• <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 ?

    Comparison of emission signals for different polarizations in femtosecond laser-induced breakdown spectroscopy

    2021-04-22 05:34:32QiuyunWANG王秋云AnminCHEN陳安民MiaoLIU劉淼YitongLIU劉奕彤QingxueLI李慶雪SuyuLI李蘇宇YuanfeiJIANG姜遠(yuǎn)飛XunGAO高勛andMingxingJIN金明星
    Plasma Science and Technology 2021年4期
    關(guān)鍵詞:安民明星

    Qiuyun WANG(王秋云),Anmin CHEN(陳安民),?,Miao LIU(劉淼),Yitong LIU(劉奕彤),Qingxue LI(李慶雪),Suyu LI(李蘇宇),Yuanfei JIANG(姜遠(yuǎn)飛),Xun GAO(高勛)and Mingxing JIN(金明星),?

    1 Institute of Atomic and Molecular Physics,Jilin University,Changchun 130012,People’s Republic of China

    2 School of Science,Changchun University of Science and Technology,Changchun 130022,People’s Republic of China

    Abstract In this study,a femtosecond laser was focused to ablate brass target and generate plasma emission in air.The influence of lens to sample distance(LTSD)on spectral emission of brass plasma under linearly and circularly polarized pulses with different pulse energies was investigated.The results indicated that the position with the strongest spectral emission moved toward focusing lens with increasing the energy.At the same laser energy,the line emission under circularly polarized pulse was stronger compared with linearly polarized pulse for different LTSDs.Next,electron temperature and density of the plasma were obtained with Cu(I)lines,indicating that the electron temperature and density under circularly polarized pulse were higher compared to that under linearly polarized pulse.Therefore,changing the laser polarization is a simple and effective way to improve the spectral emission intensity of femtosecond laserinduced plasma.

    Keywords:laser-induced breakdown spectroscopy,femtosecond pulse,polarization,lens to sample distance,emission enhancement

    1.Introduction

    Laser-induced breakdown spectroscopy(LIBS),based on atomic emission spectroscopy,is a technique for material component analysis.Its basic principle is to focus a beam of laser on the material surface,the material vaporizes instantly,forming a high-temperature and high-density plasma.The plasma can emit photons with some specific wavelengths[1-7],and some useful information can be obtained by collecting and analyzing the plasma emission signal.Because the wavelength of a spectrum corresponds to specific elements one by one,the composition and content of the elements in the target can be determined according to the emission wavelength and intensity.The LIBS technique can be used for all substances,and perform multi-element simultaneous analysis,no sample collection and pretreatment,fast,in situ,and online detection compared to some other spectral methods,such as atomic absorption spectroscopy,plasma mass spectroscopy,and atomic fluorescence spectroscopy[8-10].So it can be used in industry,agriculture,environmental detection,isotopic detection,biomedicine,and many other fields[11-15].

    In the past 50 years,LIBS has developed from long pulse nanosecond LIBS(ns-LIBS)to ultrafast pulse femtosecond LIBS(fs-LIBS)with the development of laser technology and spectral analysis instrument.The disadvantage of ns-LIBS is that the laser irradiates the target for a long time,and the interaction between laser and plasma will lead to the phenomenon of plasma shielding.As a result,the energy absorbed by the target material will decrease greatly,reducing the intensity of spectral signal[16].Relative to nanosecond laser,the pulse width of femtosecond laser is very narrow,and the peak intensity is extremely high.Therefore,femtosecond pulse energy can be injected into the target material in a very short time,generating laser-induced plasma.There is almost no interaction between the laser and the plasma,emission spectral signal is better compared to ns-LIBS[17-21].In addition,due to the signal stability of fs-LIBS,it is easier to repeat and reproduce the measured processes in various applications.Also,due to short interaction time between femtosecond laser and sample,the advantages include small heat affected area,short plasma lifetime,stronger molecular spectrum[22].This shows that fs-LIBS technique is more reliable to identify the components of material.

    Nowadays,increasing the spectral intensity of LIBS is a hot topic,it is also very important to increase the emission line intensity of fs-LIBS.Adjusting laser polarization is a simple and practical way to enhance the emission line intensity of fs-LIBS.The laser polarization can be changed by rotating a quarter-wave plate.In general,there are three typical laser polarizations:circular,linear,and elliptical.The rotation angle of circularly polarized laser is 45° +n× 90° ,and the rotation angle of linearly polarized laser isn× 90° .The optical emission of fs-LIBS under circularly polarized pulse is stronger than that under linearly polarized pulse.It is because free electrons under circularly polarized laser field are always accelerated in each optical cycle of the laser field,the kinetic energy of free electrons is relatively high.However,free electrons under linearly polarized laser field will undergo alternate acceleration and deceleration in each optical cycle,and their kinetic energy is lower than that with circular laser polarization[23,24].Researchers have carried out some relevant works.Wang et al studied fs-LIBS of brass target with linear and circular laser polarizations[25],indicating that the plasma emission under circularly polarized pulse was stronger compared to the case under linearly polarized pulse,and the lifetime of atomic lines with circular polarization was also longer.Lemos et al studied the influence of laser polarization on the emission of plasma fluorescence in femtosecond laser filamentation[26],their results indicated that as laser energy was greater than an energy threshold,circular laser polarization led to stronger fluorescence emission compared to linear laser polarization.Panow et al studied femtosecond laser filamentation under linear and circular polarizations[27],their results showed that compared with linear polarization pulse,the diameter of the filament produced by circularly polarized laser was larger and the optical signal was stronger.

    In addition,changing lens to sample distance(LTSD)can obviously change the spectral emission intensity of LIBS.It only needs to install a focusing lens on a computercontrolled stage,and which is easy to operate.Harilal et al studied the effect of the LTSD on extreme ultraviolet efficiency of nanosecond laser-ablated Sn plasma[28],indicating that the maximum extreme ultraviolet efficiency was detected at either side of focal point.Yuan et al discussed the effect of the LTSD on nanosecond laser-induced plasma under different gas pressures[29],their experimental results found that the LTSD significantly influenced the plasma plume size,shape,reproducibility,and emission intensity.Li et al discussed the influence of the LTSD on the expansion dynamics of nanosecond laser-induced copper plasmas in air[30],observing a stream-like and a hemispherical structures in the process of changing the LTSD.Guo et al investigated the influence of the LTSD on the line emission of nanosecond laser-produced silicon plasma with spatial confinement[7],their results showed that the line emission of spatially confined LIBS was improved by varying the LTSD.The excitation source used in the discussion above is nanosecond pulse laser.The change in the spectral intensity of ns-LIBS with the LTSD is attributed to the plasma shielding effect[6,31,32].However,the change in the spectral intensity of fs-LIBS with the LTSD is based on the nonlinear self-focusing effect[33-35].Xu et al discussed the influence of the LTSD on the spectral intensity of femtosecond laser-induced copper plasma[36],finding that the maximum optical emission moved towards the opposite direction of the pulse beam as the pulse energy increased.Wang et al investigated the influence of the LTSD on CN spectral signal from fs-LIBS of PMMA target[37],their results showed that the position for strongest CN signal moved toward the opposite direction of the pulse beam as the pulse energy increased.Zuhlke et al investigated lens aberrations effects on the LIBS signal strength using a plano-convex spherical lens and an aspherized achromatic lens[38].Although many works have carried out the studies on the laser polarization and the LTSD,few studies have combined the two conditions.Therefore,we wanted to change the laser polarization and the LTSD to investigate their effects on the spectral characteristics of fs-LIBS.

    In this investigation,the influence of the LTSD on the line intensity of brass plasma induced by focused femtosecond pulse with linear and circular polarizations is discussed in the atmospheric environment.The results show that the spectral emission,electron temperature and density of brass plasmas with circular pulse polarization is higher compared to that with linear pulse polarization.

    2.Experimental setup

    Figure 1.Experimental setup of fs-LIBS of brass target(L is the lens;Q is the quarter-wave plate; M is the mirror; HWP is the half-wave plate; Glan is the Glan laser polarizer).

    Figure 1 displays the schematic diagram of experimental setup in current study on fs-LIBS of brass target.The excitation source was a ultrafast Ti:sapphire femtosecond laser system(Coherent Libra),its pulse width was 50 fs with a wavelength of 800 nm.The repetition rate was adjusted to 10 Hz by setting the SDG(synchronization and delay generator).The pulse energy was changed by combining an 800 nm half-wave plate(HWP)and a Glan-laser polarizer(Glan),and the corresponding energy values used were 0.5,1.0 and 1.5 mJ,respectively.The light polarization was adjusted using a quarter-wave plate(Q).For circularly polarized pulse beam,the angle of the quarter-wave plate was 45° +n× 90° ; for linearly polarized pulse beam,the angle of the quarter-wave plate wasn× 90° .Next,a planoconvex lens(the focal distance is 201 mm at 800 nm wavelength,the diameter is 25 mm)focused the pulse beam to the brass,and the focusing lens was attached on a computer-controlled stage to vary the LTSD.A LTSD of 201 mm indicated that the geometric focal point was at the sample surface; a LTSD longer than 201 mm indicated the geometric focal point was above the sample surface; and a LTSD shorter than 201 mm indicated that the geometric focal point was below the sample surface.In the whole experiment,the geometric focal point was located at and below the sample surface,that is,the LTSD is less than or equal to 201 mm.Another computercontrolled three-dimensional stage was used to move the target position with a constant speed.The optical signal from the plasma was focused to an optical fiber with another lens.The fiber guided the optical signal to a spectrometer(Princeton Instruments,SP-500i,PI-Acton)with a 1200 grooves mm?1grating.The optical signal was detected by an ICCD camera(Princeton Instruments,PI-MAX-4,1024i).Each spectral data was an average of 20 pulses,and all of the measurements were performed in the atmospheric environment.

    Figure 2.Comparison of Zn(I)((a)and(b))and Cu(I)((c)and(d))lines from brass plasmas with circular((a)and(c))and linear((b)and(d))laser polarizations.Laser energy is 1.0 mJ.LTSD is 198.6 mm.

    3.Results and discussion

    3.1.Influence of polarization on spectra

    In the section,Cu(I)lines at 510.55,515.32 and 521.82 nm as well as Zn(I)lines at 468.01,472.21 and 481.08 nm were selected to study the influence of the polarization on fs-LIBS of brass target irradiated under linearly and circularly polarized pulses,since these lines have the characteristics of strong and clear emission line compared to other emission lines[39].To reduce the background emission intensity and enhance the emission line intensity,the delay time and gate width of the ICCD are set to 0.5 μs and 2 μs,respectively.Figure 2 presents the comparison of the Zn(I)and Cu(I)lines from the brass plasmas with circularly and linearly polarized pulses.The energy is 1.0 mJ and the LTSD is 198.6 mm.As seen from the figure,the emission line under circularly polarized pulse is stronger than that under linearly polarized pulse by comparing Zn(I)(see figures 2(a)and(b))and Cu(I)(see figures 2(c)and(d))lines.

    Figure 3.Line peak intensities of Zn(I)468.01 nm(a),Zn(I)481.08 nm(b),Cu(I)510.55 nm(c),and Cu(I)521.82 nm(d)as functions of pulse energy.LTSD is 198.6 mm.

    To better understand the effect of the laser polarization on the optical signal of fs-LIBS of the brass target,figure 3 shows the evolution of the line peak intensities of Zn(I)468.01 nm,Zn(I)481.08 nm,Cu(I)510.55 nm,and Cu(I)521.82 nm with the laser energy.The LTSD is 198.6 mm.It can be observed that the peak emission under circularly polarized pulse is stronger than that under linearly polarized pulse in the process of increasing the pulse energy.For femtosecond pulse irradiation of metal[40,41],when femtosecond pulse irradiates the target,free electrons in the target absorb the pulse energy,and electron temperature rises rapidly based on very low electron heat capacity,and then the energy of hot electrons is transferred to lattice by electronlattice coupling[42-44].The lattice temperature increases,and laser-induced plasma is generated[45].Also,the kinetic energy of free electrons under circularly polarized pulse is greater than that under linearly polarized pulse[23].After the brass target was irradiated by femtosecond pulse with circular polarization,free electrons in the brass sample obtained more energy compared with linearly polarized pulse.Therefore,the brass plasma with higher-temperature and higher-density was generated with circular polarization,resulting in stronger spectral emission(see figure 3).

    3.2.Influence of LTSD on spectral emission

    Figure 4 presents the distribution of the peak emission of the Zn(I)481.08 nm and Cu(I)521.82 nm lines with the LTSD at circular and linear laser polarizations.At the same laser energy,the line emission at circularly polarized pulse is stronger than that at linearly polarized pulse for different LTSDs.The kinetic energy of free electrons at circularly polarized pulse is greater than that at linearly polarized pulse.The speed of free electron at circularly polarized laser field is faster than that at linearly polarized laser field.As the brass plasma collides with higher-energy free electrons,an increase in the plasma temperature of the brass is more obvious,improving the plasma emission intensity.Shi et al studied the influence of the polarization on fluorescence emission of femtosecond filamentation in the atmosphere[46],they thought that the electron energy irradiated by circularly polarized femtosecond laser field was greater than that by linearly polarized femtosecond laser field.For linearly polarized femtosecond laser field,the free electrons undergo alternate acceleration and deceleration of the laser field in each electric field period,and their kinetic energy is relatively low; on the contrary,for circular polarization,the electrons are always accelerated in each optical cycle,so that their energy is relatively high.

    Figure 4.Distribution of peak emission of Zn(I)481.08 nm(a)and Cu(I)521.82 nm(b)with LTSD under circular and linear laser polarizations.

    Mitryukovskiy et al calculated electron energy irradiated by linear,elliptical,and circularly polarized laser pulses[24],finding that the electron energy under circularly polarized laser pulse was higher than that under linearly polarized laser pulse.Why free electrons are accelerated all the time under circularly polarized laser pulse,while accelerated and decelerated alternately under linearly polarized laser pulse? Bashmakov et al used a particle-in-cell and Monte-Carlo method to simulate quantum electrodynamics cascade for circular and linear polarizations in a fixed electromagnetic wave[47].For the same laser energy,the number of cascade particles in circularly polarized laser field is larger compared with the case in linearly polarized laser field.The fixed electromagnetic wave is separated into ‘electric’ and ‘magnetic’regions.Under linear polarization,electrons are accelerated in the ‘electric’ region,while in the ‘magnetic’ region,the acceleration is suppressed.The velocity of free electrons in the ‘electric’ and ‘magnetic’ regions changes periodically with time.Under circularly polarized laser pulses,electrons can be accelerated even in the ‘magnetic’ region.The speed of free electrons in the ‘electric’ and ‘magnetic’ regions increases continuously.Therefore,the electron energy irradiated by circularly polarized femtosecond pulse is greater than that in the case of linear polarization,and the collision between free electron and other particles in plasma is more intense compared with linear polarization,which results in higher emission intensity.

    In addition,the position of actual focusing point will vary as the pulse energy increases,that is,the actual focal length will become shorter.This is because femtosecond pulse laser in transparent media will be affected by self-focusing effect[34,35,48,49],resulting in a change in beam collapse distance(Lc).The collapse distance can be described by semiempirical formula[35,49]:

    where,Pcr,Pin,k0=2π/λ0,r0andλ0represent the critical power,the incident power,the wave number,the light radius,and the laser wavelength.In this experiment,Pinis higher thanPcr,so Lcis inversely proportional to Pin.For the focused laser,the focusing length can be described as follows[35,49]:

    where,f and Lcfare the focal length and the actual focusing distance.Therefore,Lcfis inversely proportional to Pin,that is,Lcfdecreases with the increase in the Pin.As a result,the position of the focusing point moves toward the focusing lens with increasing the pulse energy.

    In order to clearly observe the difference in the spectral intensity between circular polarization and linear polarization,figure 5 shows the distribution of the spectral emission ratio of circular polarization to linear polarization with the LTSD for Zn(I)481.08 nm and Cu(I)521.82 nm at different laser energies.It can be seen that the spectral intensity increases by about 20%,indicating that circularly polarized pulses can improve the spectral intensity.As mentioned in the above theory,the laser polarization can change the emission intensity of the laser-induced plasma,the increase in the spectral intensity is usually due to the increase in plasma temperature[50-53].Next,we calculated electron temperature and density of fs-LIBS of the brass target for different LTSDs under circular and linear polarizations.

    Figure 5.Distribution of spectral emission ratio of circular polarization to linear polarization with LTSD for Zn(I)481.08 nm(a)and Cu(I)521.82 nm(b).

    The electron temperature and density are important parameters to describe the plasma characteristics.To obtain the electron temperature,it is necessary to discuss the electron temperature under the assumption of local thermodynamic equilibrium.The electron temperature can be obtained by the following equation[32,54]:

    where,λki,Iki,gkand Akon the left side of the equation are the line wavelength,the line intensity,the degeneracy,and the transition probability,respectively; Ek,kB,Teand C on the right side of the equation are the level energy,the Boltzmann constant,the electron temperature,and the constant,respectively.These physical parameters can be found from NIST database[55].The Cu(I)lines at 510.55,515.32 and 521.82 nm were used to calculate the electron temperature including some previously published papers[56-58].Moreover,we chose the Cu(I)510.55 nm to calculate the electron density.The expression between the Stark broadening and the electron density is as follows[32,54]:

    where,Δλ1/2is the full width at half maximum of the measured spectrum,neis the electron number density,and ω is the electron collision coefficient.The observed spectral line broadening(Δλobserved)has instrument broadening(Δλinstrumen),Doppler broadening,and natural broadening.λΔobservedcan be fitted by the Cu(I)line at 510.55 nm.The instrument broadening is approximately 0.04 nm.Both Doppler broadening and natural broadening can be ignored,Δλobserved=0.5346Δλ1/2+

    Figure 6.Evolution of electron temperature of brass plasma with LTSD for different laser energies at circular and linear polarizations.

    Figure 7.Evolution of electron density of brass plasma with LTSD for different laser energies at circular and linear polarizations.

    Figures 6 and 7 display the evolution of the electron temperature and density of fs-LIBS of the brass target with the LTSD for circular and linear polarizations.It can be seen that the changes in the electron temperature and density under circularly polarized and linearly polarized laser irradiation are similar to the changes in the line emission,that is,the electron temperature and density at circularly polarized pulse are greater than those at linearly polarized pulse.This is because free electrons are continuously accelerated under the irradiation of the circularly polarized laser,and have higher kinetic energy.Obviously,electron temperature is equivalent to electron energy.In addition,there are two peak values of electron temperature and density with the change of the LTSD(see figures 6 and 7),and the second peak value is lower than the first peak value.When femtosecond laser propagates in transparent medium(air),self-focusing,defocusing and refocusing effects will occur[35,60].The effect of Kerr selffocusing and electron self-defocusing will change the refractive index of the transparent medium.The refractive index isn=n0+n2I?Δn1[35,60],n0is the linear Δn1=4πe2N1e/2meω2,ω is the laser frequency,e is the refractive index,n2I is the Kerr nonlinear refractive index,n2is the Kerr coefficient,and I is the laser intensity.electron charge,meis the electron mass,and N1eis the electron density.When femtosecond laser propagates in air,the Kerr self-focusing phenomenon will first occur to generate plasma.The electron defocusing phenomenon will appear with an increase in free electrons,and as the self-focusing effect is stronger than the defocusing effect,the refocusing effect will occur.According to the discussion above,changing the laser polarization in fs-LIBS is a simple and effective way to increase the electron temperature and density,and then improve the spectral emission intensity of laser-induced plasma.

    4.Conclusions

    This paper mainly discussed the effect of laser polarization on the spectral intensity,electron temperature and density of fs-LIBS of brass sample for different LTSDs.It was found that circular laser polarization could increase the spectral line intensity,electron temperature and density.In essence,the laser energy was absorbed by free electrons in metal,and free electrons under circularly polarized laser had higher kinetic energy due to continuous acceleration of laser field,leading to higher electron temperature and density in plasma.Thus,the plasma with circular polarization emitted stronger spectral line.For different LTSDs,the optical emission under circularly polarized pulse was also stronger than that under linearly polarized pulse at the same laser energy.Also,the position of actual focusing point moved toward the focusing lens with increasing the pulse energy.This is because the nonlinear self-focusing effect became stronger with the increase in laser energy.

    Acknowledgments

    We acknowledge the support by National Natural Science Foundation of China(Nos.11674128,11674124 and 11974138),and Scientific and Technological Research Project of the Education Department of Jilin Province in China(No.JJKH20200937KJ).

    猜你喜歡
    安民明星
    THE EXISTENCE AND NON-EXISTENCE OFSIGN-CHANGING SOLUTIONS TO BI-HARMONIC EQUATIONS WITH A p-LAPLACIAN*
    打羽毛球
    明星猝死背后
    南方周末(2019-11-28)2019-11-28 08:37:59
    易安民聲
    易安民聲
    交通安全小明星
    幼兒園(2017年23期)2018-02-07 15:26:54
    明星們愛用什么健身APP
    Coco薇(2017年2期)2017-04-25 03:02:27
    扒一扒明星們的
    Coco薇(2016年10期)2016-11-29 16:59:54
    龔遂治亂安民的“高招”
    誰是大明星
    国国产精品蜜臀av免费| 日本欧美国产在线视频| 亚洲久久久久久中文字幕| 亚洲成av人片在线播放无| 三级国产精品欧美在线观看| 精品久久久久久久久亚洲| 欧美一级a爱片免费观看看| 一个人看的www免费观看视频| 亚洲成人精品中文字幕电影| 日本av手机在线免费观看| 亚洲成人久久爱视频| 亚洲人成网站高清观看| 熟女电影av网| 我的女老师完整版在线观看| 亚洲精品国产av成人精品| 国产精品久久久久久久久免| 少妇高潮的动态图| www日本黄色视频网| 偷拍熟女少妇极品色| 在线免费观看不下载黄p国产| 国产亚洲av嫩草精品影院| 国产精品久久久久久久久免| h日本视频在线播放| 最好的美女福利视频网| 色吧在线观看| 六月丁香七月| 色综合色国产| 欧美日韩综合久久久久久| 亚洲在线自拍视频| 看片在线看免费视频| 成人亚洲欧美一区二区av| 日本与韩国留学比较| 国产三级在线视频| 国产精品精品国产色婷婷| 亚洲高清免费不卡视频| 久久精品国产鲁丝片午夜精品| 赤兔流量卡办理| 亚洲中文字幕一区二区三区有码在线看| 五月伊人婷婷丁香| av在线播放精品| 欧美色欧美亚洲另类二区| 国产精品电影一区二区三区| 欧美一区二区精品小视频在线| 日韩欧美三级三区| 国内精品宾馆在线| 啦啦啦观看免费观看视频高清| www.av在线官网国产| ponron亚洲| 亚州av有码| 亚洲五月天丁香| 嘟嘟电影网在线观看| 久久久欧美国产精品| 国产女主播在线喷水免费视频网站 | 免费观看的影片在线观看| 欧洲精品卡2卡3卡4卡5卡区| 国产精品1区2区在线观看.| 日韩中字成人| 99久久无色码亚洲精品果冻| 日韩欧美国产在线观看| 亚洲欧美精品自产自拍| 长腿黑丝高跟| 熟女人妻精品中文字幕| 亚洲av中文字字幕乱码综合| 亚洲精品亚洲一区二区| 91久久精品国产一区二区三区| 麻豆成人午夜福利视频| 赤兔流量卡办理| 国产乱人视频| 99九九线精品视频在线观看视频| 欧美色欧美亚洲另类二区| 日韩欧美在线乱码| 亚洲自拍偷在线| 国产一区二区三区在线臀色熟女| 性欧美人与动物交配| 国产成人午夜福利电影在线观看| 自拍偷自拍亚洲精品老妇| 亚洲精品国产成人久久av| 亚洲欧美中文字幕日韩二区| a级一级毛片免费在线观看| 两个人的视频大全免费| 综合色av麻豆| 干丝袜人妻中文字幕| 久久亚洲国产成人精品v| 亚洲精品自拍成人| 亚洲欧洲日产国产| 日韩一区二区三区影片| 麻豆成人av视频| 亚洲自拍偷在线| 欧美日韩乱码在线| 亚洲精品乱码久久久v下载方式| 九草在线视频观看| 色综合亚洲欧美另类图片| 中国美女看黄片| 亚洲精品影视一区二区三区av| 狂野欧美激情性xxxx在线观看| 久久99蜜桃精品久久| 亚洲精品自拍成人| 国产精品人妻久久久久久| 亚洲成人久久爱视频| 国产精品一区www在线观看| 日韩亚洲欧美综合| 亚洲va在线va天堂va国产| 亚洲精品久久国产高清桃花| 亚洲婷婷狠狠爱综合网| 午夜免费激情av| av女优亚洲男人天堂| 少妇人妻精品综合一区二区 | 久久亚洲国产成人精品v| 亚洲经典国产精华液单| 成人特级黄色片久久久久久久| 色吧在线观看| 亚洲成人久久爱视频| 97超碰精品成人国产| 国产极品天堂在线| a级毛片免费高清观看在线播放| 日韩 亚洲 欧美在线| 欧美变态另类bdsm刘玥| av国产免费在线观看| 成人午夜高清在线视频| 又黄又爽又刺激的免费视频.| 免费观看在线日韩| 国产精品爽爽va在线观看网站| 国产日本99.免费观看| 91狼人影院| 亚洲国产精品sss在线观看| 两个人视频免费观看高清| 人妻久久中文字幕网| 久久久久久久久久久免费av| 国产私拍福利视频在线观看| 可以在线观看的亚洲视频| 亚洲av中文字字幕乱码综合| 最新中文字幕久久久久| 午夜福利视频1000在线观看| 久久久久久久久中文| 亚洲乱码一区二区免费版| 综合色丁香网| 国产大屁股一区二区在线视频| 日本黄色视频三级网站网址| 日韩强制内射视频| 日本三级黄在线观看| 小说图片视频综合网站| 国产一区二区亚洲精品在线观看| 如何舔出高潮| 麻豆久久精品国产亚洲av| 久久精品综合一区二区三区| 人妻久久中文字幕网| 精品不卡国产一区二区三区| 色综合站精品国产| 国产91av在线免费观看| 一进一出抽搐gif免费好疼| 欧美性猛交黑人性爽| 亚洲成a人片在线一区二区| 色5月婷婷丁香| 欧美bdsm另类| 1024手机看黄色片| 久久久久久久久久成人| 久久久久久久久久黄片| a级毛色黄片| 国产精品乱码一区二三区的特点| 在线免费观看的www视频| av女优亚洲男人天堂| 中文资源天堂在线| 高清日韩中文字幕在线| 麻豆乱淫一区二区| 欧美不卡视频在线免费观看| 床上黄色一级片| 99热6这里只有精品| 麻豆成人av视频| 国产精品av视频在线免费观看| 亚洲va在线va天堂va国产| av专区在线播放| 亚洲欧美日韩无卡精品| 老司机影院成人| 国产精品人妻久久久久久| 国产一区二区在线观看日韩| 精品一区二区三区视频在线| 国内精品一区二区在线观看| 国产亚洲91精品色在线| 欧美成人精品欧美一级黄| 女同久久另类99精品国产91| 最近视频中文字幕2019在线8| 如何舔出高潮| 日本免费一区二区三区高清不卡| av卡一久久| 国内精品久久久久精免费| 亚洲av中文av极速乱| 搡老妇女老女人老熟妇| 久久久久久久亚洲中文字幕| 亚洲国产精品sss在线观看| 99riav亚洲国产免费| 99精品在免费线老司机午夜| 在线观看一区二区三区| 99热6这里只有精品| 老熟妇乱子伦视频在线观看| 亚洲精品国产成人久久av| 精品日产1卡2卡| 亚洲中文字幕日韩| 免费看美女性在线毛片视频| 久久久久久久亚洲中文字幕| 26uuu在线亚洲综合色| 美女cb高潮喷水在线观看| 日韩欧美在线乱码| 国产精品人妻久久久影院| 99热这里只有是精品在线观看| 国产精品一区二区三区四区免费观看| 精品久久久久久久久av| 蜜桃久久精品国产亚洲av| 三级国产精品欧美在线观看| 欧美激情在线99| 精品久久久噜噜| 久久99蜜桃精品久久| 国产成人影院久久av| 97超碰精品成人国产| 国产精品久久久久久精品电影| 日韩 亚洲 欧美在线| 国产精品人妻久久久久久| 午夜免费男女啪啪视频观看| 午夜福利视频1000在线观看| 狂野欧美白嫩少妇大欣赏| 如何舔出高潮| 日韩国内少妇激情av| 亚洲av二区三区四区| 大型黄色视频在线免费观看| 精品熟女少妇av免费看| 午夜福利高清视频| 我的女老师完整版在线观看| 深爱激情五月婷婷| 精品欧美国产一区二区三| 免费看日本二区| 亚洲成av人片在线播放无| 亚洲电影在线观看av| 色噜噜av男人的天堂激情| av在线天堂中文字幕| 99久久精品热视频| 国产精品久久视频播放| 国产又黄又爽又无遮挡在线| 亚洲在久久综合| 亚洲成人中文字幕在线播放| 高清毛片免费观看视频网站| 日韩国内少妇激情av| 久久人人爽人人爽人人片va| 国产乱人偷精品视频| 亚洲精品久久久久久婷婷小说 | 一本—道久久a久久精品蜜桃钙片 精品乱码久久久久久99久播 | 久久这里有精品视频免费| 人体艺术视频欧美日本| 国产成人福利小说| 午夜激情福利司机影院| 色综合色国产| www.色视频.com| 精品一区二区三区视频在线| 国产伦一二天堂av在线观看| 最新中文字幕久久久久| 给我免费播放毛片高清在线观看| 久久久欧美国产精品| 国产伦精品一区二区三区视频9| 国产成人福利小说| 欧美色欧美亚洲另类二区| 亚洲av二区三区四区| 国产男人的电影天堂91| 国产美女午夜福利| 久久久久久久久久成人| 久久国产乱子免费精品| 毛片一级片免费看久久久久| 观看免费一级毛片| 悠悠久久av| av在线天堂中文字幕| 午夜福利成人在线免费观看| 黄色日韩在线| 爱豆传媒免费全集在线观看| 老司机影院成人| 欧美高清成人免费视频www| 黄片无遮挡物在线观看| 日日摸夜夜添夜夜爱| 国产色爽女视频免费观看| 一区二区三区高清视频在线| 久久久精品欧美日韩精品| 如何舔出高潮| 免费观看在线日韩| 超碰av人人做人人爽久久| 内地一区二区视频在线| 1000部很黄的大片| 亚洲无线在线观看| 可以在线观看毛片的网站| 国产精品久久久久久精品电影| 蜜桃亚洲精品一区二区三区| 国产av在哪里看| 日本欧美国产在线视频| 亚洲人成网站在线播放欧美日韩| videossex国产| 日韩,欧美,国产一区二区三区 | 欧美成人一区二区免费高清观看| 免费无遮挡裸体视频| 国产一区二区三区在线臀色熟女| 中文字幕av在线有码专区| 中文精品一卡2卡3卡4更新| 尤物成人国产欧美一区二区三区| 男女做爰动态图高潮gif福利片| 99热这里只有是精品在线观看| 成人毛片a级毛片在线播放| 亚洲五月天丁香| 亚洲最大成人中文| 一个人免费在线观看电影| 看片在线看免费视频| 波多野结衣高清作品| 尤物成人国产欧美一区二区三区| 日韩精品有码人妻一区| 成人亚洲精品av一区二区| av天堂在线播放| 麻豆国产av国片精品| 美女脱内裤让男人舔精品视频 | 国产亚洲精品av在线| 亚洲av成人av| 啦啦啦观看免费观看视频高清| 久久中文看片网| 亚洲av电影不卡..在线观看| 亚洲精品日韩av片在线观看| 极品教师在线视频| eeuss影院久久| 国产精品一二三区在线看| 国产三级中文精品| 免费在线观看成人毛片| 亚洲精品久久久久久婷婷小说 | 老司机福利观看| 国产午夜精品久久久久久一区二区三区| 少妇人妻精品综合一区二区 | 男人的好看免费观看在线视频| 少妇高潮的动态图| av卡一久久| 久久久久免费精品人妻一区二区| 菩萨蛮人人尽说江南好唐韦庄 | 成年av动漫网址| 寂寞人妻少妇视频99o| 一级二级三级毛片免费看| 国产大屁股一区二区在线视频| 国产三级在线视频| 国模一区二区三区四区视频| 少妇的逼水好多| 国产精品免费一区二区三区在线| 性欧美人与动物交配| ponron亚洲| 男女视频在线观看网站免费| 看片在线看免费视频| 99热网站在线观看| 可以在线观看的亚洲视频| 国产精品一区二区三区四区免费观看| 欧美精品国产亚洲| 国产69精品久久久久777片| 三级男女做爰猛烈吃奶摸视频| 亚州av有码| 国产视频内射| 亚洲av二区三区四区| 久久久久久久久久黄片| 国产精品一二三区在线看| 三级男女做爰猛烈吃奶摸视频| 九九热线精品视视频播放| 欧美成人免费av一区二区三区| 身体一侧抽搐| 日韩成人av中文字幕在线观看| 久久人妻av系列| 免费看a级黄色片| 午夜福利视频1000在线观看| 亚洲,欧美,日韩| 亚州av有码| 亚洲av不卡在线观看| 国产精品综合久久久久久久免费| 成人午夜高清在线视频| 成人午夜精彩视频在线观看| 3wmmmm亚洲av在线观看| 简卡轻食公司| 精品不卡国产一区二区三区| 校园人妻丝袜中文字幕| 黄色欧美视频在线观看| 久久婷婷人人爽人人干人人爱| 特大巨黑吊av在线直播| 日本免费一区二区三区高清不卡| 美女内射精品一级片tv| 三级男女做爰猛烈吃奶摸视频| 一区二区三区免费毛片| 国产黄色视频一区二区在线观看 | 亚洲欧洲国产日韩| 99久久人妻综合| 亚洲美女视频黄频| 直男gayav资源| 日韩制服骚丝袜av| 精品久久久久久久久久免费视频| 国产成人精品婷婷| 日韩欧美在线乱码| 精品免费久久久久久久清纯| 色综合色国产| 亚洲va在线va天堂va国产| 你懂的网址亚洲精品在线观看 | 精品久久久噜噜| 亚洲内射少妇av| 啦啦啦韩国在线观看视频| 男女边吃奶边做爰视频| 免费av观看视频| 黄色视频,在线免费观看| 欧美人与善性xxx| а√天堂www在线а√下载| 少妇熟女aⅴ在线视频| 99国产精品一区二区蜜桃av| 插逼视频在线观看| 国产老妇伦熟女老妇高清| 国产免费一级a男人的天堂| 国产精品一区www在线观看| 国产三级中文精品| 91精品国产九色| 午夜a级毛片| 九九爱精品视频在线观看| 久久婷婷人人爽人人干人人爱| 午夜久久久久精精品| 亚洲精品色激情综合| 亚洲欧美日韩高清在线视频| 亚洲最大成人av| 亚洲国产日韩欧美精品在线观看| 精品免费久久久久久久清纯| 一级黄色大片毛片| 国内精品宾馆在线| 波多野结衣高清无吗| 日本撒尿小便嘘嘘汇集6| 亚洲国产精品sss在线观看| 亚洲av电影不卡..在线观看| 国产精品免费一区二区三区在线| 99久久精品一区二区三区| 黄色视频,在线免费观看| 不卡视频在线观看欧美| 亚洲精品久久国产高清桃花| 日韩欧美 国产精品| 一进一出抽搐动态| av免费观看日本| 九九爱精品视频在线观看| 久久中文看片网| 联通29元200g的流量卡| 欧美一区二区亚洲| 国产白丝娇喘喷水9色精品| 在线观看午夜福利视频| 久久热精品热| 亚洲精品456在线播放app| 色噜噜av男人的天堂激情| 亚洲天堂国产精品一区在线| 亚洲国产欧美人成| 国产成人freesex在线| 午夜福利在线观看吧| 免费观看在线日韩| 亚洲国产欧美在线一区| a级一级毛片免费在线观看| 超碰av人人做人人爽久久| 少妇高潮的动态图| 亚洲最大成人手机在线| 日本五十路高清| 精品日产1卡2卡| 亚洲av男天堂| 波多野结衣巨乳人妻| 久久综合国产亚洲精品| 国产精品一区二区在线观看99 | 亚洲熟妇中文字幕五十中出| 日日摸夜夜添夜夜添av毛片| 欧美激情在线99| 国产精品久久久久久久电影| 可以在线观看的亚洲视频| 91aial.com中文字幕在线观看| 中文字幕制服av| 丰满人妻一区二区三区视频av| 啦啦啦韩国在线观看视频| 国产精品女同一区二区软件| 国产精品1区2区在线观看.| 亚洲欧美日韩高清专用| 亚洲真实伦在线观看| 免费黄网站久久成人精品| 在线免费观看的www视频| 波多野结衣巨乳人妻| 岛国在线免费视频观看| 亚洲中文字幕日韩| 日韩一区二区三区影片| 久久精品国产亚洲av香蕉五月| 国产色婷婷99| 欧美性感艳星| 婷婷精品国产亚洲av| 亚洲国产色片| 国产一区二区三区av在线 | 有码 亚洲区| 久久精品国产亚洲av涩爱 | 波多野结衣高清无吗| 99热全是精品| 国产极品天堂在线| 嫩草影院入口| 最近2019中文字幕mv第一页| 国产精品国产高清国产av| 欧美性感艳星| 日韩一区二区视频免费看| 变态另类丝袜制服| 中文字幕久久专区| 亚洲av男天堂| 又爽又黄a免费视频| 精品一区二区免费观看| 高清在线视频一区二区三区 | videossex国产| 欧美激情国产日韩精品一区| 中国国产av一级| 麻豆一二三区av精品| 成年女人永久免费观看视频| 99精品在免费线老司机午夜| 国国产精品蜜臀av免费| 国内精品久久久久精免费| 一本—道久久a久久精品蜜桃钙片 精品乱码久久久久久99久播 | 婷婷色av中文字幕| 亚洲自拍偷在线| 久久久国产成人精品二区| 中文欧美无线码| 国产单亲对白刺激| 91av网一区二区| 色视频www国产| 日本色播在线视频| 亚洲av不卡在线观看| 26uuu在线亚洲综合色| 中文字幕免费在线视频6| 在线观看一区二区三区| 欧美高清性xxxxhd video| 日韩制服骚丝袜av| 一本精品99久久精品77| 国产精品一及| 99久久成人亚洲精品观看| 久久亚洲精品不卡| 又爽又黄a免费视频| 免费不卡的大黄色大毛片视频在线观看 | 日韩欧美精品v在线| 极品教师在线视频| 搡女人真爽免费视频火全软件| 国产乱人偷精品视频| 日韩三级伦理在线观看| 久久久久久久亚洲中文字幕| 国产亚洲91精品色在线| 欧美+日韩+精品| 亚洲最大成人手机在线| 哪个播放器可以免费观看大片| 又黄又爽又刺激的免费视频.| 青青草视频在线视频观看| 精品熟女少妇av免费看| 亚洲精品456在线播放app| 国产精品一区二区三区四区久久| 亚洲最大成人中文| 麻豆成人午夜福利视频| 亚洲欧洲国产日韩| 日韩欧美在线乱码| 亚洲欧美清纯卡通| 欧美日韩在线观看h| 十八禁国产超污无遮挡网站| 少妇裸体淫交视频免费看高清| 全区人妻精品视频| 国产黄色视频一区二区在线观看 | 亚洲美女视频黄频| 欧洲精品卡2卡3卡4卡5卡区| 久久久久久伊人网av| 老师上课跳d突然被开到最大视频| 国产精品久久久久久久电影| 午夜亚洲福利在线播放| 一个人看的www免费观看视频| 欧美色视频一区免费| 黄片无遮挡物在线观看| 在线播放国产精品三级| 国产一区亚洲一区在线观看| 成人午夜精彩视频在线观看| 亚洲av第一区精品v没综合| 欧美最新免费一区二区三区| 欧美色视频一区免费| 欧美日韩在线观看h| 级片在线观看| 色综合站精品国产| 亚洲国产精品合色在线| 亚洲激情五月婷婷啪啪| 麻豆精品久久久久久蜜桃| 婷婷色综合大香蕉| 丝袜喷水一区| 97在线视频观看| 亚洲,欧美,日韩| 高清毛片免费观看视频网站| 1000部很黄的大片| 人妻系列 视频| 亚洲国产精品sss在线观看| 久久精品国产99精品国产亚洲性色| 久久99精品国语久久久| 中出人妻视频一区二区| 精品国产三级普通话版| 午夜久久久久精精品| 波多野结衣高清作品| 国产成人午夜福利电影在线观看| 搡老妇女老女人老熟妇| 在线观看66精品国产| 1024手机看黄色片| 最好的美女福利视频网| 九九爱精品视频在线观看| 日韩欧美三级三区| 国产午夜精品一二区理论片| 日日干狠狠操夜夜爽| 精品熟女少妇av免费看| 热99re8久久精品国产| 亚洲国产精品sss在线观看| 亚洲第一电影网av| 在线免费观看的www视频| 看黄色毛片网站| 岛国在线免费视频观看| 国产精品久久久久久久电影| 日韩 亚洲 欧美在线| av免费观看日本| 老女人水多毛片| 成年女人永久免费观看视频| 少妇熟女aⅴ在线视频| 午夜福利视频1000在线观看| 男女啪啪激烈高潮av片| 中文字幕制服av| 五月玫瑰六月丁香| 国产午夜精品论理片| videossex国产| 此物有八面人人有两片|