PHYS 331 A: Advanced Laboratory: Optics

Physics 331 - Advanced Laboratory: Optics

Experiments concerning optical instruments and optical phenomena: Lenses, microscopes/telescopes, Michelson and Fabry-Perot interferometry, high-resolution diffraction gratings, Fraunhofer and Fresnel diffraction, dispersion and Faraday rotation, reflection from a dielectric surface.

Instructor

David B. Pengra
Office: Physics/Astronomy Building, Room B256A
Phone: 206-543-4783
Email: dbpengra@uw.edu

Hours & Location

Lecture: Room A118, Physics/Astronomy Building, Thursday, 11;30-12:20

Labs: Room B260, Physics/Astronomy Building

Section AB – Tuesday, 1:30–4:20
Section AD – Thursday, 1:30–4:20
Section AE - Friday, 1:30–4:20

Required Reading/Viewing Material

Website

https://courses.washington.edu/phys331 (Standard URL links to Canvas page)

Text

Optics, 5th ed., Eugene Hecht (Pearson Education, 2017), required.

Overview

Physics 331 is a combined lab+lecture course which emphasizes the laboratory aspects.  The weekly lecture is focused on material needed to understand the experiments and does not provide a full theoretical treatment of the subject.  Students are expected to read about any additional concepts or derivations they may need to understand and interpret their experimental results.

As a 300-level lab it requires lab reports and data analysis at a level higher than introductory labs, but not as extensive as those typically required for the 400-level series of advanced labs.   Experiment operation and measurements will be completed within one lab meeting.  The analysis and interpretation is expected to be done outside of class but in collaboration with other members of a 2-3 person group. 

Measurement techniques, data analysis, and experiment interpretation form the three main emphases of the UW physics advanced labs.  The first, measurement techniques, concern the things one usually associates with a lab course: experimental apparatus and its use. Measurement techniques used in the optics lab span the range of measurement apparatus from simple estimates by eye, through precision scales that use micrometers and vernier subdivisions, to specialized CCD (charge-coupled device) arrays read out via electronics and computer interfaces.  The setups use precision optical equipment, such as rigid optics tables, various mounts, precision positioning stages, medium intensity lasers, spatial filters, and corrected lenses.  Some apparatus is delicate and very expensive.  Students will be expected to treat all apparatus with care and attention.

The advanced labs focus more on data analysis and experiment interpretation than introductory labs.  Data analysis includes basic tasks often called data reduction, usually done with a variety of computer programs and computer coding, and further analysis of the reduced data to look at it in different ways, i.e., with different types of graphs, with fits to complex curves, and to consider any calibration steps.  Often, the goal of data analysis is to derive final results from the measurements to compare to predictions from theory or to the results of other experiments. In some cases uncertainty calculations must be carried out to complete one's interpretation of the results.  This lab will introduce the use of Python coding and useful Python packages in basic data analysis, curve-fitting, and making plots.

Interpretation of experimental results is distinct from data analysis.  To interpret the results means to construct a story to explain them within the framework of physical theory, and to note and describe trends, patterns and anomalies in the data.  Interpretation also combines the physics of the phenomena being measured (e.g., the coherence length of a light source) with the physics of the apparatus (e.g., the structure of an interferometer and how it produces a fringe pattern on a screen).  You will be asked to do more than take data and write code: ultimately your goal is to understand and be able to explain the physics of both the experiment technique and the phenomena studied with it.

Learning Goals

"Learning goals" are the most important skills and understanding you should expect to learn by taking this course.  At the end of this Optics Laboratory course, you should be able to

• Explain the basic concepts and operation of a variety of measurement techniques used in the experiments you perform.
• Describe how the measurements reveal the underlying phenomena being studied in terms of the physical operation and chain of cause and effect in each experiment.
• Carry out complete numerical analysis of experimental data using Python and common computer libraries (numpy, LMFit, matplotlib, etc.)
• Explain features in experimental data in terms of known physics, and point out features of data that may not be captured by the expected models.

Rules

The following are rules. The first two are safety rules and are required by University policy and Washington State law.

• No food or drink may be consumed in the lab. University of Washington policy forbids the consumption of food or drink in these labs.
• No students may work in the lab without the presence of lab staff.

In addition, experimental groups are limited to three persons. With four persons or more, there is not enough to do to keep everyone busy.  Students are allowed to work in groups of 2 or all alone, if the setups are available.

Every person is welcome in this course.  Instances of discrimination (e.g., shunning, belittling, bullying, harassment) for any reason (e.g., ethnicity, religion, sexual orientation, gender identity, different-ability, or political beliefs) will incur thorough investigation and possible sanction through University approved processes.  If you believe you have been subject to such discrimination, please contact the instructor directly, or see University Policies for information on how to contact University officials.

Course Structure

The experiments will explore basic concepts and phenomena in visible-light optics.  Optical phenomena are not only important for many technological applications, the ideas underpin much of what is also known about the quantum world.  Every experiment is rich with phenomena that go beyond specific topics treated in a given lab, and the techniques used in them continue to be used in current research.  This means that each experiment will give only a brief introduction to a deep, complex sub-field in physics; indeed, one could easily spend weeks on any one of the experiments and its related phenomena.

Each experiment will be performed in one lab meeting, and most analysis and report creation will be done outside of class.  There is also one weekly lecture meeting.  All students are expected to attend the lecture.  Topics covered in lecture will be the subject of an exam given near the end of the term. 

Grades will be derived from [1] Daily Participation in lab (Day X), [2] the Pre-Lab assignments (Pre), [3] the Notebooks (N), [4] The Written Section (WS), and [5] the Exam.  More details on each of these is given elsewhere, but briefly: the Pre-Lab assignment is designed to get students to read the instructions and think about what they will do in the lab session; the Notebook contains the group's data collection and analysis record—it includes information about apparatus, data sets, and copies of hand-written notes or calculations—the notebook will earn a common grade for all members; the Written Section should be done individually: it is a short paper (2 pages max) that answers writing prompts pertaining to each experiment; the Exam will be drawn from the lecture topics, and a "study sheet" will be provided that explains the exam and will include practice problems.

Data analysis tasks will be carried out in a Jupyter Notebook written in Python.  Portions may be copied into the Notebook as needed.

Weekly Tasks

Attend the weekly lecture on Thursday and the weekly lab session for your section.  You also need to meet with your group to carry out the measurements as well as work on data analysis and discuss your interpretations. It is expected that students will work approximately 9 hours/week on this course, 3 hours/week in the lab, 1 hour/week in the lecture, and 3-5 hours/week at home. During each week, students should plan to accomplish the following tasks during the course sessions and at home.

1. Before lab: Watch any videos associated with the experiment, if available.  These give overview of the experiment and how the apparatus is to be used. Complete the Pre-Lab assignment, as specified in the assignment instructions. (1 hour)
2. In lab: assemble and learn to operate apparatus, take data, document the experiment in your Notebook.  (3 hours)
3. After lab: Carry out data reduction and analysis in your Jupyter Notebook (1-2 hours). Create, annotate, discuss, and check each other's contributions to the group part of the Notebook (1-2 hours). Write your Written Section, based on assigned prompt(s). (1 hour)
4. In lecture: Show up, take notes, ask questions (1 hour).

Lab Meetings

During the meeting time students will work with their group on the experiment.  You are expected to attend the full scheduled period.

Participation credit will be awarded based on an attendance record taken by the instructor or TA. Late arrival or early departure may result in a lower participation grade.

Remote Participation

In the event that you are unable to attend in person, you may coordinate with the instructor and your lab partners to attend remotely and work with your group via a Zoom session.  This would happen, for example, if you contracted a mild or asymptomatic case of COVID-19 or needed to quarantine but could otherwise attend to your courses.

Videos

Course materials may include two different types of videos.

Theory Lectures are voice-over-slide videos that discuss the important theoretical ideas behind the week's experiments.  The focus of the "theory" is to help you make sense of the experiments: the essential theory relevant to an experiment or collection of experiments, how the apparatus works, and how to understand the ways that the experiments reveal the underlying physics. Theory videos will be posted after each lecture.

Experiment Operation and Data Collection videos show an experiment in detail: what the apparatus is, how it is assembled, how the electronics are configured and connected together, and any other important physical detail you would need to know in order to operate it. The videos will also show how data are collected, plus other measurements needed for calibration or analysis.  Experiment videos will be broken up into sections of variable length, typically between 5 and 25 minutes each.  For example, one video may give an overview of the apparatus, another may delve into its setup and calibration, and a third may show how data are collected. Only three out of the six experiments beyond geometrical optics have videos.   In-person instruction will prioritize those experiments that do not have video run-throughs.

Working Groups

Research is a collaborative process.  Most scientific work is done in teams, some quite large.  Even if you are a solo theorist, you need to talk to others to refine your ideas, brainstorm and challenge assumptions.  Thus, learning how to work in a group is essential.  In professional experimental research, projects are broken down into specific tasks to be accomplished by subject experts (e.g., coding, hardware, sample preparation) and those who may be learning the field (e.g., grad students).

You will be expected to form a group of 2-3 persons in your section.  You may already know people in the class you would like to work with.

You will join a group by signing up for an experiment on a Google Doc linked on the main page.  Ideally, you should communicate with possible group members before you form a group.  Any students not in a group by the time of the lab meeting will be assigned to a group by the instructor.

Group members are not  bound to the same group for the duration of the course, but if possible, those groups working well together will be preserved.

What Your Group Should Do

At minimum, your group must decide which members are primarily responsible for which tasks to complete the Notebook.  Other members will be expected to review the work entered into the Notebook, comment on it and correct it, if necessary.

For each experiment there will be a summary of tasks.  Examples: create a diagram of the apparatus, record and plot a data set, perform basic data reduction, carry out a particular calculation, or answer certain interpretive questions.  Your group should decide which members is primarily responsible for a particular tasks. 

Members should also plan to rotate tasks from experiment to experiment.  In other words, do not always have the same person draw the apparatus diagram, or carry out basic data reduction coding.

The other main purpose of the group is to work together to accomplish the data analysis tasks.

Pre-Labs

Each experiment will have a pre-lab assignment.  Pre-labs are expected to be brief, generally 1 page in length.  Some experiments will have specific tasks to carry out (see the pre-lab instructions for geometrical optics), but most will have a version of the following:

1. State the general purpose of the experiment in one or two sentences (2 points).
2. State the quantities that will be directly measured with the apparatus (3 points).  "Directly measured" means the form and source of the raw data, for examples, the carriage position of a viewing microscope on a track, a file of voltages versus pixel number from a detector, or the angle setting of a polarizer versus current in a magnet coil.
3. State how the raw data are changed into the physical quantities of interest, for example, from the above, the carriage position will, by means of a set of calibration positions of known spectral lines, be converted to the wavelength of unknown spectral lines.

The pre-lab assignments will be uploaded as a PDF to Canvas.

Notebooks

The "Notebook" is the primary product of the working group.  It should be created with a collaboration platform such as Google Docs.  The easiest way to do this is create such a document on Google Docs or Microsoft OneDrive and share it with a link.

What Goes in the Notebook?

To complete the Notebook, use the task list posted on the experiment page. It lists tasks to be completed and some information on how to accomplish them. 

Each person should indicate their contribution by initials and date.  This is standard scientific record-keeping practice.  Do not "back-date" entries into the notebook.  The number or extent of entries should be roughly equal among every member of the team.

More information on what should go into Notebooks, such as expectations for graphs, apparatus diagrams and annotations, discussion of data and results, inclusion of calculations and computer code, etc., are in Getting Started with Notebooks.

Summary of differences between group and individual notebook requirements:

If the notebook is a "group" notebook:

• Only one person in a group needs to upload a "group" notebook.
• The names of all partners that contribute to it must be stated at the beginning.
• Every member of the group must contribute substantially to the notebook.
• Each entry / section / contribution must be credited to a member ("initialed") and dated. Uncredited entries will not count toward the grade.
• For all credited partners, the same grade will apply.

If the notebook is an "individual" notebook:

• Only one person should be credited on the notebook, but lab partners should be named.
• It must clearly be the work of one person (not substantially copied from another partner).
• Data sets may be shared among partners, but that is all -- analysis, drawings, comments, discussion etc. are individually done. 
• Entries do not need to be credited; it is assumed to be the work of one person.
• If it is evident to the grader that the notebook is not "individual enough," it will be graded as a group notebook with other partners.
• The notebook must be complete - include all parts expected in a group notebook.
• The notebook grade will apply to one person only.

Data Analysis & Computation

Some tasks need to be done with computational tools.  We will use the Python programming language plus a number of standard libraries that are commonly used in scientific computing.  The coding environment is called Jupyter Notebooks.  The course webpage will have a link to this service, and all programming can be done on it.  Students do not need to install any software on their own computers.

Among the learning goals of this course is building skills with computation as applied to experimental physics.  This is part of an overall Physics department effort to teach computation within the physics major.  The use of Python is based upon current trends in physics research, data science generally, and the growth and maturation of collaborative tools associated with Python.  See Python and Jupyter Notebooks for more information.

The Written Section

Each student must also write and submit their own Written Section to the notebook, as a PDF uploaded to a separate Canvas assignment.  The structure and content of the report will be described in the assignment, and will vary as the course proceeds, but there are a few common aspects:

• It must conform to strict formatting rules and length limits.  Typically,  the section must be between 1-2 pages, be typed, single-spaced, and use 11 or 12 point font and 1 inch margins.
• It must be written well, with complete, grammatically correct sentences and structured paragraphs.
• It must address the writing prompt(s): typically questions about the experiment.
• It should have an opening paragraph to provide context so that the reader can understand what the report is about without having read the writing prompt (or done the experiment).

Experiments

Every physics student should have a basic understanding of how simple optical devices, such as lenses, telescopes and cameras work.  Thus, the first two experiments will be done by everyone during the first two weeks of lab:

Geometrical Optics: Lenses
Geometrical Optics: Optical Instruments

After those, students will work on different experiments each week according to the sign-up sheets.  These experiments mainly concern the wave nature of light and its interaction with matter.

1D Diffraction: Fraunhofer and Fresnel Diffraction
Concave Grating Spectrometer
Dielectric Reflection
Fabry-Perot Interferometer
Faraday Rotation
Michelson Interferometer

Lecture & Exam

The weekly lecture will provide physics theory behind the experiments.  But one lecture per week is insufficient to cover the topic as completely as a full lecture course could, so the focus will be on those aspects that are specific to the set of experiments on offer.  Students will be expected to read the parts of the text they need to fill in the gaps of their understanding.   

The exam will occur in one of the lecture periods near the end of the term.  It will concern topics covered in the lecture.  Prior to the exam, students will be provided a study sheet that will contain information about the exam, a summary of information to commit to memory, and practice problems that will very closely mirror those on the exam.  (There is no exam during Final Exam week.)

Grading

Overall grade portions are 10% pre-labs, 10% participation, 40% Notebook, 30% Written Portion, 10% Lecture exam.  These are further broken down as described below.

Pre-Labs

Pre-labs are graded on a 10 point scale.  For the versions following the three questions (Purpose of experiment? Raw measurements? How are raw measurements turned into final results?) the allocation is 2, 3 and 5 points, respectively.  The Pre-labs will be worth 10% of the final grade.

Participation

Participation is graded credit/no-credit.  Students receive credit by working with their partners in lab, and are not significantly late for class or leave early without consulting the TA or instructor.  Participation is worth 10% of the final grade.

Notebook

Notebook grading will reflect "real-world" assessments: the kinds of assessments that are typical in work environments and active research.  Notebook assessments will be listed as letter grades A, B, C, D, F which correspond to numerical grades 4, 3, 2, 1, 0, (or 100%, 75%, 50%, 25%, 0%) and are based on the typical workplace assessments outstanding, exceeds expectations, meets expectations, does not meet expectations, nothing to assess.  These may also have +/- refinements ("+" adds 0.3 to the numerical grade, "–" subtracts 0.3, i.e., +/- 7.5%).

Grades will depend on

• Credit: Entries / sections / contributions must be credited to one individual.  All partners are expected to contribute substantially to the notebook (i.e., in roughly equal amounts of effort).  Entries that are not credited will not count towards the notebook grade.
• Timeliness: Add information to the notebook as you do the experiment. Date the entries.  A notebook mostly created after the experiment is done will get a lower grade. Missing dates will get a lower grade
• Context: Entries should explain what is recorded and what it means.  Lack of context is the main reason notebooks receive low grades.
• Completeness: Everything produced by the group that the group needs should be in the notebook: raw data, apparatus diagrams, pictures of the setup, plots, equipment settings or operations you would need to duplicate the measurements.  But: you should NOT copy Python code from the Jupyter Notebook unless you specifically discuss it in the context of some point you want to make. 
• Discussion and interpretation: Take some time to write down how you understand the experiment and what it means.  Make your discussion quantitative and based on clear physics reasoning.
• Corrections and comments: Did you get a different result from your partner?  If so, you should notice it and say so.  Do you think that an entry needs more context? If so, provide that context, and initial/date it.  All partners are responsible for all parts of the notebook.

Group versus individual grades

The Notebook is intended to be a group effort.  Thus, the grade is a "group" grade: all students who work on it get the same score.  However, any member of a group may opt to submit an individual notebook rather that contribute to the group's notebook.  For individual notebooks, the grade may vary among the partners in the group.  If a student or students decide to submit individual notebooks, the following rules apply:

• The Notebook must be declared as an "individual" notebook when it is submitted.
• The Notebook itself will be graded as an entirety: It should be complete in all parts.  In other words, it is more work to make an individual Notebook than a group Notebook.
• If the grader observes that Notebooks which are declared as "individual" look substantially the same, the Notebooks will be graded as a single "group" Notebook, with all students earning the same grade.

Notebooks are worth 40% of the final grade.

Written Portion

The Written Portion will be subject to grading as follows:

If it is turned in by the due date (or a mutually agreed upon extension of the due date) it will be graded on a 3 level scale, corresponding to typical decisions made by scientific journals: accepted (A), accepted with revisions (AwR), and rejected (R).  These will correspond to letter/numeric grades of A/4.0, B/3.0, and F/0.0.  Reports that earn AwR or R may be resubmitted once. Exceptions to the submission process may occur if there is not enough time to grade, return, and resubmit, such as at the end of the term. A report that falls below a grade of AwR on its final submission will be graded B-, ..., R.  Reports that are originally graded R (0) but not resubmitted will retain the grade of 0.  Resubmissions are due within 1 week of the initial grade decision.

If it is turned in past the due date, even if submitted within the grace period (see below), it will be graded once on an A, AwR, B-, ..., R scale.  (Note there will be no A-, B+ grades, to make the scale consistent with the preferred submission-cycle scale.)

The last Written Portion of the term will be graded only once.  If you are concerned about earning an "Accept" grade on the final Written Portion, plan ahead: consult with the grader for that assignment before the due date to ensure your submission will meet the standard.

The Written Portions are worth 30% of the final grade.

Lecture Exam

The lecture exam will be graded on a 100 point scale.  It will be worth 10% of the final grade.

To summarize:

Due dates & Extensions

Participation is recorded by the instructor or TA for the lab session, usually within a few days of the meeting.

Pre-Labs are due by noon (11:59am) on the day of the experiment.  There is a 1 hour grace period before the assignment closes.  There are no extensions on Pre-Labs beyond the grace period.

For the Notebook and Written portion, the following rules apply:

1. There is one due date for the Notebook and Written Portion: midnight (i.e., 11:59 pm) on the 12th day past the lab session on which the experiment was done (Sunday for section AB,  Tuesday for section AD, Wednesday for section AE).
2. There is an automatic grace period of 24 hours following these due dates.  Think of this as an automatic extension, should you need to talk to the TA or instructor.  You do not need to ask for this extension.
3. Extensions beyond the grace period will be granted, but they must be requested before the end of the grace period.  A new date will be assigned to work granted an extension.  New dates will be decided by the TA or instructor.  These will typically be set to 2-3 days following the request.  There is no grace period attached to an extension; the only thing that will change is the availability date.
4. Each student must individually request an extension.
5. Without an extension granted and set in Canvas, the assignment will become unavailable following the grace period.

Grade Calculation

The final grade will be calculated according to the formula

Thus, to earn a 4.0, you need about 95%.

Writing ("W") Option

A writing "W" credit will be awarded to any student who earns at least 4 "Accept" grades on their Written Portions.

University Policies

A number of University of Washington policies pertain to this course.  See University Policies.