Multiplexed Detection of CO2 using a Novel Dual-Comb Spectrometer

A. J. Fleisher,1 D. A. Long,1 J. T. Hodges,1 D. F. Plusquellic2

1National Institute of Standards and Technology,Gaithersburg, MD, USA

2National Institute of Standards and Technology,Boulder, CO, USA

Multiplexed approach to spectroscopy

• Multiplexing• acquiring data on all available optical channels

simultaneously• increase acquisition speed

• Fast Scanning• digital control of laser frequency• electro-optic modulators

• Traditional Scanning• thermomechanical tuning• laser current tuning• mechanical laser cavity length tuning

Dave LongMJ02

Experimental overview

Gas Sample

RF Detuning

Ampl

itude

PD

RSA

Generating an EOM comb

−+

6dB

<10 kHz – 18 GHz

Dual-Drive MZM

<6 Vrms

• Fiber-coupled waveguide EOMs

• Large tenability (20 GHz)

• Low Vπ

• Generate optically flat combs

• Up to 700 comb modes

OFC generation

D.A. Long et al., Opt. Lett. 39, 2688 (2014)

Changing the mode spacing is limited by the tuning speed of our microwave sources (≤ 100 µs)

Optical frequency combs

Menlo Systems FOFC

OFC from EOM of a CW laser

D.A. Long et al., Opt. Lett. 39, 2688 (2014)

www.menlosystems.com

Sacrifice on bandwidth

Gain in power per comb mode

Targeted molecular sensing

Toptica, Thorlabs, IMRA …

Multimode cavity coupling

wC+d+wf

wC+d

cavityresonances

Comb spacingscanning

wf

D.A. Long et al., Appl. Phys. B 114, 489 (2014)

Multiheterodyne spectroscopy

Local Oscillator (LO)fn,LO = nfmod + f0

Probefn,Probe = n(fmod + δfmod

)

+ f0 + fAOM

Heterodyne RF Signalfn,RF = nδfmod

+ fAOM

f0 = 193 THzfmod = 203 MHzδfmod

= 24 kHz

fAOM = 99 MHz

Optical Detuning

RF Detuning

Ampl

itude

Ampl

itude

D.A. Long et al., Opt. Lett. 39, 2688 (2014)

Technical drawing

PD

EC

ECDL

FS FS

MZMLO

MZMprobe

AOMsample

AOMref

SampleFC

FC

FL

FL

FALocal Oscillator + Probe

andLocal Oscillator + Reference

Detector reveals two rf combs

𝑇=𝐼𝐼 0

=exp (−𝛼 𝐿)

D.A. Long et al., Opt. Lett. 39, 2688 (2014)

FSLock (5%)

Down-converted rf spectrum

𝑇=𝐼 probe𝐼ref

=exp (−𝛼𝐿 )

D.A. Long et al., Opt. Lett. 39, 2688 (2014)

MH-CEAS of CO2

PCO2 = 14 Pa

Finesse = 20,000FSR = 203 MHz

D.A. Long et al., Opt. Lett. 39, 2688 (2014)

10,000 spectra in 30 seconds

single element NEA = 310-10 cm-1 Hz-1/2

Ruggedized spectrometer

MH-DAS

PCO2 = 13.3 kPa

L = 80 cm totalwww.wavelengthreferences.com

Fiber-coupled multipass cell

single element NEA = 410-6 cm-1 Hz-1/2

D.A. Long et al., Opt. Lett. 39, 2688 (2014)

Ruggedized spectrometer

AOMs

Multipass cell

MZMs

PD

Pump laser

Frequency comb applications

EOM

Step

-sca

n

Step

-sca

n

Electro-optic

mod. combs

T.J. Kippenberg et al. Science, 332, 555-559 (2011).

EOM

Mini-comb applications

Electro-optic

modulator c

ombs

Frac

tiona

l ban

dwid

th (Δ

λ/λ)

Mode spacing (Hz)

Nonlinear spec.Targeted sensing

Cavity GDD

Molecular dispersion

Electro-optic

modulator c

ombs

Frac

tiona

l ban

dwid

th (Δ

λ/λ)

Mode spacing (Hz)

Nonlinear spec.Targeted sensing Cavity GDD

Mini-comb applications

www.maps.google.com www.usmint.gov

Laser size?

Molecular disp.

A. Bartels et al. Science 326, 681 (2009)

Summary of method

• Low cost• An order of magnitude cheaper than competing technologies• Does not require a highly trained user

• Digital control of comb spacing and power leveling

• High power per comb tooth

• Built-in reference channel

• Common mode signals (no need for complicated locking)

Acknowledgements

MMLDavid Long

Katarzyna BielskaJoseph Hodges

PMLKevin Douglas

Stephen MaxwellDavid Plusquellic

NIST Innovations in Measurement Science (IMS) award

NIST Greenhouse Gas Measurements and Climate Research Program

Insert title here

Multiplexed detection schemes

Dispersive

Fourier transformMultiheterodyne

S.A. Diddams et al., Nature 445, 627 (2007)

I. Coddington et al., Phys. Rev. Lett. 100, 013902 (2008)J. Mandon et al., Nature Photon. 3, 99 (2009)

Streak Camera

M.J. Thorpe et al., Science 311, 1595 (2006)

Mach-Zehnder modulator

−+

6dB

<10 kHz – 18 GHz

Dual-Drive MZM

<6 Vrms Control of both amplitude and phaseFlatten output over many sideband orders

Up to 700 comb modes from ONE cw laser!

MZM references here. Detuning (GHz)

Tran

smis

sion

PCH4 = 16 kPa

L = 20 cmfmod = 20 MHztacq = 2 ms

1.0

0.0-6.5 6.5

FARS experimental setup

TTL trigger

RF source (0 – 70 GHz)

ECDL

EOM 2

PDH servo

ring-down cavity

signalacquisition

PD2

PD1

probe leg

lock leg

PBSPBS

p-pols-pol

switch

EOM 1

PDH lock beam

2f PDH error signal

Cavity modes

2f lock

D. A. Long et al., Appl. Phys. B, (2013)

Experimental Overview

(c)Local Oscillator (LO)

fn,LO = nfmod + f0

Probefn,Probe = n(fmod + δfmod

)

+ f0 + fAOM

Heterodyne RF Signalfn,RF = nδfmod

+ fAOM

Optical Detuning

RF Detuning

Ampl

itude

Ampl

itude

(b)

−+

6dB

<10 kHz – 18 GHz

Dual-Drive MZM

<6 Vrms

(a)

Laser

AOM

AOM

MZM

MZMPD

FS FSFC

FC

Gas Sample

Local Oscillator

Reference

Probe

ECDL FS FS

Gas Sample

PDFC

FC

AOM

AOMMZM

MZM

A

Laser FS FS

Gas Sample

FC

FC

AOM

AOM

EOM

EOM

PD

Technical Illustrations 1 and 2

Argument for multiplexing

• Traditional Scanning• Fast Scanning• Multiplexing

Down-convert the optical frequency comb spectrum to radiofrequencies using another optical frequency comb.

Multiheterodyne Cavity-Enhanced Absorption SpectrosocpyMH-CEAS

Femtosecond optical frequency combHall and Hänsch, 2005 Nobel Prize Optical frequency comb

Frequency domain

Time domain

Single pulse Train of pulses

S. T. Cundiff, J. Ye, and J. L. Hall, Scientific American, April 2008

Frequency comb application

N.R. Newbury, Nature Photonics 5, 186 (2011).

Book ChaptersFemtosecond Laser Spectrosocpy,ed. P. Hannaford, Springer (2005).

Femtosecond Optical Frequency Comb Technology, eds. J. Ye and S.T. Cundiff, Springer (2005).

Select ReviewsA. Schliesser et. al. Nature Photonics, 6, 440 (2012).

F. Adler et. al. Annu. Rev. Anal. Chem., 3, 175 (2010).

us!

EC

ECDL

FS FS

EOM1

EOM2

AOM2

AOM1

SampleFC

FC PD

FA

Technical Scheme 3

Frequency Comb Applications

Electro-optic

modulator c

ombs

Frac

tiona

l ban

dwid

th (Δ

λ/λ)

Mode spacing (GHz)

Targeted sensing

Non-linear spec.

Molec. disp.

Mirror disp. Telecom

Potential application

• Environmental Monitoring: monitor carbon dioxide and other greenhouse gas emissions to facilitate accurate assessment of impacts on global climate change and carbon mitigation.

• Safety and Homeland Security: detection of Toxic Industrial Chemicals (TICS) and Toxic Industrial Materials (TIMs), explosives and other hazardous materials.

• Manufacturing: detection and profiling of ion and radical concentrations during electrospray ionization, chemical vapor deposition and etching processes.

• Biomedical Analysis: breath analysis.

Dual-Mini-Comb Spectroscopy

• Inexpensive alternative to optical frequency combs created using phase-stable mode-locked lasers

• Acquisition time and bandwidth can be adjusted on the fly

• Sensitive to individual optical cavity mode dispersion