Monitoring the plant water status with terahertz waves

Transcription

1 Monitoring the plant water status with terahertz waves Dr. Gunter Urbasch Experimental Semiconductor Physics AG Martin Koch

2 Fachbereich Physik Experimentelle Halbleiterphysik Arbeitsgruppe M. Koch Gunter Urbasch

3 Philipps-Universität Marburg Fachbereich Physik

4 Experimentelle Halbleiterphysik Arbeitsgruppe M. Koch (and several colleagues) at 4 th Terahertz workshop on Elba (2012)...thanx

5 Experimentelle Halbleiterphysik Arbeitsgruppe M. Koch main topics of interest ultrafast spectroscopy of semiconductor nanostructures development of semiconductor disk lasers terahertz systems and their applications

6 Electromagnetic TeraHertz (THz) radiation visible radio waves micro waves THz infrared ultraviolet Röntgen frequency (Hz) high frequency microwaves THz extreme far infrared light

7 Electromagnetic THz radiation visible radio waves micro waves THz infrared ultraviolet Röntgen frequency (Hz) frequency 0.1 THz - 10 THz photon energy 0.4 mev - 41 mev wavelength 3000 µm - 30 µm wavenumber 3.3 cm cm -1

8 First demonstration of imaging THz spectroscopy water content fresh leave 48 h after cutting the leave Bell Labs Lucent Technologies B.B. Hu and M.C. Nuss, Opt. Lett. 20(1995)1716

9 First THz monitoring of rehydration Coleus 30 Before watering % transmission After watering hours position (mm) Relative % transmission Bell Labs Lucent Technologies Time (minutes) D. Mittleman et al., IEEE Journal of Selected Topics in Quantum Electronics 2(1996)679

10 Water status of plants 90 Coffea arabica Transmission transmission (%) (%) measured Messwerte Trendlinie Tage nach Wassergabe days after watering THz transmission - close-to-real-time information about hydration and dry stress non-destructive water supply - intelligent irrigation strategies for plant breeding industry C. Jördens et al. monitoring for selective cultivation JBiologicalPhysics35(2009)255

11 but not only in the lab plants live outside

12 Pulsed THz spectroscopy

13 Laboratory setup THz time domain spectroscopy (THz TDS) beam splitter femtosecond laser pulse sample lens lens emitter detector delay line

14 THz TDS spectrometer substrate + lens collimating & focusing optics photoconductive antenna gating t pulse gating fs pulse photoconductive antenna (THz emitter) THz beam y x THz receiver THz field w/o tip with tip x70 near-field tip sample t (ps)

15 Imaging - raster scanning sample sample scanned through focus for every pixel time transient collected and processed integrated transmission over frequency window gives image pixel value typically image takes some time

16 Das Bild kann zurzeit nicht angezeigt werden. Das Bild kann zurzeit nicht angezeigt werden. Emission and detection of THz pulses silicon lens THz pulse incoming THz pulse optical pulse dipole antenna V b optical pulse I dipole antenna

17 Fiber coupled THz antennas Antenna chip Glue Glass fiber Electr. contacts N. Vieweg et al. SPIE 6616, Munich (2007) N. Krumbholz et al. PolymerTesting28(2009)30

18 Harsh environment need for fiber based system fs fiber laser transmitter unit sample (leaf) receiver unit delay unit HDPE lenses

19 Signal processing

20 Signal processing fundamental FFT time domain (THz pulse) Frequenzbereich frequency domain Fotostrom current I I / / na na 2,5 2,0 1,5 1,0 0,5 0,0-0,5 Referenz reference Probe sample Amplitude amplitude (willk. / arb. units Einheit) 10 Referenz reference Probe sample 1 0,1 0, ,0 0,5 1,0 1,5 2,0 2,5 3,0 time Zeit t / t ps / ps dielectric properties of sample Frequenz frequency f / f THz / THz n n i c 0 4 phase difference refractive index n(f) d ratio of amplitudes absorptions coefficient α(f)

21 Signal processing - advanced software commercially available The Tera Lyzer simultaneous extraction of thickness and optical parameters multi-layer analysis possible versatile time preprocessing features

22 THz transmission through water film 300 Absorption coefficient (cm -1 ) ,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,1 Transmission (%) Frequency (THz) Water film thickness ( m) cannot penetrate water film thicker than few 100 µm attenuation depends on frequency

23 Monitoring the plant water status Coffea arabica refractive index absorption f = 0.3 THz

24 Monitoring the plant water status inside the lab - works well Coffea arabica THz Transmission [%] Loss of water [%] (thermogravimetrically) time without watering [d ] C. Jördens et al. JBiologicalPhysics35(2009)255

25 Drought stress of oilseed rape (Brassica napus L.) Transmission moment of irrigation 0.50 light on light off Days after last irrigation

26 Water content analysis based on a physical model leaf consists of dry plant material + water + air effective medium theory (EMT) optical properties result from volume contents + thickness + surface scattering C. Jördens et al. JBiologicalPhysics35(2009)255 nonlinear optimization to get water content

27 Lets go outside the lab! computer controlled all fiber based THz TDS spectrometer inside rack with handheld sensor head

28 outside the lab it works! barley 100 rel. water content (grav. %) EMT-model gravimetric measurement drying time (min) deviation (%) drying time (min)

29 Application of a further system inside greenhouse

30 Sub-THz system the idea of the chef

31 Sub-THz system and what comes out 60 GHz emitter 35 GHz detector light source camera 35 GHz emitter 60 GHz detector

32 Sub-THz system Wassergehalt / g Kontrollgruppe Stress Null Kontrollgr. (grav.) Stress (grav.) Null (grav.) Zeit / Tage water content of barley plants vs time watered in different ways red: sub-thz measurements black: gravimetric measurements

33 Monitoring the plant water status with THz waves THz radiation senses through many opaque materials non-destructive and contactless sensing spatial resolution in the range of mm high sensitivity for water (inside plants) nearly ready for commercialization Thank you for your attention! Special thanks to Norman Born, Ralf Gente, Michael Schwerdtfeger, and Nino Voß