Radiation therapy of tumors progresses continuously and so do devices, sharing a global market of about $ 4 billions,
growing at an annual rate exceeding 5%. Most of the progress involves tumor targeting, multi-beam irradiation, reduction
of damage on healthy tissues and critical organs, dose fractioning. This fast-evolving scenario is the moving benchmark
for the progress of the laser-based accelerators towards clinical uses. As for electrons, both energy and dose requested by
radiotherapy are available with plasma accelerators driven by lasers in the power range of tens of TW but several issues
have still to be faced before getting a prototype device for clinical tests. They include capability of varying electron
energy, stability of the process, reliability for medical users. On the other side hadron therapy, presently applied to a
small fraction of cases but within an exponential growth, is a primary option for the future. With such a strong
motivation, research on laser-based proton/ion acceleration has been supported in the last decade in order to get
performances suitable to clinical standards. None of these performances has been achieved so far with laser techniques.
In the meantime a rich crop of data have been obtained in radiobiological experiments performed with beams of particles
produced with laser techniques. It is quite significant however that most of the experiments have been performed moving
bio samples to laser labs, rather moving laser equipment to bio labs or clinical contexts. This give us the measure that
laser community cannot so far provide practical devices usable by non-laser people.
Laser-driven electron accelerators based on the Laser Wakefield Acceleration process has entered a mature phase to be considered as alternative devices to conventional radiofrequency linear accelerators used in medical applications. Before entering the medical practice, however, deep studies of the radiobiological effects of such short bunches as the ones produced by laser-driven accelerators have to be performed. Here we report on the setup, characterization and first test of a small-scale laser accelerator for radiobiology experiments. A brief description of the experimental setup will be given at first, followed by an overview of the electron bunch characterization, in particular in terms of dose delivered to the samples. Finally, the first results from the irradiation of biological samples will be briefly discussed.
We present the results of an experiment concerning laser-plasma interaction in the regime relevant to shock ignition. The
interaction of high-intensity frequency tripled laser pulse with CH plasma preformed by lower intensity pre-pulse on
fundamental wavelength of the kJ-class iodine laser was investigated in the planar geometry in order to estimate the
coupling of the laser energy to the shock wave or parametric instabilities such as stimulated Raman or Brillouin
scattering, or to the fast electrons. First the complete characterization of the hydrodynamic parameters of preformed
plasma was made using crystal spectrometer to estimate the electron temperature and XUV probe to resolve the electron
density profile close to the critical density region. The other part of the experiment consisted of the shock chronometry,
calorimetry of the back-scattered light and hard X-ray spectrometry to evaluate the coupling to different processes. The
preliminary analysis of the measurements showed rather low energy transfer of the high-intensity pulse to back-scattered
light (< 5%) and no traces of any significant hot electron production were found in the X-ray spectra.
Inertial Confinement Fusion with Shock Ignition relies on a very strong shock created by a laser pulse at an intensity of
the order of 1016W/cm2. In this context, an experimental campaign at the Prague Asterix Laser System (PALS) has been
carried out within the frame of the HiPER project. Two beams have been used, the first to create an extended preformed
plasma (scale length of the order of hundreds of micrometers) on a planar target, the second to generate a strong shock
wave. Different diagnostics were used to study both the shock breakout at the rear surface of the target and the laserplasma
coupling and parametric instabilities. This paper is focused on back-scattering analysis to measure the backreflected
energy and to characterize parametric instabilities such as stimulated Brillouin and Raman scattering. Our
experimental data show that parametric instabilities do not play a strong role in the laser plasma coupling. Moreover,
preliminary analysis of the back reflected light from the interaction region shows that less than 5% of the total incident
laser energy was back-reflected, with only a small fraction of that light was originating from parametric instabilities.
Recently, a high efficiency regime of acceleration in laser plasmas has been discovered, allowing table top equipment to
deliver doses of interest for radiotherapy with electron bunches of suitable kinetic energy. In view of an R&D program
aimed to the realization of an innovative class of accelerators for medical uses, a radiobiological validation is needed.
At the present time, the biological effects of electron bunches from the laser-driven electron accelerator are largely
unknown. In radiobiology and radiotherapy, it is known that the early spatial distribution of energy deposition
following ionizing radiation interactions with DNA molecule is crucial for the prediction of damages at cellular or
tissue levels and during the clinical responses to this irradiation. The purpose of the present study is to evaluate the
radio-biological effects obtained with electron bunches from a laser-driven electron accelerator compared with bunches
coming from a IORT-dedicated medical Radio-frequency based linac's on human cells by the cytokinesis block
micronucleus assay (CBMN). To this purpose a multidisciplinary team including radiotherapists, biologists, medical
physicists, laser and plasma physicists is working at CNR Campus and University of Pisa. Dose on samples is
delivered alternatively by the "laser-linac" operating at ILIL lab of Istituto Nazionale di Ottica and an RF-linac
operating for IORT at Pisa S. Chiara Hospital. Experimental data are analyzed on the basis of suitable radiobiological
models as well as with numerical simulation based on Monte Carlo codes. Possible collective effects are also
considered in the case of ultrashort, ultradense bunches of ionizing radiation.
Guiding focused pulses along path lengths much larger than the depth of focus is one of the major tasks for the
progress of laser acceleration of electrons in plasmas. We will present the results of the production of hollow
plasmas to be used as guiding medium, obtained inducing optical breakdown in Helium subsonic gas-jet with
nanosecond laser pulses similar to the Amplified Spontaneous Emission (ASE) pedestal of a powerful ultrashort
laser pulse. These plasmas have been then carefully characterized by the deconvolution, with original algorithms,
of high quality interferograms obtained with high resolution interferometry and the relevant channel parameters
were measured, including length, width, electron density at the channel axis and at its boundary. The electron
density profiles we obtained match the requirements for an efficient guiding in laser wakefield acceleration (LWFA)
experiments. The acceleration length can be further increased by using longer gas-jets and larger f/N numbers.
New studies are planned with supersonic gas-jets, providing more homogeneous density profiles and steeper
In this paper we describe recent studies on X-ray emission from ultra-fast laser interactions with solids. We describe
the dedicated equipment including a powerful femtosecond, Titanium-Sapphire laser system and custom developed
diagnostics for the characterization of both the laser performance and the X-ray emission. We show the experimental
results obtained from irradiation of Aluminium and Titanium targets including X-ray yield and spectra obtained using
single-photon counting and spectroscopy. We discuss correlation of X-ray emission with the measured properties of hot
electrons emerging from the target rear side. In particular, forward accelerated fast electrons propagating through a Ti
foil are found to be emitted in a cone perpendicular to the target. A comparison of the experimental findings with the
results of a PIC simulation is also reported, aimed at identifying the physical processes responsible for the production of
this forward propagating population of fast electrons. Finally, we show results of simple optical spectroscopy
measurements of scattered light and we discuss the use of these results in view of optimization and control of this kind of
The INFN Strategic Project PLASMONX (PLASma acceleration and MONochromatic X-ray production) deals with
the creation of a High Intensity Laser Laboratory at LNF (HILL@LNF) beside the SPARC bunker, with which it will
communicate via a channel for the propagation of laser beams. In this laboratory FLAME ( Frascati Laser for
Acceleration and Multidisciplinary Experiments), a 200TW, 30fs, 10Hz Ti:Sapphire Laser, will be set up.
The main goals of this project are:
1) demonstration of high-gradient acceleration of relativistic electrons injected into electron plasma waves excited
by ultra-short, super-intense laser pulses;
2) development of a monochromatic and tuneable X-ray source in the 20-1000 keV range, based on Thomson
Scattering of laser pulses by the 20-200 MeV electrons of the LINAC of the SPARC project.
One of the aims of the project consists in the realization of a pulsed source of ionizing radiation for R&D activity in
Novel sources of energetic photons are currently studied and developed at the Intense Laser Irradiation Laboratory of
Pisa. They include: i) X-rays generated by plasmas produced with nanosecond and picosecond laser pulses. This kind of
source has been recently optimised in terms of intensity, repetition rate, monochromaticity, which allowed novel
techniques to be successfully tested as micro-radiography and differential mapping of tracing elements. ii) K-a X-ray
emission of short duration due to the collision of energetic electrons generated during ultra-short femtosecond laser-solid
interactions. iii) Monochromatic and ultra-short X-rays pulses generated via Thomson scattering of intense sub-
picosecond pulses by relativistic electron bunches are currently being studied theoretically also with the aid of numerical
codes. Electron bunches produced by both conventional beamlines and laser acceleration of electrons in plasmas are
The high order harmonic generation process due to the interaction of a multi-well quantum system with an intense laser field is examined. A plateau extension up to a photon energy of Ip + 8Up and the generation of attosecond pulses are evidenced. The influence of the intermediate ions on the conversion efficiency and on the plateau extension is studied.
Fast electrons generated during laser-plasma interactions at relativistic intensities can be studied directly using electron spectrometers, or indirectly, detecting the gamma- ray bremsstrahlung radiation generated by the interaction of these electrons with matter. In a recent experiment carried out at the Rutherford Appleton Laboratory using the Vulcan laser, the propagation of a 75 H, 1 ps Chirped Pulse Amplified pulse (CPA) in a preformed plasma channel was studied using a variety of diagnostic techniques. High energy gamma ray detectors based on NaI(Tl) scintillator coupled to photomultipliers were used to detect bremsstrahlung emission from accelerated electrons. The gamma-ray yield was studied for different plasma channel conditions by varying the delay between the channel forming pulse and the main CPA pulse. These result are correlated with the interferometric images of the plasma interaction region.
Experimental results obtained in different conditions of interaction are reported. Several instabilities have been investigated including filamentation, stimulated Brillouin and Raman scattering, two plasmon decay, harmonic generation, self-phase modulation, and hot electron acceleration. Threshold and saturation levels of some of those processes have been measured. Time-resolved spectroscopy gave detailed information on the physics involved. The effect of several beam-smoothing techniques has been tested. Particularly, random phasing and induced spatial incoherence, when properly matched with focusing optics, showed reduction or suppression of most of the above mentioned instabilities.
Laser based x-ray sources at h(upsilon) approximately equals 0.9 - 1.2 keV (Fe to Cu L-shell) developed for applications are studied from the point of view of x-ray emission spectra. X-ray spectra obtained with different laser intensities and wavelengths using Nd and KrF lasers are described. Results are qualitatively compared with the predictions of simple analytical models for plasma temperature Te and average ionization Z*. When using KrF lasers it is possible to introduce a He atmosphere in the interaction chamber to reduce the debris problem. X-ray spectra at different He pressures were recorded and x-ray L-shell emission of Fe and Cu were shown to be largely independent of the pressure.
A repetitively pulsed (5Hz) KrF laser-based X-ray source producing photons at
i-ru 1.1 keV (copper, L-shell) from a copper coated rotating target has been used to
study soft X-ray induced DNA damage effects in Chinese hamster cells. The source
was computer controlled for accurate delivery to the biological material of pre-set
doses. DNA damage was induced by exposures lasting 7s for V79 cells and 40s for AA8
cells. To minimise the debris from the laser-plasma source and for convenient
handling of biological specimens, the target chamber contained helium at 1
atmosphere with a slow flow. The X-ray yield of the source decreased by only at
most 10-20% compared to vacuum operation and a further 16% of X-rays were absorbed
in helium between target and the biological material placed outside the target
chamber behind a beryllium filter. The measured spectral and spatial distribution
of the copper X-ray emission was found to be largely independent of the ambient
helium pressure. The time resolved X-ray signal lasted for only 3 ns starting at
the beginning of the 2lns laser pulse and its shape was independent of helium
pressure in the target chamber.