There is no slide set for today's Lab. We'll be dissecting an old telescope.
Lab 10 Plan of the Day
Self-Assessment
Wednesday, October 28, 2009
Tuesday, October 27, 2009
Lab 9 Error Budgets & Chopping
Julian's Lab 9 data
If you want to add additional data you recorded to this spreadsheet, drop Julian a note (or me and I will forward).
Lab 9 was all about error budgeting an experiment. An error budget not only is a guide to understanding the sources of uncertainty in an experiment once you have data in hand, but it is also a powerful tool in experiment design. Once you know the big contributors, you can spend some effort to make them smaller, improving the overall experiment. Where's Waldo the Error Budget in this picture?
In experiment 9, chopping was an important technique in reducing noise introduced by drifts. Here is some chopping in action as Jillian alternately allows a polarized and unpolarized beam to be sensed on the photometer in order to assess the noise introduced by laser polarization and intensity drifts.
If you want to add additional data you recorded to this spreadsheet, drop Julian a note (or me and I will forward).
Lab 9 was all about error budgeting an experiment. An error budget not only is a guide to understanding the sources of uncertainty in an experiment once you have data in hand, but it is also a powerful tool in experiment design. Once you know the big contributors, you can spend some effort to make them smaller, improving the overall experiment. Where's Waldo the Error Budget in this picture?
In experiment 9, chopping was an important technique in reducing noise introduced by drifts. Here is some chopping in action as Jillian alternately allows a polarized and unpolarized beam to be sensed on the photometer in order to assess the noise introduced by laser polarization and intensity drifts.
Monday, October 26, 2009
Sunday, October 25, 2009
Friday, October 23, 2009
Lab 8 Material Available
Lab 8 Plan of the Day
Lab 8 Materials - Quantitative Polarization
Self-Assessment Form
I hugely enjoyed this lab - preparing it, and watching you execute it. The teamwork both teams showed as you all worked beautifully together to get high-quality experimental results. It is clear that you all know and respect each other well enough to easily organize yourselves to complete a complex task. My hat is off to you all.
Julian sent me his team's data spreadsheet for sharing:
Team Julian Lab 8 Spreadsheet
Here is what the data looks like (blue squares) compared to a cos^2 law with a phase shift and amplitude that best "fits by eye" (red line).
The data clearly validates the model, Malus' law to within a few percent. A detailed study of this experimental dataset could be done to determine the degree to which the cos^2 law matches the data, perhaps someone will undertake this quantitative task. Also instructive would be a plot showing the uncorrected-for-drifts readings vs angle and the cos^2 law. Since the input beam intensity varied by 40%, the comparison would be graphic in showing the value of performing a chopping experiment. Instrumental drifts are invariably present at some level in every experiment. An experiment seeking the best possible sensitivity must take these drifts into account.
Above is a snapshot of the 2 polarizers with their mounts "blocked" using 1/4-20 bolts in the table to achieve a relatively repeatable position. This technique facilitates rapidly moving each polarizer out of the beam and back in at will without having to fuss much about obtaining correct placement. Just push it (gently) up against the blocking bolts.
Team John emailed me as well. Here is that team's data:
Team John Lab 8 Spreadsheet
Lab 8 Materials - Quantitative Polarization
Self-Assessment Form
I hugely enjoyed this lab - preparing it, and watching you execute it. The teamwork both teams showed as you all worked beautifully together to get high-quality experimental results. It is clear that you all know and respect each other well enough to easily organize yourselves to complete a complex task. My hat is off to you all.
Julian sent me his team's data spreadsheet for sharing:
Team Julian Lab 8 Spreadsheet
Here is what the data looks like (blue squares) compared to a cos^2 law with a phase shift and amplitude that best "fits by eye" (red line).
The data clearly validates the model, Malus' law to within a few percent. A detailed study of this experimental dataset could be done to determine the degree to which the cos^2 law matches the data, perhaps someone will undertake this quantitative task. Also instructive would be a plot showing the uncorrected-for-drifts readings vs angle and the cos^2 law. Since the input beam intensity varied by 40%, the comparison would be graphic in showing the value of performing a chopping experiment. Instrumental drifts are invariably present at some level in every experiment. An experiment seeking the best possible sensitivity must take these drifts into account.
Above is a snapshot of the 2 polarizers with their mounts "blocked" using 1/4-20 bolts in the table to achieve a relatively repeatable position. This technique facilitates rapidly moving each polarizer out of the beam and back in at will without having to fuss much about obtaining correct placement. Just push it (gently) up against the blocking bolts.
Team John emailed me as well. Here is that team's data:
Team John Lab 8 Spreadsheet
Tuesday, October 20, 2009
Lab 8 Prep Package Available
Lab 8 Prep Package
Lab 8 will be a quantitative experiment to determine the angular dependence of the intensity of polarized light transmitted by a polarizing filter. To generate quantitative measurements we will be using the Photometer:
I will be catching a plane right after class, so we will be closing up at 8:30 PM, a little earlier than usual. On Monday, I'll open the lab up an hour early (5 PM) so you can continue any work that was left undone.
Lab 8 will be a quantitative experiment to determine the angular dependence of the intensity of polarized light transmitted by a polarizing filter. To generate quantitative measurements we will be using the Photometer:
I will be catching a plane right after class, so we will be closing up at 8:30 PM, a little earlier than usual. On Monday, I'll open the lab up an hour early (5 PM) so you can continue any work that was left undone.
Lab 7 Wrap-up
Lab 7 worked even better than I hoped it would, exploring the vector nature of polarization with hand-held plastic polarizing film. One of my goals is to give you enough "touches on the ball" so you can develop a feel for how optical phenomenon behave. You have plenty of experience with balls, wheels, blocks, and so on. But we all have only limited opportunities in everyday life to manipulate light beyond turning on and off a switch. Every now and then just walking around you will see a curious optical phenomenon. I encourage you to "step outside the box" and take a closer look, take the time to come to some conclusions, and thereby add to your experiential base. You may want to carry around a small piece or two of polarizing film in your wallet just to have a fun investigatory tool.
LOL Labz
U r makin' me haz seen the lite!
LOL Labz
U r makin' me haz seen the lite!
Sunday, October 18, 2009
Lab 7 Materials Available
I've been sent on a lightning trip by my day job to spend Monday morning at an out-of-town vendor, so lab 7 prep has been rather rushed. Even so, I managed to preflight on the table and to put together a simple lab guide. If you have some small transparent plastic items at home, you may want to bring them to class to use them in the last section.
Lab 7 Plan of the Day
Lab 7 Materials
Self-Assessment
Lab 7 Plan of the Day
Lab 7 Materials
Self-Assessment
Saturday, October 17, 2009
Lab 6 Notes on Notebooks
In lab 6 I spent 5-10 minutes one-on-one going over lab notebooks. Some comments:
1. There is a wide range in style.
2. There is a wide range in quality.
3. Not everyone seemed satisfied with their notebooks.
4. Here's a strategy for improving your notebook:
--- Refer to the checklist in the material for Lab 1.
--- Review your notebook against the checklist.
--- Pick an area to improve.
--- Spend extra effort on that area until you see improvement.
--- Iterate.
5. Not many notebooks recorded lab procedures. These are necessary to reproduce a result.
6. Good notebooks can save you in the future from extra work redoing stuff that you just didn't bother to record. Get in the habit of recording everything that makes sense, especially puzzling facts.
I will review lab notebooks in class again. At that time we will make "improvement contracts". In the meantime, use the feedback provided and these comments as an opportunity to improve your practices. Out in the wild you will find it necessary to keep good lab records in order to make reliable progress on a project and be confident of the results.
1. There is a wide range in style.
2. There is a wide range in quality.
3. Not everyone seemed satisfied with their notebooks.
4. Here's a strategy for improving your notebook:
--- Refer to the checklist in the material for Lab 1.
--- Review your notebook against the checklist.
--- Pick an area to improve.
--- Spend extra effort on that area until you see improvement.
--- Iterate.
5. Not many notebooks recorded lab procedures. These are necessary to reproduce a result.
6. Good notebooks can save you in the future from extra work redoing stuff that you just didn't bother to record. Get in the habit of recording everything that makes sense, especially puzzling facts.
I will review lab notebooks in class again. At that time we will make "improvement contracts". In the meantime, use the feedback provided and these comments as an opportunity to improve your practices. Out in the wild you will find it necessary to keep good lab records in order to make reliable progress on a project and be confident of the results.
Lab 7 Prep Package Available
Lab 7 Prep Package
Note that you will design an experiment and write the procedure for executing it. If you have or can borrow some polarizing sunglasses, bring them to class.
Note that you will design an experiment and write the procedure for executing it. If you have or can borrow some polarizing sunglasses, bring them to class.
Wednesday, October 14, 2009
Lab 5 Fringes - Cell Phone Photos
Here are 3 sets of fringes from the Lab 5 microscope slide experiment, one from each team's successful layout. An incident beam I reflects first off the front surface of the slide creating one reflected beam, and then off the back surface, creating another. These travel almost in the same direction, but not quite, due to the small tilt of surface S1 with respect to S2. This tilt is there because the slide surfaces are not perfectly parallel. The number of fringes and the size of the illumination spot on the slide measure the tilt angle, typically a few mrad.
Reflection geometry. Each reflection is about 4% as intense as incoming beam I. Not shown is the transmitted beam T that continues downward to the left.
The fringe orientation is due to the wedge orientation. In lab we rotated a slide to see that the "clock" angle of the fringes is tied to the slide, not to the rest of the optics.
We also tested what would happen if we overlapped the fringe pattern from one experiment bay on top of the beam from another experiment bay. Additional fringes or no additional fringes? At first sight we didn't see evidence for additional fringing - the pattern looked like the straight addition of the 2 fringe patterns rather than the interference of those 2 fringe patterns. Remember that the number of fringes is related to the angle between the two beams, with about 5 fringes per mrad. The two beams were incident at an angle of several hundred mrad, so there were of order a thousand of these new fringes across the pattern -- too many to resolve since there's more than one fringe per camera pixel. So we didn't see much new. If we had inserted some clever optics to overlay the two beams with a small, mrad sized, angle between them (like is done when you use 2 stacked slides), then what would we have seen at the detector/screen?
Reflection geometry. Each reflection is about 4% as intense as incoming beam I. Not shown is the transmitted beam T that continues downward to the left.
The fringe orientation is due to the wedge orientation. In lab we rotated a slide to see that the "clock" angle of the fringes is tied to the slide, not to the rest of the optics.
We also tested what would happen if we overlapped the fringe pattern from one experiment bay on top of the beam from another experiment bay. Additional fringes or no additional fringes? At first sight we didn't see evidence for additional fringing - the pattern looked like the straight addition of the 2 fringe patterns rather than the interference of those 2 fringe patterns. Remember that the number of fringes is related to the angle between the two beams, with about 5 fringes per mrad. The two beams were incident at an angle of several hundred mrad, so there were of order a thousand of these new fringes across the pattern -- too many to resolve since there's more than one fringe per camera pixel. So we didn't see much new. If we had inserted some clever optics to overlay the two beams with a small, mrad sized, angle between them (like is done when you use 2 stacked slides), then what would we have seen at the detector/screen?
Tuesday, October 13, 2009
Lab 6 Prep Package Available
Lab 6 Prep Package
During Lab 6 I will review lab notebooks for feedback. Also, we will begin designing our precision tip-tilt stage for the precision interferometer experiments. Finally, there will be open lab.
During Lab 6 I will review lab notebooks for feedback. Also, we will begin designing our precision tip-tilt stage for the precision interferometer experiments. Finally, there will be open lab.
Sunday, October 11, 2009
Lab 5 Materials Available
PDFs for Lab 5 are available:
Lab 5 Plan of the Day
Lab 5 Microscope slide interference and metrology
Self-Assessment
This is the material that we will cover in the lab. It is different from the preparation package in the previous post. Do not confuse the lab materials with the preparation package!
On Wednesday the lab will include notebook review. Be sure you are all caught up with your notes and come ready to go over them with me for feedback on your notebook practices.
On Wednesday we will also begin designing precision stages for our Michelson interferometer experiment.
And, with luck, I will have sent some post drawings to the shop for fabrication. The luck being: there are good drawings to send on Monday, and the 1/2" stainless rod stock has arrived from McMaster-Carr.
Lab 5 Plan of the Day
Lab 5 Microscope slide interference and metrology
Self-Assessment
This is the material that we will cover in the lab. It is different from the preparation package in the previous post. Do not confuse the lab materials with the preparation package!
On Wednesday the lab will include notebook review. Be sure you are all caught up with your notes and come ready to go over them with me for feedback on your notebook practices.
On Wednesday we will also begin designing precision stages for our Michelson interferometer experiment.
And, with luck, I will have sent some post drawings to the shop for fabrication. The luck being: there are good drawings to send on Monday, and the 1/2" stainless rod stock has arrived from McMaster-Carr.
Friday, October 9, 2009
Lab 5 Prep Package Available
This is the work to complete before class. I may post the lab notes prior. But they are not the preparation package. Preparation packages contain exercises for you to do and record in your lab notebook. Think of them as homework.
Lab 5 Prep Package ... in which you will explore the small angle approximation, analyze your diffraction pattern data, and generate a mechanical drawing.
Lab 5 Prep Package ... in which you will explore the small angle approximation, analyze your diffraction pattern data, and generate a mechanical drawing.
Wednesday, October 7, 2009
Lab 4 - Fringes and Interference
Working at the table with Cornell Plates to generate diffraction and interference patterns. Several captured with cell phone cameras are below:
Double slit interference pattern
Airy disk from a round aperture made with a diaphragm
The camera is now working, this is its first fringe from #2 double slit on a Cornell Plate. Below is a slice through the intensity profile that could be used for numerical work:
Lab 4 Materials Available
Note: the Lab materials are what we do in the lab. The Prep Package, which was posted earlier, needs to be done before lab and recorded in your lab notebook.
Lab 4 Plan of the Day
Lab 4 Materials
Self-assessment
On self assessment please record if you want to attend and will commit to open lab on Friday afternoon. I will begin designing a precision mount with those interested. Or play on the table with the optics.
Lab 4 Plan of the Day
Lab 4 Materials
Self-assessment
On self assessment please record if you want to attend and will commit to open lab on Friday afternoon. I will begin designing a precision mount with those interested. Or play on the table with the optics.
Tuesday, October 6, 2009
Lab 3 - Proud
Paul, Julian, Cy and Daniel just after finishing their Lab 3 layout of a beam conditioner that reduces the laser beam divergence to less than 0.5 mrad and expands the beam 10x. Nice job guys!
Sunday, October 4, 2009
Lab 3 - 5 October 2009
PDF's for Lab 3 are available:
Lab 3 - Plan of the Day
Lab 3 - Laser Beam Conditioning
Lab Self Assessment
Lab 3 - Plan of the Day
Lab 3 - Laser Beam Conditioning
Lab Self Assessment
Thursday, October 1, 2009
Lab 3 Prep Package Available
Lab 3 Prep Package
Note that there is a video to view. It is one of the Feynmann New Zealand lectures on QED where he introduces his theory to a lay audience. The link for this 98-minute streaming video is
Feynmann video: Robb Memorial Lectures Part 1: Photons - Corpuscles of Light
Note that there is a video to view. It is one of the Feynmann New Zealand lectures on QED where he introduces his theory to a lay audience. The link for this 98-minute streaming video is
Feynmann video: Robb Memorial Lectures Part 1: Photons - Corpuscles of Light
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