Experiment12/13AdjustmentandApplicationof SpectrometerIt will have a deflection in the process of light propagation due to reflection,refraction diffraction or scattering.Therefore, it is important to quantitatively describethe deflection angle when light deflection occurs. Spectrometer, also known as opticalangle measuring instrument, is an instrument that can accurately measure the angle oflight deflection and is widely used in optical experiments. Spectrometer is the basis ofmany optical instruments such as Prism Spectrometer, grating spectrometer,monochrome, etc.Its adjustment ideas, methods and techniques has a certainrepresentationintheopticalexperiment.Soitishelpfultomastermorecomplexopticalinstruments by learning the adjustment and application of Spectrometer. In thisexperiment, it is necessary to understand the design principle and structure ofspectrometer, and master the adjustment and application method.Then it isindispensable to measure the refractive index of glass prism by measuring the vertexangle and minimum deviation angle of prism, grating constant and dispersive power.ExperimentalObjectives(1) Understand the design principle and structure of spectrometer(2)Masterthe adjustmentand applicationmethod of spectrometer(3) Measure the refractive index oftriangular prism(4) Measure grating constant and angular dispersionExperimentalInstrumentsSpectrometeroftypeJJY1,plane mirror,glass prism,grating,sodium lamp,mercurylampExperimentalPrinciple1 Structure and principle of spectrometerSpectrometer has manymodels, but its structure is muchthe same.The spectrometer oftype JY1 used in this experiment consists of five parts: telescope, specimen stage,collimator, dial plateand basewhich canbe seen inFigure12-1
Experiment 12/13 Adjustment and Application of Spectrometer It will have a deflection in the process of light propagation due to reflection, refraction diffraction or scattering. Therefore, it is important to quantitatively describe the deflection angle when light deflection occurs. Spectrometer, also known as optical angle measuring instrument, is an instrument that can accurately measure the angle of light deflection and is widely used in optical experiments. Spectrometer is the basis of many optical instruments such as Prism Spectrometer, grating spectrometer, monochrome, etc. Its adjustment ideas, methods and techniques has a certain representation in the optical experiment. So it is helpful to master more complex optical instruments by learning the adjustment and application of Spectrometer. In this experiment, it is necessary to understand the design principle and structure of spectrometer, and master the adjustment and application method. Then it is indispensable to measure the refractive index of glass prism by measuring the vertex angle and minimum deviation angle of prism, grating constant and dispersive power. Experimental Objectives (1) Understand the design principle and structure of spectrometer (2) Master the adjustment and application method of spectrometer (3) Measure the refractive index of triangular prism (4) Measure grating constant and angular dispersion. Experimental Instruments Spectrometer of type JJY1, plane mirror, glass prism, grating, sodium lamp, mercury lamp Experimental Principle 1 Structure and principle of spectrometer Spectrometer has many models, but its structure is much the same. The spectrometer of type JJY1 used in this experiment consists of five parts: telescope, specimen stage, collimator, dial plate and base which can be seen in Figure 12-1
2.82.7420 1916Figure12-1Spectrometerof typeJY11 slit device; 2 slit device locking screw, 3 collimator, 4 brake frame; 5 specimen stage;6 leveling bolt of specimen stage;7locking screwof specimen stage;8telescope;9 locking screw of eyepiece; 10Abbe auto-collimating eyepiece,11 adjustment hand wheel ofeyepiece visibility12vertical adjustment screw of telescope optical axis;13horizontal adjustmentscrewoftelescopeopticalaxis;14supportarm,15finetuningscrewoftelescope;16 locking screw between rotary seat and dial plate (back side); 17 locking screw of telescope;18 electrical outlet,19 base;20 rotary seat;21 vernier;22 dial plate;23 column, 24 fine tuning screwof alidade;25locking screwofalidade;26horizontal adjustmentscrewofcollimatoropticalaxis;27 vertical adjustment screw of collimator optical axis; 28 adjustment hand wheel of slit width;(1) TelescopeTelescope 8 mounted on the support arm 14 is the Abbe auto-collimating eyepiece. Thearm and the rotary seat 20 are fixed together and are set on the dial plate. Whenlooseningthelockingscrew16therotaryseatandthedialplatecanberotatedtogether:whentighteningthelockingscrew16,therotary seatandthedisccanberotatedrelatively. The optical axis position of the telescope can be fine-tuned by adjustingscrews 12 and 13.The focal length of the eyepiece10 can be adjusted by hand wheel11.The eyepiece tube may move and rotate along the optical axis loosening the screw9.ReticleEyepieceObjective lensdLightPrismFigure12-2Auto-collimatingtelescope
Figure 12-1 Spectrometer of type JJY1 1 slit device; 2 slit device locking screw; 3 collimator; 4 brake frame; 5 specimen stage; 6 leveling bolt of specimen stage; 7 locking screw of specimen stage; 8 telescope; 9 locking screw of eyepiece; 10 Abbe auto-collimating eyepiece; 11 adjustment hand wheel of eyepiece visibility; 12 vertical adjustment screw of telescope optical axis; 13 horizontal adjustment screw of telescope optical axis; 14 support arm; 15 fine tuning screw of telescope; 16 locking screw between rotary seat and dial plate (back side); 17 locking screw of telescope; 18 electrical outlet; 19 base; 20 rotary seat; 21 vernier;22 dial plate; 23 column; 24 fine tuning screw of alidade; 25 locking screw of alidade; 26 horizontal adjustment screw of collimator optical axis; 27 vertical adjustment screw of collimator optical axis; 28 adjustment hand wheel of slit width; (1) Telescope Telescope 8 mounted on the support arm 14 is the Abbe auto-collimating eyepiece. The arm and the rotary seat 20 are fixed together and are set on the dial plate. When loosening the locking screw 16, the rotary seat and the dial plate can be rotated together; when tightening the locking screw 16, the rotary seat and the disc can be rotated relatively. The optical axis position of the telescope can be fine-tuned by adjusting screws 12 and 13. The focal length of the eyepiece10 can be adjusted by hand wheel 11. The eyepiece tube may move and rotate along the optical axis loosening the screw 9. Figure 12-2 Auto-collimating telescope Eyepiece Reticle Prism Light Objective lens
The structure of the auto-collimating telescope is shown in Figure 12-2. It is composedof eyepiece, total reflection prism, reticle and objective lens. The reticle is engravedwith double cross line and a transparentengraving line, and the top line ofreticle and the transparent “+" engraving line are symmetrical to center line ofreticle,as shown in Figure 12-3 (a). The right-angled edge of the full reflection prism clings tothe small "+" engraved line, and another right angle of the prism clings to a small holeon eyepiece tube. A green led lamp is installed under the small hole.The light ofthe ledlamp can enterthe small hole and illuminates thetransparent “+"engravingline bythe full reflection small prism. A collimated light will be emitted by the objective lensif the reticle is right on the focal plane of the objective lens. The collimated light willbe reflected back into the objective lens if there is a plane mirror in front of it. By thenit can be seen the reflection"+"image and cross hairs from eyepiece which is noparallax, as shown in Figure 10-3 (b).If the optical axis ofthe telescope is perpendicularto the plane mirror, the reflection “+"image will coincide with the top line of reticle,as shown in Figure 10-3 (c).(c)(b)(a)1toplineof reticle2centerlineofreticle3travingline4greenbackground5reflection"+"imageFigure12-3Reticleand reflection+”crossimage(2) CollimatorCollimatorismountedona columnanditsopticalaxispositioncanbefine-tunedbyadjustingscrews26and27.OneendoftheCollimatorisfittedwithaconvergentlensand a slit sleeve is inserted intothe other end.Slit1 canbemoved and rotatedalongtheoptical axis and its width can be adjusted by hand wheel 28, the adjustment range isO.2-2mm. When the slit is located on the main focal surface of the lens, the collimatorproduces a parallel light beam.(3)Specimen stageThe specimen stage is used to place the measured objects which can be rotated aroundthe center axis. When you loosening the locking screw of specimen stage, the specimenstage can be raised or lowered as needed. The specimen stage has three leveling screws6 which are used to adjust the verticality between rotation axis and object stage. Theconnectionof threescrews isa positivetriangle(4) Dial plateThe Dial plate goes all the way around the table from 0 to 360°. The major tick marksare 1° apart. They are separated by one minor tick marks, 30' (arc minutes) apart. The
The structure of the auto-collimating telescope is shown in Figure 12-2. It is composed of eyepiece, total reflection prism, reticle and objective lens. The reticle is engraved with double cross line and a transparent “十” engraving line, and the top line of reticle and the transparent “十”engraving line are symmetrical to center line of reticle, as shown in Figure 12-3 (a). The right-angled edge of the full reflection prism clings to the small "+" engraved line, and another right angle of the prism clings to a small hole on eyepiece tube. A green led lamp is installed under the small hole. The light of the led lamp can enter the small hole and illuminates the transparent “十” engraving line by the full reflection small prism. A collimated light will be emitted by the objective lens if the reticle is right on the focal plane of the objective lens. The collimated light will be reflected back into the objective lens if there is a plane mirror in front of it. By then it can be seen the reflection “十”image and cross hairs from eyepiece which is no parallax, as shown in Figure 10-3 (b). If the optical axis of the telescope is perpendicular to the plane mirror, the reflection “十”image will coincide with the top line of reticle, as shown in Figure 10-3 (c). 1 top line of reticle 2 center line of reticle 3 transparent “十” engraving line 4 green background 5 reflection “十”image Figure 12-3 Reticle and reflection “十”cross image (2) Collimator Collimator is mounted on a column and its optical axis position can be fine-tuned by adjusting screws 26 and 27. One end of the Collimator is fitted with a convergent lens and a slit sleeve is inserted into the other end. Slit 1 can be moved and rotated along the optical axis and its width can be adjusted by hand wheel 28, the adjustment range is 0.2~2mm. When the slit is located on the main focal surface of the lens, the collimator produces a parallel light beam. (3) Specimen stage The specimen stage is used to place the measured objects which can be rotated around the center axis. When you loosening the locking screw of specimen stage, the specimen stage can be raised or lowered as needed. The specimen stage has three leveling screws 6 which are used to adjust the verticality between rotation axis and object stage. The connection of three screws is a positive triangle. (4) Dial plate The Dial plate goes all the way around the table from 0 to 360º. The major tick marks are 1º apart. They are separated by one minor tick marks, 30' (arc minutes) apart. The
inner scale is thevernier.First,note theangle of theminor tick mark on theouter scalethat is just to the right of the zero (right end) of the inner scale (say, 334 30'). Now lookat the inner scale. It goes from 0 to 30' in steps of 1'. Somewhere along that scale youwill see a bright line that connects it to the outer scale. Note the position of that brightline on the inner scale (say, 17'). The present angle of the telescope is the sum of thetwovalues (334°47)20101u334345340Figure 12-4 Dial plate and vernierThe purpose of setting up two symmetric vernier is to eliminate the centering errorcaused bythemismatchbetweenthecenter of thedial plate and the center axis ofthespectrometer. In the processing process, two central axes are not easy to overlap fullywhich will inevitably produce centering error. So that the rotation angle of telescopearound the center axis is inconsistent with the angle read from dial plate, as shown infigure 12-5.The letter Orepresents the center of the spindle and the letter O'representsthe center of the dial plate. The angle is the actual rotation angle of the telescopearound the center axis,and Si and 2 aretheangle shown on two vernier.Obviously,itcan be concluded from thegeometricrelationship:(12-1)Φ+/1=0i+/2(12-2)Φ+/3=02+/4with21=/2，Z3=Z4combining（12-1）and（12-2）,weobtain theexpression:Φ=（01+02) /2It is not difficult to see that the actual rotation angle of the telescope around thecenter axis can be obtained from the average of two vernier angle
inner scale is the vernier. First, note the angle of the minor tick mark on the outer scale that is just to the right of the zero (right end) of the inner scale (say, 334º 30'). Now look at the inner scale. It goes from 0 to 30' in steps of 1'. Somewhere along that scale you will see a bright line that connects it to the outer scale. Note the position of that bright line on the inner scale (say, 17'). The present angle of the telescope is the sum of the two values (334º 47'). Figure 12-4 Dial plate and vernier The purpose of setting up two symmetric vernier is to eliminate the centering error caused by the mismatch between the center of the dial plate and the center axis of the spectrometer. In the processing process, two central axes are not easy to overlap fully which will inevitably produce centering error. So that the rotation angle of telescope around the center axis is inconsistent with the angle read from dial plate, as shown in figure 12-5. The letter O represents the center of the spindle and the letter O' represents the center of the dial plate. The angle ϕ is the actual rotation angle of the telescope around the center axis, and θ1 and θ2 are the angle shown on two vernier. Obviously, it can be concluded from the geometric relationship: Ф+∠1=θ1+∠2 （12－1） Ф+∠3=θ2+∠4 （12－2） with ∠1=∠2 ，∠3=∠4 combining（12－1）and（12－2）, we obtain the expression： Ф=（θ1+θ2）/2 It is not difficult to see that the actual rotation angle of the telescope around the center axis can be obtained from the average of two vernier angle
1Figure 12-5 The centering error between the center of the dial plate and thecenteraxisofthespectrometer.2Principle of measuring the refractive index of prismAs shown in figure 12-6, a beam of monochrome parallel light incident to the ABsurface of the triangular prism whichis refractedfrom the other sideof theAC.Therefractionlawoftheprismissinin=sin rThe deviation angle is defined as the angle between the incident light SO and theejection light O'S. As you know from figure 12-6, the vertex angle isα=r+r',andthedeviationangleisS=(i-r)+(i-r)=i+i'-αWhen incident angle i is equal to ejection angle i, the deviation angle 8 exist aminimum value which is called as minimum deviation angle mn :In this case, theindex of refraction is given bySmin+αsinsini2n(12-3)αsinrsin2
Figure 12－5 The centering error between the center of the dial plate and the center axis of the spectrometer. 2 Principle of measuring the refractive index of prism As shown in figure 12-6, a beam of monochrome parallel light incident to the AB surface of the triangular prism which is refracted from the other side of the AC. The refraction law of the prism is r i n sin sin = , The deviation angle is defined as the angle between the incident light SO and the ejection light O'S'. As you know from figure 12-6, the vertex angle is = r + r , and the deviation angle is = (i − r) + (i − r ) = i + i − . When incident angle i is equal to ejection angle i', the deviation angleδexist a minimum value which is called as minimum deviation angle min . In this case, the index of refraction is given by 2 sin 2 sin sin sin min + = = r i n (12-3)