THz-BRIDGE progress report
(Period from February 1 to June 30 2001)
The activity of the first five months of the project has been focussed on the investigation of suitable
optical materials to be used as spectroscopic cells for the various samples, as well as on the design
of the irradiation set-up for the investigation of potential damage induced on human lymphocytes.
In the following the progress of the activity is described for the infrastructure available at the
various partner sites and for the individual work-packages of the project.
THz sources and infrastructure development
ENEA:
 After a three-month stop due to a failure in the vacuum system, which required major repairs,
the Compact FEL turned back into operation late in May.
 A new type of emitting device, exploiting the interaction of an electron beam passing close to
the surface of a metal grating (Smith-Purcell effect), has been tested on the FEL beam line.
Although its output power is limited to 10 mW in 4 s pulses, this device can be easily tuned
over a wide spectral range (700 m to 4mm) and can be used for calibration purposes.
FZR:
 The ELBE superconducting accelerator at Rossendorf produced the first electron beam up to 17
MeV, which later this year will be injected into the undulator U27 to produce FEL radiation in
the range of 8 - 20 THz.
 The undulator is in place and its magnetic properties have been checked after its transport from
DESY Hamburg to still match the requirements for lasing.
 The beam line to transport the THz-radiation to the proper laboratories is under construction. Its
design is based on focussing the radiation simultaneously in x and y by using toroidal mirrors
tilted by 45 degrees with respect to the beam axis.
 The THz laboratory is presently equipped with a spectrometer and detectors needed to
characterise the radiation properties. Parallels to the preparation of the irradiation area two cell
laboratories are now in operation, one of which is very close to the FEL. In the other one a
FTIR-spectrometer is operating for a first characterisation of the probes before the much more
sensitive investigations with the FEL. In a first series of measurements different plastic
materials were studied with respect to their suitability as a container material for the cells during
THz and IR absorption measurements.
TAU:
 The Tandem–FEM at TAU was reassembled with a newly installed mm-wave transport system
permitting transport of a high power beam out of the accelerator.
 The accelerator is presently in a “Voltage Conditioning” stage, a necessary step before e-beam
transport and lasing.
 Design of the radiation transport line from the accelerator to the user room has been completed.
Main components (corrugated waveguides) have been purchased (with independent funding).
TREL:
 Progress at Teraview has been made on setting up a broadband time-domain spectroscopy
system. Broadband THz emission has been achieved up to about 10 THz as measured with a Sicomposite bolometer detector and home-built interferometer set-up. The laser source was a 12fs Ti:sapphire (from FemtoLasers) and a with reverse bias GaAs p-i-n photodiode as the THz
emitter. Details of the experimental set-up are available to partners on the project web-page.
 Other methods of detecting the broadband THz emission from the diode, such as electro-optical
sampling (EOS) will be investigated. This will allow time-domain spectroscopy to occur and
remove the requirement for the use of cryogenic liquids.
WP-1 (Spectroscopy of proteins, enzymes, biological membranes, and selected cells)
The design of a standardised spectroscopic chamber has been discussed between the various groups
involved in WP-1. Following the experience of UFRANK on the spectroscopy of proteins and
enzymes diluted in a thin layer of aqueous solution, the “model chamber” will have the typical
design shown in the following picture.
The chamber has a circular symmetry, 25 to 40 mm in diameter, with a draught milled in the bottom
plate to allow for the flow of the aqueous solution when the top plate is pressed against the Mylar
spacer, without inducing any strain on the sample. The bottom and top plates are made of a suitable
material, as discussed below, transparent in the frequency range of interest. The typical thickness of
the plates is of the order of 1 mm.
At long wavelengths the material chosen to build such a cell is polystyrene, which exhibits excellent
optical properties in the wavelength range between 200 m and 3 mm (frequency range 1.5 THz to
100 GHz)1. Other materials like Zapphire, ZnSe and ZnTe can be used at shorter wavelengths.
Specific measurements have been carried out on commercial plasticware at ENEA-Frascati and at
the University of Stuttgart by measuring both the transmission and the complex dielectric constant
over a wide spectral range (see below).
Further spectroscopic investigations will be performed on other container materials (polypropylene,
Teflon, LiTaO3 etc.). During a meeting held at Frankfurt on June 18-19, representatives of ENEA,
FZR, UFRANK and USTUTT discussed with the biomedical company ELTE’ (a subcontractor of
UFRANK) the requirements for conducting spectroscopic measurements on blood serum, plasma
and its individual constituents.
1
The Infrared Handbook – W.L. Wolf, G.J. Zissis – Infrared Information Analysis Center, Michigan 1989
WP-2 : Evaluation of biological effects in vitro after exposure to THz-radiation
WP-2.1 (DNA bases and human lymphocytes)
Preparation of Biological Samples
Conditions for the possibility of long term intermittent exposure of human lymphocytes to the THz
radiation have been studied at TAU. The analysis of the number of metaphases in blood cultures,
maintained for 10 days, is under way.
Development of an Exposure set-up
The relevant parameters for the design of the exposure set-up have been determined by ENEA,
ICEmB and TAU. The penetration depth of radiation at  = 100GHz into a water suspension of
lymphocytes will be very short (in distilled water 1/ = 0.13 mm based on L. Thrane et
al./Chemical Physics Letters 240, 330-333, 1995). Consequently, the most efficient way to
illuminate uniformly the lymphocyte cells laying due to gravity at the bottom of the liquid container
is by illumination from the bottom (TAU) or by using a thin layer of whole blood (ENEA).
ENEA & ICEmB:
 Details of the exposure protocol have been discussed during a bilateral meeting held at ENEA
on May 25. 6 ml of whole blood will be taken from each donor using sterile Vacutainers. 3
samples will be prepared (2 ml each)
and put into sterile containers with
suitable transmission properties in the
spectral range of interest. Following
the spectral measurements carried out
at ENEA and at Stuttgart, it has been
decided to use sealed „Nunclon“ dishes
made of polystyrene with an internal
diameter of 40 mm. The thickness of
the whole blood sample in this case
will be 1.6 mm. The typical exposure
layout is shown in the following
picture:

The FEL radiation at the central
frequency of 120 GHz is transported
through a copper light-pipe (25 mm
dia.) and is then fed into an aluminium
horn to match the dimension of the
irradiation container.

The FEL macropulse power is
monitored by a pick-up diode inserted
in the light-pipe to allow monitoring of
the total energy delivered in a given
irradiation time taking into account the macropulse repetition frequency.
More detailed considerations on the irradiation geometry are available as a separate file on the
project web-page.
TAU:
 Plastic containers with a base cross-section 4.5 x 2 cm2 will be used. Considering the size of the
liquid container the cross-section of the radiation beam must be expanded in order to obtain a
uniform illumination of the sample in the horizontal dimensions. A Gaussian beam with spot
size diameter 2w=12 cm will provide reasonable uniformity.
 Considering the inefficiency of illumination due to the large spot-size of the radiation beam and
due to Fresnel reflection, high power should be supplied by the source to obtain significant
exposure. An average beam power higher than 25mW is required in order to obtain
SAR=10mW/g in the sample.
 Based on the evaluation of the exposure parameters, conceptual designs have been considered.
They are all based on a commercial incubator measuring internally: 48 cm (height) x 58 cm
(width). Expansion of the beam by means of reflective optics is considered most favourable,
especially for wide range frequency tuning. However reflective optics will be considered too.
The internal surface of the incubator will be covered with special microwave absorbing
material.
Photodissociation dynamics of DNA and RNA bases.
Basic considerations on the mechanisms of the interaction of moderate intensity radiation with
organic matter at different wavelengths, from the deep-UV to mm-wave spectral region, have been
performed at NHRF.
In the general case of illuminating polymeric material with light, mainly two kind of processes are
induced on the monomers: the first being excitation followed by relaxation to the ground state, and
the second being excitation followed by molecular disintegration.
Regarding the first process, the electronic excitations of the molecular specimens could relax by
internal conversion to the vibration excitations of the molecule. Redistribution of the intermolecular
energy due to the different geometry of the molecule in the ground and the excited states, which
initially appears in a particular vibration mode of an excited molecule, has been found to be as fast
as ~1ps. A much slower process of cooling the vibration hot molecule follows the intermolecular
energy redistribution. A computer simulation of vibration cooling reveals a characteristic time of
few tens of ps in agreement with experiments. Polymeric materials are self-organised into areas
where monomers are grouped together to form polymers of longer chains. The polymeric material
consists of such areas having different dimensions. They are separated from the neighbouring areas
by a small amount of activation energy of few tenths of an electron volt. Therefore the rise of the
bulk temperature, as the radiation at long wavelengths heats it, could have the effect of:
 either breaking further down the polymeric chain due to multi-photon absorption,
 or enhancing its strength by joining together macromolecular domains, which are separated
by the activation energy, which corresponds to the rise of the temperature in the bulk.
The enhancement or breaking of the polymeric chains depends on parameters such as wavelength,
energy and intensity of light and cohesion of macromolecular chains. Therefore THz irradiation
might trigger cross-linking reactions between neighbouring molecules, leading to damage of the
DNA and RNA bases.
The experimental approach for the study of the dissociation dynamics of RNA and DNA bases, will
be mass spectroscopy following irradiation in the THz spectral region. Under THz irradiation the
parent molecule, might disintegrate to small photo-fragments, atomic, diatomic or triatomic. This
will be the fingerprint of bio-damage on the molecular scale. Due to the expected low absorption
coefficient of the DNA bases in the THz spectral region, in comparison to absorption coefficient at
shorter wavelengths, the complete breaking of the chemical bonds of the DNA and RNA bases
should be detectable only at very low background pressure, typically 10-10 mbar. In order to
evaluate quantitatively the damage at long wavelengths, it is necessary to compare it with damage
in different spectral regions where databases exist.
WP-2 : Evaluation of biological effects in vitro after exposure to THz-radiation
WP-2.2 (Membranes and epithelial cultures)
Whilst this workpackage does not become fully operational until month 12, there have been a
number of preparative steps taken.
1) Following discussions at the kick-off meeting concerning an approach to exposing cells to the
THz radiation via the use of a special chamber already in use at the Goethe University Frankfurt,. the Thermanox discs employed in Nottingham for growing cells have been sent to
partners for evaluation of their optical properties in the THz spectral range.
2) Some of the protocols, for the end-points assays, for the determination of adverse effects on the
cell lines and skin tissue models have been defined. The other protocols are being refined in the
light of experience gained with UV radiation. They are available to group members on the THzBridge web site.
3) The protocol for production of a 3D skin model that will fit a chamber the size of the
Thermanox discs is being defined. The reaction between collagen gel and fibroblasts results in
shrinkage of the dermal component of the model that can be controlled via density of collagen
and number of dermal fibroblasts.
WP-3 : Safety issues at specific occupational sites
As a first step of the WP-3 activity starting at month six, a draft-questionnaire has been prepared by
CRL/TREL and UNOTT to collect information on the main radiation parameters of THz sources,
which are currently in use at various laboratories in Europe (e.g. frequency range, power level,
modulation). The draft-questionnaire will be made available to partners for comments and
improvements. Further information will be collected on:
 biological and potential biomedical applications of THz sources
 exposure conditions (if any) of technical personnel
 safety measurements or precautions currently adopted
The next project meeting, to be held in Greece on October 1-2, 2001, will focus on the various
aspects of WP-3.