Future Impacts Of Quantum Cascade Lasers On

Spectroscopy

R. F. Curl, Anatoliy Kosterev & F. K. Tittel

Quantum cascade laser developments

• IR laser sources

• QC laser principles

• Broadly tunable QC lasers

• Spectroscopic demonstration

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)

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

Quantum well lasing

AlIn

AsInGaAs

typicallyInGaAs

InG

aAs

AlIn

As

Forming a minisubband

e-

Injection into upper state

e-injectionbarrier Levels relaxed by

optical phonons

~ 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

QCL Compared to Diode Lasers

Quantum Cascade LaserDiode Laser

Interband QC laser (ICL)

Rui YangIEEE J. Q. Elect., 38, 559 (2002)

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)

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

Bound-to-continuum design

Richard Maulini, Mattias Beck & Jerome Faist, App. Phys. Lett. 84, 1659 (2004)

Extended Gain~RT CW operation

CW external cavity QCL: output power

Richard Maulini, University of Neuchatel

Gerard Wysoki

Gerard Wysocki

Apparatus Schematic

Broadly tunable system

Laser

Lens

External cavity length

Grating angle

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

NO and H2O scan

Wide scan NO spectrum

R1/2(23.5)

R3/2(20.5)

NO v 10 R3/2(20.5)

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)

Fabry-Perot sideband suppression

R. Maulini, M. Beck, J. Faist and E. Gini, Appl. Phys. Lett. 84, 1659 (2004)

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)

Pulse train

Ethylene 100 ppb in N2

External cavity Bragg grating coupler

Zhang et al, Appl. Phys. Lett. 86, 111112 (2005)

T= 80Kpulsed

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

Future Impacts Of Quantum Cascade Lasers On Spectroscopy

Depend upon QC development and commercial drive

The future impacts on spectroscopy depend upon you!