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)
Figure12-6RefractioninthemainsectionoftheprismThe refractive index is a function of the wave length. When a non-monochrome light isrefracted by triangular prism, this will result in different minimum deviation angleswhicharedependonthelightwavelength3Principle ofmeasuring thegrating constantLight passing through a series of slits will result in interference peaks and troughsProjected on a screen, a pattern of light and dark areas is produced. Including thecentral "zero-order" peak, there can be multiple orders of the same pattern,symmetrically on each side.This is ordinarily described by the equationdsink=kaEquation 1 simply tells us that in order for the waves to constructively interfere at pointP or P' the phase difference dsino must be equal to an integral number of the lightwavelength. Where n is the order, is the wavelength, is the angle of the pattern, andd is the grating constant which equal to the space between slits (N = 1/[1000d], withNbeing numberof grating lines permm)
Figure 12－6 Refraction in the main section of the prism The refractive index is a function of the wave length. When a non-monochrome light is refracted by triangular prism, this will result in different minimum deviation angles which are depend on the light wave length. 3 Principle of measuring the grating constant Light passing through a series of slits will result in interference peaks and troughs. Projected on a screen, a pattern of light and dark areas is produced. Including the central “zero-order” peak, there can be multiple orders of the same pattern, symmetrically on each side. This is ordinarily described by the equation d sin k = k Equation 1 simply tells us that in order for the waves to constructively interfere at point P or P' the phase difference dsinθ must be equal to an integral number of the light wavelength. Where n is the order, λ is the wavelength, θ is the angle of the pattern, and d is the grating constant which equal to the space between slits (N = 1/[1000d], with N being number of grating lines per mm)
L+nALigh"Wall"Figure12-7Diffractionof light througha grating,showingthe arrangementofinterferencepeaksonabackgroundscreenThe experimental device diagram is shown in figure 12-8. The grating is placed on theplatform of the spectrometer, and the mercury vapor lamp passes vertically into thegrating through the collimator of the spectrometer.By grating diffraction, the spectrumare observed as shown in figure 12-9.The diffraction angle ofeach diffraction spectrumisreadfromthedialplateandvernierofthespectrometerMercurylampDiffraction gratingYellow579.1nmYellow577.0nmGreen546.1nmGIBlueBluePruple491.6nm435.8nmPruple404.7 nmFirst-orderspectrum lineZeroth-order spectrum lineFirst-orderspectrumlinek=+1k=-1k=0Figure 12-8 Diagram of mercury light spectrum observed by spectrometer
Figure 12－7 Diffraction of light through a grating, showing the arrangement of interference peaks on a background screen The experimental device diagram is shown in figure 12-8. The grating is placed on the platform of the spectrometer, and the mercury vapor lamp passes vertically into the grating through the collimator of the spectrometer. By grating diffraction, the spectrum are observed as shown in figure 12-9.The diffraction angle of each diffraction spectrum is read from the dial plate and vernier of the spectrometer. Figure 12－8 Diagram of mercury light spectrum observed by spectrometer
Second-orderrainbowFirst-orderrainbowCentralwhiteFirst-orderrainbowSecond-orderrainbow(a)(b)Figure 12-9 Multi-order spectrum lines of mercury light observed by spectrometerExperimental Content and Procedure1SpectrometeradjustmentThe spectrometer must be adjusted before measurement to achieve the followingrequirements:@Collimatoremitparallelbeam② The telescope can receive parallel beam (ie,the telescope is focused infinity)③ Theplaneformed bythe lightof the optical componenttobemeasured (such asincident, refraction, reflection, diffracted light, etc.) should be perpendicular to thecentral axis of the instrument. In the other words, the collimator and the optical axisof the telescope should beperpendicular to the rotation axis; the optical flat ofopticalcomponent to be measured should be parallel to the axis of rotationThe specific adjustment steps areas follows:(1)VisualcoarseadjustmentAccording to the rough estimate of the eye, adjust the screws 12 and 27 so that theoptical axis of the telescope and the collimator are substantially perpendicular to thecentral rotation axis, and adjust the three horizontal adjustment screws under the stageso that the stage is roughly horizontal. Coarse adjustment is not only the basis for fine-tuning but also the key to fine-tuning success.(2) Adjust telescope to focus on infinity by self-aligning principleThe principle of self-aligning adjustment is suitable for observing parallel light. Asmentioned above, the specific adjustment method is:(I) Connect the power supply and adjust the eyepiece to see the cross hairs on the reticleintheeyepiece(Il) Place a double-sided mirror on the stage as shown in figure 12-10(a) (or (b), androtate the stage so that a reflecting surface faces the telescope. Look for the spot
Figure 12－9 Multi-order spectrum lines of mercury light observed by spectrometer Experimental Content and Procedure 1 Spectrometer adjustment The spectrometer must be adjusted before measurement to achieve the following requirements: ① Collimator emit parallel beam ② The telescope can receive parallel beam (ie, the telescope is focused infinity). ③ The plane formed by the light of the optical component to be measured (such as incident, refraction, reflection, diffracted light, etc.) should be perpendicular to the central axis of the instrument. In the other words, the collimator and the optical axis of the telescope should be perpendicular to the rotation axis; the optical flat of optical component to be measured should be parallel to the axis of rotation. The specific adjustment steps are as follows: (1) Visual coarse adjustment According to the rough estimate of the eye, adjust the screws 12 and 27 so that the optical axis of the telescope and the collimator are substantially perpendicular to the central rotation axis, and adjust the three horizontal adjustment screws under the stage so that the stage is roughly horizontal. Coarse adjustment is not only the basis for finetuning but also the key to fine-tuning success. (2) Adjust telescope to focus on infinity by self-aligning principle The principle of self-aligning adjustment is suitable for observing parallel light. As mentioned above, the specific adjustment method is: (I) Connect the power supply and adjust the eyepiece to see the cross hairs on the reticle in the eyepiece. (II) Place a double-sided mirror on the stage as shown in figure 12-10(a) (or (b)), and rotate the stage so that a reflecting surface faces the telescope. Look for the spot
reflected from the specular surface (the blurred green cross image)from the telescopeby rotating the stage slowly.It is necessary to turn coarse adjustment again if the spotcannotbefound.(Ill) Move the eyepiece sleeve back and forth to change the distance between the reticleand the objective lens to make the green bright cross hairs image clear.(IV) Eliminate the parallax: move the eyes up, down, left and right to see whether thegreen cross image and the crosshair of the reticle has relative movement. If there is arelative movement, that is, there is parallax. It indicates that the image is not on thesameplane as the crosshair.Then thedistancebetweenthe reticleandtheobjectivelensshould be carefully adjusted until the parallax is removed. At this point the telescopehas focused on infinity.(a)(b)Figure 12-10 Position of the plane mirror on the stage(3)Vertical adjustment betweentheoptical axis ofthetelescope and rotation axis of thespectrometer.According to the principle of self-alignment adjustment, if the optical axis of thetelescope is perpendicular to the plane mirror, the reflected green cross image shouldcoincide with the upper crosshair of the reticle, see Figure 12-3(c).When the greencross image reflected by the front and rear reflection surfaces of the plane mirror canoverlap with the upper crosshair, the optical axis of the telescope is perpendicular to therotation axis of spectrometer. In general, the green cross image seen at the beginningdoes not coincide with the upper crosshair and requires careful adjustment to reach therequirements.Theadjustment stepisasfollows(I) On the basis of the previous step, Rotate the stage by 180° and find a green brightcross image reflected by the other reflecting surface from the telescope. If you can't findthe reflection image, you can use your eye directly outside the telescope to find theposition of the reflection image by looking into the plane mirror. Adjust the levelingscrew"a" properly by the position of reflection image until you can see the image fromtelescope before and after the 180° rotation.(Il) Use the asymptotic method to adjust the green bright cross image to coincide withthe upper crosshairs on the reticle. First, adjust the leveling screw"a" so that the distancebetween the image and the upper crosshair wire is reduced by half, and then adjust the
reflected from the specular surface (the blurred green cross image) from the telescope by rotating the stage slowly. It is necessary to turn coarse adjustment again if the spot cannot be found. (III) Move the eyepiece sleeve back and forth to change the distance between the reticle and the objective lens to make the green bright cross hairs image clear. (IV) Eliminate the parallax: move the eyes up, down, left and right to see whether the green cross image and the crosshair of the reticle has relative movement. If there is a relative movement, that is, there is parallax. It indicates that the image is not on the same plane as the crosshair. Then the distance between the reticle and the objective lens should be carefully adjusted until the parallax is removed. At this point the telescope has focused on infinity. Figure 12－10 Position of the plane mirror on the stage (3) Vertical adjustment between the optical axis of the telescope and rotation axis of the spectrometer. According to the principle of self-alignment adjustment, if the optical axis of the telescope is perpendicular to the plane mirror, the reflected green cross image should coincide with the upper crosshair of the reticle, see Figure 12-3(c). When the green cross image reflected by the front and rear reflection surfaces of the plane mirror can overlap with the upper crosshair, the optical axis of the telescope is perpendicular to the rotation axis of spectrometer. In general, the green cross image seen at the beginning does not coincide with the upper crosshair and requires careful adjustment to reach the requirements. The adjustment step is as follows: (I) On the basis of the previous step, Rotate the stage by 180º and find a green bright cross image reflected by the other reflecting surface from the telescope. If you can't find the reflection image, you can use your eye directly outside the telescope to find the position of the reflection image by looking into the plane mirror. Adjust the leveling screw ''a'' properly by the position of reflection image until you can see the image from telescope before and after the 180° rotation. (II) Use the asymptotic method to adjust the green bright cross image to coincide with the upper crosshairs on the reticle. First, adjust the leveling screw ''a'' so that the distance between the image and the upper crosshair wire is reduced by half, and then adjust the
vertical adjustment screw12 oftelescope optical axis to makes the image coincide withthe upper crosshair. Then Rotate the stage by 180°, repeat the above procedure until thecross image appears at theposition ofupper cross hair in both reflecting surface of theplane mirror.At this point, the optical axis of the telescope is perpendicular to therotationaxisofspectrometer.(4) Adjust the collimator to emit parallel beam(I) Remove the mirror, and illuminate the slit with a mercury lamp.(Il) Align the telescope with the collimator, and observe the slit image from thetelescopeeyepiece.(Ill) Move the slit sleeve back and forth by loosening slit device locking screw to makethe slit image clear and have no parallax. At this time, the slit is already located on thefocal plane of the collimator lens, and the light emitted from the collimator is parallelbeam.(IV)Adjusttheslitwidthtoabout0.5mm(5) Adjust the optical axis of the collimator perpendicular to the rotation axisRotatethe slit sleeve sothat the slit image is parallel tothe horizontal lineof the crosshairs.Adjustvertical adjustment screwof collimator optical axis27toraise orlowerthe position of the slit image so that the slit is symmetrical to the center of the eyepiecefield of view. At this time, the optical axis of the collimator is perpendicular to therotation axis. Rotate the slit sleeve by 90° so that the slit image is parallel to the verticalline of reticle, Be careful not to break the focus of the collimator, and then tighten theslitdevicelocking screw.2 Measuring the refractive index of the prism by the minimum deflection anglemethod()Adjust the main section of the prism perpendicular to the rotation axisSince the two bottom surfaces of the prism are generally not the main section, and thestage is not perpendicular to the rotation axis of spectrometer. Therefore, the mainsection of the prism must be adjusted so that it is perpendicular to the rotation axis, thatis, the normal of the two optical faces of the prism is perpendicular to the axis. First,place the triangular prism on the stage according to figure 12-11 so that AB, AC, andBC areperpendiculartotheconnectionlineala2,a2a3,and a3alofthethreescrews ofthe stage.When al is adjusted, only the normal direction oftheABplane is changedandthereisnoinfluenceonthenormal oftheACsurface.Whena3isadjusted,onlythe normal direction of the ACface is changed, and there is no influence on the normalof the AB face. Second, find the green bright cross image reflected by the AB surfacein the telescope using self-aligning method, and adjust the screw al to make the greenbright cross image coincide with the upper cross. Then rotate the stage to find thereflection image of theAC surface,and adjust the screw a3tomakethegreen crossimage coincide with the upper crosshair. Repeat this process until the reflected greenimages of both AB and AC sides coincide with the upper crosshairs. It means that the
vertical adjustment screw 12 of telescope optical axis to makes the image coincide with the upper crosshair. Then Rotate the stage by 180º, repeat the above procedure until the cross image appears at the position of upper cross hair in both reflecting surface of the plane mirror. At this point, the optical axis of the telescope is perpendicular to the rotation axis of spectrometer. (4) Adjust the collimator to emit parallel beam (I) Remove the mirror, and illuminate the slit with a mercury lamp. (II) Align the telescope with the collimator, and observe the slit image from the telescope eyepiece. (Ш) Move the slit sleeve back and forth by loosening slit device locking screw to make the slit image clear and have no parallax. At this time, the slit is already located on the focal plane of the collimator lens, and the light emitted from the collimator is parallel beam. (IV) Adjust the slit width to about 0.5mm (5) Adjust the optical axis of the collimator perpendicular to the rotation axis Rotate the slit sleeve so that the slit image is parallel to the horizontal line of the cross hairs. Adjust vertical adjustment screw of collimator optical axis 27 to raise or lower the position of the slit image so that the slit is symmetrical to the center of the eyepiece field of view. At this time, the optical axis of the collimator is perpendicular to the rotation axis. Rotate the slit sleeve by 90º so that the slit image is parallel to the vertical line of reticle. Be careful not to break the focus of the collimator, and then tighten the slit device locking screw. 2 Measuring the refractive index of the prism by the minimum deflection angle method (1) Adjust the main section of the prism perpendicular to the rotation axis Since the two bottom surfaces of the prism are generally not the main section, and the stage is not perpendicular to the rotation axis of spectrometer. Therefore, the main section of the prism must be adjusted so that it is perpendicular to the rotation axis, that is, the normal of the two optical faces of the prism is perpendicular to the axis. First, place the triangular prism on the stage according to figure 12-11 so that AB, AC, and BC are perpendicular to the connection line a1a2, a2a3, and a3a1 of the three screws of the stage. When a1 is adjusted, only the normal direction of the AB plane is changed, and there is no influence on the normal of the AC surface. When a3 is adjusted, only the normal direction of the AC face is changed, and there is no influence on the normal of the AB face. Second, find the green bright cross image reflected by the AB surface in the telescope using self-aligning method, and adjust the screw a1 to make the green bright cross image coincide with the upper cross. Then rotate the stage to find the reflection image of the AC surface, and adjust the screw a3 to make the green cross image coincide with the upper crosshair. Repeat this process until the reflected green images of both AB and AC sides coincide with the upper crosshairs. It means that the