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Mid-infrared semiconductor laser based trace gas

analyzers: advances, applications & future outlook

OUTLINE

S. So 1a, R. Lewicki1,2,

W. Ren2,W. Jiang2, Y. Cao2, D. Jiang2, F.K. Tittel2b

V. Spagnolo3, Pietro Patimisco3

1Sentinel Photonics, Princeton, NJ 085402 Rice University, 6100 Main St., Houston, TX 77005

3Univerity of Bari, Italy

a) sso@sentinelphotonics.com; b) fkt@rice.edu

Laser Optics2014

Philadelpia, PA

September,8-10, 2014

Research support by NSF ERC MIRTHE, NSF-ANR NexCILAS, the Robert Welch Foundation, and Sentinel

Photonics Inc. via an EPA and NSF SBIR sub-award is acknowledged

• New Laser Based Trace Gas Sensor Technology

� Novel Multipass Absorption Cell & Electronics

� Quartz Enhanced Photoacoustic Spectroscopy

• Examples of Mid-Infrared Sensor Architectures

� C2H6, NO, CO and CH4

� Future Directions of Laser Based Gas Sensor

Technology and Conclusions

Motivation for Mid-infrared C2H6 Detection

• Atmospheric chemistry and climate

� Fossil fuel and biofuel consumption,

� biomass burning,

� vegetation/soil,

� natural gas loss

• Oil and gas prospecting

• Application in medical breath analysis (a non-invasive method to identify Targeted C H(a non-invasive method to identify and monitor different diseases):

� asthma,

� schizophrenia,

� Lung cancer,

� vitamin E deficiency.

HITRAN absorption spectra of C2H6, CH4, and H2O

4

Targeted C2H6

absorption line

NOAA Monitoring & Sampling Location: Alert, Nunavut, Canada

ALT, Ethane Concentration Measurements

General View on the FacilityLatitude: 82.4508º North

Longitude: 62.5056º WestElevation: 200.00 m

5

C2H6 Detection with a 3.36 µm CW DFB LD using a Novel

Compact Multipass Absorption Cell and Control Electronics

Schematic of a C2H6 gas sensor using a Nanoplus 3.36 µm DFB laser diode

as an excitation source. M – mirror, CL – collimating lens, DM – dichroic

2f WMS signal

for a C2H6 line

at 2976.8 cm-1

at a pressure of

200 Torr

as an excitation source. M – mirror, CL – collimating lens, DM – dichroic

mirror, MC – multipass cell, L – lens, SCB – sensor control board.Innovative long path, small volume

multipass gas cell: 57.6m with 459 passes

MPC dimensions: 17 x 6.5 x 5.5 (cm)

Distance between the MPC mirrors: 12.5 cm

Minimum detectable C2H6 concentration is:

~ 740 pptv (1σ; 1 s time resolution)

� High pathlength/volume ratio

� Simple spherical mirrors

� Utilize entire mirror surface - embrace optical aberration

MULTIPASS CELL TECHNOLOGY

aberration

� Flexible design – two opposing mirrors

� Typ. 10% throughput for 459 passes

Herriott Cell Pattern Sentinel 3.7 m cell Sentinel 57 m cell

From Conventional PAS to QEPAS

Laser beam,

power P

Absorption α

Modulated

(P or λ) at f

or f/2

SWAP RESONATING ELEMENT!!!

Q>>1000

Cell is OPTIONAL!

V-effective volume

Piezoelectric crystal

Resonant at f

quality factor Q

Vf

PQS

α~

or f/2

×

∆

α=

Hz

Wcm-1

min

f

PNNEA

8

Quartz Tuning Fork as a Resonant Microphone for QEPAS

Unique properties

• Extremely low internal losses:

� Q~10 000 at 1 atm

� Q~100 000 in vacuum

• Acoustic quadrupole geometry

� Low sensitivity to external sound

• Large dynamic range (~106) – linear from thermal noise to breakdown deformation

� 300K noise: x~10-11 cm� 300K noise: x~10 cm

� Breakdown: x~10-2 cm

• Wide temperature range: from 1.6K to ~700K

Acoustic Micro-resonator (mR) tubes

• Optimum inner diameter:0.6 mm; mR-QTF gap is 25-50 µm

• Optimum mR tubes must be ~ 4.4 mm long (~λ/4<l<λ/2 for sound at 32.8 kHz)

• SNR of QTF with mR tubes: ×30 (depending on gas composition and pressure)

9

Motivation for Nitric Oxide Detection

• Atmospheric Chemistry

• Environmental pollutant gas monitoring� NOX monitoring from automobile exhaust and

power plant emissions

� Precursor of smog and acid rain

• Industrial process control

� Formation of oxynitride gates in CMOS Devices

• NO in medicine and biology� Important signaling molecule in physiological

processes in humans and mammals (1998 Nobel Prize in Physiology/Medicine)

� Treatment of asthma, COPD, acute lung rejection

• Photofragmentation of nitro-based explosives 10

NO: 5.26 µm

CO: 4.66 µm CH2O: 3.6 µm

CO2: 4.2 µm

CH4: 3.3 µm

COS: 4.86 µm

Molecular Absorption Spectra within two Mid-IR

Atmospheric Windows and NO absorption @ 5.26µm

0.06

0.08

0.10

0.12

0.14

0.16

Abso

rption

[%

]

1ppm NO at 250 Torr, L=1 m

NH3: 10.6 µm O3: 10 µm

N20, CH4: 7.66 µm

12.5 µm 7.6 µm

3.1 µm5.5 µm

Source: HITRAN 2000 database

1800 1850 1900 1950

0.00

0.02

0.04

0.06

Abso

rption

[%

]

Wavenumber [cm-1]

11

Emission spectra of a 1900cm-1 TEC CW DFB QCL

and HITRAN Simulated spectra

Output power: 117 mW @ 25 C

Thorlabs/Maxion 12

CW TEC DFB QCL based QEPAS NO Gas Sensor

Schematic of a DFB-QCL based Gas Sensor.

PcL – plano-convex lens, Ph – pinhole,

QTF – quartz tuning fork, mR – microresonator,

RC- reference cell, P-elec D – pyro electric detector

13

Performance of CW DFB-QCL based WMS QEPAS

NO Sensor Platform

2

4

6

8

10

QE

PA

S 2

f sig

nal [a

.u.]

1ppm NO + 2.4% H2O, P= 240 Torr

100

200

0.1% NO at P=200 Torr, 5 cm ref. cell

QE

PA

S 3

f sig

nal [a

.u.]

40

60

80

100

NO

con

ce

ntr

ation [

ppb]

95 ppb NO reference cylinder

NO

14

2f QEPAS signal amplitude for 95 ppb NO

when DFB-QCL was locked to the 1900.08

cm-1 line.

900 890 880 870 860 850

-4

-2

0

QE

PA

S 2

f sig

nal [a

.u.]

Laser current [mA]

-100

0

QE

PA

S 3

f sig

nal [a

.u.]

2f QEPAS signal (navy) and reference 3f signal (red)

when DFB-QCL was tuned across 1900.08 cm-1 NO

line.

Minimum detectable NO concentration is:

~ 3 ppbv (1σ; 1 s time resolution)

13:37 13:40 13:43 13:46 13:49

0

20

NO

con

ce

ntr

ation [

ppb]

Time [HH:MM]

N2N2

Motivation for Carbon Monoxide Detection

• Atmospheric Chemistry� Incomplete combustion of natural gas, fossil fuel

and other carbon containing fuels.

� Impact on atmospheric chemistry through its reaction with hydroxyl (OH) for troposphere ozone formation and changing the level of greenhouse gases (e.g. CH4).gases (e.g. CH4).

• CO in medicine and biology� Hypertension, neurodegenerations, heart failure and

inflammation have been linked to abnormality in CO metabolism and function.

15

Performance of a NWU 4.61 µm high power CW TEC DFB QCL

4

5

6

7

8

9

10

11

12

T=18 oC

T=12.5 oC

T=15 oC

λ~4.6 µm DFB QCL

cw operation

Optica

l p

ow

er(

mW

)

Vo

lta

ge

(V

)

0

100

200

300

400

500

600

700

800

900

1000

T=10 oC

2164.8

2165.4

2166.0

2166.6

2167.2

2167.8

2168.4

2169.0

2169.6

2170.2

2170.8

2171.4

R6 CO line

Wa

ven

um

be

r(cm

-1)

T=10 oC

T=12.5 oC

T=15 oC

T=18 oC

R5 CO line

0 200 400 600 800 1000 1200

Current (mA)

500 600 700 800 900 1000 1100 1200 13002164.8

Current (mA)

2166 2168 2170 2172 2174 21760.0

0.3

0.6

0.9

1.2

1.5

x10-5

R8R7

Absorp

tion

Wavenumber (cm-1)

200 ppb CO 2% H2O

x10-5

R6R5

0.0

0.1

0.2

0.3

0.4 300 ppb N

2O

Absorp

tion

CW DFB-QCL optical power and current tuning at a four different QCL temperatures.

Estimated max wall-

plug efficiency (WPE)

is ~ 7% at 1.25A QCL

drive-current.

400

500

600

700

800

900 P=760 Torr

CO

concentr

ation (

ppb)

From cigarette

CW DFB-QCL based CO QEPAS Sensor Results

-30

-15

0

15

30

45

60

2169.1 2169.2 2169.3-450

0450900

Modulation depth=50 mA

P=760 Torr

x104

QE

PA

S S

ign

al (C

nts

)

Wavenumber (cm-1)

with 2.6% H2O

dry gas

(a)

Pure Nitrogen

(b)

2f QEPAS signal for dry (red) and moisturized (blue)

10:00 11:00 12:00 13:00 14:00 15:000

100

200

300C

O c

oncentr

ation (

ppb)

Time (HH:MM)

17:00 17:20 17:40 18:00 18:200

10

20

30

40

17:00 17:05 17:10 17:15

0.0

0.5

1.0

1.5

2.0

N2

50 ppb

x104

QE

PA

S S

ign

al

(Cn

ts)

Time (HH:MM)

N2

x104

P=760 Torr

Modulation depth=40 mA

N250 ppb 100 ppb

250 ppb

500 ppb

1000 ppb

2500 ppb

QE

PA

S S

ignal (C

nts

)

Time (HH:MM)

5000 ppb

Gas with 2.6% H2O

17Dilution of a 5 ppm CO reference gas mixture when

the CW DFB-QCL is locked to the 2169.2 cm-1 R6 CO line.

2f QEPAS signal for dry (red) and moisturized (blue)

5 ppm CO:N2 mixture near 2169.2 cm-1.

Minimum detectable CO concentration is:

~ 2 ppbv (1σ; 1 s time resolution)

Atmospheric CO concentration levels on Rice University campus,

Houston, TX

QEPAS based CH4 and N2O Gas Sensor

ZnSe Pc L mR mRQTF

Ge Pc L7.83 µm

CW DFB-QCL

CH4 & N2O

Ph

Acoustic Detection Module

(ADM)

Needle valve

Gas inlet

Pressure

controller &

Flow meter

Pump

Gas outlet

-

+

QCL Driver

Pre-Amp

Temperature

controller

M

M

RCPD

Motivation for CH4 andN2O Detection

• Prominent greenhouse gases

• Sources : Wetlands, leakagefrom natural gas systems,fossil fuel production andagriculture

•Applications: Environmental, medical and aerospace (N2O)

QCL Driver

Control Electronics Unit (CEU)

Lock-in

2f

Data collection and processing

Lock-in

3f

controller

Detection Limit (1σ) with a 1-sec averaging time

Methane (CH4) (1275.04 cm-1) 13 ppbv

Nitrous Oxide (N2O) (1275.5 cm-1) 6 ppbv

440 450 460 470 480 490 500

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2f

Sig

na

l x 1

05 (a

. u.)

Injected Current (mA)

Baseline

2f signal (1.8 ppmv N2O)

2f Signal Ambient Air

2f Signal (1 ppmv CH4)

Pressure

130 Torr

T

21.5 °C

AM

4 mA

f

32760 Hz

fmod

16380 Hz

123 mW

132 mW

158 mW

161 mW

Deduced N2O concentration in the ambient

laboratory air: 331 ppbv

Submitted to The Analyst Aug. 2013

18

QEPAS based CH4 and N2O Gas Sensor

QEPAS Sensor Control BoardQEPAS Sensor Control Board

QCL Current and TEC

Driver, Performing

wavelength modulation, Data

acquisition, Applying

continuous saw-tooth current

ramping at 8 Hz, Testing

QTF and low noise pre

amplifier

NIR

VIS

Molecule (Host) Frequency, cm-1

Pressure,

Torr

NNEA,

cm-1W/Hz½

Power,

mW

NEC (τ=1s),

ppmv

O3 (air) 35087.70 700 3.0×10-8 0.8 1.27

O2 (N2) 13099.30 158 4.74×10-7 1228 13

C2H2 (N2)* 6523.88 720 4.1×10-9 57 0.03

NH3 (N2)* 6528.76 575 3.1×10-9 60 0.06

C2H4 (N2)* 6177.07 715 5.4×10-9 15 1.7

CH4 (N2+1.2% H2O)* 6057.09 760 3.7×10-9 16 0.24

N2H4 6470.00 700 4.1×10-9 16 1

H2S (N2)* 6357.63 780 5.6×10-9 45 5

HCl (N2 dry) 5739.26 760 5.2×10-8 15 0.7

CO2 (N2+1.5% H2O) * 4991.26 50 1.4×10-8 4.4 18

CH2O (N2:75% RH)* 2804.90 75 8.7×10-9 7.2 0.12

QEPAS Performance for Trace Gas Species (September 2014)

* - Improved microresonator

** - Improved microresonator and double optical pass through ADM

*** - With amplitude modulation and metal microresonator

NNEA – normalized noise equivalent absorption coefficient.

NEC – noise equivalent concentration for available laser power and τ=1s time constant, 18 dB/oct filter slope.

Mid-IR

CH2O (N2:75% RH)* 2804.90 75 8.7×10 7.2 0.12

CO (N2 +2.2% H2O) 2176.28 100 1.4×10-7 71 0.002

CO (propylene) 2196.66 50 7.4×10-8 6.5 0.14

N2O (air+5%SF6) 2195.63 50 1.5×10-8 19 0.007

C2H5OH (N2)** 1934.2 770 2.2×10-7 10 90

NO (N2+H2O) 1900.07 250 7.5×10-9 100 0.003

C2HF5 (N2)*** 1208.62 770 7.8×10-9 6.6 0.009

NH3 (N2)* 1046.39 110 1.6×10-8 20 0.006

SF6 948.62 75 2.7x10-10 18 5x10-5 (50 ppt)

For comparison: conventional PAS 2.2 ×10-9 cm-1W/√Hz for NH3

Mini Methane Sensor for UAVs

Miniaturization

21

Remote controlled quad-copter UAV

for pipeline sniffing -payload maximum only 600g!

5.0x106

1.0x107

1.5x107

2.0x107

2.5x107

2f

Lock-I

n A

mp

litud

e [a

.u.]

10ppm CH4

3.3 micron DFB Laser

3.75m optical path

Mini Methane Sensor for UAVs

Sensor Performance

22

0 20 40 60 80 100

-1.5x107

-1.0x107

-5.0x106

0.0

5.0x10

2f

Lock-I

n A

mp

litud

e [a

.u.]

Spectral Channel Number

Onboard pressure controller and pump systemContinuous measurement [10Hz] with onboard processingDirect concentration output – no post-processing necessary

Future Directions and Outlook

• New target analytes such as carbonyl sulfide (OCS), formaldehyde (CH2O), nitrous acid (HNO2), hydrogen peroxide (H2O2), ethylene (C2H4), ozone (O3), nitrate (NO3), propane (C3H8), and benzene (C6H6)

• Ultra-compact, low cost, robust sensors (e.g. C2H6, NO, CO…)

2 6

NO, CO…)

• Monitoring of broadband absorbers: acetone (C3H6O), acetone peroxide (TATP), UF6…

• Optical power build-up cavity designs

• Development of trace gas sensor networks

• QEPAS based detection at THz frequencies

23

Future Directions and Outlook

• Development of robust, compact sensitive, mid-infrared trace gas sensor technology based on room temperature, continuous wave, DFB QCL and ICLs for environmental, industrial, biomedical monitoring and security applications

• Seven target trace gas species were detected with a 1 sec sampling time:

� C2H6 at ~ 3.36 µm with a detection sensitivity of 740 pptv using TDLAS

� NH3 at ~ 10.4 µm with a detection sensitivity of ~1 ppbv (200 sec averaging time);

� NH3 at ~ 10.4 µm with a detection sensitivity of ~1 ppbv (200 sec averaging time);

� NO at ~5.26µm with a detection limit of 3 ppbv

� CO at ~ 4.61 µm with minimum detection limit of 2 ppbv

� SO2 at ~7.24 µm with a detection limit of 100 ppbv

� CH4 and N2O at ~7.28 µm currently in progress with detection limits of 20 and 7 ppbv, respectively.

• New target analytes such as CH2O, H2O2, and C2H4,

• Monitoring of broadband absorbers such as acetone, C3H8, C6H6 and UF6

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