International Journal of Emerging Trends in Engineering Science &Technology(IJETEST)
ISSN: 2476-0862
Voumel. 1, Issue. 1
Evaluation of the Gain Competition and Pumping
Mechanisms in Molecular Fluorine Laser
S. Yousef Shafiei 1, Reza Yadipour1, Pouya Faeghi2, Ali Reza Marami Iranaq3
1
Faculty of Electrical and Computer Engineering, Iran/University of Tabriz.
2
Department of Electrical Engineering, Iran/Ialamic Azad University-Tabriz Branch.
3
Networks Power Engineering, Committee Technical Office, Iran/ Mobile
Communication Company of Iran.
ABSTRACT
The molecular transitions are detected at high atmospheric pressures above ~ 2 atm, where the
gain competition with atomic fluorine laser occurs. Pumping mechanisms have been studied
between He and F2 species during excitation process by changing tube pressure.
Keywords— Gain competition, Molecular fluorine laser, Pumping mechanisms.
quenching, however that of lower state decays
much
more
rapidly
resulting
in
INTRODUCTİON
The molecular F2 laser represents the most
powerful and efficient vacuum ultra violet (VUV)
source around 157.6 nm. Photochemical vapour
deposition using materials with higher bonding
energy, photoablation, photochemistry and
spectroscopy are application of this laser.
Understanding of kinetics in the discharge pumped
F2 laser was not deep enough. The molecular
fluorine laser is predominantly produced at high
pressure interval of 2-11 atm, because of three
body collisions among the abundant F*, ionic
fluorine species and helium. Many papers have
noted that NIR lines of F* laser can be seen during
molecular fluorine laser measurements with very
weak intensities but possessing high efficiency [17]. The main pumping mechanisms for the
formation of the population density of the laser
upper level i.e. F2*(D') which come from
vibrational transition (Fig. 1) are well known to be
the neutral and ion channel reactions, as below [58]:
F *  F2  F2* ( D ' )  F
(1)
F   F   He  F2* ( D ' )  He
(2)
Moreover, during high tube pressure
operation, rapid quenching of lower state F2 (A'),
leading to shorter life time along with the greater
pump power rates, collaborates to scale up the
output energy [5].
Although the populations of the upper and the
lower states deplete due to the collisional
Fig. 1 Energy diagram of molecular fluorine laser
the gain growth [7].
Experimental Apparatus
We used an ArF excimer laser device which
had been filled with He and fluorine in 0.2%. The
wavelengths and the relative intensities of the
molecular fluorine laser were measured with a
monochromator
(Acton
VM-502)
having
resolution 0.1 nm and a VUV biplanar Phototube
(R1193U-54) detector were exploited for
molecular fluorine laser and a 400-MHz Tektronix
7844 oscilloscope.
A joule meter (Coherent. Filed Master, LMP10 and LM-P5 LP heads) was used for the
absolute-energy measurement of laser pulse too
(Fig. 1). Because of VUV (Vacuum Ultra Violet
157 nm) absorption (Schumann-Runge effect) in
atmosphere by oxygen we must use a vacuum
chamber between monocromator and detector.
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International Journal of Emerging Trends in Engineering Science &Technology(IJETEST)
ISSN: 2476-0862
Voumel. 1, Issue. 1
Laser tube
(0.2% F2/He)
Monochromat
or ACTON VM520(resolution 0.1
nm)
VUV-biplanar
detector–
phototube
(R11930-54)
for F2*
Vacuum
Ealing Neutral Density Filter
(NDF)
Joulmeter (Coherent
Field Master, LM-P10
and LM-P5 Heads and
J45LP-MUV)
PIN Diode
detector
for F*
OsciloscopeTecktronix78
44 (400MHz)
Fig. 2 Diagram of molecular fluorine laser detector and joulmeter installing
from laser transitions 3p4P → 3s4P at our pressure
interval in Equation (3):
The maximum total energy of F2* laser
obtained 30 mJ/pulse at pressure near 2 atm. In our
previous work [9] the variation and damping of
most of atomic fluorine laser lines in higher
atmospheric pressure shows that only a triple
atomic laser lines 7515, 7399 and 7552 A°
corresponding to the submanifolds modes 3p 4P →
3s4P grow above 2 atm, whereas the shorter line
157 nm due to F*2 molecular transition Dʹ (3Π2g)
→ Aʹ (3Π2u) can be detected simultaneously which
intensity enhances up to 5atm as shown in Fig. 3.
When the total tube pressure increases, then the
gain of atomic fluorine laser decreases because of
collision between excited atom F*, ions F‾ and
molecular fluorine F2 according to Eqation (1) and
(2) leading to excited molecular F2* formation. It
implies that the density of fluorine species and the
corresponding collisions must be adequate at
higher pressures. Subsequently the upper state in
molecular fluorine laser is quenched collisionally,
since the state Dʹ (3Π2g) is metastable [10]. It
indicates that strong laser transitions occur at high
pressures. The decrease of pulse energy of F2*
laser is correlated to the fluorine percentage
increase due to the enhancement of collisional
frequency by F2, F ‾ and photons [5].
The excited molecular fluorine follows the
following schemes originated from low lying
dominant excited fluorine atoms [1] which remain
F * (3s 4 P)  F2  F2* ( D ' )  F
(3)
This metastable submanifold is quenched
collisionally, so, according to reference [1] and our
results the only state that contributes in Equation
(3) is 3s4P. This level comes from the lower level
of infrared quartet submanifolds in atomic fluorine
laser which the energy level is around 103 * 103
cm-1. In our previous work after 2 atm the atomic
fluorine laser diminish drastically by increasing
tube pressure. Conversely the intensity of
molecular fluorine laser increase by using this
lower state of atomic fluorine [11]. So you can see
the laser jump from infrared to vacuum ultra violet
wavelengths in molecular fluorine laser.
40
35
Peak Power (arb. unit)
RESULTS AND DİSCUSSİON
30
25
20
15
10
5
0
2
3
4
5
Pressure (atm)
Fig. 3 Molecular fluorine laser peak power
variation by various atmospheric pressure in 0.2%
F2/ He and 14kV main voltage.
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International Journal of Emerging Trends in Engineering Science &Technology(IJETEST)
ISSN: 2476-0862
Voumel. 1, Issue. 1
This reaction gives evidence that the
population density of the precursor F*(3s4P)
increase with total gas pressure in He/F2 up to 5
atm. But the fundamental reaction in higher
pressures more than 5 atm return to Equation (2)
and the degree of contribution ion channel reaction
is larger than neutral channel reaction which the
reactants are an F+ ion and an F ‾ ion. These
reactants and three body reactions meaningfully
happen in higher pressure [7] because of large
collision rate and excitation voltage. We have not
performed F2 laser emission above 5 atm because
of limitation in solidity of laser tube.
5.
M. Kakehata, T. Uematsu, F. Kannari and M.
Obara, "Efficiency characterization of vacuum
ultraviolet molecular fluorine (F2) laser (157
nm) excited by an intense electric discharge,"
IEEE. J. Quant. Elect., Vol. 27, No. 11, pp.
2456-2463, 1991.
6.
Y. P. Kim, M. Obara, and T. Suzuki,
"Theoretical evaluation of electron – beam –
excited vacuum – ultraviolet F2 lasers," J.
Appl. Phys., Vol. 59, No. 6, pp. 1815-1818,
1986.
7.
T. Kitamura, Y. Arita, K. Maeda, M.
Takasaki, K. Nakamura, Y. Fujiwara, and S.
Horiguchi, "Small-signal gain measurements
in a discharge-pumped F2 laser," J. Appl.
Phys. Vol. 81, No. 6, pp. 2523-2528, 1997.
8.
M. Takahashi, K. Maeda, T. Kitamura, M.
Takasaki, and S. Horiguchi, "Experimental
study of formation kinetics in a dischargepumped F2 laser," Opt. Commun., Vol. 116,
No.1-3, pp. 269-278. 1995.
9.
P. Parvin, H.Mehravaran and B.Jaleh,
"Spectral lines of the atomic fluorine laser
from 2psi(absolute) to 5.5 atm," Applied
Optics, Vol 40, No. 21, pp. 3532-3538, 2001.
CONCLUSIONS
Despite insignificant molecular emission
(157.6 nm) the pressure dependent atomic and
molecular fluorine lines simultaneously appear at
the pressure interval 2 to 3.5 atm. In fact, tube
pressure near 2 atm is taken into account as the
onset of molecular fluorine laser irradiation. When
the pressure increase above 3.5 atm then the
atomic fluorine lines begins to drop leading to
major enhance meet of the molecular fluorine line.
It mainly arises from the fact that lower state
(3s4P) is metastable to contribute to populate
molecular fluorine Dʹ (3Π2g) state due to
successive collision between F* and F2 according
to Equation (1). Similarly, the collision rate
increases with tube pressure to enhance the
molecular transition gain significantly which valid
here up to 5 atm.
REFERENCE
1.
A. C. Cefalas, C. Skordoulis, M. Kompitsas
and C. A. Nicolaides, "Gain measurements at
157nm in an F2 pulsed discharge molecular
laser," Opt. Comm., Vol 55, No. 6, pp. 423426 1985.
2.
K. Yamada, K. Miyzaki, T. Hasama, and T.
Sato, "High-power discharge–pumped F2
molecular laser," Appl. Phys. Lett., Vol. 54,
No. 7, pp. 597- 599, 1989.
3.
K. Uno, K. Nakamura, T. Goto, and T.
Jitsosno, "Red-F* laser and VUV-F2 emission
pumped at low pressure by longitudinal, lamplike discharge," Plasma and Fusion Res. 3,
Vol. 037, pp. 1-4, 2008.
4.
S. M. Hooker, A. M. Haxell, and C. E. Webb,
"Influence of cavity configuration on the pulse
energy of high-pressure molecular fluorine
laser," Appl. Phys. B, Vol. 55, pp. 54-59,
1992.
10. M. Kakehata, E. Hashimoto, F. Kannari and
M. Obara, "High specific output energy
operation of a vacuum ultraviolet molecular
fluorine laser excited at 66 MW/cm3 by
electric discharge," Appl. Phys. Lett., Vol. 56,
No. 26, pp. 2599-2601, 1990.
11. H. Mehravaran, P. Parvin and D. Dorranian,
"Changeover in the molecular and atomic
fluorine laser transitions" Applied Optics, Vol.
49, No.15, pp. 2741-2748, 2010.
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