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Precision Interferometer

012-07137A

2

Equipment

The OS-9255A Precision Interferometer includes the

following equipment:

• 5 kg Base with built-in micrometer
• Adjustable Mirror
• Movable Mirror
• Beam Splitter
• Compensator Plate
• (2) Component Holder
• Viewing Screen
• Lens, 18 mm Focal Length
• Diffuser
• Fitted Storage Case

Additional Equipment Required –

• Laser (OS-9171)
• Laser Bench (OS-9172)

   

NOTE:

 The preceding equipment includes

everything needed for basic Michelson interferom-

etry. You can produce clear fringes and make

precise measurements of the wavelength of your

source. However, to perform the experiments in this

manual, you will need additional components, such

as the OS-9256A Interferometer Accessories or a

comparable set of your own components.The

Precision Interferometer is available as a complete

system. Please refer to your current PASCO catalog

for details.

Additional Equipment Recommended –

The OS-9256A Interferometer Accessories includes:

• Rotating Pointer
• Vacuum Cell
• Component Holder
• Lens, 18 mm Focal Length
• Lens, 48 mm Focal Length
• Glass Plate
• (2) Polarizer
• Vacuum Pump with Gauge

 

 NOTE:

 The OS-9255A Fitted Case also

provides storage for these accessory components.

About Your Light Source

We strongly  recommend a laser for most introductory

applications. A spectral light source can be used (see the

Appendix), but that really comprises an experiment in and

of itself for beginning students. A laser source is easy to

use and produces bright, sharp fringes.
The OS-9171 Laser and OS-9172 Laser Alignment Bench

are available from PASCO. However, any low power laser

that operates in the visible range will work well.  If you

want to demonstrate the importance of polarization in

interferometry, a non-polarized laser should be used. For

easy alignment, the beam should be approximately 4 cm

above the level of the bench top.

 OS-9171 Laser

OS-9172

Laser Alignment

Bench

Содержание OS-9255A

Страница 1: ...on Manual and Experiment Guide for the PASCO scientific Models OS 9255A thru OS 9258A 012 07137A 5 99 1990 PASCO scientific 10 00 PRECISION INTERFEROMETER Includes Teacher s Notes and Typical Experiment Results ...

Страница 2: ......

Страница 3: ...on 4 Michelson Twyman Green Fabry Perot Setup and Operation 6 Tips on Using the Interferometer 9 Sources of Error Troubleshooting Experiments Experiment1 IntroductiontoInterferometry 11 Experiment 2 The Index of Refraction of Air 13 Experiment 3 The Index of Refraction of Glass 15 SuggestionsforAdditionalExperiments 17 Maintenance 18 Teacher s Guide 20 22 ...

Страница 4: ...yrightedandallrights reserved However permission is granted to non profit educational institutions for reproduction of any part of the manual providing the reproductions are used only for their laboratories and are not sold for profit Reproduction under any other circumstances without the written consent of PASCO scientific is prohibited Limited Warranty PASCO scientific warrants the product to be...

Страница 5: ...ide asimpleintroductiontothisimportantapplicationof interferometry Fabry Perot The Fabry Perot Interferometer is also an important contemporary tool used most often for high resolution spectrometry The fringes are sharper thinner and more widelyspacedthantheMichelsonfringes sosmalldiffer ences in wavelength can be accurately resolved The Fabry Perotinterferometerisalsoimportantinlaser theory as it...

Страница 6: ...rent PASCO catalog fordetails Additional Equipment Recommended TheOS 9256AInterferometerAccessoriesincludes RotatingPointer VacuumCell ComponentHolder Lens 18 mm Focal Length Lens 48 mm Focal Length GlassPlate 2 Polarizer VacuumPumpwithGauge NOTE The OS 9255A Fitted Case also provides storage for these accessory components About Your Light Source We strongly recommend a laser for most introductory...

Страница 7: ...er Movable Mirror Adjustable Mirror Vacuum Cell Vacuum Pump withGauge Rotating Pointer Beam Splitter Compensator Plate Component Holder OS 9255A Precision Interferometer Lens 18 mm Fitted Case 2 Polarizer Base OS 9256A Interferometer Accessories Lens 18 mm Lens 48 mm Glass Plate ...

Страница 8: ...light from the two slits struck the screen a regular pattern of dark and bright bands appeared When firstperformed Young sexperimentofferedimportant evidence for the wave nature of light Young s slits can be used as a simple interferometer If the spacing between the slits is known the spacing of the maxima and minima can be used to determine the wave length of the light Conversely if the wavelengt...

Страница 9: ...rror a measured distance dm and counting m the number of times the fringe pattern is restoredtoitsoriginalstate thewavelengthofthelight l canbecalculatedas l 2dm m If the wavelength of the light is known the same proce dure can be used to measure dm Figure 2 Fringes The Twyman Green Interferometer The Twyman Green Interferometer is a variation of the MichelsonInterferometerthatisusedtotestoptical ...

Страница 10: ...r see Suggestions for Additional Experiments near the end of the manual To set up and align your PASCO Laser 1 Set the interferometer base on a lab table with the mi crometerknobpointingtowardyou 2 Position the laser alignment bench to the left of the baseapproximatelyperpendiculartotheinterferometer base and place the laser on the bench mirror is moved toward or away from the fixed mirror the fri...

Страница 11: ...rks so that the beam is reflected to the fixed mirror Adjust the angle of the beam splitter as needed so that the reflected beam hits the fixed mirror near its center 4 There should now be two sets of bright dots on the viewing screen one set comes from the fixed mirror and the other comes from the movable mirror Each set of dots should include a bright dot with two or more dotsoflesserbrightness ...

Страница 12: ... so it s at least 12 inches from the edge of the interferometerbase Fringesshouldappearinthebright disk of the viewing screen Fine adjustments of L1 may be necessary to find the fringes A piece of white paper or cardboard can be used in place of the viewing screen A 48 mm FL convex lens may also be used to magnifytheprojectedimageofthefringes Fabry Perot Mode 1 Alignthelaserandinterferometerbaseas...

Страница 13: ...rough the diffuser rather than on the viewing screen Just place the diffuser where you would normally place the viewing screen and look through it toward the interferometer Tips on Using the Interferometer Figure 9 Counting Fringes Accurate Fringe Counting Thefollowingtechniquescanhelpyoumakeaccurate measurements 1 It s not necessary that your interference pattern be per fectly symmetrical or shar...

Страница 14: ...nt and back surfaces of the mirrors and beam splitter of ten cause minor interference patterns in the back ground of the main fringe pattern These background patterns normally do not move when the mirror is moved and have no impact on measurements made using the main interference pattern 4 Convection Currents If the fringe pattern ap pears to wave or vibrate check for air currents Even a slight br...

Страница 15: ...dinterferometerintheMichelsonmode soaninterferencepatternisclearlyvisibleonyour viewing screen See Setup and Operationfor instructions 2 Adjustthemicrometerknobtoamediumreading approximately50µm Inthisposition therelationshipbe tween the micrometer reading and the mirror movement is most nearly linear 3 Turnthemicrometerknobonefullturncounterclockwise Continueturningcounterclockwiseuntilthezeroont...

Страница 16: ...ht l 2dm N then average your results If you tried the Fabry Perot mode also calculate the wavelength independently for that data The same formula applies PartII 1 From your observations in step 1 of the procedure can you determine the polarization characteristics of your light source Does it vary with time 2 Do your observations from step 2 give you any more information about the polarization of y...

Страница 17: ...y 1 A graph of index of refraction versus pressure for a gas is shown in Figure2 1 Byexperimentallydeterminingtheslope the index of refraction of air can be determined at various pressures Procedure 1 Align the laser and interferometer in the Michelson mode See Setup and Operation 2 Place the rotational pointer between the movable mirror and the beam splitter see Figure 2 2 Attach the vacuum cell ...

Страница 18: ...ghtnowgoesthroughonelessoscillationwithin the cell This has the same effect on the interference pattern as when the movable mirror is moved towardthebeam splitterby1 2wavelength Asinglefringetransitionwillhaveoccurred Originally there are Ni 2d li wavelengths of light within the cell counting both passes of the laser beam At the final pressure there are Nf 2d lf wavelengths within the cell The dif...

Страница 19: ...2 Placetherotatingtablebetweenthebeam splitter andmovablemirror perpendiculartotheopticalpath NOTE if the movable mirror is too far forward the rotating table won t fit You may need to loosen the thumbscrew and slide the mirror farther back 3 Mounttheglassplateonthemagneticbackingoftherotationalpointer 4 Position the pointer so that its 0 edge on the Vernier scale is lined up with the zero on the ...

Страница 20: ...e index of refraction of air see Experiment 2 ng the index of refraction of the glass plate as yet unknown l0 the wavelength of your light source in vacuum and N the number of fringetransitionsthatyoucounted Carryingoutthisanalysisfortheglassplateisrathercomplicated sowe llleaveyouwiththeequation shownbelowforcalculatingtheindexofrefractionbasedonyourmeasurements Nevertheless we encourageyoutoatte...

Страница 21: ...acticedueto opticalimperfections Thenremovetheviewing screenandreplacethelaserwiththespectrallight source Iffringesaren tvisiblewhenlookingintothe beam splitter proceedasfollows a Tape two thin pieces of wire or thread to the surface of the diffuser to form cross hairs b Place the diffuser between the light source and the beam splitter c Adjust the angle of the beam splitter so that when look ing ...

Страница 22: ...te the Micrometer Knob fully IN before storing the Interferometer MicrometerCalibration The micrometer is calibrated before it is shipped How ever ifrecalibrationbecomesnecessary usethefollowing procedure 1 Turn the interferometer over and remove the bot tom cover 2 Loosen the two screws showninFigureA1 Slide thebearingsurfacetoward the pivot to increase mir ror movement per turn of themicrometerd...

Страница 23: ...3 03956 MovableMirror 003 03955 ComponentHolder 003 05161 Compensator 003 03958 InterferometerManual 012 05187 VacuumPump OS 8502 Component Part No VacuumCell 003 05162 RotationalPointer 003 05160 FittedCase 650 05178 ViewingScreen 003 05119 Diffuser 003 03941 Polarizer 003 04924 GlassPlate 003 04034 Lens 18mm FL 003 03814 Lens 48mm FL 003 03806 ...

Страница 24: ... Limitingfactorsareplayinthesystemanduncertainty inourmicrometerposition 6 Losingcountoffringes andinexactpositioningofthe fringes relative to our reference mark 7 In order to interfere the two light beams must have the samepolarization Part I General Dm wavelength Michelson 1 60 x 10 5 640 0 x 10 9 1 60 x 10 5 640 0 x 10 9 1 60 x 10 5 640 0 x 10 9 Fabry Perot 1 60 x 10 5 640 0 x 10 9 1 50 x 10 5 ...

Страница 25: ...he vacuum first then count the fringes as the vacuum was released The average slope starting at a guage reading of 60 was 3 462x10 6 0 9995 0 9996 0 9997 0 9998 0 9999 1 1 0001 1 0002 1 0003 1 0004 1 0005 0 10 20 30 40 50 60 70 80 90 Pressure cm hg Answers to Questions 1 Extrapolatingfromourslopeandtheknownindexof refraction of vacuum natm 1 000263 2 Measure the index of refraction at various pres...

Страница 26: ...ndrews Prentice Hall 1960 is Thesecondtermisnegligibleforvisiblewavelengths and may be ignored Notes General It is often difficult to count large numbers of fringes due to eyestrain If you find this to be the case you may want to make a circuit such as this 741 5 15 v 56k 2 0k 1 0k 1k 1k 1 k The phototransistor should be mounted in a plate of sheet steel which can then be held in the magnetic view...

Страница 27: ... com web www pasco com Contacting Technical Support Before you call the PASCO Technical Support staff it wouldbehelpfultopreparethefollowinginformation If your problem is with the PASCO apparatus note Titleandmodelnumber usuallylistedonthe label Approximateageofapparatus Adetaileddescriptionoftheproblem sequenceof events in case you can t call PASCO right away you won tlosevaluabledata If possible...

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