THORLABS EDU-MINT1 User Manual
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THORLABS EDU-MINT1 User Manual

THORLABS EDU-MINT1 User Manual

Michelson interferometer kit
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EDU-MINT1
EDU-MINT1/M
Michelson Interferometer Kit
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  • Page 1 EDU-MINT1 EDU-MINT1/M Michelson Interferometer Kit User Guide...

  • Page 2: Table Of Contents

    Michelson Interferometer Table of Contents     Warning Symbol Definitions ..........1     Safety ................. 2     Brief Description ............... 3     Kit Components ..............4   Basic Components of the Interferometer ......  4     Components to Observe the 2  Interferometer Output ..  6     Components for the Refractive Index Measurement  ..  6    ...
  • Page 3   Modern Michelson Interferometry – LIGO ....48     Troubleshooting ............. 49     Appendix ................. 51     Regulatory ............... 53   Waste Treatment is Your Own Responsibility .... 53    Ecological Background .......... 53      Thorlabs Worldwide Contacts ........54 MTN006503-D02 Rev A, October 29 2015...

  • Page 4: Warning Symbol Definitions

    Michelson Interferometer Chapter 1: Warning Symbol Definitions Warning Symbol Definitions Below is a list of warning symbols you may encounter in this manual or on your device. Symbol Description Direct Current Alternating Current Both Direct and Alternating Current Earth Ground Terminal Protective Conductor Terminal Frame or Chassis Terminal Equipotentiality...

  • Page 5: Safety

    Michelson Interferometer Chapter 2: Safety Safety WARNING The laser module is a class 2 laser, which does not require any protective eyewear. However, to avoid injury, do not look directly into the laser beam. DO NOT STARE INTO BEAM CLASS 2 LASER PRODUCT Page 2 MTN006503-D02 Rev A, June 15, 2016...

  • Page 6: Brief Description

    Michelson Interferometer Chapter 3: Brief Description Brief Description The objective of this experiment package is to become familiar with the interferometer as a highly sensitive measuring instrument. Since the applications in technology and industry are extremely diverse, this package includes various experiments for different aspects of physics.

  • Page 7: Kit Components

    Michelson Interferometer Chapter 4: Kit Components Kit Components In cases where the metric and imperial kits contain parts with different item numbers, metric part numbers and measurements are indicated by parentheses unless otherwise noted. Basic Components of the Interferometer 1 x CPS532-C2 Collimated Laser Diode 1 x RDF1 1 x B1218FE (B3045AE)
  • Page 8 Michelson Interferometer Chapter 4: Kit Components 2 x BA2(/M) Base, 1 x LMR1(/M) 1 x EDU-VS1(/M) 2" x 3" x 3/8" Ø1" Lens Mount Plastic Viewing Screen (50 mm x 75 mm x 10 mm) 1 x LB1471 N-BK7 Bi-Convex Lens, 4 x UPH1.5 (UPH30/M) Ø1", f = 50.0 mm, Uncoated 1 x CM1-BS013...

  • Page 9: Components To Observe The 2

    Michelson Interferometer Chapter 4: Kit Components Components to Observe the 2 Interferometer Output 1 x EBS1 Ø1" Economy 1 x TR1.5 (TR40/M) 1 x LMR1(/M) Beamsplitter Ø1/2" (Ø12.7 mm) Post, Ø1" Lens Mount 1.5" (40 mm) Long Components for the Refractive Index Measurement 1 x FP01 1 x PR01(/M) General Purpose Plate...

  • Page 10: Components For The Interference With Leds

    Michelson Interferometer Chapter 4: Kit Components Components for the Interference with LEDs 2 x LEDMF 2 x LED631E 2 x LEDWE-15 LED Mount (with USB Connector) (with USB Connector) 635 nm, 4 mW, White light LED, Half FWHM 10 nm, 150 Ω Viewing Angle 7.5°, 91 Ω...

  • Page 11: Components For The Thermal Expansion Setup

    Michelson Interferometer Chapter 4: Kit Components Components for the Thermal Expansion Setup 1 x ME1-G01 Ø1" Aluminum Mirror 1 x Aluminum Post 1 x MH25 Ø12.7 mm, 90 mm Long, Mirror Holder for Ø1" Thread for MH25 Optics 2.5 - 6.1 mm Thick 1 x RA90(/M) Right-Angle Post Clamp, 1 x TR2 (TR50/M)
  • Page 12 Michelson Interferometer Chapter 4: Kit Components Imperial Kit Type Quantity Type Quantity 1/4"-20 x 1/4" Cap Screw 1/4"-20 Washer 1/4"-20 x 3/8" Cap Screw 8-32 x 1/4" Cap Screw 1/4"-20 x 1/2" Cap Screw 8-32 x 3/8" Cap Screw 1/4"-20 x 5/8" Cap Screw 8-32 x 5/8"...

  • Page 13: Setup And Adjustment

    Michelson Interferometer Chapter 5: Setup and Adjustment Setup and Adjustment This chapter discusses how to assemble the various components and explains how to set up and adjust the interferometer. Assembly of the Components First screw the four rubber feet to the four holes in the bottom of the breadboard using the 1/4"-20 x 1/2"...
  • Page 14 Michelson Interferometer Chapter 5: Setup and Adjustment The mirror is locked in place using the nylon-tipped setscrew. Now you need to assemble the laser, beamsplitter and movable mirror as additional components of the setup. Laser Beamsplitter Movable Mirror Components: Components: Components: Laser Beamsplitter Cube...
  • Page 15 Michelson Interferometer Chapter 5: Setup and Adjustment The elements installed so far are the basic components of the interferometer. The next set of components will be used with the interferometer in the various experiments explained in this manual. Ø1" Beamsplitter: To assemble the second beamsplitter, remove the retaining ring from the LMR1(/M) mount, place the beamsplitter in the mount and attach the retaining ring.
  • Page 16 Michelson Interferometer Chapter 5: Setup and Adjustment Thermal Expansion: Finally, assemble the setup for the thermal expansion experiment. Screw the BA1S(/M) base onto the post holder with a 1/4"-20 x 3/8" (M6 x 10 mm) cap screw. Place the 2" (50 mm) post into the post holder facing upside down.

  • Page 17: Setting Up And Adjusting The Michelson Interferometer14

    Michelson Interferometer Chapter 5: Setup and Adjustment Setting Up and Adjusting the Michelson Interferometer In the Michelson interferometer, a laser beam is split by a 50:50 beamsplitter; the split beams are then reflected back by mirrors and recombined at the beamsplitter. A screen at the output of the interferometer shows an interference pattern.
  • Page 18 Michelson Interferometer Chapter 5: Setup and Adjustment Placing the Beamsplitter Laser spots with misaligned (left) and aligned (right) beamsplitter Next, install the second mirror. One should ensure that the distance between the beamsplitter and the mirrors is about the same along both interferometer arms. Page 15 MTN006503-D02 Rev A, June 15, 2016...
  • Page 19 Michelson Interferometer Chapter 5: Setup and Adjustment Placement of the Second Mirror You should now see the two partial beams as bright spots on the screen. Tip and tilt the second mirror until they overlap. Finally, place the lens between the laser and the beamsplitter. You may already see interference rings.
  • Page 20 Michelson Interferometer Chapter 5: Setup and Adjustment Placement of the Lens to Observe Concentric Circles Depending on the orientation of the lens, stripes are visible instead of rings, as shown in Figure 7. A stripe pattern is produced by placing the lens behind the beamsplitter and moving the screen away from the breadboard, see Figure 6.
  • Page 21 Michelson Interferometer Chapter 5: Setup and Adjustment Alternative Placement of the Lens to Observe Lines Interference Pattern Produced by the Lens Position shown in Figure 6 Page 18 MTN006503-D02 Rev A, June 15, 2016...

  • Page 22: Theoretical Background

    Michelson Interferometer Chapter 6: Theoretical Background Theoretical Background This chapter discusses the essential theoretical foundations that apply to the experiments which follow. The chapter begins with a brief discussion of interference in general and an explanation of the form of the interference pattern. Coherence is discussed next since one experiment involves interference with LEDs.
  • Page 23 Michelson Interferometer Chapter 6: Theoretical Background Here is the phase, the value of which is established by the actual optical path. The factor √ ⋅ is therefore explained because the beam in path 1 is first transmitted and then reflected. The description of the beam in path 2 is similar, but the beam is first reflected and then transmitted.
  • Page 24 Michelson Interferometer Chapter 6: Theoretical Background Normalized intensity distribution on the screen depending on the path length difference To understand this, one has to look Cement at the phase shifts on a beamsplitter. Coating The cube beamsplitter is composed of two prisms cemented together with a beamsplitter coating applied to the hypotenuse of one of the prisms, as shown in the sketch to the...
  • Page 25 Michelson Interferometer Chapter 6: Theoretical Background Size and Shape of the Pattern We have now clarified what the interference pattern of a plane wave and/or at the central point looks like. Naturally the real interference pattern appears different than that of a plane wave, since the laser diverges on its way to the screen.

  • Page 26: Determining The Wavelength

    Michelson Interferometer Chapter 6: Theoretical Background adjust the interferometer. In order to find a configuration with nearly identical arm lengths, the central maximum needs to be as large as possible. A nice way to visualize the ring pattern is to overlap two wavefronts. In practice, we do not have a plane wave but (due to the laser’s divergence) a spherical wave.

  • Page 27: Coherence

    Michelson Interferometer Chapter 6: Theoretical Background Coherence The topic of coherence is highly complex. Terms such as the contrast of an interference pattern, correlation functions and the Wiener-Chintschin theorem are essential for a deeper understanding. Therefore only a brief abstract can be provided here, limited to the descriptive values of coherence time and coherence length Coherence in the largest sense describes the capacity of light to create interference.
  • Page 28 Michelson Interferometer Chapter 6: Theoretical Background Linked to the coherence time, the coherence length is Δ . This is the path the light can travel within the coherence time, that is: Δ ⋅ Δ (11) Here the propagation in air was assumed with the refractive index 1. While coherence is a complex topic, the coherence length in case of an interferometer is more straightforward –...
  • Page 29 Michelson Interferometer Chapter 6: Theoretical Background Interferometer with (a) plate beamsplitter and (b) compensator plate (refraction on the surface was disregarded in this sketch) First let us examine Figure 14(a). Here the laser is reflected off of the beamsplitter when it is inside of the glass substrate, then reflected by the mirror, and finally transmitted through the beamsplitter, therefore propagating through the glass substrate thrice on its way to the screen.
  • Page 30 Michelson Interferometer Chapter 6: Theoretical Background A beamsplitter cube is used in this setup instead of the combination of plate beamsplitter and compensator plate, since there is little price difference between the two versions but adjustment with the cube is significantly simpler and more reliable. Selecting the Mirrors The surface flatness of the mirrors used in this kit are specified as better than /10, compared to economy mirrors which have a surface flatness of 5 .

  • Page 31: Interferometric Determination Of The Refractive Index

    Michelson Interferometer Chapter 6: Theoretical Background Interferometric Determination of the Refractive Index Determining the refractive index of a solid (transparent if possible) is one application where a Michelson interferometer can be used as a sensitive measuring instrument. Here the solid is first placed in one arm of the interferometer. Then it is slowly rotated so that the optical path in this interferometer arm changes.

  • Page 32: Determining A Thermal Expansion Coefficient

    Michelson Interferometer Chapter 6: Theoretical Background ΔOptical Path 2 ⋅ Δ 1 ⋅ Δ 2 ⋅ (18) The factor of 2 appears in the equation because the light passes along the path twice. The path length difference is derived from the light-dark transitions via ⋅...

  • Page 33: Using The Interferometer As A Spectrometer

    Michelson Interferometer Chapter 6: Theoretical Background where the factor ½ is once again due to the path of the laser to and from the mirror that was shifted. Using the Interferometer as a Spectrometer A very elegant application of an interferometer is to use it as a spectrometer. Assume the light source emits two different wavelengths.
  • Page 34 Michelson Interferometer Chapter 6: Theoretical Background ⋅ Δ (29) 2 Δ 2 Δ The term Δ which results in the statement is neglectably small in comparison to (30) Δs 4 Δλ Equation (30) states that the contrast of the interference pattern will be worst when the two interferometer arms differ by 2 1 / 4 Δλ...

  • Page 35: Experiments And Examples

    Michelson Interferometer Chapter 7: Experiments and Examples Experiments and Examples This chapter discusses the various experiments that can be performed with this experiment package. Numerical examples that can be expected under realistic conditions are provided as well. Preliminary Tests Assemble the Michelson interferometer if you have not already done so. Experiment 1: Change the length of an interferometer arm by moving a mirror (the one in the kinematic holder).
  • Page 36 Michelson Interferometer Chapter 7: Experiments and Examples Note: Observing the pattern on the beamsplitter requires a dark room with very little stray light. Finally, place the second beamsplitter (use one of the post holders from the LED assembly) between the cube beamsplitter and the lens. This allows the two outputs to be observed on the same screen.

  • Page 37: Determining The Laser Wavelength

    Michelson Interferometer Chapter 7: Experiments and Examples Determining the Laser Wavelength One typical application of an interferometer is to determine the wavelength of the incident light. This measurement is performed through controlled shifting of one mirror, which causes a change in the interference pattern. Depending on the direction the mirror is moved relative to the second mirror, the concentric circles either expand out from the center (with new ones constantly appearing in the center) or they shrink into the center (where they disappear).

  • Page 38: Using The Interferometer As A Spectrometer

    This is consistent with the specifications of the laser diode. Here is an example of a typical spectrum (taken from www.thorlabs.com). For a more precise measurement, we recommend using piezo crystals, see Chapter 10: Ideas for Additional Experiments.

  • Page 39: Interference With Leds, Coherence

    Michelson Interferometer Chapter 7: Experiments and Examples 20°C 25°C 30°C Wavelength (nm) 531.70 531.90 532.10 532.30 532.50 532.70 The temperature is the temperature of the housing which will be different from the room temperature. Also, please note that the derivation of Equation (32) assumes two spectral components of equal intensity.
  • Page 40 Michelson Interferometer Chapter 7: Experiments and Examples the preliminary adjustment with the laser was not accurate enough. In this case repeat the alignment process with the laser. Tip: Do not turn the screw too quickly and, when changing your grip, wait briefly to see if an interference pattern develops (~1/2 second) –...
  • Page 41 Michelson Interferometer Chapter 7: Experiments and Examples pattern has decreased significantly. The path length difference between the mirrors corresponds to half the coherence length. Sample result: The result of a test measurement was approximately 25 µm. Examining the spectrum in the datasheet for the LED (see Figure 19) one can read the spectral width at half the maximum intensity (FWHM) to be approximately 20 nm.

  • Page 42: Refractive Index Determination

    Michelson Interferometer Chapter 7: Experiments and Examples Refractive Index Determination In this experiment, we use the interferometer to determine the refractive index of Plexiglas. The theoretical basis for this has already been discussed in Chapter 6. A rotation of the Plexiglas plate in the beam lengthens the optical path and leads to a change in the interference pattern.
  • Page 43 Michelson Interferometer Chapter 7: Experiments and Examples The micrometer drive and locking setscrew on the rotation platform. When the setscrew is locked, the fine adjustment is engaged. The stage is then rotated by turning the micrometer drive. First, loosen the set screw and turn the fine-thread screw as far as possible. Now the correct starting point for the measurement still has to be found, i.e.

  • Page 44: Thermal Expansion Coefficient

    Michelson Interferometer Chapter 7: Experiments and Examples Aligned Lines: 182° 20’ Sample result: The following values were determined by students in practical tests. The reference value for the refractive index of the Plexiglas plate that was used is 1.49. Number of Rotation Plate Thickness According to...
  • Page 45 Michelson Interferometer Chapter 7: Experiments and Examples Experiment 15: Start a controlled heating of the post by applying an external voltage to the heater. Count the number of transitions during expansion and make note of the respective temperature. Derive the expansion coefficient of Aluminum. Execution: Apply an external voltage to the two outer contacts of the heater by using the supplied crocodile clip to banana plug cables and your power supply of choice (up to 12 V with 2 A...
  • Page 46 Michelson Interferometer Chapter 7: Experiments and Examples Sample result: The following values were determined by students in practical tests. # of fringes Temperature Temperature Calculated in the Total # of Voltage Start length [°C] [°C] [°C] -interval fringes [cm] 9.0004 9.0013 9.0031 9.0054...

  • Page 47: Experiment Overview

    Michelson Interferometer Chapter 8: Experiment Overview Experiment Overview Preliminary Tests and Determining the Laser Wavelength Set the Michelson interferometer up and adjust it. Change the length of an interferometer arm by moving the mirror (the one in the kinematic holder). What is the effect on the interference pattern? Light a match or lighter and put it right below the laser beam in one arm.
  • Page 48 Michelson Interferometer Chapter 8: Experiment Overview Thermal Expansion Coefficient 14. Remove the rotation platform from the setup and replace the moveable mirror with the setup to measure thermal expansion. Adjust the interference pattern again so that you can count the transitions easily. 15.

  • Page 49: Questions

    Michelson Interferometer Chapter 9: Questions Questions This list of questions also provides a starting point for topics that can be examined in relation to the Michelson interferometer (even beyond this experiment package).  What is the difference in the interference patterns when the arms are (a) of the same length and (b) of different lengths? ...

  • Page 50: Ideas For Additional Experiments

    Since piezo crystals are widespread in modern nano-positioning systems, their use offers a learning experience with broad applications. One possible setup using Thorlabs components could comprise a kinematic holder with support arm (KM100PM(/M), PM3(/M)), a mirror (e.g., ME1S-G01), a Piezo stack (such as AE0203D08) and a KPZ101 Controller.

  • Page 51: Modern Michelson Interferometry - Ligo

    Michelson Interferometer Chapter 11: Modern Michelson Interferometry – LIGO Modern Michelson Interferometry – LIGO A recent application of the Michelson interferometer that attracted a lot of international attention is gravitational-wave detection. Gravitational waves are oscillations in spacetime curvature produced by colliding black holes, neutron stars, and other astrophysical processes that involve a dense concentration of mass-energy moving at relativistic speeds.

  • Page 52: Troubleshooting

    Michelson Interferometer Chapter 12: Troubleshooting Troubleshooting  The laser spots superpose, but there is no interference. Check whether all of the components have been positioned as precisely as possible (Is there a 90° beam angle after reflection? Is the height of the beam above the plate at the screen the same as it is directly at the laser?).
  • Page 53 Michelson Interferometer Chapter 12: Troubleshooting proceed with fine-tuning using the red LED and the moveable mirror. When the LED is in the setup, the mirror has to be shifted until interference can be observed. If no interference can be observed along the entire translation path of the mirror, the preliminary adjustment has to be repeated and if possible refined.

  • Page 54: Appendix

    Michelson Interferometer Chapter 13: Appendix Appendix Determining the refractive index was discussed in Section 6.4. Here the calculation that leads to equation (20) is presented in detail. The content discussed in Chapter 6 on the physical and optical path is presumed to be known here. Screen Screen Screen...
  • Page 55 Michelson Interferometer Chapter 13: Appendix We now have almost everything we need for equation (20). First we want to point our Snell’s law of refraction, according to which 1 ⋅ sin ⋅ sin (39) applies, where we assumed the refractive index of air with a good approximation of 1. For a subsequent calculation step, one still needs (40) cos arcsin...

  • Page 56: Regulatory

    Waste Treatment is Your Own Responsibility If you do not return an “end of life” unit to Thorlabs, you must hand it to a company specialized in waste recovery. Do not dispose of the unit in a litter bin or at a public waste disposal site.

  • Page 57: Thorlabs Worldwide Contacts

    Michelson Interferometer Chapter 15: Thorlabs Worldwide Contacts Thorlabs Worldwide Contacts USA, Canada, and South America UK and Ireland Thorlabs, Inc. Thorlabs Ltd. 56 Sparta Avenue 1 Saint Thomas Place, Ely Newton, NJ 07860 Cambridgeshire CB7 4EX Great Britain Tel: 973-300-3000...
  • Page 59 www.thorlabs.com...

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