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Annual Report of China Institute of Atomic Energy 2006
High Power Laser and Accelerator
Investigation of UV Single-Shot FROG Measurement
XU Yong-sheng
The traditional pulse measurement in the UV region is autocorrelation measurement based on the two
photons process. It can only offer limited information such as pulse duration, etc, but not pulse intensity
and phase distribution in the time and frequency domain. It is also scarce of enough independence because
the dependence between the response of the spectrum, signal intensity and incidence intensity must be
checked in order to avoid the distortion of autocorrelation curve. Further more, it involves severe pulse
distortion because of high material dispersion in the UV region. When all those problems occur, the
measurement itself becomes very difficult, say nothing of recovering the pulse intensity and phase. So,
some new measurements must be introduced in the UV region.
FROG measurement can measure many types of ultra-short pulse. It is the acronym of
Frequency-Resolved Optical Gating. It involves of measuring the 2-D instantaneous frequency
spectrogram as the function of time, and of recovering the pulse intensity and phase from the spectrogram
by use of the iteration numerical calculation. FROG measurement only needs to resolve the pulse
frequency nonlinearly. It can describe the pulse completely. It includes two parts: 1) The hardware part is
FROG optical elements. 2) The software is FROG recovering program. FROG has many advantages: 1) It
can resolve the pulse structure. 2) It can offer the feedback for the adjustment of laser systems. 3) It can
measure very short pulse duration. 4) It can distinguish different physical processes. 5) It can measure
complex pulse that has ultra broad bandwidth. So, FROG can measure the UV pulse that has complex
physical processes.
FROG has several types as follows: 1) SHG FROG. 2) THG FROG. 3) TG FROG. 4) PG FROG. 5)
SD FROG. In these types, TG FROG and SD FROG are applicable to measure the UV pulse, but only SD
FROG is appropriate for single shot measurement because TG FROG needs three laser beams but SD
FROG needs two. The single-shot FROG measurement has many advantages compared to the multi-shot
FROG. It can obtain single pulse’s parameters by only one pulse shot. It not only saves time and optical
elements, but also adjusts simply. The single-shot SD FROG for UV pulse needs elements as follows: 1) A
space filter (to make the laser beam smooth spacely); 2) A piece of thin fused silica as nonlinear material;
3) A reflector with a piece of slot to avoid material dispersion in the beam splitting by use of the
common beam splitor; 4) A cylindrical mirror to focus the beams linearly in the thin fused silica; 5) An
imaging spectrometer with a CCD camera to record the spectrogram; 6) A F-P etalon to calibrate pixels in
FROG spectrogram. The hardware of FROG is figured in Fig. 1.
The software of FROG is figured in Fig. 2.There are two constraints in FROG Program: one is the
mathematical form of optical nonlinearity, and another is FROG trace data. The program is iterated
between two constraints with Fast Fourier Transform. It doesn’t stop until the demanded solution is
reached. The solution is unique.
The hardware of the UV single-shot FROG can be obtained easily, and the software can be obtained
from Femtosoft Technologies Company. So, setting up the UV single-shot FROG measurement is not only
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practical, but also economical.
Fig. 1
Hardware of the SD FROG
Fig. 2
Software of the SD FROG
Study of Near-Field Nonuniformities in MOPA System of Heaven-I Laser
GAO Zhi-xing，TONG Xiao-hui，XIANG Yi-huai，LU Ze，HU Feng-ming，WANG Hua
Although induced spatial incoherence (ISI) and image relay have provided ultrasmooth illumination
at the far-field of the Heaven-I laser, where the target is located, there still be some speckle in near filed of
the laser. The average flux in angularly-multiplexed KrF systems is well below damage threshold
(1 J/cm2), but the speckle nonuniformities of ISI beams are likely to cause some damage in the optics. We
measured the nonuniformities of the near filed beam on the surface of the mirror to explore the options to
control the problem.
It is found that the peak intensity of the speckle is most likely to be twice of the average intensity of
the beam. The speckle intensity on some mirror surface is as high as five times of the average intensity
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which causes the damage easily.
To control the problem and avoid the damage the following suggestion is listed.
1) To align beam path, the average flux through the optics should be less than half of the damage
threshold.
2) The threshold of the optics for Heaven-I laser should be improved to 5 J/cm2 from 1 J/cm2.
3) Not JGS-1 quartz but the optical glass should be chose as the base of high reflective mirror to
reduce the possibility of the damage caused by the beam focusing which pass through the mirror.
The development of the speckle and near field nonuniformitis of the beam should be study more
deeply to explore the options to improve the system.
EOS Experiments Based on the Heaven-I
WANG Zhao, LIANG Jing, GAO Shuang, LU Jian-xin
A uniform planar shockwave was required by high precision equation of state (EOS) measurements.
This paper presents our work in studying shockwave generated by KrF laser. There are three kinds of
target were used, plane target without flyer, flyer plane target and single step target without flyer.
1
Plane target without flyer
These targets contain organic film, metal foil and quartz crystal. The simple structure can reduce
many complex factors in the process of generating shockwave. The impact emission of plane target
without flyer is shown in Fig. 1.
The front signals were measured by using streak camera, the interval less than 2 ns.
a
Fig. 1
b
Impact emission of plane target without flyer
a——100 m Kapton foil, 13 m Al foil; b——100 m Kapton foil, 20 m Fe foil
2
Flyer plane target
Compare with first kind, these targets contain flying distance for flyer. We have to analyze the factor
of flyer to be used in EOS experiments for increasing pressure in target.
In Fig. 2 the thin light at the top is reference signal to calculate flying time of flyer. The front of
signals become uneven, it shows that we should improve the technology of making target.
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b
Fig. 2
Impact emission of flyer plane target
a——Vacuum 50 m, E=158 J, t = 21 ns; b——Vacuum 100 m, E=170 J, t = 33 ns
3 Single step target without flyer
In order to measure the equation of state, we must measure the shockwave velocity and the particle
velocity synchronously. It is the first time for using the step target on Heaven-I. The targets were made
ourselves. Structure of single step target is shown in Fig. 3.
According to Fig. 4, the shockwave velocity can be calculated by measuring the interval.
Fig. 3 Structure of single step target
Fig. 4
Impact emission
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Research of the Characterizations of Ultra Fast Laser’s Focusing
WANG Lei-jian, ZHANG Jig
The ultra-fast laser, wavelength is 756 nm and the pulse width is 100 fs. When it transferred some
distance, self-focusing happened. In condition of serious self-focusing and no self-focusing, we compared
the far-field divergence, the size of focal spot and concentration ratio of the energy. With the same
focusing system, the far-field divergence is bigger, the pulse width is wider, and the size of focal spot
doesn’t change, 12-13 μm, when the air is breakdown. The energy witch is contained in the effective focal
spot is higher, about 60%, when there is no self-focusing. If use the aspheric lens, the focusing effect is
perfect, it almost reaches the diffraction maximum, and above 70% energy is contained in the effective
focal spot. The laser focal spot parameters in different conditions are listed in Table 1.
Simulate target practice in-axis motion, focal spot size is changing. In these experiments, target move
100 μm in each, the focal spot size will change 3 μm in average. When target surface excursion from focal
position 300 μm, the energy concentration ratio show a palpable down. In the target practice, if the
dithering of the target is controlled within 100 μm, the change of the power density caused by the focal
spot size changing have no affect on the magnitude of the power density.
Table 1
Laser focal spot parameters in different conditions
B integral value
Diffraction multiple
Focal spot size/μm
（f=1.78 m）
（f=50.8 mm）
1.5
12.5
Regenerative Amplify
（2±0.15）mJ, 100 fs
Energy in effective focal spot
Sphere lens 58%
0.3
Off-axis parabola 70%
Double-pass Power Amplify
（30±2）mJ, 100 fs
4.5
1.8
13
44%
Synchronize of RF Signal to Femtosecond Laser Pulse Train
DAI Hui
Synchrotron radiation lighting source, as the revolutionary lighting source after the electronic
lighting source, X-ray lighting source and laser lighting source, has been widely used in advanced
research work such as material, circumstance and biology technology. Compare to the third generation
lighting source of energy ring, the energy-recovery-linac driven lighting source is much easier to design
and to achieve high power output. It is generally considered as an ideal candidate for ultra bright and ultra
short pulse length free electron X-ray laser.
Generally, the energy recovery linac to generate the free electron X-ray laser has a large area over
several kilometers and consists of tens of sub-systems. Even a time jitter of picosecond will cause unlock
of the whole system, and synchronize of the sub-systems is a key elemental to fulfill the laser output. To
fulfill the precise synchronize of such huge system, pulses train from a time stabled laser is distribute to
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sub-systems with low waste fiber. An electronic-optical mixed phase lock loop has been experimental
tested to synchronize the RF signal to femtosecond laser pulses train. The Sagnac-loop Mach-Zender
interferometer in the phase lock loop is easy way to avoid the nonlinear of direct photo detect, and to lock
the RF signal on the reference femtosecond laser signals.
To avoid the nonlinear limitation caused by the phase noise of direct photo detection, two opposite
amplitude modulations are usually used in the phase detection. The laser signal is divided and guide into
two opposite amplitude modulations. When the RF signals do not lock to the laser pulses train, the output
of the opposite amplitude modulations is imbalanced, this give us a feed back signal to modify the RF
frequency to suit the laser pulse train. The Mach-Zender interferometer is traditional amplitude for this
kind of use, furthermore. To avoid the mechanics vibration and temperature fluctuation imbalance of the
two arms in the interferometer, we use a Sagnac-Loop design in the interferometer. The mechanics
vibration and temperature fluctuation affect two arms in the same time, and transfer the time field
information into intensity imbalance of two laser pulse train. With the phase lock loop, it is easy to feed
back to a voltage control oscillator to adjust the frequency of the RF signal to lock to the laser signal.
We achieve the synchronize of 1.333 GHz RF signal to Ti: Sapphire laser pulses train with the
repetition rate of 83.3 MHz. We use the RS-230A spectrum analyzer to measure the signal band phase
noise of 1.333 GHz RF signal, and measure the phase noise of the Ti: Sapphire laser by direct photo
detection. It is found that, the RF signal and the femtosecond laser pulse train is locked to each other
cover the range of 10 kHz to 1 MHz. But at the range lower than 10 kHz and higher than 10 MHz, it is
still has the potential to lower the phase noise between the RF signal and the laser pulse train. By fiber
connection, optimized circuit design and more stabilized DC input, this phase lock design is looking
forward to lower the time jitter to sub-femtosecond to fulfill the requirement of future large-scale
accelerator.
Primary Study of Line Optically-Recording
Velocity Interferometer System
LU Jian-xin, WANG Zhao, LIANG Jing, GAO Shuang, SHAN Yu-sheng, TANG Xiu-zhang
Recent development of high-power laser system leads us to investigate the equations of state (EOS)
of condensed matters at high pressures that the previous experiment methods such as gas guns and
explosives can not achieve in the lab. In order to acquire the precise equation of state date, two parameters
must be obtained independently. An optically-recording velocity interferometer system (ORVIS) with
quasi-zero path difference was be used in EOS experiments. An improved ORVIS called line
optically-recording velocity interferometer system (Line-ORVIS) is introduced, and two parameters
would be obtained independently.
In the line-ORVIS, a laser beam produced by an argon ion laser BeamLok 2060 become a line by a
cylindrical lens, and is focused on an image conduit. A line pattern is observed on the other side of the
image conduit. The line is transferred on the back surface of the target which is to be monitored by an
imaging system, and then the image is transferred into an interferometer by another imaging system. An
interference pattern is recorded by a streak camera. Shockwave velocity and free surface velocity can be
acquired by analyzing the pattern. A basic table-top experiment was carried out, and the interference
pattern is shown in Fig. 1. The line-ORVIS will be an important tool in EOS experiments.
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Fig. 1
Interference pattern of line-ORVIS
Preliminary Idea of Target Fabrication and Numerical Simulation
on EOS Measurement of Liquid Deuterium
LIANG Jing
Study of the EOS of liquid deuterium is crucial for ICF research. Here a preliminary idea of target
fabrication and numerical simulation on EOS measurement of liquid deuterium is presented.
Because you can’t cut and roll the specimen such as liquid deuterium, the target fabrication may be
relevantly complicate. First, it must have a cryogenic container to restrict the specimen, and separate from
the rest vacuum space of the target capsule. During the experiment, the cryogenic container mustn’t be
broken even a little, or a detonation may occur because the leak of liquid deuterium. Secondly, it must
bring up a flat plate to help produce a plane shock wave and another plate to offer the possible diagnosis.
Moreover, after the laser driven shock wave transfer through the specimen, it may reach the plate for
diagnosis, and reflect a shock wave back to the specimen due to the larger impedance of the plate. So the
specimen may undergo a second compression and the pressure may increase, this extends the pressure
range in our experiment. More diagnosis about the shock wave can add to the experiment due to the larger
plate for diagnosis, such as shock temperature measurement, specimen conductivity measurement, which
make enhancement to the accuracy and reliability of our experiment data and the observation of new
phenomenon may turn into truth, such as the metallization of the deuterium.
Fig.1 Pressure in the liquid deuterium versus mesh index in the HYADES simulation
a——The first compression; b——The second compression
HYADES is a one-dimension three-temperature numerical simulation code mainly use for simulate
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the physics image about the laser driven shock wave in the flyer or the target.
Base on the above target type, a numerical simulation is carried out with the use of HYADES (Fig. 1).
The result, comparing to the experiment data in the original article, shows that to the laser intensity of
1013 W/cm2, the pressure in the liquid deuterium may be several tens to one hundred megabar in the first
compression and reach four to five hundred megabar in the second compression.
Application of Side-On Shadowgraph System in EOS
GAO Shuang, TANG Xiu-zhang, WANG Zhao, LU Jian-xin, LIANG Jing
Experimental measurements of EOS have more and more attention from many physical fields, such
as physical geography, astrophysics, ICF, science of material, physics of nuclear weapons. They are
important to the practical application and the development of theory of EOS. A series of researches in
EOS done by ultraviolet long pulse laser Heaven-I, had prominent characteristics and developed very well.
As an important technique to detect the target in EOS, side-on shadowgraph has been wildly applied all
the while. In 80s, using framing camera and folded-wavefront interferometer, some laser-shocked
experiments had been carried out by some scientists in Canada. In recent years, making use of side-on
radiograph, absolute EOS measurements of low Z material had been carried out by Lawrence Livermore
Laboratory. Based on the specific condition and the practical request of the lab, with the help of argon ion
laser and internal focusing telescopes, side-on shadowgraph system has been set up to test the speed of
flyers. The experimental arrangement is shown in Fig. 1.
Fig. 1
Schematic description of side-on shadowgraph system
To avoid “fly-back” of the streak camera, a mechanical shutter and a pocket cell were applied in the
system. With the help of the frontal and lateral internal focusing telescopes, the system can be adjusted
accurately. Without the KrF laser shocking on the target, the image got from the streak camera is shown in
Fig. 2.
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Annual Report of China Institute of Atomic Energy 2006
Fig. 2
Image got from the streak camera without the KrF laser shocking on the target
As a result of the “fly-back” which had not been solved completely, the image shown in Fig.2 is not
clear, and the contrast of the image is not satisfying. It has probability to get precise results of the
experiment only when the streak camera works in its best condition. So doing something more to solve
the problem of the “fly-back” completely will be the most important task of the next step.
Side-on shadowgraph has great prospect of application. A series of researches will be carried out
orderly.
Design of Cooling-Water System for Bi-Energy Linactron
HUANG Jun，HAN Guang-wen, YIN Meng
Cooling-water system is the leading and necessary auxiliary equipment of accelerator. Heat
generated by a multitude of accelerator components is absorbed by circular cooling-water in this system.
Then the components are cooled and the accelerator will work normally. This article mainly introduced
the design of cooling-water system for bi-energy linactron.
Cooling power of this system is 7 000 W. Water temperatures are being controlled at any state
between 15 ℃ and 40 ℃ and the precision is restricted as tight as ±1 ℃. All water used for heat rejection
by accelerator equipment is deionized and filtered to provide minimum resistivity of 3 MΩ. The basic
components mainly consist of three parts. They are water flow circuit, F22 cooling circuit and X-ray part.
Entropy Characteristic on Harmonious Unifying
Hybrid Preferential Networks*
LI Yong, FANG Jin-qing, BI Qiao, LIU Qiang
The discovery of the ubiquity of small world (SW) and scale-free (SF) networks has led to many
exciting insights into fundamental underlying principles that govern complex systems. It has been realized
that, despite functional diversity, most real web like systems share important structural features, e.g.:
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small average path length, high clustering, and scale-free degree distribution. A number of network
models have been proposed to embody the fundamental characteristics. Among them Fang group has
proposed the harmonious unifying hybrid preferential model (HUHPM) to a certain class of complex
networks, which is controlled by a hybrid ratio d/r of deterministic preferential attachment (DPA) to
random preferential attachment (RPA). Within this model we study both numerically and theoretically. It
was found that the HUHPM has a key universal topological property and dynamical synchronizability,
and one of most important features is that the exponents of power γ (node degree, node strength, and
edged weight) are sensitive to the d/r or depends on the d/r strongly.
As-well known, statistical mechanics have made a great contribution towards the main advances of
topology and dynamics in complex networks, as emphasized by Albert and Barabasi. We raise a question
here: Entropy as another very important characteristic quantity for statistical mechanics, what role does
the entropy play in complex networks?
Base on the networks grown by HUHPM-BA model and HUHPM-BBV model, we compute the
general relation of the power exponent of the degree distribution with the entropy using the BG entropy
(BGS) and the Tsallis entropy (Sq). It is found that the BGS decreases as d/r increases and the current of
the BGS along with hybrid ration d/r or exponent γ of power-law is in good consistent. The relationship
between the Sq and q under different d/r is also given. And the Sq approaches to the BGS when q → 1.
These results can provide a better understanding evolution characteristic in growing complex networks
and further applications in network engineering are of prospective potential. However, there still have
some factors unconsidered while the values of BGS existing error. This indicates that there still have some
open problems for us to be solved.
However, we believe that the HUHPM networks reveal one of essential mechanisms to the actual
network to produce the SF and SW effects as well as entropy characteristic, therefore further applications
in more widespread types of network are possible. For example, because the exponents of the three power
law for the HUHPM networks have high sensitivity to the hybrid ratio d/r change, this may make a
corresponding encryption method that applies to the cryptology and privacy communication domain. Its
basic principles may be similar to chaotic communication, based on track to initiate sensitive disposition.
On the other hand, due to the fact that the power exponent, entropy, average path length and average
clustering coefficient can adjust by the hybrid ratio d/r, one may design the required network architecture
to satisfy different special requirements in network engineering.
* Supported by Key Project of National Nature Science Foundation of China (70431002) and NNSFC (70371068)
Assortativity Characteristic Transition on Harmonious
Unifying Hybrid Networks*
LI Yong, FANG Jin-qing, BI Qiao, LIU Qiang
Many systems take the form of networks—sets of vertices joined together by edges. There exist a lot
of networks around us, including social networks, information networks, technical networks and
biological networks. In past few years, many properties such as small-world phenomenon and scale-free
behavior were discovered from networked complex systems.
In order to scale the degree correlation, Newman proposed the degree assortativity coefficient r. It
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was found that in many social networks, vertices with high degrees tend to be connected with others with
high degrees. It is denoted as assortativity with r>0. However, many technological and biological
networks often own the property that vertices with high degrees mostly have neighbors with low degrees,
which is called disassortativity with r<0. The neutral networks display degree uncorrelations (i.e. r=0).
Fig. 1
Relationship of assortative coefficient r along with different g/r and f/d
a——f/d = 0/1；b——f/d = 0.5/1；c——f/d = 0.99/1；d——f/d = 1/1
►——g/r =1;◄——g/r =0.9;▲——g/r =0.8;▼——g/r =0.7;◊ ——g/r =0.6;□——g/r =0.5;
■——g/r =0.4;＋——g/r =0.3;×——g/r =0.2;○——g/r =0.1;●——g/r =0
Based on the networks grown by the harmonious unifying hybrid model, the assortativity
characteristic transition from negative to positive value for LUHNM model is investigated as the hybrid
ratio d/r is changed from smallest to biggest. In the LUHNM model two new hybrid parameters are
introduced. One is f/d, which is defined to choose corresponding deterministic linking way, and the other
is g/r, which is defined to choose corresponding random linking way. Through adjustment different g/r
and f/d, we reappear BA model, the ER model, and HUHPM model.
It is found that assortative coefficient r can be changed in the large range of (－1, 1) through
adjusting value of f/d and g/r. There exist a threshold value at nearby f/d～0.99, where r can have
transition from negative to positive value according to d/r is 1/1. In addition, the multi-extreme values
phenomenon of r along with d/r also appears. We simulated get the relations of r and f/d, r and g/r.
These results can provide a better understanding evolution characteristic in growing complex
networks between social networks and technological and biological networks. The relationship of
assortative coefficient r along with different g/r and f/d is shown in Fig.1.
* Supported by Key Project of National Nature Science Foundation of China (70431002) and NNSFC (70371068)