Experiment 32The research of light PolarizationSince 1808, Malus (1775~1812) discovered the polarization phenomenon of light. Furtherstudy of the polarization phenomenon of light proves that the light is a transversewave,whichmakes people further understand the characteristic of light.In order to make use of thepolarization of light for human service, various polarized elements and instruments have emergedand the applicationtechnologyof polarized light has been increasinglydeveloped and widelyusedin various fields.[ExperimentalPurposes]1.Observe the polarization of light and master the method of adjusting the light intensity usingapolarizer.2.Understand the principles and methods of generating and detecting polarized light.Identifydifferentpolarization states of light.3.Designexperiments tomeasuretherefractiveindexof theglassstack,andusereflectionprinciple to measure the Brewster angle.【AlternativeInstruments】Computer and control software, Glan-Foucault prism, /2 waveplate, /4 waveplate,glass stack,adjustment frame controlled by stepper motor, photoelectric receiving system, He-Ne laser.[Experimental Principle】The interference and diffraction of light reveals the wave character of light. The polarizationof light indicates that light is a transverse wave. The light vector changes follow different rules, ifone observes the light from the plane perpendicular to the propagation direction. According tothese rules, the light can be divided into different polarization states.1. The polarization state of lightThe endpoint of optical vector for the fully polarized light changes regularly with time. If thetrajectory is linear, it is called linearly polarized light or plane polarized light. If the trajectory iselliptical (or circular), it is called elliptical (circular) polarized light.Theordinary light sources emits natural light directly.The discontinuity and randomness ofatomic irradiancydetermines that natural light is composed of a largenumber of linearlypolarizedlight with different polarization directions, different initial phases and uncorrelated.In the planeperpendicular to the propagation direction, the probability of the light vector vibrating is equal inall directions. Therefore, the monochromatic natural light can be regarded as the superposition oftwo linearly polarized light with same frequencies, orthogonal optical vectors, equal intensity, anduncorrelated (the phase difference is uncertain).Monochromatic polarized light can be equivalentto two linearly polarized light with the samefrequency,orthogonal optical vector, and certainphase difference.Partially polarized light can be thought as a mixture of fully polarized light and natural light2. Birefringent crystalReflection occurs if a beam of light incidents on the surface of the crystal. In some crystals,1
1 Experiment 32 The research of light Polarization Since 1808, Malus (1775~1812) discovered the polarization phenomenon of light. Further study of the polarization phenomenon of light proves that the light is a transverse wave, which makes people further understand the characteristic of light. In order to make use of the polarization of light for human service, various polarized elements and instruments have emerged, and the application technology of polarized light has been increasingly developed and widely used in various fields. 【Experimental Purposes】 1. Observe the polarization of light and master the method of adjusting the light intensity using a polarizer. 2. Understand the principles and methods of generating and detecting polarized light. Identify different polarization states of light. 3. Design experiments to measure the refractive index of the glass stack, and use reflection principle to measure the Brewster angle. 【Alternative Instruments】 Computer and control software, Glan-Foucault prism, λ/2 waveplate, λ/4 waveplate, glass stack, adjustment frame controlled by stepper motor, photoelectric receiving system, He-Ne laser. 【Experimental Principle】 The interference and diffraction of light reveals the wave character of light. The polarization of light indicates that light is a transverse wave. The light vector changes follow different rules, if one observes the light from the plane perpendicular to the propagation direction. According to these rules, the light can be divided into different polarization states. 1. The polarization state of light The endpoint of optical vector for the fully polarized light changes regularly with time. If the trajectory is linear, it is called linearly polarized light or plane polarized light. If the trajectory is elliptical ( or circular), it is called elliptical (circular) polarized light. The ordinary light sources emits natural light directly. The discontinuity and randomness of atomic irradiancy determines that natural light is composed of a large number of linearly polarized light with different polarization directions, different initial phases and uncorrelated. In the plane perpendicular to the propagation direction, the probability of the light vector vibrating is equal in all directions. Therefore, the monochromatic natural light can be regarded as the superposition of two linearly polarized light with same frequencies, orthogonal optical vectors, equal intensity, and uncorrelated (the phase difference is uncertain). Monochromatic polarized light can be equivalent to two linearly polarized light with the same frequency, orthogonal optical vector, and certain phase difference. Partially polarized light can be thought as a mixture of fully polarized light and natural light. 2. Birefringent crystal Reflection occurs if a beam of light incidents on the surface of the crystal. In some crystals
the refracted light splits into two beams, which is called birefringent phenomenon of crystal.Among the two refracted lights, one beam of light obeys the law of refraction and it is calledordinarylight,shorterforo-light.Theotherbeam of lightdoes notfollow the lawofrefractionandit is called extraordinary light, referred as e-light. The propagation rate ofo-lights is isotropic. Thepropagation rate of e-light is related to the direction of propagation. Along the optical axis, thepropagation rate of e-light is same as that of o-light. The difference between o-light and e-light isthe largest in the direction perpendicular to the optical axis.The characteristic is of greatsignificanceforthewaveplatepresented later.It should be noted that o-light and e-light are only existed inside the crystal. There is noo-light or e-light when the light leaves the crystal.3.PolarizerThere aremany ways to generate polarized light.The reflected light is generally partiallylinearly polarized light, when natural light incident on the interface of different media. Withcertain conditions, linearlypolarized light canbegenerated.Linearlypolarized light is also calledplane polarized light.We often use a polarizer to obtainplane polarized light. The polarizer can be made of a natural birefringent crystal or an artificialdichroic polycrystalline film, which is capable of absorbing light in a certain vibration directionand the transmitted direction is perpendicular to the certain vibration direction.The direction ofthe optical vector passing through the polarizer is called the polarization direction of the polarizer.Thepolarizer is divided into a polarizer and an analyzeraccording to its effect in the applicationThe polarizer is used to generate polarized light. The analyzer is used to detect polarized lightFigure32-1 shows theprincipleof thegeneration and detectionof linearlypolarized light.I71PolarizerPolarizationanalyzerFigure 32-1 The principle of the generation and detection of linearly polarized light.The Glan-Taylor prism is called Glan prism for short. Itconsists of two right-angle prisms of uniaxial crystal ofIceland spar, with an airgap between the two slopes.Theoptical axis is parallel to the incident end face. When theFigure32-2Glan-Taylor prismincident direction of natural light is vertical to the opticalaxis, the o-light and the e-light travel in the same directionwith different velocities in the first right-angle prism. At the slopes of the two right-angle prisms,2
2 the refracted light splits into two beams, which is called birefringent phenomenon of crystal. Among the two refracted lights, one beam of light obeys the law of refraction and it is called ordinary light, shorter for o-light. The other beam of light does not follow the law of refraction and it is called extraordinary light, referred as e-light. The propagation rate of o-lights is isotropic. The propagation rate of e-light is related to the direction of propagation. Along the optical axis, the propagation rate of e-light is same as that of o-light. The difference between o-light and e-light is the largest in the direction perpendicular to the optical axis. The characteristic is of great significance for the wave plate presented later. It should be noted that o-light and e-light are only existed inside the crystal. There is no o-light or e-light when the light leaves the crystal. 3. Polarizer There are many ways to generate polarized light. The reflected light is generally partially linearly polarized light, when natural light incident on the interface of different media. With certain conditions, linearly polarized light can be generated. Linearly polarized light is also called plane polarized light. We often use a polarizer to obtain plane polarized light. The polarizer can be made of a natural birefringent crystal or an artificial dichroic polycrystalline film, which is capable of absorbing light in a certain vibration direction and the transmitted direction is perpendicular to the certain vibration direction. The direction of the optical vector passing through the polarizer is called the polarization direction of the polarizer. The polarizer is divided into a polarizer and an analyzer according to its effect in the application. The polarizer is used to generate polarized light. The analyzer is used to detect polarized light. Figure 32-1 shows the principle of the generation and detection of linearly polarized light. Figure 32-1 The principle of the generation and detection of linearly polarized light. The Glan-Taylor prism is called Glan prism for short. It consists of two right-angle prisms of uniaxial crystal of Iceland spar, with an air gap between the two slopes. The optical axis is parallel to the incident end face. When the incident direction of natural light is vertical to the optical axis, the o-light and the e-light travel in the same direction with different velocities in the first right-angle prism. At the slopes of the two right-angle prisms, Polarizer Polarization analyzer Figure 32 32-2 -2 格兰棱镜 Glan-Taylor prism
the propagation direction of e-light is unchanged, and the o-light will be totally reflected. If theo-light from the side of the prism is absorbed, only e-light is left along the original incidentdirection, The Glan prism can be used as a polarizer, and can of course also be used as an analyzerFigure 32-2 shows the optical path of the Glan prism.Direction oftransmission4.Waveplateof the polarized lightThe wave wafer is made of birefringentcrystal. A wave plate is cut from a uniaxialbirefringentcrystal with two surfaces paralleled to thecrystaloptical axis.It is also called phase retarder.AsDirection of thevibrationplanshown in Figure 32-3, when a beam ofmonochromatic linearlypolarized light isincident normally (perpendicular to the opticalaxis of the crystal) onto the wave plate, inFigure 32-3 The transmission of linearlygeneral, it decomposes into o-light and e-lightpolarized light through a crystalinside the crystal. Since o-light and e-light have different propagating velocities in the directionperpendicular to the optical axis, the corresponding refractive index is also different and the pathlength is different after passing through the wave plate with a certain thickness.If the thickness of the wave plate is d, there will be a phase difference between o-light ande-light afterthetwobeams passingthroughthewaveplate2元(32-1)(n。-n,)do1whererepresentthewavelengthof light invacuum.When a linearly polarized light incidents perpendicularly into the wave plate, it decomposesinto the o-light and the e-light. An additional phase difference is generated after the two beamspassing through the wave plate. The polarization state of the polarized light after passing throughthe waveplatedepends on and the direction of incident optical vector.(1) When =2k, the optical path difference is (n。-n.)d=ka , that is, the optical pathdifferencebetween o-light and e-light equal to ka after passing throughthe wafer plate withthickness d. The wave plate is called full wave plate (a wave plate).The combined vibration ofthe o-light and e light is plane polarized light, and the vibration plane is the same as the vibrationsurface of incident light.(2) When -(2k+1), the optical path difference is (n。-n.)d=(2k+1)a/2 , that is, theoptical path difference between o-light and e-light equal to (2k+1)a/2 The wave plate is calledhalf wave plate (a/2 wave plate). The combined vibration of the o-light and e light is planepolarized light. However, the vibrating surface rotates by 20 angle with respect to the vibrating3
3 the propagation direction of e-light is unchanged, and the o-light will be totally reflected. If the o-light from the side of the prism is absorbed, only e-light is left along the original incident direction. The Glan prism can be used as a polarizer, and can of course also be used as an analyzer. Figure 32-2 shows the optical path of the Glan prism. 4. Wave plate The wave wafer is made of birefringent crystal. A wave plate is cut from a uniaxial crystal with two surfaces paralleled to the optical axis. It is also called phase retarder. As shown in Figure 32-3, when a beam of monochromatic linearly polarized light is incident normally (perpendicular to the optical axis of the crystal) onto the wave plate, in general, it decomposes into o-light and e-light inside the crystal. Since o-light and e-light have different propagating velocities in the direction perpendicular to the optical axis, the corresponding refractive index is also different and the path length is different after passing through the wave plate with a certain thickness. If the thickness of the wave plate is d, there will be a phase difference between o-light and e-light after the two beams passing through the wave plate 2 ) o e n n d = − （ (32-1) where represent the wavelength of light in vacuum. When a linearly polarized light incidents perpendicularly into the wave plate, it decomposes into the o-light and the e-light. An additional phase difference is generated after the two beams passing through the wave plate. The polarization state of the polarized light after passing through the wave plate depends on and the direction of incident optical vector. (1) When = 2k , the optical path difference is (n n d k o e − = ) , that is, the optical path difference between o-light and e-light equal to k after passing through the wafer plate with thickness d . The wave plate is called full wave plate ( wave plate). The combined vibration of the o-light and e light is plane polarized light, and the vibration plane is the same as the vibration surface of incident light. (2) When = + (2 1 k ) , the optical path difference is (n n d k o e − = + ) (2 1 2 ) , that is, the optical path difference between o-light and e-light equal to (2 1 2 k + ) . The wave plate is called half wave plate ( 2 wave plate). The combined vibration of the o-light and e light is plane polarized light. However, the vibrating surface rotates by 2θ angle with respect to the vibrating Figure 32 图 32-3 -3线偏振光在晶体中的传输 The transmission of linearly polarized light through a crystal birefringent crystal Direction of transmission of the polarized light Direction of the vibration plane
surface of the incident light ( is the angle between the vibrating surface of the incident light andthe optical axis of the wave plate, as shown in Figure 32-3).(3) When 8=(2k+1)元/2, the optical path difference is (n。-n.)d =(2k+1)a/4 , that is, theoptical path difference between o-light and e-light equal to (2k+1)/4. The wave plate is calledquarter wave plate (a/4 wave plate).The combined vibration is generally elliptically polarizedlight. When the incident optical vector is parallel or perpendicular to the optical axis of the waveplate, the transmitted light is linearly polarized light. When the incident optical vector is at anangle of /4 to the optical axis of the wave plate, the transmitted light is circularly polarized.It shows that >/4 can change the plane polarized light into elliptically polarized light orcircularly polarized light, otherwise, it can also turn elliptically polarized light or circularlypolarized light into plane polarized lightWhether it is a full wave plate, a half wave plate, or a quarter wave plate, it is specific for acertainwavelength5.BrewsterlawWhen lightisobliquelydirected onto anon-metallic smooth surface(suchaswater,wood,glass, etc.), both the reflected and transmitted light will be polarized. The degree of polarizationdepends on the angle of incidence ofthe light and the relative refractive indices of the two mediaWhen the incident angle is a certain value, the reflected light is linearly polarized light and thecorresponding incident angle i,is called a declination angle, also called a Brewster angle, whichsatisfies(32-2)tani, =nThis relationship is called the Brewsterlaw,where n is the refractive index ofthesecond medium relative tothe firstmediumIn this case, the optical vector of thereflected light is perpendicular to theincident surface, as shown in figure 32-4. Ifthe light incidents from air to the glass with aFigure32-4Glassstackrefractive index of about 1.5, one can obtaini, = arctan(n)= 57If the natural light ncidents on the glass stack with angle of i, the light transmitted from theglass stack finally is generally partially polarized after multiple reflections. If the number of glass4
4 surface of the incident light (θ is the angle between the vibrating surface of the incident light and the optical axis of the wave plate, as shown in Figure 32-3). (3) When = + (2 1 2 k ) , the optical path difference is (n n d k o e − = + ) (2 1 4 ) , that is, the optical path difference between o-light and e-light equal to (2 1 4 k + ) . The wave plate is called quarter wave plate ( 4 wave plate). The combined vibration is generally elliptically polarized light. When the incident optical vector is parallel or perpendicular to the optical axis of the wave plate, the transmitted light is linearly polarized light. When the incident optical vector is at an angle of π/4 to the optical axis of the wave plate, the transmitted light is circularly polarized. It shows that 4 can change the plane polarized light into elliptically polarized light or circularly polarized light; otherwise, it can also turn elliptically polarized light or circularly polarized light into plane polarized light. Whether it is a full wave plate, a half wave plate, or a quarter wave plate, it is specific for a certain wavelength. 5. Brewster law When light is obliquely directed onto a non-metallic smooth surface (such as water, wood, glass, etc.), both the reflected and transmitted light will be polarized. The degree of polarization depends on the angle of incidence of the light and the relative refractive indices of the two media. When the incident angle is a certain value, the reflected light is linearly polarized light and the corresponding incident angle b i is called a declination angle, also called a Brewster angle, which satisfies tan b i n = (32-2) This relationship is called the Brewster law, where n is the refractive index of the second medium relative to the first medium. In this case, the optical vector of the reflected light is perpendicular to the incident surface, as shown in figure 32-4. If the light incidents from air to the glass with a refractive index of about 1.5, one can obtain arctan( ) 57 b i n = = If the natural light ncidents on the glass stack with angle of b i , the light transmitted from the glass stack finally is generally partially polarized after multiple reflections. If the number of glass Figure 32-4 Glass stack
pieces is large enough, the transmitted light is approximately linearly polarized6. Detection of polarized lightPhotoelectric receiving system can not detect thepolarization state of polarized light directly.It can onlydetect light intensity and its changes. Therefore, onlythrough some physical changes,such as throughpolarizers and waveplates,thepolarizationstateoflight can be changed and then distinguished byFigure32-5Malus law of raysdetectors. Marius's law plays an extremely importantrole in the detection of polarized lightA beam of linearly polarized light with intensity of Io, the transmitted light intensity afterpassing through the analyzer is expressed by(32-3)I=locos0where is the angle between the direction of vibration (optical vector) of the linearly polarizedlight and the polarization direction of the analyzer as shown in figure 32-5.This is the law ofMalus.When the analyzer rotates with the direction of light propagation as the axis, the maximumand minimum of transmitted light intensity will appear alternately.If partlypolarized light orelliptically polarized light passes through the analyzer, there is no extinction position, although thetransmittedlightintensitychangesfrommaximumtominimumorfromminimumtomaximumforevery 90 when the analyzer rotates. If the circularly polarized light or natural light passesthrough the analyzer, the transmitted light intensity does not change and when we rotate theanalyzer.It should be emphasized that the Malus's law is only suitable for the linearly polarized lightincidenting on the polarizer.For natural light incidenting on the polarizing plate, nomatter howthe polarizing plate rotates, the outgoing light intensity is always constant, namely, half of theintensity of the incident natural light:(32-4)I = 1./2When we use a analyzer to detect the partially polarized light, the intensity of the transmittedlightchanges with its polarization direction.If the maximum and minimumvalues of transmittedlight intensity are Imax and Imin respectively,thegreater the difference between thetwo values,thehigher polarization degree of the partiallypolarized light We define a polarization degree todescribe the partially polarized light5
5 pieces is large enough, the transmitted light is approximately linearly polarized. 6. Detection of polarized light Photoelectric receiving system can not detect the polarization state of polarized light directly. It can only detect light intensity and its changes. Therefore, only through some physical changes, such as through polarizers and wave plates, the polarization state of light can be changed and then distinguished by detectors. Marius's law plays an extremely important role in the detection of polarized light. A beam of linearly polarized light with intensity of 0 I , the transmitted light intensity after passing through the analyzer is expressed by 2 0 I I = cos (32-3) where θ is the angle between the direction of vibration (optical vector) of the linearly polarized light and the polarization direction of the analyzer as shown in figure 32-5. This is the law of Malus. When the analyzer rotates with the direction of light propagation as the axis, the maximum and minimum of transmitted light intensity will appear alternately. If partly polarized light or elliptically polarized light passes through the analyzer, there is no extinction position, although the transmitted light intensity changes from maximum to minimum or from minimum to maximum for every 90 when the analyzer rotates. If the circularly polarized light or natural light passes through the analyzer, the transmitted light intensity does not change and when we rotate the analyzer. It should be emphasized that the Malus's law is only suitable for the linearly polarized light incidenting on the polarizer. For natural light incidenting on the polarizing plate, no matter how the polarizing plate rotates, the outgoing light intensity is always constant, namely, half of the intensity of the incident natural light: I I = 0 2 (32-4) When we use a analyzer to detect the partially polarized light, the intensity of the transmitted light changes with its polarization direction. If the maximum and minimum values of transmitted light intensity are Imax and Imin respectively, the greater the difference between the two values, the higher polarization degree of the partially polarized light. We define a polarization degree to describe the partially polarized light P1 P2 E0cos 图Figure 32 32-5 马吕斯定律 -5 Malus law of rays
-1(32-5)max+IIn fact, the denominator in the equation above is the sum of the light intensities of twomutually orthogonal components, which is the total intensity of partially polarized lightObviously, for natural light of Imax=Imin, we have P = O, for linearly polarized light of Imin= O, wehave P =1, that is, linearly polarized light has the highest polarization degree.[ExperimentalReminders]1.Optical pathadjustmentAs shown in Figure 32-6, adjust the laser or signal receiver to ensure that the laser beamenters the small hole in the center of the signal receiver.signal receiverlaserLaserbeamsThe magnetic table mountainFigure 32-6 The reference line of the instrumentInserting P2 (analyzer or polarizer Pi) into the system, by shifting and lifting adjustment,makesurethelaserbeampasses throughthetransparentpart inthecenterof P2toreach thesignalreceiver.Then,turnP2left andright (releasethelock of magnetictable)toprojectthe reflectedlight back into thevertical planeof the laser.Next, adjust thehorizontal andpitch screws on theP2bracket sothatthereflected spot coincides with the exit spot substantially(by adjusting thethree-dimensional fine adjustment of P2 and P2, the reflected spot falls into the exit spot) as shownin Figure32-7, which means that the optical surface (principle section)of P2 isperpendicular tothe reference line of the system (i.e.the laser beam).The vertical end surfaceof the laserEmergent light spotReflected light spotFigure 32-7 The diagram of the system collimation6
6 max min max min I I I I P + − = (32-5) In fact, the denominator in the equation above is the sum of the light intensities of two mutually orthogonal components, which is the total intensity of partially polarized light. Obviously, for natural light of Imax=Imin, we have P = 0; for linearly polarized light of Imin= 0, we have P =1, that is, linearly polarized light has the highest polarization degree. 【Experimental Reminders】 1. Optical path adjustment As shown in Figure 32-6, adjust the laser or signal receiver to ensure that the laser beam enters the small hole in the center of the signal receiver. Inserting P2 (analyzer or polarizer P1) into the system, by shifting and lifting adjustment, make sure the laser beam passes through the transparent part in the center of P2 to reach the signal receiver. Then, turn P2 left and right (release the lock of magnetic table) to project the reflected light back into the vertical plane of the laser. Next, adjust the horizontal and pitch screws on the P2 bracket so that the reflected spot coincides with the exit spot substantially (by adjusting the three-dimensional fine adjustment of P2 and P2, the reflected spot falls into the exit spot) as shown in Figure 32-7, which means that the optical surface (principle section) of P2 is perpendicular to the reference line of the system (i.e. the laser beam). 图 32-6 确定系统的基准线 laser Laser beams signal receiver The magnetic table mountain Figure 32-6 The reference line of the instrument 图 32-7 系统准直标准示意 图 Figure 32-7 The diagram of the system collimation Reflected light spot The vertical end surface of the laser Emergent light spot
2.Experimental contents(1) The test of the polarization characteristics of the source.Use the Glan prism as a polarizer, record and save the satisfied curve of the transmitted lightintensity with angle.Then, explain the polarization of the light source (Is it natural light? Ifnot, what kind of polarized light is it?).(2)The test of linearly polarized light.Understand theinfluenceof theanglebetweenthepolarization of thepolarizerand theanalyzer on the transmitted light intensity-angle curve after the analyzer.Save the satisfiedcurve ofthe transmitted light intensity with the angle (Does it satisfy Marius's law?What are the characteristics?). Make data table by yourself to record 10~20 sets ofmeasurementdata(3)The verification of Brewster angle.Describe theexperimental operation process.(4)Generation of elliptical and circularly polarized light and identification of differentpolarization states.Rotated theoptical axis of the/4 waveplatefordifferentanglesto changethepolarizationstate ofthe incidentpolarized light.(1)Rotate the analyzer to makePand P2 orthogonal (howto read and retrieve theangle ofthe analyzer). Tips: use the “ESC key" to interrupt the program according to thetransmitted light intensity-angle curve and extinction. Then use the “manualadjustment" (describe the operation steps):(2)Inserta/4waveplatebetweenPiandP2,andadjustthe/4waveplatetomakelaserbeam passing through the optical center and perpendicular to the wave plate. Then,rotate the /4 wave plate to extinction (At this time, the optical axis of the /4 waveplate is theparallel orperpendicular to thepolarizationdirectionof P)(3)Taking the angle of the optical axis of the /4 wave plate obtained above as a reference,rotatethe/4waveplatesequentiallyfor150、300、45、600、750、90o.RotateP2for360at each angle.Observeand analyze thecharacteristics and variation of thecorresponding six intensity-angle curves to determine the characteristics of thepolarized light generated at the six positions (pay attention to the maximum value,minimum value and extinction). Finally, compare and record the intensity variationand extinction characteristics of the six curves. Draw the curve, analyze thepolarization state of the light from the data table, and discuss the influence ofthe /47
7 2. Experimental contents (1) The test of the polarization characteristics of the source． Use the Glan prism as a polarizer, record and save the satisfied curve of the transmitted light intensity with angle．Then, explain the polarization of the light source (Is it natural light? If not, what kind of polarized light is it?)． (2) The test of linearly polarized light． Understand the influence of the angle between the polarization of the polarizer and the analyzer on the transmitted light intensity-angle curve after the analyzer．Save the satisfied curve of the transmitted light intensity with the angle ( Does it satisfy Marius's law? What are the characteristics?). Make data table by yourself to record 10~20 sets of measurement data. (3) The verification of Brewster angle． Describe the experimental operation process． (4) Generation of elliptical and circularly polarized light and identification of different polarization states． Rotated the optical axis of the λ/4 wave plate for different angles to change the polarization state of the incident polarized light． （1）Rotate the analyzer to make P1 and P2 orthogonal (how to read and retrieve the angle of the analyzer). Tips: use the “ESC key” to interrupt the program according to the transmitted light intensity-angle curve and extinction. Then use the “manual adjustment” (describe the operation steps) ． （2）Insert a λ/4 wave plate between P1 and P2, and adjust the λ/4 wave plate to make laser beam passing through the optical center and perpendicular to the wave plate．Then, rotate the λ/4 wave plate to extinction (At this time, the optical axis of the λ/4 wave plate is the parallel or perpendicular to the polarization direction of P1)． （3）Taking the angle of the optical axis of the λ/4 wave plate obtained above as a reference, rotate the λ/4 wave plate sequentially for 15o 、30o 、45o、60o 、75o、90o ．Rotate P2 for 360 o at each angle. Observe and analyze the characteristics and variation of the corresponding six intensity-angle curves to determine the characteristics of the polarized light generated at the six positions (pay attention to the maximum value, minimum value and extinction). Finally, compare and record the intensity variation and extinction characteristics of the six curves. Draw the curve, analyze the polarization state of the light from the data table, and discuss the influence of the λ/4
waveplateonthepolarizationofthelight(5) Find the angle of between the polarization direction of the polarizer and the opticalaxisofthe/2waveplate.[PreviewandReportRequirements]Find relevant information accordingtotheexperimental requirements,determine theexperimentalplan and specific operation steps, and submit the report in the form of research papers.[Discussions】]1.Inthisexperiment,wecontrol therotationof themotorthrougha computer.Thesystemprovides two control methods. What is the characteristic of each method? How to choosecorrectly?2.In the quantitative measurement and study of elliptically polarized light, we recorded theangle-energy curve of the polarized light received by the signal receiver when the optical axisof the/4waveplate isrotatedby15°、30°、45°、60°、75°和90°fromtheextinctionposition.Comparing these 6 curves, pay attention to their intensity variation and theminimum value to the x-axis, and fill the table. Thinking about what characteristics andvariations can be summarized of threetypes of polarized light based on these characteristics?3.How to indentify circularly polarized light and natural light? How to indentify ellipticallypolarized light and partially polarized light?[References]1 Sihua Lv, Jiaqi Duan.New basic physics experiment.Beijing:Higher Education Press,20052 Jianqun Huang,Xianfeng Hu, Zhihua Yong.University physics experiment. Sichuan: SichuanUniversity Press, 2005.3 Weishen Zhan. Physics experiment tutorial. Dalian: Dalian University of Technology Press.2004,4Hong Yu.University Physics (Second Edition).Beijing: Science Press, 2008Ying Qin, Yanhui Wang, Hong Yu, Yuan Liu, Qiao Wang00
8 wave plate on the polarization of the light． (5) Find the angle of between the polarization direction of the polarizer and the optical axis of the λ/2 wave plate． 【Preview and Report Requirements】 Find relevant information according to the experimental requirements, determine the experimental plan and specific operation steps, and submit the report in the form of research papers． 【Discussions】 1． In this experiment, we control the rotation of the motor through a computer. The system provides two control methods. What is the characteristic of each method? How to choose correctly? 2． In the quantitative measurement and study of elliptically polarized light, we recorded the angle-energy curve of the polarized light received by the signal receiver when the optical axis of the λ/4 wave plate is rotated by 15o 、30o 、45o、60o 、75o 和 90o from the extinction position. Comparing these 6 curves, pay attention to their intensity variation and the minimum value to the x-axis, and fill the table. Thinking about what characteristics and variations can be summarized of three types of polarized light based on these characteristics? 3． How to indentify circularly polarized light and natural light？How to indentify elliptically polarized light and partially polarized light? 【References】 1 Sihua Lv, Jiaqi Duan. New basic physics experiment. Beijing: Higher Education Press, 2005. 2 Jianqun Huang, Xianfeng Hu, Zhihua Yong. University physics experiment. Sichuan: Sichuan University Press, 2005. 3 Weishen Zhan. Physics experiment tutorial. Dalian: Dalian University of Technology Press, 2004. 4 Hong Yu. University Physics (Second Edition). Beijing: Science Press, 2008. Ying Qin, Yanhui Wang, Hong Yu, Yuan Liu, Qiao Wang