Mechanisms of micro-voids formation caused by optical breakdown in KCl single crystals under laser emission
The phenomenon of optical breakdown has been studied experimentally for KCl single crystals exposed to laser emission focused on the neodymium glass with modulated quality-factor, pulse duration 5·10⁻⁸ s, wavelength λ = 1054 nm, and pulse energy of the order 1 J in the regime of local intrinsic...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2014
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| Цитувати: | Mechanisms of micro-voids formation caused by optical breakdown in KCl single crystals under laser emission / М.А. Volosyuk // Вопросы атомной науки и техники. — 2014. — № 4. — С. 55-59. — Бібліогр.: 25 назв. — англ. |
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irk-123456789-803542016-04-15T13:48:18Z Mechanisms of micro-voids formation caused by optical breakdown in KCl single crystals under laser emission Volosyuk, М.A. Физика радиационных повреждений и явлений в твердых телах The phenomenon of optical breakdown has been studied experimentally for KCl single crystals exposed to laser emission focused on the neodymium glass with modulated quality-factor, pulse duration 5·10⁻⁸ s, wavelength λ = 1054 nm, and pulse energy of the order 1 J in the regime of local intrinsic absorption of the laser emission by the single crystal. Evaluations of local heat flash energetic constituents and characteristic durations for both local area heating and relaxation processes and following comparison with experimental results have shown that the relaxation process takes place in two stages: the first is fast phase followed by crowdion mass transfer with shock wave participation, and the second is slow phase with participation also dislocation mass transfer. Экспериментально исследовано явление оптического пробоя монокристаллов KCl сфокусированным излучением лазера на неодимовом стекле с модулированной добротностью, длительностью импульса 5·10⁻⁸ с, длиной волны λ = 1054 нм, энергией импульса порядка 1 Дж в режиме локального собственного поглощения излучения лазера монокристаллом. Оценки энергетических составляющих процесса локальной тепловой вспышки и характерных времен продолжительности разогрева локальной области и длительности релаксационного процесса и сравнение их с экспериментальными данными показали, что процесс релаксации в таких условиях протекает в две стадии: первая – быстрая, сопровождаемая краудионным массопереносом с участием ударной волны, и вторая – медленная, с участием и дислокационного массопереноса. Експериментально досліджено явище оптичного пробою монокристалів KCl сфокусованим випромінюванням лазера на неодимовому склі з модульованою добротністю, тривалістю імпульсу 5·10⁻⁸ с, довжиною хвилі λ = 1054 нм, енергією імпульсу порядка 1 Дж у режимі локального власного поглинання випромінювання лазера монокристалом. Оцінки енергетичних складових процесу локального теплового спалаху і характерного часу тривалості розігрівання локальної області і тривалості релаксаційного процесу та порівняння їх з експериментальними даними показали, що процес релаксації в таких умовах протікає в дві стадії: перша – швидка, супроводжувана краудіонним масопереносом за участю ударної хвилі, і друга – повільна, за участю і дислокаційного масопереносу. 2014 Article Mechanisms of micro-voids formation caused by optical breakdown in KCl single crystals under laser emission / М.А. Volosyuk // Вопросы атомной науки и техники. — 2014. — № 4. — С. 55-59. — Бібліогр.: 25 назв. — англ. 1562-6016 РАСS: 83.50. – v http://dspace.nbuv.gov.ua/handle/123456789/80354 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
| language |
English |
| topic |
Физика радиационных повреждений и явлений в твердых телах Физика радиационных повреждений и явлений в твердых телах |
| spellingShingle |
Физика радиационных повреждений и явлений в твердых телах Физика радиационных повреждений и явлений в твердых телах Volosyuk, М.A. Mechanisms of micro-voids formation caused by optical breakdown in KCl single crystals under laser emission Вопросы атомной науки и техники |
| description |
The phenomenon of optical breakdown has been studied experimentally for KCl single crystals exposed to laser
emission focused on the neodymium glass with modulated quality-factor, pulse duration 5·10⁻⁸ s, wavelength
λ = 1054 nm, and pulse energy of the order 1 J in the regime of local intrinsic absorption of the laser emission by the
single crystal. Evaluations of local heat flash energetic constituents and characteristic durations for both local area
heating and relaxation processes and following comparison with experimental results have shown that the relaxation
process takes place in two stages: the first is fast phase followed by crowdion mass transfer with shock wave
participation, and the second is slow phase with participation also dislocation mass transfer. |
| format |
Article |
| author |
Volosyuk, М.A. |
| author_facet |
Volosyuk, М.A. |
| author_sort |
Volosyuk, М.A. |
| title |
Mechanisms of micro-voids formation caused by optical breakdown in KCl single crystals under laser emission |
| title_short |
Mechanisms of micro-voids formation caused by optical breakdown in KCl single crystals under laser emission |
| title_full |
Mechanisms of micro-voids formation caused by optical breakdown in KCl single crystals under laser emission |
| title_fullStr |
Mechanisms of micro-voids formation caused by optical breakdown in KCl single crystals under laser emission |
| title_full_unstemmed |
Mechanisms of micro-voids formation caused by optical breakdown in KCl single crystals under laser emission |
| title_sort |
mechanisms of micro-voids formation caused by optical breakdown in kcl single crystals under laser emission |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2014 |
| topic_facet |
Физика радиационных повреждений и явлений в твердых телах |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/80354 |
| citation_txt |
Mechanisms of micro-voids formation caused by optical breakdown in KCl single crystals under laser emission / М.А. Volosyuk // Вопросы атомной науки и техники. — 2014. — № 4. — С. 55-59. — Бібліогр.: 25 назв. — англ. |
| series |
Вопросы атомной науки и техники |
| work_keys_str_mv |
AT volosyukma mechanismsofmicrovoidsformationcausedbyopticalbreakdowninkclsinglecrystalsunderlaseremission |
| first_indexed |
2025-07-06T04:19:22Z |
| last_indexed |
2025-07-06T04:19:22Z |
| _version_ |
1836869812305788928 |
| fulltext |
ISSN 1562-6016. ВАНТ. 2014. №4(92) 55
MECHANISMS OF MICRO-VOIDS FORMATION CAUSED BY OPTICAL
BREAKDOWN IN KCl SINGLE CRYSTALS UNDER LASER EMISSION
М.А. Volosyuk
Kharkov National Auto-Road University, Kharkov, Ukraine
E-mail: marina_andreevna@inbox.ru
The phenomenon of optical breakdown has been studied experimentally for KCl single crystals exposed to laser
emission focused on the neodymium glass with modulated quality-factor, pulse duration 5·10-8 s, wavelength
λ = 1054 nm, and pulse energy of the order 1 J in the regime of local intrinsic absorption of the laser emission by the
single crystal. Evaluations of local heat flash energetic constituents and characteristic durations for both local area
heating and relaxation processes and following comparison with experimental results have shown that the relaxation
process takes place in two stages: the first is fast phase followed by crowdion mass transfer with shock wave
participation, and the second is slow phase with participation also dislocation mass transfer.
РАСS: 83.50. – v
INTRODUCTION
Under radiation influence by elementary particles or
electromagnetic quanta onto solids, there appear
structure defects. As a rule the primary defects are
Frenkel pairs: vacancy−interstitial atom. The interstitial
atoms may be positioned simply in interstitial spaces or
can form dumbbell or crowdion configurations which
can form more complex defect configurations during
interactions. Various radiation damages of the
crystalline lattice strongly affect strength and plastic
properties of materials, so, are the subject of permanent
attention [1-4].
Optical range laser emission transmitting transparent
bodies under definite conditions – high density of the
emission flux, existing absorbing inhomogeneities in the
material structure – is locally absorbed that results in
substantial local heating, plasma formation under high
pressure, and local breakdown of the crystal with
formation of micro-voids (optical breakdown) [5]; this
degrades exploitation properties of functional materials
[6]. The problem is complex. For its solution it is
necessary: 1) revealing the mechanisms of the local
absorption and heating of the crystal; 2) studying the
mechanisms and kinetics of the substance transfer from
the heated area resulting in void formation.
From very general considerations, the mechanisms
of laser emission local absorption for high-pure
materials may be as following: impact ionization of
lattice atoms by electrons originating from
photoionization of impurity atoms by laser emission;
multi-photon ionization of the lattice atoms [5];
“metallization” of a dielectric with narrow enough
band-gap under laser high density emission [7]; or
generation of primary electrons due to cascade Auger-
transitions in the valence band of alkali-haloid crystals
[8]. At high enough laser emission density achieved,
specifically, by the emission focusing, the laser
emission intrinsic absorption by the substance may
occur enough, possibly at crystalline structure defects
where local properties differ from average over bulk
causing lowered barriers to optical quanta absorption
[5]. In real solids, the absorbing extrinsic inclusions, as
a rule, are the sources of the optical breakdown [9, 10].
Taking into account the observed strongly dislocated
crystal structure near pores, the mass transfer was
considered to be realized by the dislocation mechanism.
However, consecutive studying the dislocation
structures near appeared small (about micron size) pores
has shown that only about 5% of the pore volume is
caused by the dislocation mechanism of mass transfer
[11]. The hypothesis has been made that the main
carriers are the crowdions in spite of the existing
conception that for different type interstitial atoms, the
formation energy is rather high (of the order of several
electron-volts) [12]. The crowdion energy in copper,
for instance, is of the order of 5.5 eV [13].
In this connection, analysis of the mass transfer
process in a locally heated area of a crystal is thought
actual taking into account the dynamics of heating and
substance movement under conditions of high pulse
intensity of the process from the point of view of
continuum mechanics.
The aim of the work is studying the mechanisms of
mass-transfer in a locally heated area during a micro-
void formation as a result of optical breakdown in the
KCl single crystal under laser emission.
EXPERIMENT AND RESULTS
In the experiments carried out at room temperature,
KCl single crystals grown by Kyropulos method from
raw material of ХЧ (chemically pure) grade were used.
For irradiation, the pulse laser with modulated quality
on the neodymium glass with pulse duration
τ ≈ 5·10-8 s, wavelength λ = 1054 nm, and energy per a
pulse near 1 J was used. The laser with infra-red
emission and short pulse duration was chosen in order
to lower the losses for absorption and scattering,
including that at the crystal non-polished surfaces, and
to obtain high energy flux density enough for optical
breakdown due to the crystal intrinsic absorption in the
lens focal plane. The laser emission was focused by a
lens with focus distance F = 10 cm and working
aperture diameter 2b ≈ 1.5 cm. The emission flux
density in the working zone of the focal plane was
determined by the pulse energy and the focal zone size.
According to [14], the focal zone in the lens focus has
elongated, to a first approximation, cylindrical shape,
56 ISSN 1562-6016. ВАНТ. 2014. №4(92)
with l׀׀ length and l┴ radius which are determined by the
relation [14]:
l׀׀ = λ (F/b)2; l┴ = λ (F/b), (1)
where F is lens focus distance, λ is the wavelength of
incident light.
Taking into account the values of the parameters
included, for our case we obtain: l10-4·130 ≈ ׀׀ m,
l┴ ≈ 10·10-6 m. The focal area volume is V ≈ 4·10-14 m3.
In order to provide precise positioning the crystal
relative to the light beam under laser exposure, in the
previous experiments we found precise spatial position
of the laser beam axis and focus under microscope using
the glasses with deposited thin metallic films. The
crystal was positioned in the point of the light beam
geometric focus and irradiation was carried out. The
irradiation conditions were chosen in order to obtain
pores of micron size.
The main result of these experiments was that the
formed voids were always positioned practically on the
beam axis close to the center of the focal area
(geometric focus). Most often only one pore formed,
rarely – two pores, more rarely – more than two. In
Fig. 1 the case is shown where two pores positioned
practically on the axis of the focal area have appeared.
Fig. 1. Dislocation structure near the pore formed
Formation of a pore chain, most likely, begins from
the distant (along the beam) pore. New voids develop
towards the beam, because every time the emission
weakens and defocuses behind the void. Thus, in our
experiments every time the optical breakdown takes
place near the lens focal area, on its axis. This is not
occasional fact as the detailed analysis of the light field
intensity distribution in the lens focus shows that the
field in the focus vicinity is complex [15]. In the
meridian plane along the optical axis, the intensity is
characterized by a function [(1/x)·sinx]2. In the focus
there is a principal maximum and a number of
additional maxima of lower intensity are along the lens
axis, their intensity lowers as the distance from the
focus increases (symmetrically – before and behind the
focus) [15]. In our case, the distance to lateral maxima
is about 150± μm. The second pore appeared at the
distance only 19 μm (see Fig. 1), i.e. in the vicinity of
the principal maximum.
The fact that voids are formed preferentially in the
area of light maximum intensity allows assuming the
role of intrinsic absorption (including non-linear one
connected with emission flux high density and multi-
photon absorption [10]) being predominant. The
following supports such conclusion. Using the light-
scattering method as in [16] we determined the
concentration N of inhomogeneity particles in the
crystals under study and also their size d: N ≤ 1014 m-3,
d ≤ 10-6 m. As the focal area volume is V ≈ 4·10-14 m3,
probably several (≈ 4 ones) foreign particles can be
within it. Evidently, the probability of occasional being
of even one particle in the center of the focal area is
significantly less than a unity; at the same time, the
optical breakdown was always observed just near the
center of the focal area. It is worth to be taken into
account as well that among the inhomogeneities
revealed by light scattering method in pure enough
alkali-haloid single crystals, the micro-voids non-
absorbing the light are predominant [17, 18].
DYNAMICS OF LOCAL HEATING
AND PLASMA FORMATION DISCUSSION
For constructing the model best of all describing the
dynamics of destruction in a single crystal it is
necessary to estimate its characteristic durations and
energetic constituents. Let us evaluate the duration of
heating the crystal area where plasma with temperature
Тpl ≈ 5.5·103 К. The plasma temperature was taken from
[6] and supported by many other works where it was
determined by spectroscopic investigations.
The average value of laser emission flux density
J per a pulse in the lens focal plane is determined by
the relation:
J =Еpulse /τ·π (l┴ )2, (2)
where Еpulse is the pulse energy (Еpulse ≈ 1 J); τ is the
pulse duration (τ ≈ 5·10-8 s), l┴ is an average value of
the focal zone radius (defined by (1)). After substitution
of numerical values we obtain J ≈ 6.37·1016 W/m2.
To concretize further estimations it is necessary to
take the shape and sizes of some initial area of
absorption. In [19] the filming of destruction process
was made, and in the first shots of the film, the optical
contrast zone with size about 70…100 nm was observed
which was identified as a void occupied by plasma.
Taking into consideration the identity of our
experimental conditions, we take for estimations the
initial absorption area (plasma nucleus) as a cube with
100 nm edge. The energy flux Iabs,which is absorbed by
such nucleus is:
Iabs =J·S·k, (3)
where S is the irradiated square; k is absorption
coefficient which is unknown precisely, but it is known
that infra-red radiation is practically completely
absorbed by a plasma layer of micron size [19]. In [20]
it was shown that luminous substance is non-
transparent, so in following we take k = 1. Assuming for
simplicity that the radiation enter into the cubic nucleus
through one of the cube face with square S = 10-14 m2
we obtain Iabs = 6.37·102 W.
Let us evaluate the energy losses caused by heat
radiation and thermal conductivity in the crystal. The
heat radiation flux density Jrad is defined as
Jrad =σΤ4, (4)
where σ = 5.669·10-8 W(/m2·К4) is Stephan-Boltzmann
constant; Т is plasma temperature. Substituting σ and
Т = 5500 К in (4) we obtain Jrad ≈ 5.2·107 W/m2. The
flux of energy losses for heat radiation Irad is defined as
Irad =Jrad·6S. (5)
10 μm
ISSN 1562-6016. ВАНТ. 2014. №4(92) 57
Substituting the numerical values we obtain
Irad ≈ 3·10-6 W.
The flux density of losses for thermal conductivity
Jtherm into the surrounding crystal we estimate writing
the equation for the flux density as follows:
Jtherm= – λ grad T = – a2 ρcV grad T, (6)
where λ is thermal conductivity coefficient; a2 is
thermal diffusivity coefficient; ρ is KCl crystal density;
cV is specific heat of KCl crystal.
The temperature gradient at the plasma-crystal
boundary we evaluate in assumption that the maximum
temperature Tmax = 5.5·103 К falls to room value at the
distance about the taken size of plasma cloud
1pl ≈ 10-7m, therefore
grad T≈ Tmax /1pl . (7)
Taking into account a2 = 7.3·10-6 m2/s,
ρ = 2·103 kg/m3
, cV ≈ 580 J/(kg·К), we obtain
Jtherm ≈ 4.7·1011 W/m2. The heat energy losses flux from
the plasma cloud into the crystal is
Itherm= Jtherm·6S ≈ 2.8·10-2
W. Thus, the energy losses for
heat radiation and thermal conductivity are found to be
by orders of value less than the absorption energy flux
Iabs that provides fast local heating and plasma
formation.
To evaluate the time period of plasma formation at
temperature 5.5·103 К we estimate the energy value
necessary for its formation Еheat neglecting the losses.
To a zero approximation, neglecting dependences of
specific heat on aggregate state and temperature of the
heating volume we can write:
Еheat= m [cV (Тpl – Тm)+(∆Hm+∆Hev )]. (8)
Taking the temperatures of melting and evaporation
as Тm = 1045 K and Тev = 1686 К, respectively, the
plasma temperature Тpl = 5.5·103 К, the heats of melting
and evaporation ∆Hm = 3.43·105 J/kg,
∆Hev = 21.7·105 J/kg, respectively, for the plasma cloud
of ≈ 10-7 m size we obtain estimation Еheat = 10-11 J.
Taking into consideration the absorption flux value
(Iabs = 6.37·102 W) and the obtained energy Еheat, we
evaluate the heating time τheat, which essentially defines
the dynamics of whole relaxation process:
τheat = Еheat/Iabs ≈ 1.57·10-14 s. This evaluation can be
found noticeably understated on account of inexactly
known both absorption coefficient (k) and growing with
time absorbing area size.
Finite size of the plasma cloud is found to be of the
same order [11, 19, 20], as the size of the void formed;
therefore, if the cloud shape is taken also cubic but with
edge of the order of 10-6 m, the size of heating area
increases by three orders of value, and the absorption
flux increases only by two orders, the fact in turn results
in increasing the heating time by an order of value:
τ`heat ≈ 1.57·10-13 s.
Thus, the time of plasma formation and heating is by
orders of value less than the laser pulse duration
5·10-8 s; the plasma cloud size variation does not
practically change the relation between the absorption
flux and the energy loss one, and consequently does not
practically influence on the plasma heating time.
The pressure in the energy release area at Т = Тpl can
be estimated by the expression Pmax ≈ K (δV/V)
(assuming the heating area remaining as a compact
formation), where К is the modulus of volume
compression, δV/V = 3α∆Τ is the volume jump
connected with heating. Taking into account К=
1.74·1010 N/m2, α = 48·10-6 К-1, and ∆Τ ≈ 5200 К we
obtain Pmax ≈ 1.3·1010 N/m2. From the viewpoint of the
mechanics of continua the process under study where
the pressure achieves value exceeding the theoretical
strength limit for the time less 10-6 s, should be
considered as explosion-like [21] or shock process [22].
From the experiment (see Fig. 1) it is follows that
the substance from the “explosion area” jumps out at a
distance about 10 sizes of the pore formed, i.e. in our
case, at the distance of the order of 10-5 m in the
directions of easy sliding. The process of the mass
transfer follows the heating process overlapping to some
degree, therefore the duration of the main mass transfer
correlates with the heating time period τheat ≈ 10-13 s,
while the former remaining always more but not
exceeding the laser pulse duration 5·10-8 s. Indeed, the
pulse duration variation from 5·10-8 s to 10-8 s in no way
influences the destruction picture [11]. It was shown in
[19] that the void becomes practically formed for tens
nano-seconds.
The minimum time of plastic relaxation τrel due to
deformation by dislocation mechanism (as the most
fast) can be obtained in assumption of dislocation
movement with extremely high velocity close to
acoustic speed. In aluminium, for example, the
dislocation speeds of the order of 0.8 υac were observed
under extremely high loads [23]. In our case, the
destruction area size is about 10-5 m, therefore the
relaxation time is τrel ≈ 2·10-9 s, i. e. the dislocation
mechanism is, in principle, could be realized, but
experimentally it was not observed in the beginning
stage. In Fig. 1 we observe dislocation loops with
diameter larger than the void diameter. That indicates
the dislocations have appeared more later, seemingly,
before crystallization of melt remained in void walls
[11], and the total contribution of dislocations into pore
formation, as mentioned, is very small.
Taking into account the observed explosion-like
heating dynamics we can assume that in such process an
shock wave appears which can move with supersonic
velocity. It was shown in [24] that under certain
conditions crowdions can move with velocity exceeding
the acoustic value. In [25] using computational
modeling for Ni 2D-model the crowdion movement
speed range was established as (12.3…14)·103 m/s.
These two factors: existing the shock wave and high
velocity of crowdions can provide the necessary high
speed of mass transfer in the beginning stage of the
process during the shock wave passes the relaxation
area.
The general scheme of plastic deformation arising
from abovementioned estimations and observations is
seemed as follows. In the beginning, under action of the
shock wave the crowdions are generated which carry the
substance from the high pressure area and move along
close-packed atomic rows (‹110› type directions in KCl
crystals); the void is formed almost completely during
the shock wave passing the relaxation zone cross-
section. This time is of the order of τrel, i. e.
10-9…10-8 s. After falling temperature and pressure and
vapor condensation into liquid, at the end of relaxation
58 ISSN 1562-6016. ВАНТ. 2014. №4(92)
process, the void boundaries expand already under
liquid melt pressure, and the mass transfer dislocation
mechanism comes into action providing additionally
some enlarging the void volume. This process continues
also after stopping the laser emission, during the crystal
cooling down to the melt crystallization in the void and
formation of a pore with size observed.
In [19] the data are presented on the micro-filming a
void growth during irradiating the crystal by laser short
pulses with duration 80 ns. The obtained in [19] data we
showed at the plot (Fig. 2) in the linear scale with axes
d/d0 and t (d is diameter of optical contrast picture
which is considered in [19] as the void boundary, d0 is
the finite diameter of the void formed). In such
presentation of results [19], concerning to the stage of
the void growth, indeed as it was supposed, two
characteristic parts are observed. If the beginning part of
the void fast growth (about from 80 to 200 ns) and the
second part – slow growth (from 300 ns to 10 μs) are
extrapolated by direct lines, one can see that the void
growth velocity in the second stage decreases by about
four orders of value in comparison to the first stage
(from 102 to 10-2 m/s). At that in the first stage, the void
quickly reaches practically its finite size as it is
observed at the end of the experiment (see Fig. 1).
Fig. 2. Growth kinetics of a void transverse size in the
stage of radiation exposure to 10 μs (laser pulse
duration 80 ns, d is pore size in t time moment,
d0 is the pore finite size)
It can be assumed that the following drastic slowing
the void growth speed is connected with increasing the
void volume and decreasing the pressure in it, as well as
stopping the plasma heating by laser pulse. It is in this
stage the dislocation mechanism comes into action. This
follows from the fact that observed in Fig. 1 dislocation
loops have size larger than the observed finite size of
the void d0. Their size corresponds to the void size in
the second (slow) part of its growth (see Fig. 2).
The observations and conclusions described above
are in logical accordance both with estimations of the
process dynamics and the developed scheme for action
of void formation mechanisms under optical
breakdown.
Of interest is the evaluation of energy expended to
void formation in the stage of crowdion mechanism
action. This can be evaluated by the order of value as
the energy for generating crowdions in necessary
quantity (taking into account crowdion high mobility),
i. e. Еcr = (Vvoid/ω)·εf, where Vvoid is void volume; ω is
atomic volume; εf is formation energy of a single
crowdion. Substituting the numerical values we obtain:
Еcr ≈ 5·10-8
J. If consider the total energy of a void
formation Еtotal = Pmax·V ≈ 8·10-8 J, the obtained Еcr
seems reasonable and logically agrees with Еtotal ;
therefore, the developed conception is thought to be
right and experimentally supported.
CONCLUSIONS
The experiments have been carried out where the
conditions for effective realization of optical breakdown
were provided in KCl single crystal due to local
intrinsic absorption. Evaluations of energetic
constituents and characteristic durations of the process
in different stages have been fulfilled. Based on the
evaluations and the picture of the breakdown it has been
shown that the single real mechanism of substance
carryout from the energy release zone in the beginning
stage may be the mechanism of crowdion generation
and moving with high, even supersonic velocity,
possibly, with shock wave participation.
The dislocation mechanism enters practically at the
end of the process and contributes a little. A void grows
under melt pressure and emits prismatic dislocation
loops with size larger than the size of the void
remaining after melt crystallization.
In conclusion I’d like to extend thanks to Dr. of
Phys.-Math. Sci., Prof. V.G. Kononenko for the work
idea, discussion, and constructive helpful consults.
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Статья поступила в редакцию 20.06.2014 г.
МЕХАНИЗМЫ ОБРАЗОВАНИЯ МИКРОПОЛОСТЕЙ ПРИ ОПТИЧЕСКОМ ПРОБОЕ
МОНОКРИСТАЛЛОВ KCl В УСЛОВИЯХ ЛАЗЕРНОГО ОБЛУЧЕНИЯ
М.А. Волосюк
Экспериментально исследовано явление оптического пробоя монокристаллов KCl сфокусированным
излучением лазера на неодимовом стекле с модулированной добротностью, длительностью импульса
5·10-8 с, длиной волны λ = 1054 нм, энергией импульса порядка 1 Дж в режиме локального собственного
поглощения излучения лазера монокристаллом. Оценки энергетических составляющих процесса локальной
тепловой вспышки и характерных времен продолжительности разогрева локальной области и длительности
релаксационного процесса и сравнение их с экспериментальными данными показали, что процесс
релаксации в таких условиях протекает в две стадии: первая – быстрая, сопровождаемая краудионным
массопереносом с участием ударной волны, и вторая – медленная, с участием и дислокационного
массопереноса.
МЕХАНІЗМИ УТВОРЕННЯ МІКРОПОРОЖНИН ПРИ ОПТИЧНОМУ ПРОБОЇ
МОНОКРИСТАЛІВ KCl В УМОВАХ ЛАЗЕРНОГО ОПРОМІНЮВАННЯ
М.А. Волосюк
Експериментально досліджено явище оптичного пробою монокристалів KCl сфокусованим
випромінюванням лазера на неодимовому склі з модульованою добротністю, тривалістю імпульсу 5·10-8 с,
довжиною хвилі λ = 1054 нм, енергією імпульсу порядка 1 Дж у режимі локального власного поглинання
випромінювання лазера монокристалом. Оцінки енергетичних складових процесу локального теплового
спалаху і характерного часу тривалості розігрівання локальної області і тривалості релаксаційного процесу
та порівняння їх з експериментальними даними показали, що процес релаксації в таких умовах протікає в
дві стадії: перша – швидка, супроводжувана краудіонним масопереносом за участю ударної хвилі, і друга –
повільна, за участю і дислокаційного масопереносу.
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