1. OUTLINE Introduction „Tera-to-Nano“: Our Novel Near-Field Antenna 80 GHz CW Frequency Domain Measurements Picosecond Pulse Time Domain Measurements 2D Scans Summary and Outlook Institute of Physics Czech Academy of Science WIRMS 2005, Rathen, June 26-30, 2005

2. We present an antenna-based approach to near-field imaging and spectroscopy, which can be used for both continuous-wave and pulsed broadband electromagnetic radiations from microwave to terahertz frequencies. Our near-field antenna consists of a rectangular-shaped block of low-loss dielectric material sharpened to a pyramidal tip which is partially metallized and terminated by a micron-sized plane facet. At this facet the entire energy of the incident wave is concentrated as a very high but strongly localized electric field, which can be used as a sensitive near- field microprobe for electromagnetic radiation. Currently, experiments in reflection geometry with pulsed terahertz radiation and continuous-wave radiation near 80 GHz reveal a frequency-independent spatial resolution of about 20 µm corresponding to /200 at 80 GHz, which is only limited by the size of the facet terminating the tip. We present an antenna-based approach to near-field imaging and spectroscopy, which can be used for both continuous-wave and pulsed broadband electromagnetic radiations from microwave to terahertz frequencies. Our near-field antenna consists of a rectangular-shaped block of low-loss dielectric material sharpened to a pyramidal tip which is partially metallized and terminated by a micron-sized plane facet. At this facet the entire energy of the incident wave is concentrated as a very high but strongly localized electric field, which can be used as a sensitive near- field microprobe for electromagnetic radiation. Currently, experiments in reflection geometry with pulsed terahertz radiation and continuous-wave radiation near 80 GHz reveal a frequency-independent spatial resolution of about 20 µm corresponding to /200 at 80 GHz, which is only limited by the size of the facet terminating the tip.

3. new approach Mode converter: Linear polarized plane wave  dielectric waveguide mode  stripline type mode  bipolar capacitor near field „Tera-to-nano“: A novel near-field antenna 1 mm E k flat output facet with partial metallization N. Klein et al, published in Journal of Applied Physics, July 2005 A broadband metal-dielectric near-field antenna

4. „Tera-to-nano“: A novel near-field antenna Manufacturing of NFAs high-resistive silicon or sapphire needles prepared by mechanical polishing (by J. Fryštacký, FZU) partial metal coating by a highly directed ultrahigh vacuum deposition method like electron beam evaporation (by H. Wingens, FZJ) 40  m N. Klein et al, to be published in Journal of Applied Physics, July 2005

5. „Tera-to-nano“: our novel near-field antenna NFA converts the fundamental mode of a dielectric waveguide into a stripline-type mode low losses and high confinement in 3 dimensions due to combination of metal guiding and total reflection wave reflection mainly at the end of the tip due to constant wave impedance along the NFA broadband operation due to low waveguide dispersion very high electric field at the tip proportional to 1 / d Numerical field simulations (CST Microwave Studio) N. Klein et al, to be published in Journal of Applied Physics, July 2005

6. Tera-to-nano: our novel near-field antenna Numerical field simulations (CST Microwave Studio)

7. 80 GHz CW Frequency Domain Measurements Resonant waveguide coupling

8. 80 GHz CW Frequency Domain Measurements properties of sample alter frequency and Q factor of standing wave resonance fast (millisecond) detection by recording amplitude and phase of reflected signal at a selected frequency resonance should allow for independent detection of real and imaginary part of dielectric constant (conductivity) N. Klein et al, to be published in Journal of Applied Physics, July 2005

9. Picosecond Pulse Time Domain Measurements spatial resolution about 17  m for both scanning directions slightly assymmetric response function due to non-perfect geometry Test of spatial resolution of a 40 x 40  m 2 NFA by a patterned metal film 1 mm line 30  m lines separated by 30  m gaps

10. Picosecond Pulse Time Domain Measurements Experimental setup THz spot size in our current time-domain setup: 3 mm N. Klein et al, to be published in Journal of Applied Physics, July 2005

11. Picosecond Pulse Time Domain Measurements Experimental setup

12. Picosecond Pulse Time Domain Measurements reflected pulse yields spectroscopic information on the sample properties total integrated power of reflected pulse is about 10 % of incident pulse multiple echoes are likely caused by the launcher  novel setup with spot size of 1 mm under construction („TERASCOPE v1“) N. Klein et al, to be published in Journal of Applied Physics, July 2005

13. 2D Scans scanning speed about 40  m / s at one frequency control of tip-sample distance by an optical microscope scanning setup by U. Poppe, FZJ

14. 2D Scans resolution test: scan over 1 mm metal stripe and an array of 30  m wide stripes separated by 30  m wide gaps N. Klein et al, to be published in Journal of Applied Physics, July 2005

15. 2D Scans Water distribution in plant leafs at 80 GHz NFA with 100  m resolution NFA with 20  m resolution

16. 2D Scans Doping by ion implantation 5 keV, 10 15 / cm 2 arsenic,  30 nm doped layer doping level before implantation: 10 15 /cm 3 doping level after implantation: 10 19 /cm 3 sample provided by E. Rije, FZJ

17. OUTLINE Introduction „Tera-to-Nano“: Our Novel Near-Field Antenna 80 GHz CW Frequency Domain Measurements Picosecond Pulse Time Domain Measurements 2D Scans Summary and Outlook Institute of Physics Czech Academy of Science WIRMS 2005, Rathen, June 26-30, 2005

18. Summary and Outlook Summary First nearfield approach with bandwidth from DC to several THz Near field antenna provides almost complete conversion of a THz wave into a strongly localised quasistatic field Resolution of / 200 demonstrated for f = 80 GHz 2D imaging feasible

19. Summary and Outlook Next steps Deconvolution of complex dielectric function for resonant CW mm wave experiments Deconvolution of broadband THz spectra from pulsed time domain measurements Realization of TERASCOPE V1 Realization of a coaxially coupled low-frequency nearfield setup from 0 to 40 GHz Optimization of NFA preparation including submicron NFAs

20. Summary and Outlook Potential applications Subcell resolution tissue imaging THz spectroscopy on single cells THz spectroscopy on single molecules Contact - free spectroscopic imaging of ferroelectric domains Fingerprint detection of very small amounts of hazardous substances Spatially resolved pump-probe experiments Water inclusion in minerals