Perspectives for 3D THz cameras. P. Haring Bolívar Institut für Höchstfrequenztechnik und Quantenelektronik Universität Siegen

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1 Perspectives for 3D THz cameras P. Haring Bolívar Institut für Höchstfrequenztechnik und Quantenelektronik Universität Siegen

2 Outline THz Applications, Past and Present Astronomy and earth sensing Gas and plasma diagnostics Material analysis and device characterization Medical imaging and sensing Biomolecular, chemical analysis Potential security applications Industrial process monitoring THz technology Electronic THz technologies Optical THz technology Recent developments Conclusions

3 The THz frequency range ν = 300 GHz 10 THz λ = 1mm 30µm k = 10cm cm -1 the most scientifically rich, yet most underutilized region of the electromagnetic spectrum T. Crowe, NATO ASI, Chateau de Bonas (2000)

4 Astronomy / remote sensing THz waves are crucial for astronomy: 50% of luminosity and 98% of photons emitted since the big bang are THz. CO emission at 345GHz D. Leisawitz et al.,, Proc. SPIE, 4013, Black body emission in the 4K.. 100K range peaks at THz wavelengths CMB peaks at GHz Sharp THz gas lines => imaging of composition, temperature, reactions, motion, (e.g. galaxy formation). THz can penetrate dark clouds

5 Gas/Plasma monitoring Cheville and Grischkovsky, OL 20, 1646 (1995). D.M. Mittleman, et al., IEEE J. Sel. T. Quant. Electr. 2, 679 (1996).

6 Imaging of semiconductors Wafer inspection (layer thickness, doping, mobility, ) SiC epilayer Dicke (µm) 9.0 Y-Koordinate (mm) Brucherseifer, et al (RWTH Aachen) X-Koordinate (mm) 6.5 Transillumination (packaging control) Nuss et al (Lucent)

7 Tumor detection (skin) Determine lateral extent of tumor (basal cell carcinoma) on and below surface cw THz image (dog tumor) Visible Image R.M. Woodward, et al. J. of Biol. Phys. 29, 257 (2003). Löffler et al, Phys. Med. Biol (2002)

8 Biomolecular sensor arrays Label-free DNA probing with femtomol sensitivity Nagel et al. Appl. Opt. 41, 2074 (2002). Single base mutation detection Single base mutation detection Nagel et al. APL 80, 154 (2002) DNA-capture probe Patient-DNA Linker molecule Linker-ACA CTG TGC CCA TCT ACG AG TGT GAC ACG GGT AGA TGC TC

9 Security Security screening with nonionizing radiation motivates efforts. Example: passive imaging at mm-waves. Interest in higher resolution images motivates THz efforts e.g. mm-wave image R. Abbleby, et al. (QinetiQ) e.g. THz image (RAL)

10 Security II II chemical identification THz radiation seems to enable the detection of chemicals and bioagents, e.g. screening of drugs of abuse, including automatic recognition by multispectral THz analysis (Kawase et al, Opt. Expr. 11, )

11 Security III - explosives Publications indicate that terahertz spectroscopy can identify explosives, nevertheless controversial discussions remain. Data Datacourtesy courtesyteraview TeraviewLtd, Ltd, UK UK D.J. D.J. Funk Funk et et al, al, CLEO CLEO

12 Industrial process control, e.g. 3D imaging THz tomography polarizers x-coordinate (mm) E-Field (a.u.) surface 2 Laser source (100 fs) THz emitter parabolic mirrors THz pulse THz detector antenna sample (x-y movable) time (ps) boundary layer thickness 0.2 time delay shaker -0.6 Dicke (µm) Application example: characterization of (ceramic) solid oxide fuel cells Y-Koordinate (mm) M. Brucherseifer, et al., Appl. Phys. B (2000) X-Koordinate (mm) 23

13 Process monitoring & quality control Dark field THz system for detection of mm to micron dents and protrusions on steel. Hasegawa, et al. APL 83, 3996 (2003) Non destructive testing of composite materials, e.g. delamination of space shuttle isolation Courtesy: X.C. Zhang (Rensselaer)

14 Pharmaceutical sensing THz radiation can be used to monitor active component content in pharmaceuticals Teraview (UK) P.F. Taday, Phil. Trans. Roy. Soc. A (2004)

15 Widespread application fields Astronomy e.g. microwave backgroud, interstellar clouds,... Earth sensing e.g. atmospheric chemistry (ozone, trace gas,...), climate,... Medical e.g. tumor or caries recognition Biotech e.g. genetic & proteomic sensing, biochips Tumor Fat Connective tissue Tooth decay THz imaging & sensing t /t 0,3 0,2 0,1 denatured (sample A) hybridized (sample B) hybridized (sample C) 0,0 0,5 1,0 1,5 2,0 frequency (THz) Industrial e.g. package inspection, process control Security e.g. drug & explosives detection DNA MDMA 3D imaging Non-destructive fuel-cell film analysis aspirin Amphetamine

16 Outline THz Applications, Past and Present Astronomy and earth sensing Gas and plasma diagnostics Material analysis and device characterization Medical imaging and sensing Biomolecular, chemical analysis Potential security applications Industrial process monitoring THz technology Electronic THz technologies Optical THz technology Recent developments Conclusions

17 THz technology drivers Electronic sources (higher ν) Laser (longer λ) T. Crowe, THz sources and systems (2000) R. Köhler et al., Nature 417, 156 (2002)

18 Electronic THz technologies Overview: P. H. Siegel, IEEE Trans. Microw. Theor. & Techn. 50, 910 (2002) Motivated by astronomy and earth sensing missions, electronic THz or sub-millimeter technologies have been developed since the late 50 s. Traditional concept is mixing, but transistors might soon enter the field. Whisker contacted Schottkydiodes(Erlangen) HBV (Lille, Chalmers) IBM s SiGe HBT, f T =350GHz (Rieh, et al, IEDM 2002)

19 Fs-laser based THz technology Pioneers: Auston, Nuss, Grischkowsky and Zhang Wiederholrate Fernsehbild ISDN Bandbreite PC clock, Optische Mobilfunk Netze fs-laserpulses 1Hz 1kHz 1MHz 1GHz 1THz 1PHz 1s 1ms 1µs 1ns 1ps 1fs 1 / / / / / s s s s s Femtosecond lasers (1fs = s, c 1fs = 0,3 µm) have enabled since the 90 s the rapid development of the most flexible THz techniques 11 fs Bartels, et al OL 24, 996 (1999)

20 Femtosecond laser based THz imaging systems 3D imaging systems are available BUT cost is prohibitevely high for many applications

21 Quantum Cascade Lasers (QCL) quantum cascade laser design R. Köhler et al., Nature 417, 156 (2002) Potentially, much cheaper imaging systems could be enabled by QCL State of the art: Min. freq. 2.8 THz Max. temp. 137K Power >20mW

22 Cw-Photomixer Sources/detectors Vϕ traveling fringes E Backplane metallisation electrode photoconductor LT - InGaAs ground plane radiating aperture for THz signals THz Substrate photo-mixer and spiral antenna (Lille) Photomixing enables broadly tuneable THz systems at reduced cost Power generated is still limited (2µW at 1 THz), but new concepts could relieve problems First spectrometers and imaging systems have been demonstrated Dual frequency laser Photo-mixer antenna THz Brown, et al., APL 64, 3311 (1994). (MIT) (also work in Lille, Frankfurt, Braunschweig, )

23 MSM transducers MSM tranducers are already standardly used in THz technology Auston, et al, APL 45, 284 (1984) 3 voltage (a.u.) fs time (ps) Nanocluster in GaAs