Digest Journal of Nanomaterials and Biostructures Vol. 7, No. 2, April - June 2012, p. 687 - 696
STUDY ON FOUR-DIMENSION NUMERICAL MODELING OF SRRS EFFECTS
ON BEAM DISTRIBUTION IN NEAR FIELD AFTER ICF HIGH POWER
ULTRAVIOLET LASER PROPAGATING THROUGH A LONG AIR PATH
YING LIU
a,b
, DIANYANG LIN
a
,
ZHIWEI LU
a*
a
National Key Laboratory of Tunable Laser Technology, Harbin Institute of
Technology, Harbin,150080,China
b
School of Mathematics Science, Harbin Normal University, Harbin,150080,
China
It is necessary for high power ultraviolet laser to propagate through a long air path during
experiments of inertial confinement fusion (ICF), when beyond stimulated rotational
Raman scattering (SRRS) threshold, the high power ultraviolet laser beam would be
subject to loss of energy and a decrease in beam quality , results in the reduction of
conversion efficiency of triple-harmonics, even causing the optical components to be
destroyed. This paper studies the four-dimension numerical modeling of SRRS effects
on ICF condition, emphasizing on beam intensity distribution in near field. We settled the
simultaneous equations by finite element method of MATLAB without slowly varying
amplitude approximation or process neglecting. Finally the rule of four-dimension
numerical modeling of SRRS affecting on beam intensity distribution in near field after
ICF high power ultraviolet laser propagating through a long air path was got and the first
independence simulation of pump and Stokes laser ‘s transverse diffraction effects were
got.
(Received January 21, 2012; Accepted May 18, 2012)
Keyword: Ultraviolet laser, Stimulated rotational Raman scattering,
Distribution in near field
1. Instruction
All energy comes from nucleus fusion of the sun .For people have grasped the technology
of uncontrollable nucleus fusion, namely hydrogen bomb, then how to control nucleus fusion has
become an important task. There are two methods to realize controllable nucleus fusion, one is
magnetic confinement fusion, the other is inertial confinement fusion (ICF) which was first
suggested by Lebedev and N.G.Basov from former Soviet Union in 1960s[1].
The strict requirements to ICF’s high power laser drive
[2]
are(1) enough ensemble output
capability to assure high temperature and high density conditions; (2)good beam quality to insure
target practice experiment, to satisfy the basic requirements of high energy conversion efficiency
of the triple- harmonic, running stability and safety; and (3)strengthen beam and pulse control to
assure the black cavity radiation field can be strong enough in indirect driving of the physical
experiment and to satisfy the drive running stability. These requirements suggest that the even
quality of beams in the near field is important for running the laser drive. In the ICF laser drive,
the power of the beam is far higher than the self focusing critical power and usually is 10 times
that of the latter one. In this case the beam’s uneven quality in near field leads to small size self
focusing easily which divides the beam into silk, then makes partial of the beam destroy optics
components. From above we know the beam’s even quality in the near field determines the
*
Corresponding author: zw_lu@sohu.com