Condition of constancy of mass flow gives
and possible write for pressure of return
(3)
where 
-a velocity
a pair near bottom of channel(Pic.2).
Value now value of source velocity a pair VK
on the day of channel.
Do this, ïðèðàâíÿâ
density of flow a pair from the bottom JK = q ´V
attitude of density of power on the evaporation, to the specific heat vaporization
units of mass equal for water under 100° C :
2.26´
0.00000000001 erg/g.
As a result of will have :
(4)
whence for pressure of return easy to find
(5)
that means that at the evaporation under the
atmospheric pressure a pressure of return grows on second degrees heat
input.
A numerical evaluation under
q@
10000 Wt\cm·cm gives V@
7.6 ´
100 cm\sec.
Apropos, such evaluation means that
This fact justifies a main thesis models on vicinity
of spot co to
the bottom a channel.
Really, adjustment because of end value of velocity
to pressureform 
that on
four orders less under discussion effects.
Main equation.
(*)
or in the detailed form:
(**)
where g = 4 ´
10000 erg\cm ´
cm´
cm´
hail (refer
to. Formula(2) ), ST - an overheat of
vaporize surface.
Do, resulting this point, evaluations of orders
of values of members in (**)
Thereby, overheat of liquid
near bottom of channel must not exceed 0.1
degree.
II. Factors, influence upon the depth of channel.
Main equation (**) links a depth h vapour-gas channel
and its width beside basis 2R with density of power , walking on 
the evaporation, and overheat borders - ST.
However these values are bound and other correlations, which and are to
allow to calculate or value experimental observed dependencies of depth
of crater from the temperature, focal length of lens and degrees an defocusing.
Focusing of lazer bunch by walls a channel.
Value first distinctive sizes light
of caustic light bunch with packed angular divergence Q
, , with diameter
on focusing lens with focal length
(Pic.5):
(6)
For experimental parameters
q =7 ´
0.003 , = 0.5cm ,
will have for F =50cm and F =350cm accordingly ( refer to. Table 1 ):
r = 0.175mm and 1.25mm; Z = 0.45cm and 15cm.
These evaluations show that for lenses with F > 160mm possible with confidence to take that length light of caustic Z much more lengths h the vapour-gas channel. So for experiments with F > 160mm falling bunch possible to consider collimate , indivergence.
These evaluations allow offer an explanation of
changing a form of channel at variational focal length of lens and temperatures
of liquid. For the event of the length-focus lenses (F>
160mm) light bunch passes bottoms up channel, practically not not
have time will be knock on walls and saving its diameter, then for the
short-focus lenses F =50ìì and 100mm
- periphery rays of bunch, reflecting from walls, are focused in
central /axial/ area of bunch, raising there its intensity.
(Pic.6a,b)
May be to say that in the second event of reflecting
from walls focus a bunch on the day of channel,
do sharpen of profile of its intensity, but
signifies and transverse profile of density of evaporation , and hereunder,
profile of crater.
With raising a temperature of liquid, lead by the
light bunch an the short-focus lens a heat on walls of channel near its
tip, are intensify an evaporation not only with the bottom, as well as
with adjoin to him walls of channel . Appear at pulse of return increases
a channel in lower part, retutn him constancy of diameter. Here to follows
to add that if in the event of, it is represent on Pic.6a,
area of transverse section of bunch on the day approximately is areas of
section an caustic, for the event on the Pic.6b
efficient radius of bunch on the day R
can be cast from the radius of bunch in caustic
r.
