph T. Hodges Material Measurement Laboratory National Institute of Standards & Technology Gaithersburg, MD 20899, USA

Strong molecular transitions Near-infrared CRDS mature technology lasers, modulators, detectors, mirrors overtone + combination bands S = 1.7x10 −23 cm/molecule CO 2 at 1.57 µm Retrieved from HITRANonline at hitran.org on 6/23/2015 Mid-infrared CRDS maturing technology lasers, modulators, detectors, mirrors fundamental vibrations S = 3.5x10 −18 cm/molecule CO 2 at 4.23 µm

Targeting weak isotopologues Zoom in 60,000,000,000X 12 CO 2 14 CO 2 I. Galli et al., PRL 107, (2011); Erratum 108, (2012).

Motivation at NIST 14 C Partitioning GHG sources Biobased product verification Biofuel feedstock identification Pollutant source identification

Motivation at NIST Photo from LLNL Accelerator Mass Spectrometry (AMS) Very sensitive (<1 fmol/mol) Expensive (~$6M/facility) Require large faculty and highly trained staff Only ~10 facilities in the U.S. Lead time >10 days

Status update Detail instrument design – quantum cascade laser Demonstrate spectrometer performance – quantum-noise-limited decays Coarse spectral scanning and high-resolution scanning Future low-temperature CRDS (≥185 K)

Experimental methods TEM 00

Autocorrelation of the decay Quantum-Noise-Limited Fit Residuals Detector-Noise-Limited Fit Residuals low noise PD high noise PD

QNL decays recorded at DC Quantum-Noise-Limited Fit Residuals low noise PD H. Huang and K.K. Lehman, JPCA 117, (2013).

Allan variance of the decay time MDA < 2×10 −11 cm −1 at 3 s NEA = 2.3x10 −11 cm −1 Hz −1/2 MDA < 6×10 −12 cm −1 at 4 s NEA = 1.0x10 −11 cm −1 Hz −1/2 L 0 ≈ 100 ppmτ 0 ≈ 50 µs

Coarse scanning α noise < 4x10 −10 cm −1 change temperature of QCL or change current of QCL to jump between FSR 100 MHz coarse scanning

Improved CO 2 detection limits Near-infrared CRDHS S = 1.7x10 −23 cm/molecule CO 2 at 1.57 µm NEA = 6x10 −14 cm −1 Hz −1/2 NEC < 130 ppt Hz −1/2 10 Torr of total pressure Retrieved from HITRANonline at hitran.org on 6/24/2015 Mid-infrared CRDS S = 3.5x10 −18 cm/molecule CO 2 at 4.23 µm NEA = 2x10 −11 cm −1 Hz −1/2 NEC < 80 ppq Hz −1/2 10 Torr of total pressure D.A. Long et al., Opt. Lett. 39, 2688 (2014)

Low-temperature CRDS S. Kassi et al., CPL 477, 17 (2009). invar rods mirror mount assembly sample cold cell vacuum sample cooling liquid

Status update Detail instrument design – quantum cascade laser Demonstrate spectrometer performance – quantum-noise-limited decays Coarse spectral scanning and high-resolution scanning Future low-temperature CRDS (≥185 K)

Acknowledgements David Long, Joseph Hodges, Roger van Zee, Zachary Reed K. Bielska, M. Ghysels, H. Lin, Q. Liu, V. Sironneau, S. Wójtewicz, H. Yi NIST Innovation in Measurement Science (IMS) Award Good postdocs always wanted:

Mirror birefringence

Effects of birefringence

Non-exponential decays

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Comparison with the literature