Mid-IR ethene detection using
a quasi-phase matched
LiNbO3 waveguide
Mid-IR ethene detection using
a quasi-phase matched
LiNbO3 waveguide
• 64th OSU International Symposium on Molecular Spectroscopy
• 23rd June 2009
Biogenic sources
- Plant Hormone 'ripening hormone'
Anthropogenic sources
- Organic chemical industry (polyethylene products)
- Vehicle exhaust
(Ethene as indicator of UV-induced lipid peroxidation)
OH ~ 20 hoursO3 ~ 9.7 daysNO3 ~ 5.2 months
Why ethene?
Urban Area ~ few ppbv
Remote Area < 1 ppbv
2900 3000 3100 3200 6148 6152
0.0
0.2
0.4
0.6
0.8
1.0
1.2
line
/ 10-2
0 cm2 m
olec
ule-1
cm
-1
Wavenumber /cm-1
C2H4
A.M.Parkes et al., Phys. Chem. Chem. Phys., 6 (2004) 5313-53178HITRAN Database, 2008
Mid-IR vs Near-IR
Mid-IR Near-IR
DFG (2 to 5m)
QCLs (5 to 11m)
3080.9 3081.0 6150.2 6150.3 6150.4-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
/
10-1
8 cm
2 mo
lecu
le-1
wavenumber /cm-1
C2H4
HITRAN Database, 2004
3081.002 cm-1 6150.300 cm-1
cm-1 (FWHM) 0.00717 0.01432
line / cm2 molecule-1 cm-1 1.124 10-20 5.08 10-22
Gain ~ 46
Mid-IR vs Near-IR
ELECTRONICS LETTERS 17th August 2006 Vol. 42 No. 17Applied Physics Letters 88, 061101, 2006
ps
ips
i
Frequency mixing and phase matchingPerfect phase matchingQuasi-phase matchingWithout phase-matching
deff= 17 pm/V
0i
i
s
s
p
p nnn
ks
kp
ki
1
2k
01
Bulk vs waveguide
Applied Physics Letters 88, 061101, 2006
Waveguide structure improves conversion efficiency with respect to bulk
WGBulk
300
PZT
Experimental set-up (OA-CEAS)
90 mW
28 mW
~ 200 W
Characterization of the laser source
Conversion efficiency = 12.3 % W-1
Experimental phase matching curve in good agreement with the simulated one
Beam profile analysis gave a Gaussian beam waist of ~2 mm.
30 40 50 60 70 80
0.0
0.2
0.4
0.6
0.8
1.0
Nor
mal
ized
Con
vers
ion
Eff
icie
ncy
TCrystal
/ oC
2
sin 2 Lkc
3220 3225 3230 3235 3240 3245 3250 3255 32600
2
4
6
8
10
12
14
pump
/nm
1062.0671062.3561062.7031063.1101063.3601063.6501064.0041064.150
Con
vers
ion
Effi
cien
cy %
/W
Idler
/nm
Tunability of the laser sourceWide tunability range of 35 cm-1
FWHM ~ 7 cm-1
Multi-pass absorption + WMS
3080.94 3080.96 3080.98 3081.00 3081.02 3081.04
-0.2
0.0
0.2
0.4
0.6
WM
S S
igna
l a.u
.
Wavenumber /cm-1
Upper-state Local Quanta
Lower-state
Local Quanta
Molecule /cm-1
Term Symbol
Integrated cross section /cm2 cm-1
J' Ka' Kc' J'' Ka'' Kc''
C2H4 3081.0016 RP0(14) 1.09 · 10-20 13 1 13 14 0 14
C2H4 3081.0016 PR6(10) 1.64 · 10-22 11 5 6 10 6 5
C13CH4 3081.0016 PQ3(10) 1.76 · 10-22 10 2 8 10 3 7
1.29 Torr of C2H4 in Ar (500 ppmv)
Slow modulation = 1 Hz
Fast modulation = 20 kHz
c = 5 ms
Idler power = 193 W
L = 56 m
Modulation depth → b = 2
min (BW)= 1.63 x 10-8 cm-1 Hz-1/2 (2)
3080.96 3080.98 3081.00 3081.02 3081.04 3081.06
0.00
0.04
0.08
0.12
0.16
c = 5 ms
c = 50 ms
3080.96 3081.00 3081.04
0.0
0.1
0.2
(I0-I
)/I
/cm-1
(Io-I
)/I
/cm-1
OA-CEAS
1.8 Torr of C2H4 in Ar (21.8 ppmv)
Slow modulation = 0.8 Hz
Chopper frequency = 2.6 kHz
= 0.01232 cm-1
= 0.00717 cm-1
3080.97 3081.00 3081.03 3081.06 3081.09
0.0
0.1
0.2
0.3
0.4
0.5
0 1 2 3 40
2
4
6
area
/ 10
-3 c
m-1
[C2H
4] / 1012 molecule cm-3
(Io-I
)/I
/ cm-1
OA-CEAS
R = 99.901 ± 0.002 % min (BW)= 1.6 x 10-8 cm-1 Hz-1/2 (2)
L = 1110 ± 20 m
Conclusions and future work
Mid-IR light has been characterized. The CONVERSION EFFICIENCY of the
waveguide, the BEAM PROFILE and the TUNABILITY of the system have been
tested.
Applications of the DFG spectrometer as a new laser sources @ 3.2 m for
ethene detection have been proved using MULTI-PASS ABSORPTION coupled
with WMS, and OA-CEAS.
A.M.Parkes et al., Phys. Chem. Chem. Phys., 6 (2004) 5313-53178
Technique[C2H4]min
/ molecule cm-3 (in air)Mixing ratio
/ ppbv (in air)
Near-IR(@ 1.6 m)
cw-CRDS 1.6 1012 64
cw-CRDS + preconc. 4.7 1010 1.9
Mid-IR(@ 3.2 m)
MPA + WMS 5.4 1011 21.8
OA-CEAS 2.2 1011 8.9
Acknowledgements
Prof. Andrew Orr-Ewing
Dr. Mike Nix
Keith Rosser
Dr James Smith
Charles Murray
Bristol Laser Group
Prof. Gus Hancock
Dr Grant Ritchie
Dr Rob Peverall
Luca Ciaffoni
10 15 20 25 30 35
Inte
nsit
y / a
rb. u
nits
Frequency / MHz
EDFA Pump 1 ( = 980 nm) Pump 2 ( = 1480 nm) Both Pumps
FWHM ~ 0.5 MHz
10 15 20 25 30 35
1583 nm DFB Diode LaserFWHM ~ 1.1 MHz
inte
nsity
/ ar
b. u
nits
Frequency /MHz50 100 150 200-85
-80
-75
-70
-65
-60
N
oise
(dB
VR
MS)
Frequency / kHz
Pseed
= 0 mW P
seed = 0.4 mW
Pseed
= 0.8 mW P
seed = 1.2 mW
Spectrum analysis of the EDFA output- Fabry-Perot spectrum analyzer → laser bandwidth ~ 500 kHz- 1480 nm pump more noisy than 980 nm- FFT spectrum analyzer → ASE at seeding powers < 1 mW
Characterization of the laser source
Noise Analysis
330-370 kHz
0 20 40 60 80 100
0
100
200
300
400
500
600
shot-noise
background
N = a0 + a
1 I + a
2 I2
a
0 = 147.1 ±7.6
a1 = 0.32 ±0
a2 = 0.0355 ±0.0016
No
ise
N (
pA
2 /Hz)
Detector Current I (A)
Noise Analysis
Applied Physics B 76, 473-477 (2003)
0.025 (200-500kHz)
N 2
B2eI
N 2eIB
cw-CRDS with Laser Detuning Technique
Cavity
Signal
Laser
Cur
rent
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