Quantum Cascade Laser (QCL) Technology and Applications

Transcription

1 Quantum Cascade Laser (QCL) Technology and Applications Anish Goyal IEEE Photonics Society 10 September

2 Outline Background Mid-infrared (MIR) QCLs High power QCLs for IRCM QCLs for MIR Spectroscopy Relevant characteristics of QCLs Primer on MIR spectroscopy Some examples of QCLs for o Gas sensing o Surface sensing Closing thoughts 2

3 Mid-Infrared (MIR) Important Applications: Thermal sensing Chemical sensing Wavenumber [cm -1 ] NIR MIR FIR MWIR LWIR Transmittance (1-km Horiz. Path) H 2 O H 2 O CO 2 H 2 O CO 2 400K Blackbody Spectral Radiance [a.u.] K Wavelength [microns] 3

4 QCL History QCL was invented by Federico Capasso and Jérôme Faist Concept proposed in 1971 by Kazarinov and Suris LT pulsed RT pulsed DFB Alpes Broadband RT CW Heterogeneous THz cascade Arrays RT 27% WPE CW W-level Freq. combs PICs Receiving 1998 IEEE William Streifer Scientific Achievement Award 4

5 QCL Operation Energy-Band Diagram View of Laser Facet TEM Cross-Section Light output Ref: Capasso, Quantum Cascade Lasers, Physics Today,

6 MIR Semiconductor Lasers at Room Temperature Wavenumber [cm -1 ] Diode ICL QCL Wavelength [microns] Diode laser QCL ICL Emission wavelength Inter-band transition Diode Inter-subband transition Cascade Inter-band transition Cascade Spontaneous carrier lifetime ~ nanosecond ~ picosecond ~ nanosecond Material systems (primary) GaAs, InP, GaN, GaSb InP GaSb Threshold power dissipation ~0.3 kw/cm 2 ~10 kw/cm 2 ~1 kw/cm 2 Thermal resistance Low High High Maximum drive limitation Facet damage Doping in active region? 6

7 Infrared Countermeasures (IRCM) Requires high power MIR lasers QCLs have significant advantages over competing laser technologies o Compact, rugged, reliable Army s Common Infrared Counter Measure (CIRCM) System For rotary-wing, small fixed-wing (e.g., Black Hawk helicopters) Won by Northrup Grumman, Selex ES, Daylight Solutions o $35M deal announced Aug 28, 2015 for engineering & development o May lead to acquisition of 4,000+ units 7

8 High Power Requires very efficient heat removal At l ~ 4.9 m, P = 5.1 W [Bai, APL 98 (2011)] At l ~ 9 m, P = 2 W [Lyakh, Optics Express (2012)] Advanced Fabrication / Packaging Highest CW power QCL Refs: Bai, APL 98 (2011); Bai, APL 97 (2010); Razeghi, SPIE 7230 (2007) 8

9 Outline Background Mid-infrared (MIR) QCLs High power QCLs for IRCM QCLs for MIR Spectroscopy Relevant characteristics of QCLs Primer on MIR spectroscopy Some examples of QCLs for o Gas sensing o Surface sensing Closing thoughts 9

10 Fourier-Transform Infrared Spectrometer (FTS) FTS are the work horse for MIR spectroscopy Thermal source (Globar) Michelson interferometer The first practical FTS spectrometer developed at Block Engineering Rapid scan Automated computer analysis Commercially available in

11 Comparison Between FTS and Laser Spectrometers FTS Laser Low radiance source Transmit over long distances High resolution large & slow Standoff detection Spectrally broadband High sensitivity gas detection High spectral brightness >10 6 higher with DFB QCL Fast measurements Incoherent Coherent 11

12 Phase of Matter Analyte Spectral Width Signature Simple gas Narrow Absorption Complex gas Broad Absorption Liquid on surface Broad Related to complex index Solid on surface Broad Related to complex index 12

13 Distributed Feedback (DFB) QCL Tuning rate of cm -1 /K Grating is built into the laser chip to select wavelength Linewidth CW: ~1 MHz (< cm -1 ) Pulsed: ~300 MHz (0.01 cm -1 ) Thermal tuning is usually accomplished by changing drive current ~5 cm -1 13

14 Broadband Heterogeneous Cascades Groups of cascades have different emission wavelengths to collectively lase over a broader bandwidth Faist group demo tuning of 432 cm -1 ( um) using 5 cascades o [Hugi, APL 95 (2009)] Thorlabs demo tuning 580 cm -1 ( m) o [Xie, Opt Lett 40 (Sep 2015)] Northwestern demo tuning 760 cm -1 ( m) using 6 cascades o [Bandyopadhyay, Opt Ex 23 (Aug 2015)] 14

15 Broadly Tunable QCLs External-cavity Diffraction grating Block Engineering Daylight Solutions Fraunhofer Institute Pranalytica, etc. Broadband tuning Fast (~msec) Compact Generally multi-mode External-cavity Acousto-optic Modulator Pranalytica Very fast (~1 sec) Large External-cavity Tunable etalons RedShift Single-mode Broadband Slow Multi-wavelength DFB array EOS Photonics Single-mode Broadband Extremely fast (<1 s) Cost? 15

16 Outline Background Mid-infrared (MIR) QCLs High power QCLs for IRCM QCLs for MIR Spectroscopy Relevant characteristics of QCLs Primer on MIR spectroscopy Some examples of QCLs for o Gas sensing o Surface sensing Closing thoughts 16

17 Example MIR Spectrum for Resin Melamine Formaldehyde-Modified Alkyd Resin Vibrational Mode Frequency [cm -1 ] Aliphatic C-H stretch 2900 [1] 6 Carbonyl, C=O stretch 1730 [2] 5 Ester, C-O stretches 1285 [3] 1122 [4] Aromatic ring bending 743 [5] 706 [6] Symmetric Stretch Asymmetric Stretch Wagging Twisting From: Beveridge, et al., Use of infrared spectroscopy for the characterization of paint fragments, in Forensic Examination of Glass and Paint, ed. Caddy (2001). 17

18 Infrared Active Vibrations Two major classes of vibrational spectroscopy probe different optical effects Mid-IR optical dipole interactions Raman molecular polarizability Typical White Paint Ref: Bell, Appl. Spectroscopy 59, 1333 (2005). Infrared Different vibrations have different interaction strengths Some are more Infrared Active, while others are more Raman Active Raman cm cm cm cm -1 Methane: IR Active IR Active 18

19 Vibrational Modes for Simple Gases Degrees of freedom = 3N = translational + rotational + vibrational Diatomic molecule (N=2) o 3 translational modes, 1 vibrational mode, 2 rotational modes 3 m 1 m 2 R n = = J vibration rotation E K n B J J 1 n,j 2 1 n = B Selection rules: Dn = ±1, DJ = ±1 19

20 Carbon Monoxide Center = cm -1 (4.67 m) Spacing = 2B = 3.9 cm -1 Linewidth at P = 1 atm ~0.13 cm -1 = 4 GHz Absorption Cross-Section [a.u.] Carbon Monoxide 1 atm 0.5 atm 0.25 atm cm Wavenumbers [cm -1 ] 20

21 Nitrous Oxide N 2 O 3 vibrational modes Overtone and combination bands extend to higher energy Due to anharmonicity of vibration and coupling between modes Gives rise to bands in NIR for detection using TDLAS 2282 cm cm cm -1 Overtone Bands 21

22 Freon-113 (C 2 Cl 3 F 3 ) 1:1210 2: : : : 903 6: 813 7: 654 8: 531 9: : : : : : : : : : 62 C Cl F

23 EPA Method 325 Gas List LWIR Wavelength ,4-Dichlorobenzene o-xylene Styrene (monomer) p-xylene m-xylene Ethyl benzene Chlorobenzene Tetrachloroethylene Toluene 1,1,2-Trichloroethane Trichloroethylene 1,2-Dichloropropane Carbon tetrachloride Benzene 1,1,1-Trichloroethane 1,2-Dichloroethane 1,1-Dichloroethane Freon-113 Allyl chloride 1,1-Dichloroethene Wavenumbers 23

24 Gas Detection Long-path gas cells White & Herriot multi-pass cells o Few 100 meters Off-axis integrated cavity output spectroscopy (OA-ICOS) o Multiple kilometers o PPT concentrations of NO 2 Cavity-ring down spectroscopy (CRDS) o Requires narrow-linewidth laser Photo-acoustic spectroscopy Conventional & Quartz-enhanced 24

25 Commercial DFB Lasers & Systems DFB vendors Alpes Lasers Hamamatsu Adtech Thorlabs Nanoplus etc. Gas detection systems by, for example, Cascade Technologies Emissions Monitoring Gas DetectionRange Detection Limit Nitric Oxide (NO) ppm 20ppm Nitrogen Dioxide (NO2) Sulphur Dioxide (SO2) Carbon Dioxide (CO2) 0-300ppm 3ppm ppm 17.5ppm 0-10% 0.10% 25

26 Miniaturized external-cavity QCL Extremely compact: ~ 2 x 2 x 5 cm Very broad tuning: typically 250 cm -1 (for some modules up to 400 cm -1 ) Block s Broadly Tunable Mini-QCL TM High-speed tuning: ~100 Hz Custom-designed electronics for spectroscopy capability Mini-QCL TM Normalized Intensity Wavenumbers [cm -1 ] 26

27 Multi-Gas Detection Hydrocarbon analysis needed for oil & gas industry Quantify %-level concentrations within few seconds 1.2 Pure Component Spectra 1.2 Mixture Spectra 1 1 mixture Transmittance methane ethane propane n-butane iso-butane n-pentane iso-pentane Transmittance Measured Conc. C1:23.5% C2: 9.1% C3 = 8.4% nc4 = 1.1% ic4 =0.9% nc5 = 0.8% ic5 = 1.2% Wavenumber, cm Wavenumber, cm -1 27

28 Open-Path Atmospheric Sensing Laser transceiver plus retro-reflector used to measure the round-trip atmospheric transmittance Two Mini-QCLs covers the LWIR transmission window (l ~ m) Transceiver C Retro-Reflector L Range 28

29 Some Applications Fixed installations Protection of critical infrastructure Environmental monitoring On-the-fly configurations Emergency responders Protection of Critical Infrastructure Release in the HVAC Monitoring of Fugitive Emissions Retro Emergency Responders Mirrors Mirrors Retros Retros Gas Cloud Toxic Cloud 29

30 Long-Range Outdoors Data 310-meter LaserWarn Block Engineering Facility 562-meter Retro 2 retroreflector 562-m RT 310-m RT 30

31 Measurement period 2.5 s (integration time 2 s) Convert transmittance spectra to absorbance Apply simple algorithms to identify and quantify the gas concentration PPB-level detection limit Experimental Results 562-meters Round-Trip Absorbance Wavenumbers Concentration [ppm-meter] Difluoroethane Tetrafluoroethane Time [s] 31

32 Surface Sensing General Purpose Surface Sensing Gas Sensing LaserTune + Detector LaserScan LaserSense LaserWarn sample 32

33 Identification of Bulk Plastics 33

34 Detection of Disturbed Earth LaserScan-DE Hand-portable system for standoff detection of disturbed earth Completed several field tests and implemented detection algorithms 34

35 Identification of Chemical Residues CWA Simulant on Linoleum Explosive Residue on Car Panels Reflectance Reflectance Wavenumber [cm -1 ] Wavenumber [cm -1 ] 35

36 Future Directions: Hyperspectral Imaging Contaminated Fingerprint on Car Panel From Book Chapter: Goyal & Myers, Active mid-infrared reflectometry and hyperspectral imaging, in Laser-based optical detection of explosives, CRC Press (2015). 36

37 Closing Thoughts Very selective overview of QCLs and their applications Did not even discuss the wide range of applications Rapidly changing technology New applications are constantly emerging Commercial landscape is very dynamic It is an exciting time to be working in this field 37