Advances in mid and far infrared coherent sources and their

applications

Valdas PasiskeviciusApplied Physics, KTH

Outline

• Spectral ranges• Application areas• Radiation sources:

coherent vs incoherent• MIR, FIR coherent sources:

technology options• Developments at KTH• Beyond state of the art

Spectral ranges

MIR: = 2 µm – 30 µm (150 THz – 10 THz)

Cr2+, Fe3+

Spectral ranges

FIR: = 300 µm – 30 µm (0.1 THz – 10 THz)

Options: coherent vs incoherent

0 20 40 60 80 10010-6

10-4

10-2

100

102

104

106

QCL LD

Er:ZBLAN

NLONLO

TBB

=2000 K, =1cm-1, A=10 mm2

P, W

/cm

-1

, m

[G. P. Williams, Rev. Sci.Instr. 73, 1461 (2002)]Advantages of coherent sources:• High power• High spectral power density• High brightness• High wall-plug efficiency

Benefiting Applications:• All except simple spectroscopy

Advantages of incoherent sources:• Broad range• Inexpensive

Main application:• Spectroscopy

Applications: Sensing• Strong transitions at fundamental frequencies• Molecular fingerprints • MIR – ro-vibrational transitions (all material states)• FIR – rotational transitions (gasses, liquids)• FIR – collective vibrational modes (solids)

Sensing (monitoring) requirements:• Several fixed (tunable) wavelengths• Narrow linewidth: ~GHz or less• High power and high brightness for DIAL and countermeasures

Applications: Proteomics

[T.J.Johnson et al Chem.Phys.Lett. 403, 152 (2005)][C. Kötting et al Proc.Nat.Acad.Sci. 103, 13911 (2006)]

• Label-free• Site specific information• Time resolved protein reactions

Spores of B. thuringiensis ssp. kurstaki and B. subtilis 49760

Applications:Imaging, Inspection

Fuel tank of Schuttle launch rocket behind foam

THz stress-induced birefringence imagingCarbon-fiber composite helicopter stator

[M.Koch, OPN, 18,21 (2007)]

[Picometrix, Inc.]

• Dielectric solids: no rotational DoFs• Transparent in FIR• Low scattering losses

Applications: Fuel industry

[M.A. Aliske et al Fuel, 86, 1461 (2007)]

Applications:Surgical

MIR lasers: • High H2O absorption• Less tissue-specific• Smaller heated volume• Lower collateral damage

Applications:SurgicalDefficiencies of current procedures

[A.Vogel et al Chem.Rev. 103, 577 (2003)]

Laser induced shock-wave effect on waterEr:YAG 100 ns, 50 MW/cm2 Shock-wave damage

Applications: Detection of explosives

Applications: XUV and as pulse generationAtom in high optical field: Tunnel ionization , classical axceleration in electric field

XUV photon cutoff energy: 20

2

17.3~17.3

EIUI pppXUV Ionization potential + Ponderomotive energy

High intensity (ultrashort) in MIR are advantageous

[M. Levenstein et al, PRA, 49, 2117 (1994)]

Applications: XUV and as pulse generation

[R. Kienbergeret al Nature, 427, 817 (2004)]

• CEP phase-stabilized pulses required• Currently all-passive CEP stabilization by (2):(2) or (3) NLO processes

State of the art: QCL

[B. S. Williams, Nature Photonics, 1, 517 (2007) ]

Main breakthroughs:• Resonant optical-phonon depopulation• Metal-metal waveguides

1THz ~ 4.1 meV ~ 47.6 K hphonon ~ 30meV

State of the art: Solid state lasersEngineering toolbox:• Crystal field – Tailorable transition energies• Structural disorder - inhomogeneous broadening – Gain spectral width (fs)• Phonon Spectrum – thermal conductivity, nonratiative lifetime• Growth technologies – size, cost • Coating technologies – damage threshold• Laser diode technology – reliability, power, new materials (1.9µm InGaAsSb/GaSb)

MIR high power (W-kW) laser options:CO2 – 10µmCO - 5µmEr3+ - 3µmCr2+ – 2.2 -2.8 µmHo3+ - 2.1 µmTm3+ - 1.85µm – 2.1 µm

Beyond state of the art: New SSL materials

Main search strategy:• Low phonon energy materials• Enhanced transparency in MIR

Generic formula: Re3+:MePb2Hal5

Re=Pr, Nd, Er, Tb, Dy, HoMe=K,RbHal=Cl, Br

Transparency regions:KPb2Cl5 0.4 µm – 20 µmKPb2Br5 0.4 µm – 30 µmRbPb2Br5 0.37 µm – 30 µm

Nonlinear optical sourcesCharacteristics:• Tunable – depends on nonlinear material• No quantum defect – High peak and average power• From CW to fs • High efficiency

DFGOPA

OPO

spi

isp

Nonlinear optical materials for MIR, FIRRequired and Desirable properties:

• High transmission at pump wavelength around 1µm• Absence of two-photon absorption at pump wavelength • High transmission in MIR• High nonlinearity• High optical damage threshold• Engineerability (QPM structuring or composition variation)• Non-hygroscopic• Feasibility of large-volume crystal growth

Main classes of MIR, FIR NLO materials:• Oxides: KTiOPO4 (KTP), RbTiOPO4 (RTP), LiNbO3, LiTaO3...

Engineerable, can be pumped in NIRMIR Transmission limited to ~4 µm, 80µm - 300µm

• Semiconductors: GaAs, GaP, ZnGeP2 (ZGP), AgGa1−x InxS2, ...MIR tranmission to 20 µm, FIR 60µm – 300 µmAbsorbing at 1 µm

• Organic: 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium tosylate (DAST)Very high nonlinearity 30xKTP, good MIR, FIR transmissionVery difficult to grow, Hygroscopic

Engineerable nonlinear optical materialsOP-GaAs (Stanford)

PP-KTP (KTH) period 800 nm, over 5 mm

[L.A.Eyres et al APL, 79, 904 (2001)]

[C. Canalias et al Nature Photonics,1, 459 (2001)]

State of the art: OPOs

20 40 60 80 100 120 140 160 180

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

3.2

3.4

38.2 m 37.8 m

37.4 m

36.4 m36.0 m

S

igna

l / Id

ler w

avel

engt

h (

m)

Temperature (°C)

35.4 m

PP-RbTiOPO4

High-energy ns tunable OPO

[A.Fragemann, Optics Lett., 83, 3092 (2003)]

State of the art: OPOs

Cascaded PPKTP – ZGP OPO for active countermeasures

[M.Henriksson, Appl. Phys.B, 88, 37 (2007)]

Beyond state of the art: OPO

Surgical ns OPO at 6.45 µm and 6.1 µm

Target: Peak power 0.5 MW, average power 1W

1000 2000 3000 4000-30

-20

-10

0

p=827nm, =28µm

Pow

er, l

og s

cale

Wavelength , nm

[M.Tiihonen, etal, Appl. Phys. B, 85, 73 (2006)]

State of the art: OPAs

Optical parametric amplifiers for ultrashort pulses

[P.S.Kuo, etal, Optics Lett., 31, 71 (2006)]

PP-KTP OPA (KTH) OP-GaAs (Stanford)

FWHM 115 THz (~1 octave)1.08 µm - 3.8 µm

Beyond state of the art: Near-field MIR-FIR• MIR, FIR polariton optics in ferroelectrics• Tailoring polaritonic FIR waves with photonic crystals • Functionalized surfaces • Sub-wavelength sensing

[K. A. Nelson etal Nature Materials, 1, 95 (2002)][J. Faist, etal Optics Express, 15, 4499 (2007)]