Transcript Laser Ablation - INFN-LNL

Laser Ablation Characterization in LNL
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Scarpa ,
P.
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Nicolosi , A.
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Franci , A.
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Tomaselli ,
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Manzolaro ,
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Corradetti ,
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Vasquez ,
M.
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J.
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M. Calderolla , A. Monetti , M. Lollo , A. Andrighetto , G. Prete .
M.
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Rossignoli ,
1.INFN, Laboratori Nazionali di Legnaro, Legnaro (Padova), Italy. 2Dipartimento di Ingegneria dell'Informazione,
2.Università degli Studi di Padova. 3 IFN-CNR UOS Padova 4Dipartimento di Scienze Chimiche dell’Università di Padova, Padova, Italy. 5 Dipartimento di Ingegneria dell'informazione dell’Università di Padova, Padova, Italy. 6 Università degli Studi di Pavia, Dipartimento di
Ingegneria Industriale e dell'Informazione,, Via Ferrata 1, Pavia, Italy.
Laser Ablation
Ablation Chamber Setup
An high power laser pulse focalized onto a surface (target) is capable to
produce a rapid local increase of the temperature. This process implies
an evaporation or direct sublimation of part of the target material.
If laser power density in space and time is enough is possible to have
formation of high density plasma, and production of high charge state
ions, expelled from the target surface.
Preliminary studies of these processes are starting in new SPES Laser
Laboratory in Laboratori Nazionali di Legnaro.
The aim of this work is to start investigation and building first know-how
on Laser Ion Sources.
Ablation Vacuum Chamber was entirely
designed in LNL, it can reach vacuum down
to 10-6 mbar by diffusion oil pump.
It guests ablation target, ion collector and
several electrical connections.
ND:YAG Laser
Ablation laser is a QUANTEL YG 980 Nd:YAG laser.
It is capable of 2 J, 20 nsec pulses at maximum repetition rate of 10 Hz.
First tests:
As first test we decided to duplicate a documented
experimental setup to certify our equipment.
This setup was chosen due to its simplicity, involving
only a target and a collector plate. Successive
improvements was implemented adding plates
polarization by high voltage generator.
Pulse duration
Collector signal
Spot size
Target signal
↑ΔV
↑ΔV
Data show good qualitative agreement
between the reference work and our
preliminary measurements.
Several power regime used during
the experiments are characterized
by different pulse durations.
Ablated area data will provide a
preliminary estimation of vaporized
material to compare with ion
current data. Results on current on
plates show several peaks due to
several ion state of charge. Some
peaks are due to impact of neutral
material on collector which extract
electrons.
Different
plates
polarization potential show several
peak appearing and disappearing
due to their state of charge.
Future developements: The vacuum chamber will be updated to guest a Time of Flight mass spectrometer. Thank to this improvement it will be possible to
fully characterize the state of charge of the ions coming out from the plasma plume.
Other experiments will be executed with other target material; the final goal is to have a complete characterization of the ablation
process on refractory materials like Tungsten and Tantalum to investigate the design of a Laser Ion Source for stable atomic species.
OTHER ACTIVITIES:
Aluminum reasonant laser ionization experiment
SPES facility will provide accelerated ions of exotic species for applied physics experiments. To provide such species a Uranium Carbide target will be impinged by protons and
setup
fission products will be ionized to be accelerated towards the experiment. Among the three suitable ionization methods: surface, plasma and laser; Laser Resonant Ionization, is
the one that involves the major number of equipment's, but it is the one that assure better results in terms of beam purity and beam properties. During this process, just atoms
belonging to the specie of interest are stepwise-excited leading to finally to continuum, obtaining an extremely pure ionization process. Usually these kind of laser are tunable, in
order to match atoms absorption levels, they are pulsed to provide high energy peak and they run in high repetition rate to better match a continuous yields beam provided by
target. Nowadays in the SPES off-line laboratory a first resonant laser ionization test for Aluminum is done with an Excimer laser and a two step – one color ionization path.
FC
FC
The laser used for ionization is a broadband excimer
laser LPX200 by Lambda Phisyk, which can charged
with XeCl gas and emits laser radiation centered
around 308 nm.
Laser radiation is delivered by a focusing telescope
6 meter far away, and enters in the 3 mm diameter
hot cavity, producing ionization.
Wien Filter
Quadrupoles
Deflectors
IS
LASER
IONS
Due to the off-line front end setup in order to allows laser radiation to reach the hot
cavity, is mandatory to displace the FC and redirect the beam by quadrupoles and
electrostatic deflector, to collect anyway a signal. The vertical displacement does
not affect the mass separation which is in the horizontal plane.
LNL new laser laboratory
Since March 2013 a new laser laboratory is operative in LNL. In this laboratory is nowadays present a Nd:YAG Quantel Laser used for ablation studies and will be housed and
tested the new all solid state tunable laser system for the SPES project.