Includes Teacher's Notes and Typical Experiment Results Instruction Manual and Experiment Guide for the PASCO scientific Models OS-9255A thru OS-9258A 012-07137A 5/99 PRECISION INTERFEROMETER © 1990 PASCO scientific $10.
012-07137A Precision Interferometer Table of Contents Section Page Copyright, Warranty, and Equipment Return ................................................... ii Introduction ...................................................................................................... 1 Equipment ........................................................................................................ 2 Theory of Operation .........................................................................................
Precision Interferometer 012-07137A Copyright, Warranty, and Equipment Return PleaseFeel free to duplicate this manual subject to the copyright restrictions below. Copyright Notice Equipment Return The PASCO scientific 012-05187C Precision Interferometer manual is copyrighted and all rights reserved.
012-07137A Precision Interferometer Introduction The OS-9255A Precision Interferometer provides both a theoretical and a practical introduction to interferometry. Precise measurements can be made in three modes: Michelson The Michelson Interferometer is historically important, and also provides a simple interferometric configuration for introducing basic principles. Students can measure the wavelength of light and the indices of refraction of air and other substances.
Precision Interferometer 012-07137A 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 Recommended – The OS-9256A Interferometer Accessories includes: Rotating Pointer Vacuum Cell Component Holder Lens, 18 mm Focal Length Lens, 48 mm Foc
012-07137A Precision Interferometer Adjustable Mirror Lens 18 mm Fitted Case Viewing Screen Beam Splitter (2) Component Holder Diffuser Movable Mirror Compensator Plate OS-9255A Precision Interferometer Lens 18 mm Component Holder Base Lens 48 mm OS-9256A Interferometer Accessories (2) Polarizer Glass Plate Rotating Pointer Vacuum Pump with Gauge Vacuum Cell 3
Precision Interferometer 012-07137A Theory of Operation Interference Theory The Michelson Interferometer A beam of light can be modeled as a wave of oscillating electric and magnetic fields. When two or more beams of light meet in space, these fields add according to the principle of superposition. That is, at each point in space, the electric and magnetic fields are determined as the vector sum of the fields of the separate beams. In 1881, 78 years after Young introduced his two-slit experiment, A.A.
012-07137A Precision Interferometer In this way the original beam of light is split, and portions of the resulting beams are brought back together. Since the beams are from the same source, their phases are highly correlated. When a lens is placed between the laser source and the Figure 2. Fringes beam-splitter, the light ray spreads out, and an interference pattern of dark and bright rings, or fringes, is seen on the viewing screen (Figure 2).
Precision Interferometer 012-07137A The Fabry-Perot Interferometer In the Fabry-Perot Interferometer, two partial mirrors are aligned parallel to one another, forming a reflective cavity. Figure 4 shows two rays of light entering such a cavity and reflecting back and forth inside. At each reflection, part of the beam is transmitted, splitting each incident ray into a series of rays.
012-07137A Precision Interferometer Component holder Laser beam Interferometer base VIEWING SCREEN MICHELSON, TWYMAN-GREEN VIEWING SCREEN MICHELSON, TWYMAN-GREEN PRECISION INTERFEROME C O M MP IC E H NS EL A SO TO N R ER TT N LI O SP ELS AM ICH BE M Component holder Beam splitter ➤ NOTE: For ease of installation the placement of the individual components in the various modes is indicated on the label. Michelson Mode 1. Align the laser and interferometer base as previously described.
Precision Interferometer 012-07137A Twyman-Green Mode Fabry-Perot Mode 1. Set up the interferometer in the Michelson mode, as 1. Align the laser and interferometer base as described in 3. Remove the original lens (L1) from in front of the laser. Observe the two sets of dots on the viewing screen one set from the movable mirror and one set from the adjustable mirror. Adjust the position of L2 until both sets of dots are the same size. 4.
012-07137A Precision Interferometer Tips on Using the Interferometer Accurate Fringe-Counting The following techniques can help you make accurate measurements. 1. It's not necessary that your interference pattern be perfectly symmetrical or sharp. As long as you can clearly distinguish the maxima and minima, you can make accurate measurements. 2. It's easy to lose track when counting fringes. The following technique can help.
Precision Interferometer Sources of Experimental Error Backlash Although PASCO's carefully designed mirror movement reduces backlash considerably, every mechanical system is susceptible to backlash. However, the effects of backlash can be practically eliminated by using proper technique when counting fringes (see item 3 under Accurate Fringe-Counting, on the previous page). Mirror Travel The amount of mirror movement per dial turn of the micrometer is constant to within 1.5%.
012-07137A Precision Interferometer Experiment 1: Introduction to Interferometry EQUIPMENT NEEDED: Basic Interferometer (OS-9255A) Laser (OS-9171) Laser Alignment Bench (OS-9172) Interferometer Accessories (OS-9256A) Component Holder , (2) Calibrated Polarizers Lens 18mm FL Component holder VIEWING SCREEN MICHELSON, TWYMAN-GREEN PRECISION INTERFEROMETER OS-9255A Viewing screen Procedure C O M MP IC E H NS EL A SO TO N R Adjustment Thumbscrews 30 25 15 5 10 ADJUSTABLE MIRROR MICHELS
Precision Interferometer 6. Record dm, the distance that the movable mirror moved toward the beam-splitter according to your readings of the micrometer knob. Remember, each small division on the micrometer knob corresponds to one µm (10-6 meters) of mirror movement. 7. Record N, the number of fringe transitions that you counted. 8. Repeat steps 3 through 7 several times, recording your results each time. 9. Go on to part two.
012-07137A Precision Interferometer Experiment 2: The Index of Refraction of Air For light of a specific frequency, the wavelength l varies according to the formula: 0 0 Gas Pressure (cm Hg) Figure 2.1.
Precision Interferometer 012-07137A 4. Be sure that the air in the vacuum cell is at atmospheric pressure. If you are using the OS-8502 HandHeld Vacuum Pump, this is accomplished by flipping the vacuum release toggle switch. 5. Record Pi, the initial reading on the vacuum pump gauge. Slowly pump out the air in the vacuum cell. As you do this, count N, the number of fringe transitions that occur. When you're done, record N and also Pf, the final reading on the vacuum gauge.
012-07137A Precision Interferometer Experiment 3: The Index of Refraction of Glass EQUIPMENT NEEDED: Basic Interferometer (OS-9255A) Laser (OS-9171) Laser Alignment Bench (OS-9172) Interferometer Accessories Rotating Table, Glass Plate C O M MP IC E H NS EL A SO TO N R R TE N LIT O SP ELS AM ICH BE M 30 25 15 5 10 ADJUSTABLE MIRROR MICHELSON, TWYMAN-GREEN 0 Rotational pointer -5 In Experiment 2, the index of refraction of air was measured by slowly varying the density of air along a f
Precision Interferometer 012-07137A Data Analysis In principle, the method for calculating the index of refraction is relatively simple. The light passes through a greater length of glass as the plate is rotated. The general steps for measuring the index of refraction in such a case is as follows: 1. Determine the change in the path length of the light beam as the glass plate is rotated. Determine how much of the change in path length is through glass, dg(q), and how much is through air, da(q). 2.
012-07137A Precision Interferometer Suggestions for Additional Experiments Twyman-Green Twyman-Green operation gives students a quick, qualitative look at how interferometry can be used to test optical components. See Twyman-Green Mode in the Setup and Operation section of the manual. Any distortion of the circular fringe pattern is due to spherical aberration from the test lens. Turn the lens until it sits at various angles to the optical path and watch the fringe pattern change.
Precision Interferometer 012-07137A ä IMPORTANT The Vacuum Cell is not designed to be heated. Index of Refraction for Gases Measure the indices of refraction for various gases. Caution: The PASCO Vacuum Chamber is NOT designed to hold positive pressures. You will need to provide your own gas chamber. Fabry-Perot Spectroscopy The Fabry-Perot mode is customarily used as a highresolution spectrometer.
012-07137A Precision Interferometer Replacement Parts Component Part No. Component Part No.
Precision Interferometer 012-07137A Teacher's Guide Experiment 1: Introduction to Interferometry Part I General Reference to Analysis (Part II) Dm Michelson Fabry-Perot wavelength 5 9 1.60 x 10 1.60 x 105 1.60 x 105 640.0 x 10 640.0 x 109 640.0 x 109 1.60 x 105 1.50 x 105 1.55 x 105 640.0 x 109 600.0 x 109 620.0 x 109 average: actual: % diff. 630.0 x 109 ±16.7 x 109 632.8 x 109 0.44% Part II General 1.
012-07137A Precision Interferometer Experiment 2: The Index of Refraction of Air Reference to Procedure Answers to Questions 1. The chamber will be properly aligned when the reflec- 1. Extrapolating from our slope and the known index of tions off the front and back end-plates are aligned with each other and with the main interference pattern. (This alignment may actually cause a secondary interference pattern, but it will be very faint and will not affect your measurements.) 2.
Precision Interferometer 012-07137A Experiment 3: The Index of Refraction of Glass Reference to Procedure Notes General 1. The glass plate must be absolutely perpendicular to the 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: laser for accurate measurement of the index of refraction.
012-07137A Precision Interferometer Technical Support Feedback Contacting Technical Support If you have any comments about the product or manual, please let us know. If you have any suggestions on alternate experiments or find a problem in the manual, please tell us. PASCO appreciates any customer feedback. Your input helps us evaluate and improve our product.
