future impacts of quantum cascade lasers on spectroscopy r. f. curl, anatoliy kosterev & f. k....
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Future Impacts Of Quantum Cascade Lasers On
Spectroscopy
R. F. Curl, Anatoliy Kosterev & F. K. Tittel
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Quantum cascade laser developments
• IR laser sources
• QC laser principles
• Broadly tunable QC lasers
• Spectroscopic demonstration
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IR laser sources•Difference Frequency Generation (DFG)LiNbO3(2-5µm), AgGaS2(3-9µm),GaSe(7-18µm)
•QC lasers3.4-120 µm, ~5cm -1,power 10-100mW,rugged•Lead Salt Diode Laserseach diode ~100 cm-1,3-30 µm P<1mWundesirable discontinuities, require liq N2
•III-V diodes <3.8 µm P~1-10 mW•Color Center Lasers tunable from 1-4 µm, require liq N2 P~1-10mW
•CO and CO2 Lasers (sidebands)
•Optical Parametric Oscillators (OPO)
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Quantum cascade laser; Basic facts
• Semiconductor lasers (III-V materials)• Multiple-quantum-well heterostructure• Intersubband transitions• Band-structure engineering (emission wavelength
defined by the layer thickness – MBE, MOCVD etc.)• Independent of material energy bandgap• Cascading (each electron creates N laser photons)• Number of periods N determines laser power• High reliability, long lifetime• Compact
Frank Tittel, Federico Capasso, Claire Gmachl, Jerome Faist, Rui Yang
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Quantum well lasing
AlIn
AsInGaAs
typicallyInGaAs
InG
aAs
AlIn
As
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Forming a minisubband
e-
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Injection into upper state
e-injectionbarrier Levels relaxed by
optical phonons
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~ 1.5 periods with one active region
Injection barrier
Exit barrier
4 QW active region
Injector regionFaist et al., IEEE J.Quant. El.,38, 533 (2002)
MINIBAND
MINIGAP
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QCL Compared to Diode Lasers
Quantum Cascade LaserDiode Laser
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Interband QC laser (ICL)
Rui YangIEEE J. Q. Elect., 38, 559 (2002)
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QCL and ICL
QCL:• Wavelengths 3.5 – 160µm
(limited by the conduction-band offset on the short wavelength side)
• Relatively high threshold current density (typically > 1kA/cm2)
• High efficiency• High power
ICL:• Wavelengths 3 – 5 µm• Type II quantum wells• Low threshold current• High efficiency• High power
SOURCE: J. Faist and C. Sirtori (2001)
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Tuning and frequency puritySolitary laser - just the chip: multimode ~2-3
tunes ~3 cm-1
DFB - single mode, tunes ~3 cm-1, limits T range
Wider tuning requires:
• Extended gain region•AR coated facet for external grating cavity near RT operation OR clever outcoupling scheme
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Bound-to-continuum design
Richard Maulini, Mattias Beck & Jerome Faist, App. Phys. Lett. 84, 1659 (2004)
Extended Gain~RT CW operation
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CW external cavity QCL: output power
Richard Maulini, University of Neuchatel
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Gerard Wysoki
Gerard Wysocki
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Apparatus Schematic
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Broadly tunable system
Laser
Lens
External cavity length
Grating angle
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UECL – amplitude of the voltage controlling PZT tuning external cavity length UGR – amplitude of the voltage controlling PZT tuning diffraction grating angle EC – external cavity; FP mode – Fabry-Perot resonator mode
Scanning mode tracking
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NO and H2O scan
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Wide scan NO spectrum
R1/2(23.5)
R3/2(20.5)
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NO v 10 R3/2(20.5)
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External cavity laser: Pulsed
950 1000 1050 1100cm-1
2
1
0
40
80
0
R. Maulini, M. Beck, J. Faist and E. Gini, Appl. Phys. Lett. 84, 1659 (2004)
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Fabry-Perot sideband suppression
R. Maulini, M. Beck, J. Faist and E. Gini, Appl. Phys. Lett. 84, 1659 (2004)
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Using a pulsed QC laser
Damien Weidman, A.A. Kosterev, C. Roller, R. F. Curl, M. P. Fraser, and F. K. Tittel, Appl.Opt. 43, 3329-3334 (2004)
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Pulse train
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Ethylene 100 ppb in N2
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External cavity Bragg grating coupler
Zhang et al, Appl. Phys. Lett. 86, 111112 (2005)
T= 80Kpulsed
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Status of QC lasers• Commercial Availability
– Alpes Lasers (http://www.alpeslasers.ch/)– Hammatsu Photonics
(http://www.hpk.co.jp/Eng/products/ld.htm)*
• Anywhere from 80 to 3300 cm-1 (most regions not yet commercially available)
• Tunability - a few non-commercial lasers tunable over 100 cm-1, but typically <5 cm-1
• Line width - CW <1 MHz ; pulsed ~500 MHz (chirp from heating; lifetime linewidth)
• Power 1-500 mW (mostly near low end)
*Just announced, not yet on this web site
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Future Impacts Of Quantum Cascade Lasers On Spectroscopy
Depend upon QC development and commercial drive
The future impacts on spectroscopy depend upon you!