Post on 31-Mar-2018
Mid-infrared multiheterodyne spectroscopy using quantum and interband cascade lasers
Jonas Westberg1*, Lukasz Sterczewski1, Link Patrick1, and Gerard Wysocki11Department of Electrical Engineering, Princeton University, Princeton N.J. 08544
*email: westberg@princeton.edu
PrincetonUniversity
Laser
Sensing
Laboratorypulse.princeton.edu
October, 2016
Motivation
Acknowledgments
Future work
Results
Experimental methods and procedures
Conclusions
• Broadband, non-invasive trace gas sensing with multimode Fabry-Pérot Quantum Cascade Lasers (QCLs) or Interband Cascade Lasers (ICLs).
• Direct down-conversion of optical modes to multiheterodyne beat notes.
• Separate access to individual radio-frequency (RF) beat notes for broadband measurement.
• Conventional (wavelength modulation) and advanced modulation techniques (e.g. Faraday modulation) to increase sensitivity of multiheterodyne beat note spectroscopy.
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LO
Sig. sample cell+
-
FSRsig
νopt.
-1
-2+1
+2
0
-3
νopt.
0
-1-2
-3
+1
+2
FSRLO
sig. det.
νopt.
-1
-2+1
+2
0
-3
νRF
νRF
absorption dispersion
+
-
50 mA 3V
νopt.
-1
-2+1
+2
0
-3
20 GS/s
ICL1
ICL2
FTIR
50 mA 3V
a
*
cm-1
*
b
Locking procedure
Frequency discriminator
log PID
28-46 MHz
RFToptica
mFALC 110LO
RF
40 MHz
OPLL
Sam
ple
sig
nal
LO
Sig.sample cell
absorption dispersion
QCL1
QCL2
Reference signal
Dis
crim
inat
or
volt
age
(V)
70 mV/MHz
Locking stability
Figure a: Experimental schematic of the multiheterodyne setup. The light sources in this particular example are a pair of ICLs operating around 3.2 μm. The setup is based on the conventional dual-comb spectroscopy configuration.
Figure b: FITR spectra of the signal and local oscillator multi-mode lasers.
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2 MHz
2 kHz†
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Frequency (MHz)
0 200 400 600 800
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*†
Pow
er
(dB
)
Frequency (MHz)
Offset and repetition rate corrected
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Pow
er
(dB
)
Offset-corrected†
*
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Pow
er
(dB
)
Raw spectrum†
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0.0
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1.0
1.2
Tra
nsm
issio
n
Wavenumber (cm-1)
MH Measurement
HITRAN fit
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0.0
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1.0
1.2
Tra
nsm
issio
n
Wavenumber (cm-1)
MH Measurement
HITRAN fit
-0.2 -0.1 0.0 0.1 0.2 0.340
80
120
160
200
Am
plit
ude (
a.u
.)
Time (ms)
MH DAS
Ref.-corr.
-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3
1 s averaging
Detuning (GHz)
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1.0
Tra
nsm
issio
n
-0.2 -0.1 0.0 0.1 0.2 0.3-40
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20
40 1 s averaging
Phase (
°)
Time (ms)
MH DS meas.
Neighbor-corr.
-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3
Detuning (GHz)
20 μs acq. time
Frequency [MHz]
Dete
cto
r sig
nal [V
] 0 -1+1 -2
+2-3 +3 -4 +4
-5 +5 -6 +6-7
+7-8 +8
-9 +9-10 +10 -11
FWHM 1.9 MHz
QCL RF beat note spectrum
• Multiheterodyne spectroscopy using FP-QCLs and ICLs
• Intermutual frequency stabilization/locking• Frequency discriminator (low cost)• OPLL
• Single mode detection• swept direct absorption (ramp rate 1 kHz)• wavelength modulation (fm = 10 kHz, 2f lock-in
det.)• dispersion spectroscopy (ramp rate 1 kHz)
• Multimode (broadband) detection• 25 cm-1 coverage• Rapid response time (10 μs)
• Fully electronically controlled• Seamless switching between detection modes
• Opto-mechanically simple setup• Complexity on the detection/signal
processing side
• Phase and timing correction.
• Post-processing algorithm to improve SNR and enable coherent averaging.
• ICL multiheterodyne spectroscopy of ethylene and methane.
• Swept absorption and dispersion measurements at 1 kHz ramp rate.
• Short acquisition times (20 μs) for broadband measurements.
• QCL multiheterodyne measurements of N2O at low pressure
• absorption
• dispersion
• QCL multiheterodyne measurement of N2O at low pressure using 2fwavelength modulation.
• Broadband QCL multiheterodyne measurement of isobutane.
• 10 μs acquisition time.
• 25 cm-1 spectral coverage.
ref. det.
νRF
νRF
RSA
RSA
40 MHz
40 MHz
phase det.
P(t
)
t
P(t
)
oscilloscope
t
sig. det.
• Dispersion engineering of devices to expand stable bias and temperature regions.
• Explore THz QCL multiheterodyne spectroscopy.
• Coherent averaging to increase sensitivity for longer acquisition times.
• Broadband measurements ( 100 cm-1)• Rapid response time ( μs)• High resolution ( MHz)
Challenges:
The authors gratefully acknowledge F. Capasso, L. Diehl, M. Troccoli for providing FP-QCLs, and J. Meyerfrom the Naval Research Laboratory for providing the FP-ICLs used in this study.
The work is supported by • DARPA SCOUT program (W31P4Q161001), • U.S. Environmental Protection Agency (U.S.
EPA), RD-83513701-0 • National Science Foundation (NSF ERC
MIRTHE), EEC-0540832.