Advances in mid and far infrared coherent sources and their applications

1. Advances in mid and far infrared coherent sources and their applications Valdas Pasiskevicius Applied Physics, KTH

2. Outline • Spectral ranges • Application areas • Radiation sources: • coherent vs incoherent • MIR, FIR coherent sources: • technology options • Developments at KTH • Beyond state of the art

3. Spectral ranges MIR: = 2 µm – 30 µm (150 THz – 10 THz) Cr2+, Fe3+

4. Spectral ranges FIR: = 300 µm – 30 µm (0.1 THz – 10 THz)

5. Options: coherent vs incoherent • Advantages of coherent sources: • High power • High spectral power density • High brightness • High wall-plug efficiency • Benefiting Applications: • All except simple spectroscopy [G. P. Williams, Rev. Sci.Instr. 73, 1461 (2002)] • Advantages of incoherent sources: • Broad range • Inexpensive • Main application: • Spectroscopy

6. 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

7. Applications: Proteomics • Label-free • Site specific information • Time resolved protein reactions Spores of B. thuringiensis ssp. kurstaki and B. subtilis 49760 [C. Kötting et al Proc.Nat.Acad.Sci. 103, 13911 (2006)] [T.J.Johnson et al Chem.Phys.Lett. 403, 152 (2005)]

8. Applications:Imaging, Inspection Fuel tank of Schuttle launch rocket behind foam • Dielectric solids: no rotational DoFs • Transparent in FIR • Low scattering losses THz stress-induced birefringence imaging Carbon-fiber composite helicopter stator [Picometrix, Inc.] [M.Koch, OPN, 18,21 (2007)]

9. Applications: Fuel industry [M.A. Aliske et al Fuel, 86, 1461 (2007)]

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

11. Applications:Surgical Defficiencies of current procedures Laser induced shock-wave effect on water Er:YAG 100 ns, 50 MW/cm2 Shock-wave damage [A.Vogel et al Chem.Rev. 103, 577 (2003)]

12. Applications: Detection of explosives

13. Applications: XUV and as pulse generation Atom in high optical field: Tunnel ionization , classical axceleration in electric field XUV photon cutoff energy: Ionization potential + Ponderomotive energy [M. Levenstein et al, PRA, 49, 2117 (1994)] High intensity (ultrashort) in MIR are advantageous

14. 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

15. State of the art: QCL 1THz ~ 4.1 meV ~ 47.6 K hphonon ~ 30meV • Main breakthroughs: • Resonant optical-phonon depopulation • Metal-metal waveguides [B. S. Williams, Nature Photonics, 1, 517 (2007) ]

16. State of the art: Solid state lasers • Engineering 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 – 10µm CO - 5µm Er3+ - 3µm Cr2+ – 2.2 -2.8 µm Ho3+ - 2.1 µm Tm3+ - 1.85µm – 2.1 µm

17. 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, Ho Me=K,Rb Hal=Cl, Br Transparency regions: KPb2Cl5 0.4 µm – 20 µm KPb2Br5 0.4 µm – 30 µm RbPb2Br5 0.37 µm – 30 µm

18. Nonlinear optical sources • Characteristics: • Tunable – depends on nonlinear material • No quantum defect – High peak and average power • From CW to fs • High efficiency DFG OPA OPO

19. Nonlinear optical materials for MIR, FIR • Required 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 NIR • MIR Transmission limited to ~4 µm, 80µm - 300µm • Semiconductors: GaAs, GaP, ZnGeP2 (ZGP), AgGa1−xInxS2, ... • MIR tranmission to 20 µm, FIR 60µm – 300 µm • Absorbing at 1 µm • Organic: 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium tosylate (DAST) • Very high nonlinearity 30xKTP, good MIR, FIR transmission • Very difficult to grow, Hygroscopic

20. Engineerable nonlinear optical materials OP-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)]

21. State of the art: OPOs High-energy ns tunable OPO PP-RbTiOPO4 [A.Fragemann, Optics Lett., 83, 3092 (2003)]

22. State of the art: OPOs Cascaded PPKTP – ZGP OPO for active countermeasures [M.Henriksson, Appl. Phys.B, 88, 37 (2007)]

23. 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

24. State of the art: OPAs Optical parametric amplifiers for ultrashort pulses OP-GaAs (Stanford) PP-KTP OPA (KTH) [P.S.Kuo, etal, Optics Lett., 31, 71 (2006)] [M.Tiihonen, etal, Appl. Phys. B, 85, 73 (2006)] FWHM  115 THz (~1 octave) 1.08 µm - 3.8 µm

25. 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)]