Abstract -CVD mono-crystalline diamond films were employed as detectors of the Introduction -Laser-generated plasma is characterized by high temperature and density

A M Mezzasalma

A Mangione

A Velyhan

C Tuvè

D Margarone

E Krousky

E Milani

G Verona-Rinati

J Krása

J Ullschmied

L Láska

L Ryć

L Torrisi

M Marinelli

M Pfeifer

R Potenza

S Cavallaro

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DIAMOND DETECTORS FOR CHARACTERIZATION OF  
LASER-GENERATED PLASMA 
 
L. Torrisi
1,2
, S. Cavallaro
1,3
, E. Milani
4
, G. Verona-Rinati
4
, M. Marinelli
4
, C. Tuvè
3
, R. 
Potenza
3
, D. Margarone
1,2
, L. Láska
5
, J. Krása
5
, M. Pfeifer
5
, A. Velyhan
5
, E. Krousky
5
, 
J. Ullschmied
6
, A. Mangione
2
, A.M. Mezzasalma
8
 and L. Ryć
7
 
 
1
INFN-Laboratori Nazionali del Sud, V. S. Sofia 62, 95123 Catania, Italy 
2
Dip.to di Fisica, Università di Messina, Ctr. Papardo 31, 98166 S. Agata, Messina, Italy 
3
Dipartimento di Fisica, Università di Catania, V. S. Sofia 62, 95123 Catania, Italy 
4
Ingegneria Industriale, Università Tor Vergata, V. Politecnico 1, 00133 Roma, Italy 
5
Institute of Physics ASCR v.v.i, Na Slovance 2, 182 21 Prague, Czech Republic 
6
Institute of Plasma Physics ASCR v.v.i, Za Slovankou 2, 182 21 Prague, Czech Republic 
7
Institute of Plasma Physics and Laser Microfusion, Hery 23, 00-908 Warsaw, Poland 
8
Dip. SMTFA, Università di Messina, Ctr. Papardo 31, 98166 S. Agata, Messina, Italy 
 
Abstract - CVD mono-crystalline diamond films were employed as detectors of the radiation 
emitted from the laser-generated plasma obtained with a Nd:Yag laser at the INFN-LNS in 
Catania (10
10
 W/cm
2
 ) and a high-power iodine PALS laser in Prague (10
15
 W/cm
2
). Plasmas 
were obtained using different targets: Al, Ta, Au, and CF2. The plasma characterization was 
carried out by the use of diamond detectors and  ion collectors placed at different distances 
and angles with respect to the position of the ablated target. Diamond detectors measure UV, 
X-rays, electrons and ions. Time-of-flight technique was exploited to separate photon, 
electron and particle contributions. The TOF diamond spectra were compared with 
traditional ion collector spectra. The results indicate that the ion energy resolution of 
diamond detector is high and that the mean energy of soft X-rays could be obtained by 
analyzing the spectra acquired for different absorber films. 
 
Introduction – Laser-generated plasma is characterized by high temperature and density, 
which can reach values of the order of 10 keV and 10
20
/cm
3
, respectively. These plasmas emit 
high intensity photons, from IR to visible, to UV and X-ray regions, and high energetic 
electrons and ions, which energy is of the order of tens of keV and MeV, respectively [1]. 
Generally, the characterization of the plasma properties uses different detectors, such as fast 
semiconductors for photons, ion collectors for ions and electrons and ion energy analyzer for 
energy distribution measurements. Often, detectors are employed in time-of-flight (TOF) 
configuration and are placed at different angles and distances from the laser irradiated targets.  
The main properties of CVD-based diamonds are radiation hardness, low electric constant, 
low leakage current, fast signal collection time, room temperature operation and high gap 
energy (5.48 eV). Photons, electrons and ions hitting the sensible volume of the detector 
34th EPS Conference on Plasma Phys. Warsaw, 2 - 6 July 2007 ECA Vol.31F, P-5.011  (2007)
generate electron-hole pairs, (loosing 13 eV for a pair) that results in arising a voltage signal 
at the device electrodes which is proportional to the deposited energy. The high efficiency 
charge collection permits to use the diamond to detect soft X-rays, electrons and ion beams. 
Due to these properties, diamond detector can be employed with success to monitor laser-
generated plasmas in TOF configuration.  
In this work a CVD diamond is employed to monitor the photons and particles emission 
ejected from a plasma obtained at INFN-LNS in Catania and at PALS laboratory in Prague, 
using a laser pulse intensity of about 10
10
 W/cm
2
 and 10
16
 W/cm
2
, respectively. Results are 
compared with traditional TOF ion collector measurements. 
 
Experimental section – The Nd:Yag laser of INFN-LNS (Catania) used 1064 nm wavelength 
and a pulse energy of about 400 mJ with 9 ns duration. The Asterix laser of PALS (Prague) 
was employed at fundamental (1315 nm) and 3
rd
 harmonics (348 nm wavelength) and pulse 
energy ranging from 50 J up to 200 J with 400 ps duration. Thick Al, Ta, Au and Teflon (CF2) 
were employed as targets. The incidence angle was 30°, an anular ion collector (ICR) was 
employed as ion collector at 179 cm from the target along the normal direction. The CVD 
diamond detector was employed, without an with different mylar absorbers, at different 
known distances from the target and at different angles with respect to the normal direction. 
The used mono-crystal detector has 25 µm thickness, growth on high B-doped diamond, and 5 
mm x 5 mm surface, which is glued on an thick Al backing and covered by a thin Al film 
(100 nm). Typically operates at 100 V polarization at which the electric field is 40 kV/cm [2].  
 
Results and discussion - Two typical TOF spectra obtained at INFN-LNS (400 mJ laser 
energy, Ta and Al target, 25 cm target-detector distance) are reported in Fig. 1. Three 
different regions are observable vs. time: the first is the photo-peak region, representing a 
peak intensity proportional to the UV and soft X-ray intensity and energy, which duration 
generally is below 10-20 ns; the second is represented by a continuum region, from about 30 
ns to about  300 ns, due to fast electrons detection; the third, is an intense region due to 
energetic ion detection occurring for times higher than 1 µs, as reported in Fig. 1a. The photo-
peak yield, which details for Al ablation are reported in Fig. 1b, decreases exponentially with 
the mylar thickness absorber, as shown in Fig. 2a.  The mylar absorption coefficient of 
detected photons can be measured from this exponential decay. Thus, by knowing the 
absorption dependence on the photon energy, as reported in Fig. 2b, it is possible to know, as 
a first approximation, the mean X-ray energy, according to literature [3]. 
34th EPS 2007; L.Torrisi et al. : DIAMOND DETECTORS FOR CHARACTERIZATION OF LASER-GENERATED ... 2 of 4
 
 
 
 
 
 
 
 
 
Fig.1: TOF diamond spectra for Ta (a) and Al (b) plasmas obtained at INFN-LNS. 
 
Fig. 2b indicates that the mean energy of the X-ray emission at INFN-LNS was 260 eV at 
which corresponds an electronic plasma temperature of about 110 eV assuming the electron 
energy to be due to thermal interactions and to thermal gas expansion in vacuum. Such energy 
should be about a factor three or four lower with respect to the maximum energy of the 
electron Bremsstrahlung spectrum in the plasma.  
 
 
 
 
 
 
 
 
Fig. 2: X-ray yield vs. absorber thickness (a) and absorption coefficient vs. energy (b). 
 
The signal due to electrons detection is less evident than for photons and ions because a large 
continuum spectrum characterize the electron plasma emission, moreover a soft X-ray signal, 
due to the late recombination of ions, could be overlapped to the electron peak, as reported in 
literature [4]. The spectrum of Fig. 1b indicates an electron energy emission from aluminium 
ranging approximately between 20 eV and 300 eV, while the spectrum of Fig. 1a indicates an 
ion energy emission from tantalum ranging between 600 eV and 10 eV. In this last spectrum, 
the peak detected at 4 µs is due to nitrogen and oxygen contaminants ion emission, which 
energy is about 300 eV. Higher temperature and particle energies can be obtained increasing 
0 20 40 60 80
-0,25
-0,20
-0,15
-0,10
-0,05
0,00 a)
Photo Peak
Ion Peak
 
 
 
 
A
m
p
li
tu
d
e
 (
V
)
Time of fligth (µs)
Ta, E
L
= 400 mJ, φ
inc.
= 43°, 1ω
SCD53, no filter, V = +50 V
φ
det.
= 23°, d
det.
= 25 cm
0,00 0,03 0,06 0,09
-1,2
-0,8
-0,4
0,0
b)
Electron Peak
Photo Peak
Al, E
L
= 400 mJ, φ
inc.
= 43°, 1ω
SCD53, no filter, V = +50 V
φ
det.
= 23°, d
det.
= 25 cm
Time of fligth (µs)
 
 
 
 
A
m
p
li
tu
d
e
 (
V
)
INFN-LNS 
INFN-LNS 
 
0 10 20 30 40 50
0.01
0.1
1
µ
exp.
= 0.615 µm
-1
µ
exp.
= 0.035 µm
-1
 
 
 
 
PALS
Au, E
L
= 150 J
LNS
Al, E
L
= 400 mJ
X
-r
a
y
 n
o
rm
a
li
z
e
d
 y
ie
ld
, 
I/
I 0
Mylar Thickness (µm)
a) b) 
0.0 0.5 1.0 1.5 2.0 2.5 3.0
0.01
0.1
1
10
E
T-PALS
 = 2.4 keVE
T-LNS
 = 260 eV
Mylar Absorber
µ
exp.
(LNS) = 0.615 µm
-1
A
b
s
o
rp
ti
o
n
 C
o
e
ff
ic
ie
n
t[
9
] , 
µµ µµ
 (
µµ µµ
m
-1
)
Photon Energy (keV)
µ
exp.
(PALS) = 0.035 µm
-1
 
 
34th EPS 2007; L.Torrisi et al. : DIAMOND DETECTORS FOR CHARACTERIZATION OF LASER-GENERATED ... 3 of 4
the laser pulse intensity. A typical TOF spectrum obtained at PALS (155 J laser energy, CF2 
target, 176 cm target-detector distance) is reported in Fig. 3a. Also in this case three different 
regions are observable vs. time: the first is the photo-peak region, which duration generally is 
below 50 ns; the second represents a continuum region due to fast electrons detection, 
extended from photo-peak to the ion peak position; the third, is the intense region due to 
energetic ion detection occurring for higher times. In this case the photo-peak yield 
decreasing with the mylar absorber thickness gives an absorption coefficient of  0.035 µm
-1
, at 
which corresponds a mean X-ray energy of 2.4 keV. Thus the electronic plasma temperature 
in this case becomes 1.02 keV. The signal due to electrons detection is less evident than for 
photons and ions because a large continuum characterize the plasma emission. The spectrum 
indicates an electron energy ranging approximately between 1 keV and 11 keV and an ion 
(carbon) energy ranging between about 90 keV and 10 MeV.  
 
 
 
 
 
 
 
 
 
Fig. 3: Typical TOF spectra for diamond (a) and ion collector (b) from PALS experiment. 
 
Fig. 3b reports, for comparison, the ion collector spectrum obtained contemporary to the 
diamond spectrum of Fig. 3a. The ion energy measurements, due to collection of C and F ions 
at different charge state and energy, are in good agreement with those obtained by the 
diamond detector. Obtained results indicate that the diamond is a good detector to 
characterize the laser-generated plasmas; it shows high efficiency and good energy resolution 
to be employed in TOF configuration and to detect contemporary energetic photons, electrons 
and ions ejected from the plasma. 
References 
[1] D. Giulietti and L.A. Gizzi; Riv. del Nuovo Cimento 21 (10), 1, (1998). 
[2] M. Marinelli, E. Milani, G. Prestopino et al.; Appl. Phys. Lett. 89 143509 (2006). 
[3] L. Torrisi and E. Amato; Rad. Eff. and Def. in Solids 160 (9), 391-399 (2005). 
[4] J.L. Weaver et al.; Rev. Sci. Instrum. 74 (12) 5076-5083 (2003). 
0.0 5.0x10
-7
1.0x10
-6
1.5x10
-6
2.0x10
-6
0
4
8
12
16 b)
CF
2
, E
L
= 150 J, 1ω
φ
inc.
= 30°, ICR, V = -100 V
φ
det.
= 0°, d
det.
= 179 cm
 
 
A
m
p
li
tu
d
e
 (
V
o
lt
)
Time of fligth (second)
0.0 5.0x10
-7
1.0x10
-6
1.5x10
-6
2.0x10
-6
-0.8
-0.6
-0.4
-0.2
0.0
0.2
 
 
 
CF
2
, E
L
= 150 J, 1ω
φ
inc.
= 30°, SCD53 
no filter, V = +100 V
φ
det.
= 21°, d
det.
= 175.5 cm
Time of fligth (second)
A
m
p
li
tu
d
e
 (
V
o
lt
)
a) 
34th EPS 2007; L.Torrisi et al. : DIAMOND DETECTORS FOR CHARACTERIZATION OF LASER-GENERATED ... 4 of 4


DIAMOND DETECTORS FOR CHARACTERIZATION OF LASER-GENERATED PLASMA

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DIAMOND DETECTORS FOR CHARACTERIZATION OF LASER-GENERATED PLASMA

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