Physics 492 Again!

Physics 492 Advanced Optics Lab is offered again during the Fall 2012 quarter at Cal State LA. We will be meeting at 6:30 PM Mondays and Wednesdays. The class is an opportunity to get some hands-on and in-depth experience with photon-based quantum mechanical systems in a typical optics lab environment. Photons are easily generated, manipulated, and detected with simple apparatus. Among other topics, we will explore the physics of quantum interference and superposition in the two state system as we build various interferometers and poke at them with polarization probes.

I've structured the class so participants can develop important lab skills: lab safety, preparation, experiment planning, design and fabrication of apparatus, equipment handling, working in teams and individually, keeping a notebook, and presenting results. Grades are based in part on preparation, demonstrated lab skills, lab notebook quality, and a 10-minute presentation in lieu of a final exam. Grading thus mimics evaluation that occurs in an academic or industrial lab. There are no graded exams, quizzes or formal lab writeups.

Class will meet twice weekly in a brand new facility with plenty of workspace. Lab will be open after class for individual and team work on projects. Available equipment includes an optical table, laser source, beam expander, lenses, mirrors, ccd detector, desktop PC, beamsplitters, polarizing filters and various opto-mechanical components for locating and positioning optics on the table.

While there are no formal prerequisites, students are typically upper division and masters students familiar with optics at the freshman physics level (simple raytracing), the solution to the free-space wave equation ("e to the i omega t"), and math with 2x2 matrices (linear algebra). If interested in taking the class you should sign up as early as possible as there are a limited number of seats.

Lab 19 Wrap-Up

Lab 19 met in the lecture room for a trip down memory lane. I followed the sequence of labs, describing how they built on one-another to give you all a good exposure to the optics lab: environment, procedures, tools, lasers, optical components, experiment design, error budgeting, and the physics of diffraction, interference, image formation, and polarization. For me the class was a blast to teach and you all have been the best set of students I could imagine - inquisitive, responsible, creative, good team workers, and go-getters. I'd be proud to have any of you on an experiment team.

The final is 7:30 December 7 in PS 306, where we met for the last class. I have all your presentations and we'll project them on the screen. My plan is to have a book or CD with all the presentations as a class momento. If you would like to invite anyone along, please feel free to do so. In the meantime, best wishes for success in your other classes' finals. I hope getting the presentations fully prepared early helped there.

Lastly, Dr. Terebey and I will be conducting a quantum optics experiment starting next quarter on photon orbital angular momenta - if you are interested in participating, please see her. It will involve a Mach-Zehnder setup on the table, some new components, mounts, digital data taking, and hopefully some fun results that may lead to further work on orbital angular momentum spectroscopy of natural photon streams.

Lab 18 Prep / Materials

Preparedness will be demonstrated by sharing presentation status - you should have slide titles and content identified. Final versions are due Wednesday.

Today is lab notebook review for those who don't have a "bye".

The table will be open until 7:50.

Some possibilities for work on the table during class time include: a Sagnac (ring laser) interferometer; a Mach-Zehnder interferometer with a microscope slide in one arm to generate path differences and fringe modulation, solutions to various made-up alignment puzzles, michelson fringe imaging w/ the camera to assess wavefront error.

After 7:50 there is a holography experiment scheduled on the table that needs the room dark.

Lab 17 Wrap Up

Tonight Team "Wednesday" was tasked with creating a Mach-Zehnder interferometer (MZI) from scratch on the table. While some online notes suggest that an MZI is easier to align than a Michelson, I think everyone in the class would disagree. The MZI has an extra degree of freedom at each of the two 45-degree angle mirrors that is coupled to its rotation around the vertical axis. Of these two degrees of freedom, the Michelson only has the rotational degree of freedom - the return mirrors can be placed anywhere along the direction of the arms and still obtain laser fringes. Here's a diagram showing the MZI coupled degrees of freedom:

Aligning optics on a table is a little like riding a bicycle. After a while your body just "gets it" as you learn the effect of exercising each of the many degrees of freedom in an optic's mount. Of course you need to have an overall alignment strategy as well, such as working optic by optic down-beam. In this alignment, the "aha" moment is when you translate and rotate the mirror at the same time, keeping the location "A" constant. Having a second location "B" helps a lot.

We learned several other alignment tricks. "Chopping" a card in and out of beam rapdily by hand as the card is moved downstream gives a strong and fairly persistent visual impression of the beam's location in 3D akin to as if there were smoke or mist to mark the beam's location. This trick is especially helpful if there are features (bolt-hole row, tape w/ line down middle) on the table showing the direction the beam should go. I'll post up the other trick later.

Here are some in-progress alignment photos:

This one showing mirror translation along a bolt-hole row, and below, showing by-eye alignment looking down a bolt-hole row from one end of the table to make sure everything is in the right place. It is amazing how important it is to keep moving around the table and eye-balling optic locations! It is just too darned easy to plop things down off-by-one because of the repetitive pattern on the table top.

Oh, by the way, the fringes were good:

I'll hold open lab Friday 1PM on.
Good Thanksgiving everyone!

Lab 17

... is a repeat of 16 with team assignments swapped.


Above: Team "Monday MZ" fringes from their Mach-Zehnder interferometer.

Look ahead:
Your FINAL presentation in digital or (scannable) paper form is due next Wednesday, December 2.
Your DRAFT presentation (slide titles and content identified) is due next Monday, November 30.
Your lab notebooks will be reviewed Monday (Lab 18). Some of you have byes on this for having stupendous notebooks last time and already have full credit on this score.

Prep today will be a status on your presentations:
Lab work begun
Lab work finished
Lab work written up
Presentation slide titles complete
Presentation draft content complete
Presentation final content complete

Remember that I will be reviewing your lab notebook at the time of the presentations.

Lab 16 Materials

Lab 16 Plan of the Day
Lab 16: Mach-Zehnder Interferometer
Self-Assessment (note addition of more of/less of items)

Today and Wednesday we'll break into 2 groups. One group will build a Mach-Zehnder interferometer, and the other will learn optics cleaning techniques. Then on Wednesday we'll switch. The interferometer build will take 1-2 hours.

Here's a pdf with optics cleaning instructions:
Meilse Griot cleaning instructions.
Because of the importance of minimizing damage to an optic's surface, cleaning is done very carefully. Many years of experience has developed a practical and safe approach. The key ingredient is patience and losing all desire to rush. A little practice helps too.

Lab 16 Prep

There is no separate prep package. Work on your projects. Be prepared to give status of work accomplished (not time spent, or work planned).
I have a pile of photos from Friday's open lab. Too many to email or upload. Instead I'll burn them to CDs and bring them to lab. I note, however, that with 5 dozen photos it is hard to keep track. My advice for future photo taking is that you write a little placard to appear in the frame when the photo is taken to identify it better.
I'll post up this one photo though. It was the highlight of the day when Sy's Mach-Zehnder interferometer gave fringes.