• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Numerical simulation of nanosecond laser ablation and plasma characteristics considering a real gas equation of state

    2022-01-10 14:51:10QiangLIU劉強QiMIN敏琦MaogenSU蘇茂根XingbangLIU劉興邦ShiquanCAO曹世權DuixiongSUN孫對兄ChenzhongDONG董晨鐘andYanbiaoFU符彥飆
    Plasma Science and Technology 2021年12期
    關鍵詞:興邦晨鐘劉強

    Qiang LIU (劉強), Qi MIN (敏琦),2,?, Maogen SU (蘇茂根),2, Xingbang LIU(劉興邦), Shiquan CAO (曹世權),2, Duixiong SUN (孫對兄),2,Chenzhong DONG (董晨鐘),2 and Yanbiao FU (符彥飆),2,?

    1 Key Laboratory of Atomic and Molecular Physics and Functional Material of Gansu Province,College of Physics and Electronic Engineering,Northwest Normal University,Lanzhou 730070,People’s Republic of China

    2 Joint Laboratory of Atomic and Molecular Physics,Northwest Normal University and Institute of Modern Physics of Chinese Academy of Sciences, Lanzhou 730070, People’s Republic of China

    Abstract Based on the governing equations which include the heat conduction equation in the target and the fluid equations of the vapor plasma, a two-dimensional axisymmetric model for ns-laser ablation considering the Knudsen layer and plasma shielding effect is developed.The equations of state of the plasma are described by a real gas approximation, which divides the internal energy into the thermal energy of atoms,ions and electrons,ionization energy and the excitation energy of atoms and ions.The dynamic evolution of the silicon target and plasma during laser ablation is studied by using this model,and the distributions of the temperature,plasma density,Mach number related to the evaporation/condensation of the target surface, laser transmissivity as well as internal energy of the plasma are given.It is found that the evolution of the target surface during laser ablation can be divided into three stages: (1) the target surface temperature increases continuously; (2) the sonic and subsonic evaporation; and (3) the subsonic condensation.The result of the internal energy distribution indicates that the ionization and excitation energy plays an important role in the internal energy of the plasma during laser ablation.This model is suitable for the case that the temperature of the target surface is lower than the critical temperature.

    Keywords: ns-laser ablation, hydrodynamic model, Knudsen layer, equation of state

    1.Introduction

    A ns-laser ablation has been extensively applied to the micromachining [1], pulsed laser deposition [2, 3], laserinduced breakdown spectroscopy [4, 5], and material surface treatment [6, 7] in recent years.The development of each application is closely related to the physical mechanism of the interaction between laser pulse, target and plasma.

    Nanosecond laser ablation of solid targets is a complex process, including absorption of laser energy by the target,evaporation/condensation of the target surface, formation of transient plasma,expansion of plasma to surrounding gas and absorption of laser energy by plasma (the shielding effect)[8–10].In this process, Knudsen layer (KL) [11–13] and shielding effect have significant effects on the dynamic evolution of target and plasma.KL is a transient non-equilibrium layer and jump phase boundary between the vapor and condensed phase.The non-equilibrium degree is determined by the particle flow through the layer,and can be expressed as the function of the Mach number of the vapor near KL.The total particle flow through KL includes the particle flow leaving the condensed phase by evaporation and the particle flow returning to the target surface by collision from the vapor phase.At the same time, KL as the phase boundary between the condensed and vapor phase leads to the discontinuity of parameters (such as temperature, density, etc) between the target surface and the vapor phase.But KL only exists when the temperature of the target surface is lower than the critical temperature.Above the critical temperature, KL disappears and the liquid and vapor phases mix together [14].In addition, the plasma shielding effect also has a significant influence on the dynamic evolution of target and plasma.For nslaser,the plasma mainly absorbs the laser energy through the photoionization (PI) and inverse bremsstrahlung (IB) processes [15, 16], which makes the electron density and temperature increase and the laser energy reaching the target surface decrease significantly.

    Up to now, many hydrodynamic models including KL and plasma shielding effect [17–24] have been proposed to simulate the interaction between ns-laser, target and plasma.However, most of the models [17, 20, 24] only consider the contribution of thermal energy and ionization energy to the internal energy of the plasma in the equation of state,ignoring the excitation energy.Some models[18,19,23]even used the ideal gas approximation of the plasma,and the ionization and excitation energies in the internal energy have been neglected.Actually, such approximation only holds when the number densities of ions in the plasma are far less than those of atoms(the average charge state is much less than 1)and most atoms are in the ground state.Unfortunately, this is not the case for laser-induced plasma [25].

    In the present work, a two-dimensional axisymmetric model for ns-laser ablating the silicon target is established based on the time-dependent heat transfer equation and fluid equations.Such equations are coupled by the KL condition.The equations of state of the plasma are described by a real gas approximation,which divides the internal energy into the kinetic (thermal) energy of atoms, ions and electrons, ionization energy and the excitation energy of atoms and ions.A Gaussian laser pulse with the peak laser intensity of 5.0 ×108W cm?2,full width at half maximum of 10 ns,and wavelength of 1064 nm is selected.The Si target is in a vacuum with a pressure of5.0 ×10?4Pa.The model is valid for the case that the temperature of the target surface is less than the critical temperature.

    2.Theoretical model

    Table 1.Thermal parameters of the Si target [27, 28].

    The energy transfer inside the Si target is calculated by the following heat transfer equation [22], which was solved by using an alternating direction implict scheme [26]where the subscript‘c’represents the solid/liquid medium,Tcis the target temperature,vcis the surface recession velocity.Kcis the thermal conductivity,Cpis the specific heat,andρcis the target density.The corresponding thermal parameters of the Si target [27, 28] are shown in table 1.

    The initial and boundary conditions of equation (1) can be expressed as follows:

    whereTais initial temperature,Ris the reflectivity of the target surface,ΔHlvis the latent heat of vaporization, ( )I r t,is the laser intensity.

    The surface recession velocityvcin equation (1) can be written asWherem˙+is the mass flux of particle flow leaving the condensed phase by evaporation,which is given by Hertz–Knudsen formula [20].˙?mis the mass flux of particle flow returning to the target surface by collision from the vapor phase,which can be expressed as the function of the Mach number of the vapor near the KL, and calculated by Knight’s approach [29].

    Since the density of plasma generated by ns-laser pulse is so high that the number of collisions between evaporated atoms is sufficient for hydrodynamics to apply [9], the vapor plasma flow can be described by the fluid equations mentioned in our previous work [30, 31].Electron–atom and electron–ion IB as well as PI are considered in the absorption of laser energy by the plasma, and the corresponding expressions can be found in [15, 16].

    Figure 1.The temperature distributions of the Si target in r–z plane for the delay times of 13, 20, 25, and 30 ns, respectively.

    In this model,the internal energy density of the plasma is given by a real gas approximation, which divides the internal energy into the thermal energy of atoms, ions and electrons,ionization energy and the excitation energy of atoms as well as ions:

    whereρεis the internal energy density,nandneare the total atomic and electron number density, respectively.Tis in degrees Kelvin,kis the Boltzmann constant.Elrefer to the ionization energy oflth ionization state, =l0 corresponds to atoms.ΔEis a correction to the ionization energy and calculated by Debye shielding.Ej z,is the excitation energies of the energy leveljwith respect to the ground state energy.j0represents the ground state of each ion.fzandfj z,are the relative ionization fractions and excitation fractions, respectively, and can be calculated by the Saha equation and Boltzmann distribution.

    3.Results and discussion

    3.1.Characteristic of the Si target during ns-laser ablation

    The initial temperature of the Si target is 300 K.However,with the ns-laser pulse acting on the target surface, the target temperature increases rapidly.The temperature distributions of the target which located inr–zplane for different times have been displayed in figure 1.According to simulation results, the surface temperatures of the target (z=0) are always higher than the internal temperatures (z<0) at different times.When the time evolves, the range of heating region inside the target is expanded due to the thermal conduction,and the decrease rate of the maximum temperature gradually slows down.At 13 ns, the radial distribution of temperatures is consistent with the Gaussian distribution of laser intensity, and the temperature at the center of the target surface (r=0,z=0) is the highest,reaching 8120 K.At 20 ns, the radial distribution is no longer Gaussian shape, and the temperatures at the edge(r≈0.3 mm, ?1.5μm

    The temperature distributions of the Si target shown in figure 1 can be attributed to the combined effects of laser irradiation, heat conduction, evaporation/condensation and plasma shielding.In order to explain the influence of evaporation/condensation and plasma shielding effect on the temperature distributions of the target, the temporal evolutions of the temperature with and without plasma shielding,the Mach number of the vapor near KL, and the laser transmissivity (which is defined as the laser intensity reaching the target surface divided by the original laser intensity) at the center of the target surface (r=0,z=0), as well as the temporal profile of original laser intensity are shown in figure 2.As the original laser intensity (Io, dash line)increases, the surface temperature without plasma shielding(Ts-np,wine line)also increases.However,the time forTs-npto reach the maximum (att=16 ns) is later than that forIo(att=15 ns).After reaching the maximum,Ts-npdecreases gradually, but the decrease of temperature is slower than that of original laser intensity, which is due to the thermal inertia of the target.Therefore,an asymmetric distribution ofTs-npis caused by a symmetric laser pulse.

    Figure 2.The temporal evolutions of the temperature with and without plasma shielding(red and wine line,respectively),the Mach number(blue line), and the laser transmissivity (black line) at the center of the target surface (r=0, z=0).Dashed line indicates the temporal profiles of original laser intensity.

    In figure 2,the Mach number(M,blue line)of the vapor near KL can indicate the evaporation/condensation process and the non-equilibrium degree of KL.Here,=M1 corresponds to the sonic evaporation, the total particle flow through the KL is the highest, and the evaporation process takes place under a strongest non-equilibrium.The condition of =M0 and the surface temperature is less than the boiling point, means that evaporation has not started yet.But the condition ofM=0 and the surface temperature is larger than the boiling point, means that the total particle flow through KL is zero, and the particle flow leaving and returning to the condensed phase is in equilibrium.When 0

    According to the Mach number in figure 2, the laser ablation process includes three stages.The first stage is from 0 to 9 ns, the surface temperature with plasma shielding (Ts,red line) grows monotonically but it does not reach the boiling point.This means that the evaporation process has not yet occurred, so the Mach number is always 0, and the laser energy can reach the target surface completely without absorption.The second stage is from 9 to 15 ns, in whichTscontinues to rise from 10 to 13 ns and is higher than the boiling point,reaching a maximum of 8120 K at 13 ns.At the same time, both the Mach number and laser transmissivity(black line) are equal to 1, which means that there is a sonic evaporation and the plasma has not yet formed.At 14 ns, the Mach number is still equal to 1,butTsand laser transmissivity decrease, which indicates that the vapor breakdown occurs at about 14 ns and forms a plasma,and a part of the laser energy is absorbed by the plasma, which reduces the laser energy reaching the target surface.At 15 ns,the Mach number equals 0.1,which corresponds to subsonic evaporation.The subsonic condensation (M< 0) occurs at stage 3, 16 ns≤t≤30 ns.At this stage, the profile ofTshas a downward trend as a whole, but increases slightly between 17 and 21 ns, which is due to the energy of particles returning to the target surface compensates for the energy loss caused by heat conduction.Except for the first stage, the surface temperature in the second and third stages is quite different when plasma shielding is considered or not.

    At 20 and 25 ns, the radial distributions of the temperature, Mach number and laser transmissivity at the target surface (z=0) are shown in figure 3.It can be seen that the parameters’distributions of the central region(? 0 .25 mm≤r≤0.25 mm) and the edge region(? 0 .5 mm≤r< ?0.25 mm and 0.25 mm

    Figure 3.The radial distributions of the temperature (red line), Mach number (blue line) and laser transmissivity (black line) at the target surface (z=0) at 20 and 25 ns.Dashed line indicates the spatial profiles of original laser intensity at 20 and 25 ns, respectively.

    Figure 4.The temperature distributions of the Si plasma in r–z plane for the delay times of 15, 20, 25, and 30 ns, respectively.

    Figure 5.The (a) density and (b) axial velocity distributions of the plasma at =r 0 along the z-axis for the delay times of 15, 20, 25 and 30 ns, respectively.

    3.2.Characteristic of the vapor plasma during ns-laser ablation

    The two-dimensional contour distributions of the Si plasma temperature inr–zplane at 15, 20, 25 and 30 ns have been shown in figure 4, respectively.It is clearly seen that the plasma has been formed at 15 ns and the maximum temperature has reached 1.4 eV.Therefore, the subsequent laser pulse will be absorbed by the plasma, which makes the plasma temperature continue to rise and the laser energy reaching the target surface will be reduced.At 20 ns, due to the continuous input of laser energy, the maximum temperature of the plasma reaches 3.9 eV.At 25 and 30 ns, the maximum temperatures decrease slightly compared with that at 20 ns, and the radial and axial dimensions of the plasma increase significantly.The distribution of the target temperature in figure 1 is closely coupled with the distribution of the plasma temperature in figure 4.On one hand, the laser intensity acting on the target surface after being absorbed by plasma should be considered in the boundary condition(equation(2))of the heat transfer equation.On the other hand,the parameters of target surface provide the boundary conditions for the fluid equations by the discontinuity of KL.In addition,the absorption of laser pulse by plasma represents an important coupling,which is related to both plasma expansion and laser-target interaction.The laser energy will be greatly attenuated before reaching the target,resulting in low heating and evaporation efficiency of the target.

    The density and axial velocity distributions of the plasma at =r0 along thez-axis for the delay times of 15,20,25 and 30 ns are shown in figure 5.During the period of ns-laser ablation, especially when the delay time is less than 15 ns, a large number of ablated silicon materials enter into the plasma domain, thus forming a high-density region near the target surface (figure 5(a)).Such dense and hot plasma expands in vacuum at a speed of 10–30 km s?1along the direction perpendicular to the target surface (figure 5(b)).Due to the free expansion of plasma in vacuum and the sharp decrease of laser energy reaching the target surface after 15 ns (figure 2),the plasma density decreases obviously as functions of time and distance from the target surface.The axial velocity increases gradually along thez-axis, reaches the maximum and then remains stable,and finally decreases rapidly to zero.It is worth noting that the axial velocity near the target surface decreases as a function of time and becomes negative at 20 ns(?205 m s?1),25 ns(?1416 m s?1)and 30 ns(?2562 m s?1).This is consistent with the distribution of the Mach number in figure 2, and indicates that the pressure of plasma near the target surface exceeds the saturated vapor pressure of target surface, which makes the vapor plasma move back towards the target and form condensation.In this model,the saturated vapor pressure of the target surface is calculated by the Clausius–Clapeyron equation [20].

    As functions of delay times, the energy density distributions of the internal energy, thermal energy, ionization energy as well as the energy of electronic excitations are shown in figure 6(a), and the distributions of the Si I-III ions as well as the average charge state in the plasma are shown in figure 6(b),respectively.From 15 to 17 ns,the internal energy of the plasma is mainly contributed by the thermal energy of atoms and electrons, as well as the energy of electronic excitations of atoms(figure 6(a)).This is because the particles in plasma are mainly neutral atoms(figure 6(b)),and most of these atoms are in the excited state under the assumption that the energy level population satisfies the Boltzmann distribution(the plasma temperature has reached about 1.7 eV in this time period).As time evolves, the internal energy density decreases with the decrease of plasma density, but the proportion of ionization energy in the internal energy increases with the increase of the fractions of Si II and III ions.The results of internal energy distribution in figure 6(a) indicate that the contribution of the energy of electronic excitations must be considered in the internal energy of plasma during laser ablation, that is, the real gas approximation(equation(3))should be used to describe the equation of state of plasma.

    Figure 6.The distributions of(a)the internal energy,thermal energy,ionization energy as well as the energy of electronic excitations of the plasma,and(b)the ion fractions as well as average charge state of Si in the plasma as a function of delay time at r=0, z=0,respectively.

    Figure 7.The spatial distributions of the internal energy, thermal energy, ionization energy, and energy of atomic excitations at 30 ns,respectively.

    Moreover,the spatial distributions of the internal energy,thermal energy, ionization energy, and energy of atomic excitations at 30 ns are shown in figure 7.The distribution of the energy of atomic excitations inr–zplane is consistent with that of neutral atoms in this plane.This result further confirms our conclusion that the contribution of the energy of electronic excitations to internal energy during laser ablation cannot be ignored.

    Figure 8.The distributions of the plasma temperature based on three different equations of state as a function of delay time at r=0, z=0,respectively.Case I is real gas approximation,Case II is ideal gas approximation and Case III is ideal gas approximation combined with ionization energy.

    Finally, to explain the influence of the equation of state on the plasma parameters, we calculate the plasma temperature based on three different equations of state, which are real gas approximation (equation (3), Case I), ideal gas approximationCase II) and ideal gas approximation combined with ionization energyCase III).The distributions of the plasma temperature as a function of delay time atr=0,z=0 are shown in figure 8.It should be noted that the plasma temperature calculated by ideal gas approximation (Case II) is much higher than that of the real gas approximation (Case I), since the supplied energy goes entirely into the thermal energy, while in the real gas approximation, most of the energy goes into the ionization and atomic excitation, thus reducing the plasma temperature.Combined with the results of figures 6–8, we predict that the equation of state of plasma needs to be described by a real gas approximation during ns-laser ablation, and this prediction is consistent with the conclusion in [25].In addition, the applicability of the real gas approximation also needs to be verified by experimental results.In our previous work [32],we measured the temperature and electron density of Si plasma using time-resolved spectra, and obtained a plasma temperature of 2.75 eV at 30 ns.It can be seen from figure 8 that the plasma temperature calculated by the real gas approximation is 2.71 eV at 30 ns and most consistent with the experimental result.Unfortunately, we did not get the spectrum before 30 ns,so the experimental result at only 30 ns cannot fully verify the applicability,and we need to get more experimental results in the future.

    4.Conclusions

    In summary, a two-dimensional axisymmetric model for nanosecond laser ablation considering surface evaporation/condensation and plasma shielding effect is developed.The equations of state of the plasma are described by a real gas approximation, which divides the internal energy into the thermal energy of atoms,ions and electrons,ionization energy and the excitation energy of atoms as well as ions.The spatial-temporal distributions of the target temperature, Mach number of the vapor near KL, laser transmissivity, plasma temperature and density,and internal energy of the plasma are given.It is found that the laser ablation process consists of three stages: (1) the target surface temperature increases continuously and does not exceed the boiling point at the beginning of laser ablation; (2) the sonic and subsonic evaporation occurs in the middle stage of laser ablation; (3) the laser energy is absorbed by the plasma and subsonic condensation occurs.The composition of internal energy of the plasma during laser ablation is analyzed, a key conclusion that the contribution of the energy of electronic excitations to internal energy during laser ablation cannot be ignored is obtained.The model is valid for the case that the temperature of the target surface is lower than the critical temperature.

    Acknowledgments

    This work is supported by the National Key Research and Development Program of China (No.2017YFA0402300),National Natural Science Foundation of China (Nos.11904293, 12064040 and 11874051), the Science and technology project of Gansu Province (No.20JR5RA530), the Young Teachers Scientific Research Ability Promotion Plan of Northwest Normal University(No.NWNU-LKQN-18-32),and the Funds for Innovative Fundamental Research Group Project of Gansu Province (No.20JR5RA541).

    猜你喜歡
    興邦晨鐘劉強
    山東晨鐘機械股份有限公司
    中國造紙(2022年8期)2022-11-24 09:43:40
    Improved sensitivity on detection of Cu and Cr in liquids using glow discharge technology assisted with LIBS
    沉痛悼念石興邦先生
    考古與文物(2022年6期)2022-08-04 01:19:14
    劉強畫廊
    Isotope shift of the 2s 2S1/2 →2p 2P1/2,3/2 transitions of Li-like Ca ions*
    Calculations of atomic polarizability for beryllium using MCDHF method?
    百十初心不忘 樹人扶農興邦
    ——華南農業(yè)大學建校110周年歷史回眸
    百十初心不忘 樹人扶農興邦
    ——華南農業(yè)大學建校110周年輝煌成就
    劉強作品
    劉強作品
    免费在线观看亚洲国产| 97超级碰碰碰精品色视频在线观看| 岛国视频午夜一区免费看| 伊人久久精品亚洲午夜| 人妻久久中文字幕网| 中文字幕熟女人妻在线| 色在线成人网| 亚洲国产精品合色在线| 久久人妻av系列| 午夜精品久久久久久毛片777| 国产一区二区亚洲精品在线观看| 99久久九九国产精品国产免费| 成熟少妇高潮喷水视频| 91久久精品国产一区二区成人 | 搡老熟女国产l中国老女人| 精品欧美国产一区二区三| 亚洲aⅴ乱码一区二区在线播放| 少妇丰满av| 国产免费一级a男人的天堂| 看免费av毛片| 美女cb高潮喷水在线观看| 国产三级黄色录像| www日本黄色视频网| 国产午夜精品论理片| 非洲黑人性xxxx精品又粗又长| 综合色av麻豆| 男女下面进入的视频免费午夜| 亚洲av二区三区四区| 亚洲人成网站在线播| 制服丝袜大香蕉在线| 国内少妇人妻偷人精品xxx网站| 日韩欧美在线乱码| aaaaa片日本免费| 少妇裸体淫交视频免费看高清| 久久久久亚洲av毛片大全| 久久久久国产精品人妻aⅴ院| 欧美日韩亚洲国产一区二区在线观看| 欧美xxxx黑人xx丫x性爽| 亚洲精品国产精品久久久不卡| 黄色女人牲交| 亚洲 欧美 日韩 在线 免费| 人人妻人人看人人澡| 免费观看精品视频网站| 国产视频内射| 日本一二三区视频观看| 欧美激情在线99| 久久久精品欧美日韩精品| 有码 亚洲区| 五月伊人婷婷丁香| 日韩精品青青久久久久久| 悠悠久久av| 精品国产亚洲在线| 成年女人看的毛片在线观看| 欧美日韩瑟瑟在线播放| 中文字幕人妻熟人妻熟丝袜美 | 手机成人av网站| 香蕉久久夜色| 成人精品一区二区免费| 最近最新中文字幕大全电影3| 狂野欧美激情性xxxx| 国产成人av教育| 日本一二三区视频观看| av视频在线观看入口| 亚洲av成人av| 国产免费男女视频| 久99久视频精品免费| 性色av乱码一区二区三区2| 最近视频中文字幕2019在线8| 色吧在线观看| 国产私拍福利视频在线观看| 国产精品av视频在线免费观看| 欧美又色又爽又黄视频| 亚洲一区二区三区色噜噜| 欧美绝顶高潮抽搐喷水| 国产精品99久久久久久久久| 久久精品国产亚洲av涩爱 | 12—13女人毛片做爰片一| 亚洲精品在线美女| 欧美精品啪啪一区二区三区| 国产在线精品亚洲第一网站| 校园春色视频在线观看| 亚洲一区高清亚洲精品| 久久精品国产99精品国产亚洲性色| av片东京热男人的天堂| 在线免费观看不下载黄p国产 | www日本在线高清视频| 在线播放无遮挡| 9191精品国产免费久久| 在线观看舔阴道视频| 成人精品一区二区免费| 欧美日本视频| 中文字幕av在线有码专区| 午夜视频国产福利| 最近最新中文字幕大全电影3| 国内精品久久久久精免费| 国内精品久久久久精免费| 看免费av毛片| 国产高清三级在线| 最新美女视频免费是黄的| 国产精品永久免费网站| www.熟女人妻精品国产| 精品99又大又爽又粗少妇毛片 | 一区二区三区高清视频在线| 国产精品国产高清国产av| 手机成人av网站| 欧美三级亚洲精品| 99久久久亚洲精品蜜臀av| 免费在线观看影片大全网站| 国产99白浆流出| 亚洲中文字幕一区二区三区有码在线看| 国产精品一区二区三区四区免费观看 | 一进一出好大好爽视频| 久久国产乱子伦精品免费另类| 免费看a级黄色片| 久久久久久人人人人人| 亚洲中文字幕一区二区三区有码在线看| 国产99白浆流出| 亚洲成人久久性| 国产高清视频在线播放一区| 国产爱豆传媒在线观看| 国内精品美女久久久久久| 国产免费一级a男人的天堂| 亚洲精品亚洲一区二区| 91字幕亚洲| 亚洲国产高清在线一区二区三| 一区二区三区激情视频| 精品国产超薄肉色丝袜足j| 国产乱人视频| 国产精品久久久久久亚洲av鲁大| 日韩人妻高清精品专区| 日本免费一区二区三区高清不卡| 成人av一区二区三区在线看| 黄片小视频在线播放| 久久精品人妻少妇| 一区二区三区高清视频在线| 欧美日本亚洲视频在线播放| 丁香欧美五月| 国产精品,欧美在线| 日本精品一区二区三区蜜桃| 成人特级av手机在线观看| 噜噜噜噜噜久久久久久91| av视频在线观看入口| 最近在线观看免费完整版| 国产视频内射| 黄色丝袜av网址大全| 久久久久久久亚洲中文字幕 | 女人被狂操c到高潮| 又爽又黄无遮挡网站| 亚洲第一电影网av| 成人欧美大片| 国内精品一区二区在线观看| 久久精品91蜜桃| 内射极品少妇av片p| 国产免费男女视频| 黄色日韩在线| 全区人妻精品视频| 国产高潮美女av| 3wmmmm亚洲av在线观看| 免费电影在线观看免费观看| 久久精品综合一区二区三区| 色综合站精品国产| 男女之事视频高清在线观看| 夜夜爽天天搞| 亚洲人成电影免费在线| 成年女人毛片免费观看观看9| 精品人妻一区二区三区麻豆 | 给我免费播放毛片高清在线观看| 母亲3免费完整高清在线观看| 日韩欧美精品免费久久 | 一边摸一边抽搐一进一小说| 精品欧美国产一区二区三| 久久久久性生活片| 亚洲久久久久久中文字幕| 制服人妻中文乱码| 精品久久久久久久人妻蜜臀av| 伊人久久精品亚洲午夜| 国产精品1区2区在线观看.| 在线观看免费视频日本深夜| 好男人电影高清在线观看| 亚洲成人精品中文字幕电影| 男人舔女人下体高潮全视频| 黄片小视频在线播放| 国产三级黄色录像| 亚洲欧美日韩卡通动漫| 成人性生交大片免费视频hd| 三级毛片av免费| 老司机福利观看| 国产成人啪精品午夜网站| 亚洲男人的天堂狠狠| 天堂影院成人在线观看| 久久久久久久久中文| 欧美日韩精品网址| 不卡一级毛片| 无遮挡黄片免费观看| 国产欧美日韩一区二区三| 亚洲精品色激情综合| 国产黄色小视频在线观看| 给我免费播放毛片高清在线观看| 亚洲性夜色夜夜综合| 精品免费久久久久久久清纯| 午夜亚洲福利在线播放| 69av精品久久久久久| 日韩欧美精品免费久久 | 免费人成视频x8x8入口观看| 给我免费播放毛片高清在线观看| 51国产日韩欧美| 亚洲avbb在线观看| 窝窝影院91人妻| 欧美绝顶高潮抽搐喷水| 在线观看66精品国产| 国产三级在线视频| 香蕉av资源在线| 国产精品爽爽va在线观看网站| 日韩欧美免费精品| 久久久久九九精品影院| 可以在线观看的亚洲视频| 99久久综合精品五月天人人| 国产在线精品亚洲第一网站| 欧美绝顶高潮抽搐喷水| 欧美日韩综合久久久久久 | 亚洲,欧美精品.| 国产亚洲欧美在线一区二区| 日韩av在线大香蕉| 国产真实乱freesex| 老司机福利观看| 免费在线观看日本一区| 亚洲最大成人中文| 中文亚洲av片在线观看爽| 免费看a级黄色片| 男女床上黄色一级片免费看| 免费人成视频x8x8入口观看| 两人在一起打扑克的视频| 国产在视频线在精品| 国产精品亚洲美女久久久| 12—13女人毛片做爰片一| 日韩 欧美 亚洲 中文字幕| 久久久久久久午夜电影| 禁无遮挡网站| 欧美日韩亚洲国产一区二区在线观看| 免费在线观看日本一区| 岛国在线观看网站| 日韩欧美 国产精品| av国产免费在线观看| 天堂√8在线中文| 深爱激情五月婷婷| 欧美日韩福利视频一区二区| 丰满人妻熟妇乱又伦精品不卡| 国产精品亚洲美女久久久| 亚洲人成网站在线播放欧美日韩| 又粗又爽又猛毛片免费看| 国产不卡一卡二| 亚洲国产欧美人成| 老鸭窝网址在线观看| 非洲黑人性xxxx精品又粗又长| 国产成人啪精品午夜网站| 精品久久久久久久久久免费视频| 亚洲人成网站在线播放欧美日韩| 久久精品91蜜桃| 男女做爰动态图高潮gif福利片| 最近视频中文字幕2019在线8| 美女cb高潮喷水在线观看| 国产美女午夜福利| 好男人在线观看高清免费视频| 国产精品国产高清国产av| www日本在线高清视频| 国产主播在线观看一区二区| 国产精品98久久久久久宅男小说| 在线观看免费视频日本深夜| 国产精品一区二区三区四区免费观看 | 哪里可以看免费的av片| a级毛片a级免费在线| 毛片女人毛片| 色av中文字幕| 丁香六月欧美| 欧美不卡视频在线免费观看| 身体一侧抽搐| 少妇丰满av| 叶爱在线成人免费视频播放| 久9热在线精品视频| 在线播放国产精品三级| 国产欧美日韩精品一区二区| 欧美最新免费一区二区三区 | 成人欧美大片| 亚洲最大成人中文| 亚洲精品亚洲一区二区| 久久中文看片网| 两个人视频免费观看高清| 亚洲欧美日韩高清专用| 精品久久久久久久久久久久久| 伊人久久精品亚洲午夜| 日韩精品青青久久久久久| 日本精品一区二区三区蜜桃| 一个人观看的视频www高清免费观看| x7x7x7水蜜桃| 可以在线观看毛片的网站| 国产亚洲精品久久久久久毛片| 老熟妇仑乱视频hdxx| 免费av毛片视频| 亚洲欧美日韩卡通动漫| x7x7x7水蜜桃| 搡老熟女国产l中国老女人| 变态另类成人亚洲欧美熟女| 欧美+亚洲+日韩+国产| 色噜噜av男人的天堂激情| 在线观看美女被高潮喷水网站 | 国产精品影院久久| 亚洲熟妇熟女久久| 久久久久国内视频| 特大巨黑吊av在线直播| 国产亚洲精品综合一区在线观看| 国内精品美女久久久久久| 久久婷婷人人爽人人干人人爱| 亚洲av一区综合| 在线观看免费午夜福利视频| 国产 一区 欧美 日韩| 日韩精品中文字幕看吧| 日本五十路高清| 变态另类丝袜制服| 日本一二三区视频观看| 国产久久久一区二区三区| 成年版毛片免费区| 欧美在线黄色| 亚洲av第一区精品v没综合| 免费在线观看成人毛片| 国产欧美日韩精品一区二区| 一个人看的www免费观看视频| 男女午夜视频在线观看| 老汉色av国产亚洲站长工具| 午夜老司机福利剧场| 一卡2卡三卡四卡精品乱码亚洲| 国产精品99久久久久久久久| 男女午夜视频在线观看| 久久久精品欧美日韩精品| 一级黄片播放器| 18+在线观看网站| 12—13女人毛片做爰片一| 欧美黑人欧美精品刺激| 日韩欧美精品免费久久 | 欧美3d第一页| 99精品在免费线老司机午夜| 亚洲精品一卡2卡三卡4卡5卡| 午夜a级毛片| 久久天躁狠狠躁夜夜2o2o| 高清在线国产一区| 国产乱人伦免费视频| 成人三级黄色视频| 日本免费a在线| 国产单亲对白刺激| 熟妇人妻久久中文字幕3abv| 日韩精品青青久久久久久| 一个人免费在线观看的高清视频| 国产美女午夜福利| 在线国产一区二区在线| 国产三级中文精品| 琪琪午夜伦伦电影理论片6080| 久久精品91无色码中文字幕| 欧美黄色淫秽网站| 亚洲最大成人中文| 男人舔女人下体高潮全视频| 69av精品久久久久久| 成人亚洲精品av一区二区| 白带黄色成豆腐渣| 久久精品国产亚洲av香蕉五月| 欧美xxxx黑人xx丫x性爽| 校园春色视频在线观看| 少妇熟女aⅴ在线视频| 精品国产美女av久久久久小说| 51午夜福利影视在线观看| 少妇熟女aⅴ在线视频| 午夜福利18| 天美传媒精品一区二区| 亚洲av不卡在线观看| 99国产精品一区二区三区| 日韩 欧美 亚洲 中文字幕| 老鸭窝网址在线观看| 日本在线视频免费播放| 在线观看免费视频日本深夜| www.色视频.com| 成年人黄色毛片网站| 国产激情欧美一区二区| 中文字幕av成人在线电影| 乱人视频在线观看| 首页视频小说图片口味搜索| 欧美+日韩+精品| 少妇丰满av| a在线观看视频网站| 免费观看精品视频网站| 97碰自拍视频| 精品免费久久久久久久清纯| 法律面前人人平等表现在哪些方面| 欧美最新免费一区二区三区 | 国产黄片美女视频| 亚洲成人中文字幕在线播放| 国产精品女同一区二区软件 | 国产一区二区三区视频了| 亚洲av免费在线观看| 非洲黑人性xxxx精品又粗又长| 亚洲成av人片在线播放无| 日韩 欧美 亚洲 中文字幕| 啪啪无遮挡十八禁网站| 内地一区二区视频在线| 色哟哟哟哟哟哟| 一个人免费在线观看的高清视频| 女人被狂操c到高潮| 国产黄片美女视频| 国产成年人精品一区二区| tocl精华| 9191精品国产免费久久| 3wmmmm亚洲av在线观看| 黄片大片在线免费观看| 国产欧美日韩精品一区二区| 91久久精品电影网| АⅤ资源中文在线天堂| 免费在线观看亚洲国产| 成人永久免费在线观看视频| 日本 av在线| 真人一进一出gif抽搐免费| 日日摸夜夜添夜夜添小说| 最好的美女福利视频网| av视频在线观看入口| 国产av一区在线观看免费| 999久久久精品免费观看国产| 岛国视频午夜一区免费看| 亚洲成人久久爱视频| 国产免费男女视频| 国产精品一及| 成人av在线播放网站| 网址你懂的国产日韩在线| 国产国拍精品亚洲av在线观看 | 男女那种视频在线观看| 12—13女人毛片做爰片一| 中文字幕熟女人妻在线| 欧美黄色淫秽网站| 成人特级黄色片久久久久久久| 琪琪午夜伦伦电影理论片6080| 亚洲第一欧美日韩一区二区三区| 国内精品美女久久久久久| 听说在线观看完整版免费高清| 婷婷丁香在线五月| 两性午夜刺激爽爽歪歪视频在线观看| 欧美日本亚洲视频在线播放| 久久久久国内视频| 亚洲中文日韩欧美视频| 国产精品香港三级国产av潘金莲| 成年人黄色毛片网站| 内射极品少妇av片p| 国产私拍福利视频在线观看| 51国产日韩欧美| 成年版毛片免费区| 九色成人免费人妻av| 国产69精品久久久久777片| 欧美日韩综合久久久久久 | 中文字幕精品亚洲无线码一区| 国产探花极品一区二区| 亚洲av免费在线观看| 色视频www国产| 国产极品精品免费视频能看的| av在线天堂中文字幕| 国产综合懂色| 久久国产乱子伦精品免费另类| 青草久久国产| 亚洲无线观看免费| 亚洲av美国av| 特大巨黑吊av在线直播| 我的老师免费观看完整版| 91久久精品国产一区二区成人 | 欧美日韩综合久久久久久 | 99久久精品国产亚洲精品| 亚洲精品一卡2卡三卡4卡5卡| 国产亚洲欧美在线一区二区| 国产精品 欧美亚洲| 大型黄色视频在线免费观看| 久久精品91无色码中文字幕| 免费一级毛片在线播放高清视频| 午夜福利高清视频| 亚洲欧美日韩卡通动漫| 一区二区三区国产精品乱码| 国产主播在线观看一区二区| 亚洲人成电影免费在线| 国产乱人伦免费视频| 欧美性猛交黑人性爽| 色尼玛亚洲综合影院| 此物有八面人人有两片| 成人无遮挡网站| 伊人久久精品亚洲午夜| 麻豆国产97在线/欧美| 色尼玛亚洲综合影院| 神马国产精品三级电影在线观看| 高清毛片免费观看视频网站| 亚洲va日本ⅴa欧美va伊人久久| 麻豆国产97在线/欧美| svipshipincom国产片| av中文乱码字幕在线| 亚洲乱码一区二区免费版| 性色avwww在线观看| 搞女人的毛片| 女生性感内裤真人,穿戴方法视频| 丰满人妻熟妇乱又伦精品不卡| 亚洲精品一区av在线观看| 亚洲av免费高清在线观看| 精品福利观看| 国产精品精品国产色婷婷| 国内久久婷婷六月综合欲色啪| 在线观看av片永久免费下载| 成人无遮挡网站| 搞女人的毛片| 国产一区二区三区在线臀色熟女| av黄色大香蕉| 国产一区在线观看成人免费| x7x7x7水蜜桃| 国产精品综合久久久久久久免费| 午夜福利在线观看吧| 国产熟女xx| 国产一区二区亚洲精品在线观看| 国产aⅴ精品一区二区三区波| www日本黄色视频网| x7x7x7水蜜桃| 12—13女人毛片做爰片一| 日韩高清综合在线| 国产精品99久久99久久久不卡| 最近视频中文字幕2019在线8| 精品国内亚洲2022精品成人| 久久精品国产清高在天天线| 校园春色视频在线观看| 男女午夜视频在线观看| 99在线视频只有这里精品首页| 亚洲人成网站在线播放欧美日韩| 国产高清有码在线观看视频| 亚洲无线观看免费| 九九热线精品视视频播放| 免费人成在线观看视频色| 免费av毛片视频| 亚洲avbb在线观看| 亚洲成人中文字幕在线播放| 成年免费大片在线观看| 大型黄色视频在线免费观看| 最近在线观看免费完整版| 三级男女做爰猛烈吃奶摸视频| 欧美在线一区亚洲| 国产精品乱码一区二三区的特点| 欧美性感艳星| 99久久精品一区二区三区| 男女床上黄色一级片免费看| 国产在视频线在精品| www.色视频.com| 色尼玛亚洲综合影院| 久久精品国产自在天天线| 欧美丝袜亚洲另类 | 少妇人妻精品综合一区二区 | 叶爱在线成人免费视频播放| 精品国内亚洲2022精品成人| 国产真人三级小视频在线观看| 国产精品久久久久久人妻精品电影| 欧美另类亚洲清纯唯美| 老熟妇乱子伦视频在线观看| 波多野结衣高清无吗| 国产精品爽爽va在线观看网站| 国产97色在线日韩免费| 久久精品国产亚洲av涩爱 | 国产aⅴ精品一区二区三区波| 黄片小视频在线播放| 亚洲av电影不卡..在线观看| 91av网一区二区| 成人鲁丝片一二三区免费| 人人妻,人人澡人人爽秒播| 俺也久久电影网| 九九在线视频观看精品| 亚洲国产精品成人综合色| 国产精品国产高清国产av| 亚洲七黄色美女视频| 欧美绝顶高潮抽搐喷水| 在线观看美女被高潮喷水网站 | 别揉我奶头~嗯~啊~动态视频| 国产午夜福利久久久久久| 国产亚洲精品久久久com| 999久久久精品免费观看国产| 日本一二三区视频观看| 日韩中文字幕欧美一区二区| 欧美黑人巨大hd| av天堂中文字幕网| 中国美女看黄片| 精品不卡国产一区二区三区| 国产精品 国内视频| 欧美最新免费一区二区三区 | 香蕉av资源在线| 欧美大码av| 亚洲av美国av| 脱女人内裤的视频| 国产一区二区激情短视频| 成人精品一区二区免费| 欧美性猛交黑人性爽| 久久精品国产综合久久久| 欧美性猛交╳xxx乱大交人| 久久久久免费精品人妻一区二区| 欧美性感艳星| 日本熟妇午夜| 老鸭窝网址在线观看| 国产老妇女一区| 美女cb高潮喷水在线观看| 三级国产精品欧美在线观看| 亚洲欧美日韩高清专用| 国产爱豆传媒在线观看| 精品无人区乱码1区二区| 最好的美女福利视频网| 欧美3d第一页| 少妇丰满av| 老师上课跳d突然被开到最大视频 久久午夜综合久久蜜桃 | 久久精品亚洲精品国产色婷小说| 亚洲av一区综合| 色老头精品视频在线观看| 日韩av在线大香蕉| 久久国产精品影院| 久久午夜亚洲精品久久| 日韩免费av在线播放| 国产日本99.免费观看|