Quantum-Noise-LimitedCavity Ring-Down Spectroscopyin the Mid-InfraredAdam J. Fleisher,* David A. Long, Qingnan Liu, and Joseph T. Hodges

Material Measurement LaboratoryNational Institute of Standards & TechnologyGaithersburg, MD 20899, USA

Strong molecular transitions

Near-infrared CRDS• mature technology• lasers, modulators, detectors,

mirrors

• overtone + combination bands

• S = 1.7x10−23 cm/molecule• CO2 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• CO2 at 4.23 µm

Targeting weak isotopologues

Zoom in 60,000,000,000X

12CO2 14CO2

14CO2

I. Galli et al., PRL 107, 270802 (2011); Erratum 108, 179902 (2012).

Motivation at NIST

14C

Partitioning GHG sourcesBiobased

product verification

Biofuel feedstock identification

Pollutantsource 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

PC

L1

InSb

PD

Optical C

avity

Wavem

eter

AOM

DFB

QCL

λ/2

L2 L3

trigger

servo + tr

igger

λ DFB-QCL

T DFB-QCL, I D

FB-QCL

TEM00

Autocorrelation of the decay

Quantum-Noise-Limited Fit ResidualsDetector-Noise-Limited Fit Residuals

low noise PDhigh noise PD

QNL decays recorded at DC

Quantum-Noise-Limited Fit Residuals

low noise PD

H. Huang and K.K. Lehman, JPCA 117, 13399 (2013).

Pdet < 100 µW NEP < 70 fW Hz−1/2 facq > 30 Hz

NEA = 2.3x10−11 cm−1 Hz−1/2

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

L0 ≈ 100 ppm τ0 ≈ 50 µs

Coarse scanning

αnoise < 4x10−10 cm−1

change temperature of QCLor

change current of QCLto jump between FSR

100 MHz coarse scanning

Improved CO2 detection limits

Near-infrared CRDHS• S = 1.7x10−23 cm/molecule• CO2 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• CO2 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: adam.fleisher@nist.gov

Mirror birefringence

Effects of birefringence

Non-exponential decays

Blank

Comparison with the literature

3.00 3.50 4.00 4.50 5.00 5.50 6.001.00E-12

1.00E-11

1.00E-10

1.00E-09

1.00E-08

Fleisher

MaisonSilanderGalli

Lee

Foltynowicz

Halmer

HalmerBasum

Gorrotxategi-Carbajo

PoramboCrabtree

Malara Mürtz

Wang

McManus

GalliNIST

Mid-IR Sensitivities in the Literature

Wavelength (µm)

NEA

coe

ffici

ent (

cm−1

Hz−

1/2)