• <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 ?

    Asymmetric coherent rainbows induced by liquid convection?

    2021-12-22 06:49:04TingtingShi施婷婷XuanQian錢軒TianjiaoSun孫天嬌LiCheng程力RunjiangDou竇潤江LiyuanLiu劉力源andYangJi姬揚
    Chinese Physics B 2021年12期
    關鍵詞:力源

    Tingting Shi(施婷婷) Xuan Qian(錢軒) Tianjiao Sun(孫天嬌) Li Cheng(程力)Runjiang Dou(竇潤江) Liyuan Liu(劉力源) and Yang Ji(姬揚)

    1State Key Laboratory for Superlattices and Microstructures,Institute of Semiconductors,Chinese Academy of Sciences,Beijing 100083,China

    2College of Materials Science and Opto-Electronic Technology,University of Chinese Academy of Sciences,Beijing 100049,China

    3College of Physical Sciences,University of Chinese Academy of Sciences,Beijing 100049,China

    4Center of Materials Science and Optoelectronics Engineering,University of Chinese Academy of Sciences,Beijing 100049,China

    Keywords: coherent interference,thermal lens effect,convection,numerical simulation

    1. Introduction

    Coherent rainbows are colorful interference rings formed by injecting white laser into liquids or solids. It has been observed in pure solvents (e.g., water, acetone, and anhydrous ethanol),plastics,wax and ice.[1–3]Interference rings induced by single-wavelength lasers were reported much earlier (e.g.,liquid crystals,[4–6]tea,[7]nano-material suspensions,[8–18]and organic solvents).[19,20]There are mainly two models to explain interference rings in liquids: the thermal lens effect[8,16,19]and the electronic third-order nonlinear selfphase modulation.[9,10,12,14,17]While different materials and models were used in these studies, the asymmetric shapes of the interference rings (when appeared) were ascribed to convection,but no detailed discussion was given. Here we report experimental study of the effect of convection on the shape of interference rings. We also clarify the mechanism behind the coherent rainbows in the liquid. The optical path difference necessary for the interference comes from the local change of the refractive index,which in turn comes from the temperature distribution in the liquid induced by laser heating. The liquid behaves as a non-ideal plane concave lens, i.e., the thermal lens effect. When the temperature of the liquid in the middle part of the laser beam becomes much higher than that of the outer part, convection occurs in the upper part of the liquid,while the lower part stays still. This makes the temperature distribution in the liquid asymmetric (an up–down asymmetry),thus leading to the asymmetric interference rings.We also numerically simulate the effect of heat conduction on the temperature distribution in the liquid in two-dimensional cases,with and without convection, respectively. The numerical results agree well with our experimental observations.

    2. Experimental systems and observations

    2.1. Experimental setup

    The experimental setup is shown in Fig. 1. A fiber laser with white light pulse is used(Model: SC-PRO,Wuhan Yangtze Soton Laser Company). Its wavelength ranges from 400 nm to 2400 nm,with a pulse width~100 ps,a beam diameter~2 mm(@633 nm),and an emission angle<1 mrad.The repetition rate is 1 MHz and the visible light power is continuously adjustable from 0 to 1 W.When the shutter(SH)is opened, the white laser (WL) beam from the fiber laser is focused through the lens (L) into the sample (S), and colorful interference rings(coherent rainbows)appear on the image screen(IS),an interference filter(IF)can be inserted into the laser beam,just behind the sample. The free-fall part(FF,enclosed by the dash line)has all the components fixed to a stage and we can let it go a free-fall. The focal length of the lens is about 10 cm,the sample is placed in a quartz cuvette,and the distance between the imaging screen and the sample is about 30 cm. The optical path is 10 mm in the liquid. Colorful images are recorded with a commercial cell-phone,and blackwhite images are recorded with a high-speed camera, which can capture 1000 frames per second with an image resolution of 800×600 pixels.[21]

    Fig.1. Schematic diagram of the experimental set-up: when the shutter(SH)opens,the white laser(WL)beam from a pulsed fiber is focused through the lens(L)into the sample(S),and the colorful interference rings(coherent rainbows)appear on the image screen(IS).An interference filter(IF)can be inserted behind the sample. The FF part(enclosed by the dash line)is fixed to a stage and we can let it go a free-fall.

    2.2. Experimental materials

    Samples are water and/or dimethicone. Dimethicone is a kind of hydrophobic silicone material, also known as polydime-thylsiloxane. It has a wide range of molar mass(162–500000 g/mol),with viscosity varying from 0.65 mm2/s to 1000000 mm2/s. By adjusting the amount of chain stopper during synthesis,or mixing two kinds of dimethicone with different viscosity,one can obtain dimethicone with any specific viscosity.[22]The viscosity of dimethicone used in the experiment is 50 cst, 500 cst, 5000 cst, and 50000 cst, respectively(1 cst=1 mm2/s). The viscosity of water is about 0.89 cst at room temperature.

    2.3. Experimental results

    Multi-order colorful rings are observed in water and dimethicone with various viscosity, as show in Fig. 1 for the case of water. To make observation and analysis easier, we insert an IF (central wavelength 632.8 nm, half width of full magnitude 10 nm±2 nm)behind the sample and record blackand-white images with the high-speed camera, as shown in

    Fig. 2. The interference rings of water (Fig. 2(a)) have an oval shape, with the distance between rings becoming wider and wider from the center to the edge. Obviously they are asymmetric, i.e., instead of concentric circles, they are oval with a core sitting in the upper part. The interference patterns from dimethicone with viscosity 50 cst,500 cst,5000 cst and 50000 cst are shown in Figs.2(b)–2(e). They are much bigger than that from water. The interference rings from the dimethicone with viscosity 50 cst (Fig. 2(b)) deviate from the circular symmetry most significantly, similar to water shown in Fig. 2(a). With the increase of the viscosity, the shape of the rings gradually changes from oval ones to circular ones. As for the dimethicone with viscosity 50000 cst,the shape of the interference rings is almost circular(Fig.2(e)).

    After the shutter opens, we record the dynamics of the interference rings with the high-speed camera mentioned before. It takes much shorter time for water to form a stable oval shape than the dimethicone. We choose water as the sample in the following dynamic experiments, though the results of dimethicone are similar. The laser beam goes in the horizontal plane. As shown in Fig. 3(a), concentric circles start to appear when the shutter opens. Then the rings gradually spread out and the number of rings increases. The number of the rings reaches the maximum at~0.08 s, and the interference rings distort more and more and reach a stable oval shape after~0.20 s. When the white light goes perpendicularly,along the direction of the gravity,there are only a set of concentric circles.[1]This suggests that the asymmetric rings are caused by the convection in the liquid. To check it,we let the FF part go a free-fall and open the shutter simultaneously.As shown in Fig. 3(b), the interference rings also spread out(and the number of rings increases,too),however,their shape remains circular. When the shape of the interference rings is stable in static state, we reduce the laser power from 1 W to 0.6 W in less than 1 ms,the shape of the rings will remain the same,but the intensity of the rings will drops(Fig.3(c)).After a few milliseconds(ms),they begin to shrink inward,and the number of rings decreases gradually.

    Fig.2. Interference rings from(a)water,(b)–(e)dimethicone with different viscosity.

    Fig.3. Dynamic of the interference rings from water: (a)in static state,(b)in free-fall. (c)In static and stable state,the laser power is reduced from 1 W to 0.6 W in less than 1 ms.

    3. Theoretical analysis and numerical simulation

    Multi-order colorful interference rings in the liquid come from the change of local refractive index for sure. The controversy lays on which mechanism induces the refractive index change. Wuet al.explained it with electronic thirdorder nonlinear self-phase modulation and proposed a windchime model to account for the emergence of the ac electron coherence.[17]Many others took the thermal lens effect as the mechanism,such as Pillaet al.,[8]Wanget al.[16]and Zhanget al.[19]They ascribed the optical path difference to the temperature gradient in the liquid. However,the effect of convection in the liquid has not be discussed in details,though it has been mentioned before.[4,9–11,14,16–18]Here we clarify the formation mechanism of interference rings in the liquid with and without convection,respectively.

    We make a gross assumption that the laser heating of liquid along the laser direction is uniform in a finite lengthlnear the focal point. In other words,we only consider the thermal conduction perpendicular to the laser propagation direction.In this way,the three-dimensional problem is transformed into a two-dimensional one,which greatly simplifies our subsequent theoretical analysis and numerical simulation.

    The laser heating process of the liquid can be divided into two stages. In the first stage, the liquid at room temperature is suddenly irradiated by laser. The temperature rises continuously,but the temperature gradient is not big enough to start convection in the liquid. In the second stage, as the heating goes on,the temperature of the liquid in the middle part of the laser beam becomes much higher than that of the outer part,and convection is generated and it affects the heat conduction.

    3.1. The first stage: no convection

    First,we consider the case without convection. When the Gaussian-shape laser beam is absorbed,the local temperature goes up. The heating process of liquid can be expressed by the following heat conduction equation:

    whereβis the thermal conductivity coefficient;x,yare the coordinate axes;the planexoyis perpendicular to the laser direction;?is the heat flux density;ρis the density of the liquid;cpis the constant pressure specific heat capacity of the liquid;andtis the time.

    This is a typical thermal conduction process. The refractive indexnchanges accordingly, since the latter is inversely proportional to temperature for most media. The higher the temperature is,the smaller the refractive index is. Figure 4(a)shows the two-dimensional distribution of refractive index in the planexoy. Black circle indicates the Gaussian-shape laser spot, and its beam waist radiusw0is 100 μm in the simulation. The distribution of refractive index remains unchanged in the direction of laser beamz,so the optical-path difference??=∫?ndlpassing through the liquid also shows a bump shape when ?nx=nx ?nx=0, as shown in Fig. 4(b). In other words, we regard the optical-path difference at the center of the beam as zero, and then normalize the optical-path difference at each position, with laser wavelengthλ=632.8 nm.Figure 4(c)shows the radial gradient of the optical-path,which determines the outgoing direction of each sub-beamφ. The highest point corresponds to the maximum outgoing angle(i.e.,the outgoing direction),which determines the size of the outermost ring.[3]When the outgoing angle is smaller than its maximum value,there are two sub-beams going into the same direction(φr1=φr2),whose optical path difference can be expressed ass=(??r1???r2)?(r1?r2)·φin far-field regime.They may interfere constructively or destructively,depending on the optical-path differencesbetween them. The constructive(destructive)interference occurs whens/λ=mkπfor integermbeing even(odd). As the liquid temperature increases,the maximum optical path difference and the maximum outgoing angle also increase. The radial distribution of interference rings may be simulated,as shown in Figs.4(d)and 4(e).The rings are dense at the center, and become sparser as the outgoing angle increases,in agreement with the experimental observations.

    Fig.4. Formation mechanism and numerical simulation of interference rings without convection. (a) The two-dimensional distribution of refractive index in the plane xoy. Black circle indicates the Gaussianshape laser spot, and its beam waist radius w0 is 100 μm in the simulation. (b) The distribution of optical path difference ?? along the radial direction. (c) The radial gradient of the optical path difference. Two sub-beams at r1 and r2 are refracted into the same angle φr1 = φr2, whose optical path difference can be expressed as ?s =(??r1 ???r2)?(r1 ?r2)·φ in far-field regime. The constructive (destructive)interference occurs when s/λ =mkπ for integer m being even(odd). (d), (e) The radial distribution of interference rings obtained in the planes xoy and xoz by simulation,respectively.

    3.2. The second stage: convection starts

    As the heating goes on,the temperature difference of the liquid reaches a threshold, and convection starts. This is a result of Rayleigh instability which relates to the thermal gradient,the gravity and viscosity of the liquid. It is worth noting that convection occurs in the upper part of the liquid, while the lower part stays still. The reason is the following. With the laser beam being the center,from the center to the upper outmost part,the temperature is lower and lower,i.e.,the density becomes heavier. This results in buoyancy which can oppose gravity and viscosity of the liquid,thus leading to convection.In the lower half, no convection occurs since the temperature gradient is along the direction of the gravity. This leads to an asymmetric temperature distribution in the liquid,and thus the asymmetric interference rings. The higher the viscosity of the liquid is,the stronger the internal friction is in the flow,and it is more difficult to start convection. This is why the shape of the interference rings changes from oval ones to circular ones as the viscosity increases,as shown in Figs.2(b)an 2(e).

    The dynamic experiment (Fig. 3(a)) also proves that the asymmetry comes from the convection. After the injection of the laser, but before the convection starts, heat conduction is symmetric and circular-shape rings are observed.As time goes by,convection starts. Accordingly,a non-circular temperature distribution forms, which turns the circular shape of the interference rings into an oval shape. When the FF part makes a free-fall, the convection cannot start, since the gravity does not act on the liquid(“weight-loss”).So,the interference rings remain circular(Fig.3(b)).

    For the convenience of calculation,we may regard the effect of the convection as an additional thermal conductivity?β. As shown before,the convection exists only in the upper half of the perpendicular plane. In other words, the effective thermal conductivity of the upper part is larger than that of the lower part, as shown in Fig. 5(a). The heat-conduction convection differential equation is the following:

    Because of the additional thermal conductivity ?β,the refractive index distribution (temperature distribution) of the upper half plane is less dramatic than the lower half, in other words, the refractive index gradient (temperature gradient) is smoother, as shown in Fig. 5(b). The maximum value of the gradient is smaller,i.e.,the outgoing direction of the maximum ring decreases. Therefore, the shape of the interference rings is an oval with a small top and a big bottom. The fitting result verifies the theoretical explanation,as shown in Fig.5(c).This also explains why the size of interference rings from water is smaller than that from dimethicone. Table 1 shows some thermophysical parameters of water and dimethicone.The thermal diffusivityK=β/ρcp,which describes the diffusion ability in the process of heat conduction,of water(~1.5×10?7m2/s)is 1.5 times that of dimethicone(~1.0×10?7m2/s). The power of the incident light is the same, but the absorptivity of water is greater than that of dimethicone,of water is just 1.5 times that of dimethicone. So according to Eq.(1), when the steady state is reached(?T/?t=0),the temperature gradient of water and dimethicone is the same. The refractive temperature coefficient of water is?1.37×104K?1, while that of most liquid organic compounds is from?3×104K?1to?5×104K?1,[23]thus the maximum optical path difference gradient (the maximum outgoing angle) of water is smaller than that of dimethicone. So the size of the interference rings from water is smaller. Besides that,because the thermal conduction of water is greater than that of dimethicone, this explains why the time for water to reach steady state is shorter than that of dimethicone(~0.20 s and~2 s,respectively).

    Fig. 5. Formation mechanism and numerical simulation of interference rings with convection. (a) Equivalent model of heat convection. (b)The distribution of refractive index in the plane xoy. (c)The radial distribution of interference rings obtained by simulation.

    Table 1. Thermophysical parameters of water and dimethicone.

    In addition, when the laser power is reduced suddenly,the temperature distribution in liquid remains unchanged(for a few ms),so the interference pattern does not change,as shown in Fig. 3(c). In other words, its response time is longer than 1 ms. This also suggests that the mechanism behind the interference rings is a thermal effect—the response time of refractive index change caused by thermal effect is about 10?3–1 s,while the response time of other effects is much shorter (for instance, the high frequency Kerr effect related to polarized molecules is about 10?11–10?12s).[24]All in all,the above experiments have confirmed that the asymmetry of interference rings is due to the convection,along with a local change of the refractive index induced by laser heating(thermal lens effect).

    4. Discussion and conclusion

    Focus a white light laser on different viscosity of dimethicone,different shapes of interference rings will appear. Increase the viscosity,the shape of the interference rings changes from oval to circular shape. When the liquid is free-fall, the interference rings remain symmetrical. The reason for the formation of interference rings is that the temperature distribution in the liquid changes due to laser heating, which affects the refractive properties and leads to optical path difference. The symmetry of the rings is caused by the convection, which makes the temperature distribution asymmetric.The two-dimensional heat conduction simulation is consistent with the observation results, thus verifying the rationality of the physical mechanism.

    猜你喜歡
    力源
    南北方越冬對皺紋盤鮑生長的影響
    “童心向黨”征集作品展示
    未來教育家(2021年9期)2021-12-24 08:24:22
    一種光傳送網的建模及其價值評估
    軟件(2020年3期)2020-04-20 01:45:48
    包力源、鐘琦翔作品
    降低永磁同步電動機噪聲的方法
    力源信息“變形計”
    包力源、鐘琦翔作品
    包力源、鐘琦翔作品
    PSO_SA算法在水下結構激勵力源識別中的應用
    健力源16字理念致勝
    餐飲世界(2012年4期)2012-01-18 02:56:28
    免费人成在线观看视频色| 又黄又粗又硬又大视频| 国产精品日韩av在线免费观看| 国产97色在线日韩免费| 精品国产亚洲在线| 桃红色精品国产亚洲av| 欧美不卡视频在线免费观看| 91在线精品国自产拍蜜月 | 天堂动漫精品| 大型黄色视频在线免费观看| 午夜免费男女啪啪视频观看 | 国产91精品成人一区二区三区| 天堂影院成人在线观看| 亚洲激情在线av| 国产精品永久免费网站| 国产私拍福利视频在线观看| 国产色爽女视频免费观看| 久久精品国产清高在天天线| 99久国产av精品| 日韩欧美精品免费久久 | 午夜福利欧美成人| 麻豆成人av在线观看| 午夜久久久久精精品| 亚洲欧美精品综合久久99| 久久久久久久久大av| 亚洲在线自拍视频| 90打野战视频偷拍视频| 久久精品亚洲精品国产色婷小说| 最近最新中文字幕大全免费视频| 网址你懂的国产日韩在线| 午夜免费激情av| 国产高潮美女av| 亚洲欧美激情综合另类| 亚洲乱码一区二区免费版| 中出人妻视频一区二区| 久久久成人免费电影| 日韩欧美国产在线观看| 国产欧美日韩精品亚洲av| 亚洲中文日韩欧美视频| 叶爱在线成人免费视频播放| 真人做人爱边吃奶动态| 极品教师在线免费播放| 熟妇人妻久久中文字幕3abv| 国产黄色小视频在线观看| 欧美日韩精品网址| 成年人黄色毛片网站| 精品电影一区二区在线| av片东京热男人的天堂| 久久精品国产自在天天线| 日韩欧美国产在线观看| 亚洲国产欧美人成| 一个人看视频在线观看www免费 | 国内精品久久久久精免费| 噜噜噜噜噜久久久久久91| 在线十欧美十亚洲十日本专区| 久久久久久久精品吃奶| 精品一区二区三区视频在线观看免费| 成人av一区二区三区在线看| 在线天堂最新版资源| 韩国av一区二区三区四区| 欧美成人性av电影在线观看| 全区人妻精品视频| 免费在线观看亚洲国产| eeuss影院久久| 国产又黄又爽又无遮挡在线| 成年女人永久免费观看视频| 国产免费男女视频| 久久久久九九精品影院| 亚洲精品在线观看二区| 亚洲久久久久久中文字幕| 老汉色av国产亚洲站长工具| 欧美乱码精品一区二区三区| 色精品久久人妻99蜜桃| 国产高清视频在线播放一区| 欧美中文日本在线观看视频| 高清日韩中文字幕在线| 亚洲中文日韩欧美视频| 亚洲精品影视一区二区三区av| 久久精品91蜜桃| 国内精品久久久久精免费| 免费一级毛片在线播放高清视频| 国产精品98久久久久久宅男小说| 国产成人系列免费观看| 嫩草影院精品99| 久9热在线精品视频| 尤物成人国产欧美一区二区三区| 亚洲色图av天堂| 亚洲国产精品sss在线观看| 久久久久久久久大av| 岛国在线免费视频观看| 一进一出抽搐动态| 99热只有精品国产| 757午夜福利合集在线观看| 精品欧美国产一区二区三| 亚洲成人精品中文字幕电影| 国产色爽女视频免费观看| 在线观看美女被高潮喷水网站 | 免费观看的影片在线观看| 亚洲自拍偷在线| 99热这里只有是精品50| 91在线精品国自产拍蜜月 | 亚洲国产精品成人综合色| 国产乱人视频| 国产又黄又爽又无遮挡在线| 男女之事视频高清在线观看| 三级国产精品欧美在线观看| 色av中文字幕| 国产一区二区三区在线臀色熟女| 亚洲成人免费电影在线观看| 国产v大片淫在线免费观看| 亚洲精品粉嫩美女一区| 日本成人三级电影网站| 一个人看的www免费观看视频| 久久久久久九九精品二区国产| 亚洲真实伦在线观看| 1000部很黄的大片| 日韩中文字幕欧美一区二区| 国产精品一区二区三区四区免费观看 | 搞女人的毛片| 精品无人区乱码1区二区| 亚洲国产欧洲综合997久久,| 白带黄色成豆腐渣| 深爱激情五月婷婷| 日本一本二区三区精品| 国产精品女同一区二区软件 | 色综合站精品国产| 亚洲国产精品成人综合色| or卡值多少钱| 日本精品一区二区三区蜜桃| 精品国产三级普通话版| 国产真实伦视频高清在线观看 | 亚洲国产欧洲综合997久久,| 国产黄a三级三级三级人| 中文资源天堂在线| 欧美日韩福利视频一区二区| 男女床上黄色一级片免费看| 黄色成人免费大全| 国产v大片淫在线免费观看| 听说在线观看完整版免费高清| 91久久精品电影网| 淫妇啪啪啪对白视频| 久久天躁狠狠躁夜夜2o2o| 在线观看一区二区三区| 又黄又粗又硬又大视频| 在线免费观看不下载黄p国产 | 国产淫片久久久久久久久 | 国产在视频线在精品| 亚洲av熟女| 村上凉子中文字幕在线| 久久精品国产综合久久久| 少妇人妻精品综合一区二区 | 欧美午夜高清在线| 精品福利观看| 亚洲avbb在线观看| 日本免费a在线| 久久久久亚洲av毛片大全| 看片在线看免费视频| 国产欧美日韩一区二区精品| 高清日韩中文字幕在线| 精品不卡国产一区二区三区| 亚洲国产精品久久男人天堂| 日本 欧美在线| 久久久成人免费电影| 变态另类成人亚洲欧美熟女| 黄色丝袜av网址大全| 欧美xxxx黑人xx丫x性爽| 欧美午夜高清在线| 熟女电影av网| 国产色婷婷99| 又紧又爽又黄一区二区| 国产真人三级小视频在线观看| 欧美区成人在线视频| 精品人妻一区二区三区麻豆 | 欧美激情久久久久久爽电影| 狂野欧美激情性xxxx| 日日干狠狠操夜夜爽| 精华霜和精华液先用哪个| 婷婷亚洲欧美| 亚洲不卡免费看| 欧美成人一区二区免费高清观看| 久久久成人免费电影| 一区二区三区激情视频| 亚洲人成网站高清观看| 亚洲国产色片| 噜噜噜噜噜久久久久久91| 久久国产乱子伦精品免费另类| 特级一级黄色大片| 欧美极品一区二区三区四区| 夜夜爽天天搞| 香蕉av资源在线| 欧美最新免费一区二区三区 | 日本精品一区二区三区蜜桃| 一区二区三区高清视频在线| 看黄色毛片网站| 狂野欧美激情性xxxx| 欧美成人a在线观看| 在线免费观看的www视频| 成人av一区二区三区在线看| 人人妻人人看人人澡| 成年女人毛片免费观看观看9| 69av精品久久久久久| 在线免费观看的www视频| 精品电影一区二区在线| 国产午夜精品论理片| 亚洲男人的天堂狠狠| 免费观看的影片在线观看| 久久久国产成人免费| 麻豆国产97在线/欧美| 神马国产精品三级电影在线观看| 亚洲无线观看免费| 色av中文字幕| 国产亚洲精品久久久com| 亚洲人成网站在线播| 无限看片的www在线观看| 国产精品乱码一区二三区的特点| 欧美不卡视频在线免费观看| 日本成人三级电影网站| 老汉色∧v一级毛片| 大型黄色视频在线免费观看| 日韩精品中文字幕看吧| 亚洲欧美日韩高清在线视频| 色视频www国产| 美女cb高潮喷水在线观看| 听说在线观看完整版免费高清| 色综合亚洲欧美另类图片| 麻豆久久精品国产亚洲av| 欧美乱色亚洲激情| 亚洲人成网站高清观看| 国产97色在线日韩免费| 桃红色精品国产亚洲av| 最近视频中文字幕2019在线8| 亚洲成av人片免费观看| xxxwww97欧美| 欧美成人免费av一区二区三区| 中文字幕人妻熟人妻熟丝袜美 | 男女下面进入的视频免费午夜| 国产精品一及| 两个人视频免费观看高清| 99在线人妻在线中文字幕| 国内揄拍国产精品人妻在线| 亚洲专区中文字幕在线| 亚洲内射少妇av| 可以在线观看的亚洲视频| 久久6这里有精品| 国产三级黄色录像| 国产伦精品一区二区三区视频9 | 日韩欧美国产一区二区入口| 亚洲专区国产一区二区| 91在线观看av| xxx96com| 精品久久久久久成人av| 人妻丰满熟妇av一区二区三区| 免费观看人在逋| 搡老岳熟女国产| 色老头精品视频在线观看| 美女被艹到高潮喷水动态| 欧美中文综合在线视频| 可以在线观看的亚洲视频| 久久天躁狠狠躁夜夜2o2o| 黄色视频,在线免费观看| 18禁国产床啪视频网站| 成人三级黄色视频| 精品人妻偷拍中文字幕| 欧美av亚洲av综合av国产av| 国内毛片毛片毛片毛片毛片| 日本黄色片子视频| 色尼玛亚洲综合影院| 97超级碰碰碰精品色视频在线观看| 国产激情欧美一区二区| 中文字幕av成人在线电影| 欧美在线黄色| 极品教师在线免费播放| 狂野欧美激情性xxxx| 亚洲国产高清在线一区二区三| 久久精品综合一区二区三区| 99在线视频只有这里精品首页| 蜜桃久久精品国产亚洲av| 国产成+人综合+亚洲专区| 网址你懂的国产日韩在线| 好男人电影高清在线观看| 天美传媒精品一区二区| 尤物成人国产欧美一区二区三区| 国产极品精品免费视频能看的| 久久久久久国产a免费观看| 国产麻豆成人av免费视频| 真实男女啪啪啪动态图| 在线观看免费视频日本深夜| 亚洲 国产 在线| 日本三级黄在线观看| 亚洲一区高清亚洲精品| 国产美女午夜福利| 久久久国产成人免费| 亚洲五月婷婷丁香| 免费看十八禁软件| 母亲3免费完整高清在线观看| 乱人视频在线观看| 欧美一区二区国产精品久久精品| 88av欧美| 亚洲激情在线av| 亚洲美女视频黄频| 3wmmmm亚洲av在线观看| 伊人久久大香线蕉亚洲五| 成人av一区二区三区在线看| 精品国产亚洲在线| 色精品久久人妻99蜜桃| 亚洲av一区综合| 欧美性感艳星| 国内毛片毛片毛片毛片毛片| 一个人免费在线观看的高清视频| 免费高清视频大片| 丰满人妻一区二区三区视频av | 美女免费视频网站| 国产午夜精品久久久久久一区二区三区 | 美女免费视频网站| 国产真实伦视频高清在线观看 | 精品免费久久久久久久清纯| 欧美性猛交╳xxx乱大交人| 丰满乱子伦码专区| 欧美日韩中文字幕国产精品一区二区三区| 老汉色av国产亚洲站长工具| 天堂√8在线中文| 99在线人妻在线中文字幕| 免费高清视频大片| 国产黄a三级三级三级人| 久久香蕉国产精品| 成年女人永久免费观看视频| 久久久国产精品麻豆| 露出奶头的视频| 舔av片在线| 少妇裸体淫交视频免费看高清| 免费观看人在逋| 日日干狠狠操夜夜爽| 69av精品久久久久久| 母亲3免费完整高清在线观看| 欧美成人a在线观看| 亚洲精品久久国产高清桃花| 最后的刺客免费高清国语| 久久九九热精品免费| tocl精华| 久久九九热精品免费| 久久久国产成人免费| 亚洲成人久久爱视频| 亚洲成a人片在线一区二区| 久久草成人影院| 成熟少妇高潮喷水视频| 日本在线视频免费播放| 高清在线国产一区| 国产色爽女视频免费观看| 欧美一级a爱片免费观看看| 国产欧美日韩精品一区二区| 欧美日本视频| 日韩国内少妇激情av| 亚洲av五月六月丁香网| 国产精品99久久99久久久不卡| 婷婷精品国产亚洲av| 成人特级黄色片久久久久久久| 成人特级黄色片久久久久久久| 老汉色∧v一级毛片| 日韩精品青青久久久久久| 亚洲国产精品sss在线观看| 九九久久精品国产亚洲av麻豆| 91麻豆精品激情在线观看国产| 深夜精品福利| 午夜激情福利司机影院| 看黄色毛片网站| 久久国产乱子伦精品免费另类| 国产一区二区三区在线臀色熟女| 国产淫片久久久久久久久 | 日韩av在线大香蕉| 久久久久久久亚洲中文字幕 | av黄色大香蕉| 99热精品在线国产| 久久精品国产亚洲av涩爱 | 亚洲片人在线观看| 国产欧美日韩精品亚洲av| 我要搜黄色片| 性色avwww在线观看| 三级毛片av免费| 99热这里只有精品一区| 日韩大尺度精品在线看网址| 亚洲成av人片在线播放无| 精品国产美女av久久久久小说| 99在线视频只有这里精品首页| 国产激情欧美一区二区| 大型黄色视频在线免费观看| 九九热线精品视视频播放| 51国产日韩欧美| 在线国产一区二区在线| 女人高潮潮喷娇喘18禁视频| 亚洲av一区综合| 久久人妻av系列| 老司机深夜福利视频在线观看| 日韩中文字幕欧美一区二区| 亚洲乱码一区二区免费版| 亚洲av免费在线观看| 国产黄色小视频在线观看| 1024手机看黄色片| 精品99又大又爽又粗少妇毛片 | 此物有八面人人有两片| 黄色女人牲交| e午夜精品久久久久久久| 国产精品 欧美亚洲| 好男人电影高清在线观看| 日韩欧美一区二区三区在线观看| 国产一区二区激情短视频| 天天躁日日操中文字幕| 非洲黑人性xxxx精品又粗又长| 亚洲第一电影网av| 91九色精品人成在线观看| 动漫黄色视频在线观看| 美女免费视频网站| 亚洲国产欧美人成| 俺也久久电影网| 少妇的丰满在线观看| 中文字幕久久专区| h日本视频在线播放| 在线观看av片永久免费下载| 男女下面进入的视频免费午夜| 成人特级av手机在线观看| 啪啪无遮挡十八禁网站| 日本撒尿小便嘘嘘汇集6| 淫妇啪啪啪对白视频| 国产乱人伦免费视频| 亚洲乱码一区二区免费版| 国产国拍精品亚洲av在线观看 | 成年人黄色毛片网站| 99热这里只有精品一区| 久久精品国产综合久久久| 欧美日韩黄片免| 久久99热这里只有精品18| av在线天堂中文字幕| 成人av在线播放网站| 中文在线观看免费www的网站| 两性午夜刺激爽爽歪歪视频在线观看| 麻豆久久精品国产亚洲av| 一区二区三区免费毛片| 午夜老司机福利剧场| 成人鲁丝片一二三区免费| 看片在线看免费视频| 国产午夜福利久久久久久| 久久亚洲精品不卡| 超碰av人人做人人爽久久 | 国产精品久久久久久久久免 | 观看美女的网站| x7x7x7水蜜桃| a级一级毛片免费在线观看| 在线天堂最新版资源| 亚洲美女视频黄频| 欧美成人性av电影在线观看| 欧美色欧美亚洲另类二区| 亚洲av中文字字幕乱码综合| 国产一级毛片七仙女欲春2| 免费av毛片视频| 国产精品久久视频播放| 亚洲欧美日韩东京热| 国产男靠女视频免费网站| 色综合站精品国产| 久99久视频精品免费| 人妻丰满熟妇av一区二区三区| 九九在线视频观看精品| 精品国产三级普通话版| 岛国在线免费视频观看| 免费看日本二区| 一本综合久久免费| 精品人妻1区二区| or卡值多少钱| aaaaa片日本免费| 亚洲成av人片在线播放无| 久久精品人妻少妇| 久久久久久久午夜电影| 成人性生交大片免费视频hd| 怎么达到女性高潮| 麻豆久久精品国产亚洲av| 天堂动漫精品| 99在线视频只有这里精品首页| 久久久精品大字幕| 三级国产精品欧美在线观看| 十八禁网站免费在线| 真人一进一出gif抽搐免费| 高潮久久久久久久久久久不卡| 在线天堂最新版资源| 99热只有精品国产| 精品欧美国产一区二区三| 怎么达到女性高潮| 老熟妇仑乱视频hdxx| 欧美一区二区国产精品久久精品| 18禁黄网站禁片午夜丰满| 午夜免费男女啪啪视频观看 | 免费一级毛片在线播放高清视频| 日韩免费av在线播放| 成年女人永久免费观看视频| 51国产日韩欧美| 韩国av一区二区三区四区| 亚洲成人精品中文字幕电影| 男女之事视频高清在线观看| 老司机福利观看| 亚洲av五月六月丁香网| 国产伦精品一区二区三区视频9 | 成人av在线播放网站| 人人妻人人看人人澡| 国产午夜精品久久久久久一区二区三区 | 欧美三级亚洲精品| 亚洲aⅴ乱码一区二区在线播放| 成人精品一区二区免费| 国产精品一及| 亚洲精品456在线播放app | 在线观看午夜福利视频| 韩国av一区二区三区四区| 综合色av麻豆| 亚洲成av人片在线播放无| 日本免费a在线| 欧美一级a爱片免费观看看| 久久欧美精品欧美久久欧美| 国产高清有码在线观看视频| 99久久成人亚洲精品观看| 麻豆久久精品国产亚洲av| 舔av片在线| 国产成人啪精品午夜网站| 亚洲中文字幕一区二区三区有码在线看| 天堂√8在线中文| 欧美色欧美亚洲另类二区| 精品福利观看| 国产欧美日韩精品亚洲av| 在线看三级毛片| 亚洲av二区三区四区| www.999成人在线观看| 在线看三级毛片| 波野结衣二区三区在线 | 欧美一区二区亚洲| svipshipincom国产片| eeuss影院久久| 熟女少妇亚洲综合色aaa.| 村上凉子中文字幕在线| 在线观看日韩欧美| 亚洲人成网站在线播放欧美日韩| 在线观看美女被高潮喷水网站 | a在线观看视频网站| 亚洲最大成人中文| 九九热线精品视视频播放| 欧美国产日韩亚洲一区| 老熟妇仑乱视频hdxx| 欧美激情在线99| 成人欧美大片| 久久精品国产自在天天线| 久9热在线精品视频| 亚洲最大成人中文| 一二三四社区在线视频社区8| 性欧美人与动物交配| 亚洲电影在线观看av| 欧美一区二区亚洲| 国产精品一区二区免费欧美| 国产午夜精品久久久久久一区二区三区 | 久久久久性生活片| 日本成人三级电影网站| 国产一区二区三区在线臀色熟女| svipshipincom国产片| 又粗又爽又猛毛片免费看| 久久亚洲真实| 亚洲国产欧美网| 宅男免费午夜| 狂野欧美激情性xxxx| av在线蜜桃| 99久久无色码亚洲精品果冻| 看片在线看免费视频| 国产蜜桃级精品一区二区三区| 非洲黑人性xxxx精品又粗又长| 久久国产精品影院| 欧美一区二区亚洲| 国产色婷婷99| 亚洲片人在线观看| 亚洲人成伊人成综合网2020| 亚洲中文字幕日韩| 51午夜福利影视在线观看| 国产探花在线观看一区二区| 久久精品夜夜夜夜夜久久蜜豆| 少妇人妻精品综合一区二区 | 成人高潮视频无遮挡免费网站| 亚洲内射少妇av| 天堂影院成人在线观看| 亚洲自拍偷在线| 精品熟女少妇八av免费久了| 久久国产精品影院| 免费观看人在逋| 国产精品野战在线观看| 午夜免费观看网址| 亚洲av电影不卡..在线观看| 午夜福利在线在线| 精品欧美国产一区二区三| 免费av不卡在线播放| 搡老妇女老女人老熟妇| 中文字幕高清在线视频| 亚洲精品色激情综合| 成人18禁在线播放| 精华霜和精华液先用哪个| 午夜激情福利司机影院| 不卡一级毛片| 99国产精品一区二区蜜桃av| 国产亚洲精品综合一区在线观看| 亚洲国产欧洲综合997久久,| 色尼玛亚洲综合影院| www日本黄色视频网| 免费在线观看成人毛片| 日韩欧美 国产精品| 在线观看午夜福利视频| 国产精品一区二区三区四区免费观看 | 中文字幕人妻熟人妻熟丝袜美 | 国产真实乱freesex| 日本黄色视频三级网站网址| 国产精品 国内视频| 搞女人的毛片| 乱人视频在线观看| 少妇的逼水好多| 麻豆国产97在线/欧美| 天堂网av新在线| 99热只有精品国产|