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WIRMS 2005, Rathen, June 26-30, 2005
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

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 nearfield 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.
„Tera-to-nano“: A novel near-field antenna
A broadband metal-dielectric near-field antenna
E
flat output facet
with partial
metallization
k
1 mm
new approach
Mode converter:
Linear polarized plane wave  dielectric waveguide mode 
stripline type mode  bipolar capacitor near field
N. Klein et al, published in Journal of Applied Physics, July 2005
„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
„Tera-to-nano“: our novel near-field antenna
Numerical field simulations (CST Microwave Studio)
• 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
N. Klein et al, to be published in Journal of Applied Physics, July 2005
Tera-to-nano: our novel near-field antenna
Numerical field simulations (CST Microwave Studio)
300
|E| [KV/m]
250
n=14, f0=63.608 GHz
n=13, f0=61.205 GHz
200
150
100
50
0
0
2
4
6
8
10
12
position on the sample [mm]
14
80 GHz CW Frequency Domain Measurements
Resonant waveguide coupling
sample
NFA
10dB directional
coupler
mm-wave
source
~
crystal
detector
80 GHz CW Frequency Domain Measurements
0
Vaccum (Air)
Conductive (Copper)
Water (Wet Paper)
Dielectric (Sapphire Substrate)
-27
-20
Pout [dBm]
S11 [dB]
-10
ca 3 GHz
-28
-29
-30
40
50
60
70
f [GHz]
80
90
100
110
85,6
85,8
f [GHz]
86,0
86,2
• 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
Picosecond Pulse Time Domain Measurements
Test of spatial resolution of a 40 x 40 m2 NFA by a
patterned metal film
1 mm line
30 m lines
separated by
30 m gaps
• spatial resolution about 17 m for both scanning directions
• slightly assymmetric response function due to non-perfect
geometry
Picosecond Pulse Time Domain Measurements
Experimental setup
sample
NFA
wire grid
polarizer
horn
launcher
reflected
pulse
incident
pulse
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
Picosecond Pulse Time Domain Measurements
Experimental setup
Picosecond Pulse Time Domain Measurements
THz electric field (arb. u.)
6
4
free space
metal
substrate
reference
5 ps
2
0
-2
-4
79
80
Time (ps)
81
• 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
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
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
2D Scans
Water distribution in plant leafs at 80 GHz
NFA with 100 m resolution
NFA with 20 m resolution
2D Scans
Doping by ion implantation
5 keV, 1015 / cm2 arsenic,  30 nm doped layer
doping level before implantation: 1015 /cm3
doping level after implantation: 1019 /cm3
sample provided
by E. Rije, FZJ
WIRMS 2005, Rathen, June 26-30, 2005
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
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
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
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