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 PhysicsCzech Academy of Science

WIRMS 2005, Rathen, June 26-30, 2005

WIRMS 2005, Rathen, June 26-30, 2005

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

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 facetwith partialmetallization

N. Klein et al, published in Journal of Applied Physics, July 2005

A broadband metal-dielectric near-field antenna

„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

• 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

Tera-to-nano: our novel near-field antenna

Numerical field simulations (CST Microwave Studio)

0 2 4 6 8 10 12 140

50

100

150

200

250

300

n=14, f0=63.608 GHz

n=13, f0=61.205 GHz

|E| [

KV

/m]

position on the sample [mm]

80 GHz CW Frequency Domain Measurements

Resonant waveguide coupling

sample NFA mm-wave

source

crystal detector

10dB directional coupler

~

80 GHz CW Frequency Domain Measurements

85,6 85,8 86,0 86,2

-29

-28

-27

Vaccum (Air) Conductive (Copper) Water (Wet Paper) Dielectric (Sapphire Substrate)

Po

ut [

dB

m]

f [GHz]

• 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

40 50 60 70 80 90 100 110

-30

-20

-10

0

ca 3 GHz

S11

[dB

]

f [GHz]

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 m2 NFA by a patterned metal film

1 mm line 30 m lines separated by 30 m gaps

Picosecond Pulse Time Domain Measurements

sample NFA

horn launcher

wire grid polarizer

reflected pulse

incident pulse

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

Picosecond Pulse Time Domain Measurements

Experimental setup

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“)

79 80 81Time (ps)

6

4

2

0

-2

-4

TH

z el

ectri

c fie

ld (a

rb. u

.)

free spacemetalsubstratereference

5 ps

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

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 PhysicsCzech Academy of Science

WIRMS 2005, Rathen, June 26-30, 2005

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