三级实验一普效应

1、实验一普效应实验目的验证偏振光中的普效应测量普实验概述单元的半波电压当自然光射到一些特殊的晶体表面时，会被分解成两束光，一束叫寻常光（o 光），符合普通的折射定律，另一束则不符合，叫非常光（e 光）。其折射率no 和ne 合称为晶体的主折射率。LiNbO3（铌酸锂）在强电场作用下能够变成双折射物质，由于o 光、e 光在晶体内的速度不同，通过晶体后，两光间产生相位差。进而在屏幕上出现图样。改变电压值，实验原理图样中的双曲线系会通过中心移向另外的线系。The Pockels effect is the name given to the occurrence of birefringence an

2、d to the change in existingbirefringence phenomena in an electric field linearly proportional to the electric field strength. It is related tothe Kerr effect, althoughhe latter case the birefringence increases exponentially with the electric fieldstrength. For reasons of symmetry, the Pockels effect

3、can only occur in crystals with no invercenter,whereas the Kerr effect can occur in all substan.When the direction of the light beam and the opticalaxis of birefringence are pendicular to each other,we call this a “transverse configuration” (see Fig. 1).The electric field is app dhe direction of the

4、optical axis. For Pockels cellshe transverseconfiguration, lithium niobate (LiNbO3) is most often used.Lithium niobate crystals are optically uniaxial, negatively birefringent and have the main refractive indexes no= 2.29 for the ordinary beam, and ne = 2.20 for the extraordinary beam (measured usin

5、g the wavelength of the He-Ne laser, l =632.8 nm.Birefringence in a conoscopic beathThe proof of birefringence in a conoscopic beath is described in numerous optics textbooks. A crystalwith planeparallel cut fais illuminated widivergent, linearly polarized light beam, and the light passingthrough it

6、 is observed behindrpendicularly alignedyzer .heerference image, as it is indicated by theThe optical axis of the birefringence is clearly apparentsymmetry in its vicinity.his experiment, the optical axis is parallel to the entrance and exit surfa; this iswhy theerference pattern consists of two set

7、s of hyperbolas which are roed by 90 with respect to oneanother. The real axis of thehyperbola set is parallel to the optical axis, whilet of the second setis pendicular to the optical axis.The dark lines of theerference image are caused by light rays for which the difference betn the opticalpaths o

8、f the extraordinary and the ordinary partial beamhe crystal is anegral multiple of the wavelength.These light rays retain their original linear polarization after passage through the crystal, and areextinguishedheyzer.The light rays reaching the center of theFor these rays, the path difference beter

9、ference image are normally incident on the surface of the crystal. n the extraordinary and the ordinary partial beam is(I)= d (no ne),where d = 20 is the thickness of the crystalhe direction of the beam. The path difference corresponds toapproxima y 2800 wavelengths of the laser light used. however,

10、 is not usually precisely a whole , but rather m = m m+1 = (m + 1) . The dark lines inmultiple ofs betn two values,and m+1, m+2, m+3, etc., and those of ition of the dark lines, or better their distancethehyperbola set thus correspond to the path differen m, m-1, m-2, etc. (Fig. 3). Thethe second se

11、t ton and m .from the center, depends on the magnitude of the difference betFig. 3:erference patternhe conoscopic beath with theoptical axis of the crystalhe direction of the arrow. Thenumbers represent the path difference betn the ordinaryand the extraordinary partial beam. Thus for exlethe lines w

12、ith the value +1( 1) have the path differencem+1 ( m-1)The Pockels effect magnifies or reduthe difference of themain refractive indino ne, depending on the sign of the m l, andapp d voltage. Thisurn alters the differencethus theition of the darkerference lines. If the so-calledhalf-wave voltage Up i

13、s app d, the value of is changed by one-half wavelength. The darkerferencelines shift to theis increased by Up.itions of the bright lines, and vice versa. This pros repeats itself each time the voltage全不要直视出射或反射的激光。危实验装置及调试元件的具体布置参照图4。光学元件的布置-依次安装He-Ne激光器、5-mm透镜(a)、50-mm透镜(b)和半透明屏，仔细调整好激光器和5-mm透镜的高度

14、，使得50-mm透镜得到最适宜的照明。在屏上得到一个均匀明亮的光场。-安置检偏器，转动其黄色手柄来改变检偏器的偏振方向，直到屏上的亮度最暗。-将普盒放置到元件队列中，务必保证两个高压插头已插接到位。将其滑动到一个精确的位置，要求该处的激光束的横截面最小。转动其手柄，定在相对检偏器旋转+45or 45的位置。这时应该在屏上看到图样。细调-调整激光、5-mm透镜和普单元的高度直到图样的双曲线系的中心位于视野的中心。-如果必要，沿支架杆轴线转动普实验步骤a)验证双折射单元。-观测开始时图中双曲线系的位置和普单元基准点的位置。-转动手柄，慢慢改变普单元基点位置，描述图样的改变，并回答（1）第一双曲线系

15、的实轴是否总平行于晶体的光轴（以基点的方向标示）？（2）屏幕上图样最清晰和最模糊时，光轴和检偏器的夹角值分别为多少，为什么？，b)验证普效应-将普单元的基点旋回至起始位置（相对检偏器45）电连接 （高压。请始终保持电线与电源、普单元的良好连接。）-确定普单元与高压电源的左输出相连（最大短路电流100A），确保负端与地相连。-将电压源的电压计始终旋到左端，打开高压源的开关，用选择钮激活左路输出。高压U不超过2 kV-要避免对普晶体的较大的电冲击，故关闭电源和变换极性时，一定要先将电压降至0v后再操作。-缓慢升高电压U（不超过2 kV），观测图的改变。-将电压降至0 V，将高压电源的正负插头对调，即普盒的电连接反向。-再次升高电压U（不超过