Project 1 (30%)

Setting Up A Simple DIY Michelson Interferometer

⚠️ IMPORTANT

• Use only the provided LASER.
  Do not substitute any other LASER for this experiment.
• Never look directly into the laser beam or its reflections.
  Even a low-power (Class 2) laser can cause eye damage.

Quick Summary

1. This activity contributes 👤 10% (individual) and 👥 20% (group) towards your grade.
2. Follow the instructions and, as a group, set up the interferometer during Week 7 and Week 8.
3. Book a 1-hour group viva slot in Week 9 using the this Google Sheet.

Deliverable: A working interferometer that can detect and respond to tiny vibrations or distortions of the table.

Source of Inspiration

This activity is adapted from the San Franciso Exploratorium’s Science Snack “Simple Interferometer”.

Figure 1: A possible setup for the Michaelson Interferometer. (Image from the Exploratorium)

Instructions

What You Have to Do

You need to set up the ‘DIY’ Michelson Interferometer we discussed in class (see also the notes).

Once aligned correctly, the interference pattern will become sensitive enough to detect even tiny distortions of the solid table such as those caused by gently pressing on its surface with your fingertips.

This experiment may look deceptively simple, but it is very (very) challenging to set up.

• Be prepared to spend time on trial and error and careful adjustments.
  
• Work iteratively: make small changes, test, and gradually refine the alignment.

Figure 2: A possible setup for the Michaelson Interferometer. (Image from the Exploratorium)

Consultation & Assistance: Note also that we will not have any more lectures or IS sessions. Instead, these time slots will now be protected periods for you to work on the 76 Projects. During these times, the instructors will be available in the Dry Lab for consultations and to provide help with your projects.

Safety

Working with lasers and dimmed lighting requires extra care. Please follow these guidelines at all times:

• Never look directly into the laser beam or its reflections.
  Even a low-power (Class 2) laser can cause eye damage.

• Do not bend down in front of the setup while the laser is active.
  The beam may be at head height and can enter your eyes unexpectedly.

• Take extra caution when working in the dark.
  Move slowly and deliberately; avoid rushing or making sudden adjustments.

• Be mindful of reflective objects.
  Watches, jewellery, and phones can accidentally redirect the beam—keep them away from the optical path.

• Wear covered shoes.
  This protects your feet from tripping hazards and any dropped equipment.

Tips

Understand what is going on

1. Look at the printed setup and draw a diagram showing how the light beam will traverse the multiple arms.
   
2. Write down the path difference relationship for the light arriving at the screen or lens.
3. Take note of the things that can impact the interference at the screen

Set things up

1. Do not place all components at once.
   
2. Instead, plan and discuss the order, then set up one component at a time, checking alignment after each step.
   
3. When the setup is correct, even a tiny disturbance (e.g., a light touch with a fingertip on the table) will shift the interference pattern. This is the level of sensitivity you can achieve.
   The adjoining video shows this movement when Ryan and I tested the setup.

Logistics and Such

Logistics

• You will be allocated a dedicated spot in the Dry Lab for Weeks 7, 8, and 9.
  
• You are free to work on this activity at any time during Weeks 7 and 8.
• Please be considerate and do not disturb or alter other groups’ setups.
  

Material Provided

1. Red class 2 LASER pointer.
2. Two pieces of silicon to use as mirrors
3. Coverslip to use as beam splitter
   • Please collect from Ryan.
   • These easily break and shatter. Please be careful!
4. Two wooden block
5. A converging lens.
6. An A3 layout guide.
7. Binder clips, Blu Tack.

Gotchas

1. A key challenge is to align the mirrors so that the light reflects at 90°. In other words, the laser beam should return in its original direction, along the same path.
   • Use a piece of paper placed ‘behind’ to see where the reflected beam is going.
2. Remember that you are working in 3D.
   • A misaligned mirror or slide can reflect the beam at odd angles, even though the law of reflection (angle in = angle out) is still satisfied.
     
   • Small sideways or vertical tilts can make a big difference, so adjust carefully.
     
3. Be aware that this system can produce many different interference patterns.
   • Not every pattern you see will be the one you are looking for. How can you check if it is due to the beams from both arms?
     
   • Part of the challenge is learning to recognise and stabilise the relevant fringes.
     
4. Many laser pointers have shiny surfaces that reflect stray light and disrupt the interference pattern. Cover these shiny areas (e.g., with tape or paper) to reduce unwanted reflections and improve your results.

Grading Rubric

Quality of the Interferometer(10%, 👥)

Note:

1. You must have a working interferometer setup ready to demonstrate at the start of your viva session. Please ensure it is fully aligned and functioning before the graders arrive.
2. You must also maintain a group logbook that documents your work together. This logbook should record the date and time of each session, note which aspect of the experiment your group was working on, and include your plans for next steps. It should also capture observations made during the process, as well as any refinements you are considering or have implemented. The purpose of this logbook is to give graders a clear picture of how your group approached planning, troubleshooting, and improvements throughout the experiment.
3. The following carries 50% of the group score which is equivalent to 10% of the course grade.

	Needs Improvement	Satisfactory	Good	Accomplished	Distinguished
Quality of the Interferometer	■ Setup is incomplete or poorly aligned ■ No clear interference pattern ■ Pattern looks incorrect or is the wrong pattern ■ No change when the table is tapped or disturbed	■ Rough alignment attempted ■ Pattern is faint, jumpy, or unclear ■ Setup barely works ■ Pattern responds only slightly when the table is moved	■ Pattern is visible but shaky or unstable ■ Setup mostly works ■ Some success in alignment ■ Pattern reacts a little to table movement	■ Pattern is clear and stable ■ Setup is well aligned and works reliably ■ Pattern shifts clearly when the table is disturbed	■ Excellent interference pattern ■ Precisely aligned and optimised ■ Pattern is highly sensitive to distortion of the table.
Logbook Use	■ Few or no entries ■ No evidence of planning ■ Problems and fixes not recorded ■ Entries are illegible or indecipherable	■ Basic notes present ■ Some mention of what was planned or attempted ■ Limited record of problems and outcomes	■ Regular entries ■ Records planned steps and actual attempts ■ Notes what worked and what didn’t	■ Consistent, well-structured entries ■ Clearly documents planned actions, attempted fixes, and results ■ Shows awareness of cause–effect in troubleshooting	■ Detailed and organised log ■ Thorough record of planned steps, attempts, and results ■ Highlights patterns in what worked/didn’t ■ Demonstrates reflective insight into planning and troubleshooting

Table 1: Rubrics for the interferometer setup for Project 1

Understanding, Troubleshooting and Communication (👤 10%, 👥 10%)

Note: The following criteria will be used for both the group and individual assessment at the viva.

Criterion (Weight)	Needs Improvement	Satisfactory	Good	Accomplished	Distinguished
Iterative Problem-Solving & Troubleshooting Skills (30%)	■ Passive or unreactive when problems arise ■ Fails to identify key issues ■ No evidence of refinement ■ Depends entirely on others	■ Recognises issues but responds inconsistently ■ Suggests superficial fixes ■ Trial-and-error without learning ■ Needs prompting to adjust setup	■ Identifies and responds to problems ■ Contributes to adjustments ■ Shows basic understanding of cause and effect	■ Diagnoses and resolves issues thoughtfully ■ Uses observations or feedback to guide refinement ■ Acts independently when improving setup	■ Anticipates and addresses problems proactively ■ Strategically applies theory in troubleshooting ■ Demonstrates purposeful, effective iteration
Scientific Understanding & Application (30%)	■ Misunderstands key concepts ■ Explanations are vague or incorrect ■ Cannot relate theory to experiment	■ Understands terms but struggles to apply them ■ Explanations are shallow or incomplete ■ Some conceptual confusion	■ Understands core concepts ■ Explains theory in own words ■ Connects theory to experiment with minor gaps	■ Applies theory clearly and appropriately ■ Explains how concepts influence design and outcomes ■ Identifies assumptions or limitations	■ Demonstrates deep understanding ■ Explains abstract ideas with clarity and accuracy ■ Connects theory beyond immediate context
Communication & Reasoning (30%)	■ Difficult to follow ■ Disorganised or unsupported ideas ■ Avoids questions or gives unclear responses	■ Communicates basic points ■ Reasoning is inconsistent or shallow ■ Needs prompting to clarify	■ Generally clear and structured ■ Reasoning mostly sound ■ Responds to most questions with some confidence	■ Communicates confidently and clearly ■ Uses appropriate terminology and logic ■ Offers well-reasoned responses	■ Highly articulate and insightful ■ Explains complex ideas with clarity ■ Uses analogies or examples to support understanding
Collaboration & Contribution (10%)	■ Minimal participation ■ Withdraws or dominates ■ Individual role unclear or absent	■ Participates occasionally ■ Relies heavily on others ■ Offers limited input	■ Actively engaged ■ Contributes ideas and supports peers ■ Clear individual role visible	■ Balances collaboration and individual input ■ Encourages group engagement ■ Demonstrates initiative	■ Enhances team performance ■ Integrates insight with team effort ■ Models effective and inclusive leadership

Table 2: Rubrics for the viva for Project 1