Final Project Lab Checklist (PDF)
Final projects this year face several major constraints.
- First, final projects will be presented at the end of the regular term, rather than during the exam period. That means less time to plan a good experiment, do all the lab work, and document your results.
- Second, holographic materials are in world-wide short supply. We face the very real possibility of not being able to teach this class in the future because we cannot obtain suitable holographic plates or film. We need to conserve materials as much as possible during final projects (while still allowing to you do some good science).
- Third, the class is quite large this year. Lab time will be at a premium.
With those points in mind, we are all looking forward to seeing you put your new knowledge of holography and your scientific, engineering, and creative skills to work during your final projects. We just ask that you design reasonable and attainable goals for yourself.
Invariably each year, people take on very ambitious projects and run out of time, energy, or other resources required to complete them. The constraints above make such attempts even less desirable. Instead, try to focus on a very specific aspect of holography (processing, image formation, lab practice, materials, optics, etc), construct and experiment, and carry it out efficiently. Demonstrate good science and engineering sensibilities. Make a contribution to the field. Many options are available. Remember, too, that a good experiment that disproves something, even something you hoped would work, can still be good science if it’s analyzed and documented well.
Students usually work in groups to complete their final projects: groups of three to four people are most common. Everyone in a group should understand the basics of what’s going on, and your lab notebooks should each document the planning process, your lab time, and your final results. Distribute your skills, share your strengths, learn something together, and finish a good project.
Your group will sign out blocks of lab time as we’ll describe in class. As a rule of thumb, keep in mind that it’s difficult for even an experienced holographer to make even the simplest hologram from scratch in less than an hour. As you know from lab, holography takes a long time, even when you’re just following lab directions. Plan ahead, plan conservatively, and have contingency plans in case something doesn’t work out. By the week before projects are due, there will most likely be no extra lab time not signed out.
Here’s a list of some possible project ideas. Depending on the group working on them, they may or may not be accomplishable in the given amount of time. Talk with the TA’s and lecturers about your ideas and try to come up with something that works for you. This isn’t an exhaustive list: feel free to suggest your own!
Materials and Chemistry
Studies of Hologram Developers and Bleaches
Several simple developers and bleaches work well, but there are significant advantages and disadvantages to each, depending on the situation. A few tests of some alternates should help you generate some recommendations.
Understanding Alternate Silver Halide Materials
The Agfa plates we use in class are no longer made, but several other types of silver halide plates are available. What’s the best way to characterize the photosensitive characteristics of these plates? Good lab technique will be important.
This project is related to the one above. Other types of silver halide plates are very insensitive to light. Several ways exist to increase this sensitivity, including presoaking and gas sensitization. If you document a reliable method, you too could help save holography from obscurity!
Dichromated Gelatin Holograms
Take a break from the silver halide routine, and dabble in really arcane chemistry. Expose would-be desserts with deep blue lasers, rinse in hot rubbing alcohol, and behold peculiarly bright and clear 3-D images. Some chemistry experience needed. Lasers may not be available for this project.
Embossed Rainbow Holograms
Fool your friends and make phony credit cards at home by converting volume silver halide holograms to surface relief images that can be pressed into common plastics. Possibilities include: exposure of photoresist coated plates, and severe tanning development of silver halide emulsions. Images are reproduced by solvent casting of vinyl sheet.
Photopolymer is another holographic material, but it isn’t very sensitive to light. It produces very bright holograms. Propose an experiment that explores photopolymer holography without the need for huge lasers.
Pseudoscopic Image Effects
It seems to be very difficult to grasp the structure of a pseudoscopic “outside in” image. Well-designed holograms that show clearly this effect, perhaps quantitatively, would be great.
Projection of Dimensional Images
What about projecting a 3-D image right into thin air? Or a cloud of smoke? It doesn’t work very well, but it might be interesting to figure out exactly why. This would involve making a few test holograms, and seeing what can be done with them in various situations.
Aberrations in Holography
A few well-thought-out demos of astigmatism, coma, and spherical aberration in holography would help people grasp these concepts more easily. Any ideas for making these things come clear?
Interesting rainbow holograms can be created in a single optical step if the subjects are shadows of three dimensional objects. Shooting is quick enough to encourage experimentation. Refracting elements can be added to produce fascinating color modulations. The mathematics aren’t as complex either.
One-Step Image-Plane Holograms
Large lenses and mirrors can be used to create “image plane” holograms in a one-step “holocamera,” which makes image experimentation much easier. Control of distortions is important, so some optical exploring will also be needed.
Reduced Image Holography
Demagnifying the image of a subject brings a certain charm to the resulting hologram. Although this is most interesting for pulsed-laser portraits, the optics can also be explored with continuous-wave table-top holography. The main problem seems to be spherical aberration, which causes a strong “swinging” of the image.
There are three classes of interferometry with holograms: 1) “live fringe” holograms, such as the coffee-cup demo, 2) double exposure holograms, with some stress in between, and 3) continuous exposure holograms for repetitively moving objects. We need some interesting-looking demos of all of these!
Lab Techniques, Equipment, and Holographic Characteristics
Holography with Diode Lasers
Improvements of diode lasers, with higher power further into the visible spectrum, may make He-Ne lasers obsolete! The coherence of these lasers is somewhat limited at the moment, but it is possible to make some impressive holograms with them nonetheless. Imaging and non-imaging applications (ie, showing coherence length and evidence of diffraction) are both possible projects
Room Light Sensitivity
Holographic plates are relatively insensitive to light. Yet, we expose and process them under relatively dark conditions. What is good lab practice and what is folklore? When can we get way with turning on more light, how much, and why?
Print Out – Light Sensitivity of Bleached Holograms
Bleached silver halide holograms are photosensitive. How much so? Design an experiment to compare the sensitivity of some controlled set of different materials, different processing chemistries, different storage environments, or different light levels. This kind of good science could lead to a publishable paper.
This project would attempt to fabricate a holographic collimator without the use of a glass collimator. Simple optical design as well as careful exposure and processing will be required.
Design of Holographic Optical Elements
Holograms can be used to replace many simple conventional optical elements and devices. This project would identify a few examples and make an initial try at one or two.
Polarization Effects in Holography
Only the component of the reference beam that is polarized the same as the object beam will be recorded. Deliberate manipulation of the object beam polarization therefore offers an interesting level of control that can be explored in several ways, such as the suppression of highlights, of reflections, of woodgrain noise, and so forth.
Reflection False-Color Studies
The swelling of a holographic emulsion prior to exposure can decrease the eventual reconstruction significantly. Control of this swelling by paining the swellant on the plate, for example, can offer a new type of creative control of the medium, but must be based on careful prior calibration studies.
Signal and Noise in Holograms
The brightness and contrast of holographic images are not always easy to quantify, but a few simple experiments ought to reveal the basic dependencies on exposure and beam ratio that we have talked about in class.
The reproduction of all colors by additions of three primary colors is central to the future of color holography. A few demos should clarify some of the problems of holographic color rendition. This may require using several different lasers, so be sure to check that they are available!
Conventional two-step holographic stereograms involve a process that is so elaborate and time-consuming as to discourage the kind of interactive “try something else this time” approach that is so important to successful innovation. A much simpler one-step approach may be possible if the number of perspective views is held to a bare minimum, perhaps even two, as a way of “previsualizing” the outcome of the more elaborate procedure.
Reciprocity Failure in Holography
In principle, if the exposure of a hologram is divided into N equal incoherent parts, each sub-hologram’s diffraction efficiency goes down as 1/n^2. In practice, there is a strong effect of the ordering of the exposures, termed “reciprocity failure.” These observations need to be verified for the materials and processes used here.
One way to build up a 3-D image from a series of cross sections is to array them in space via a series of multiple exposures. This project would explore the strengths and weaknesses of such a simple optical slice stacking method.
A variation of a simple hologram can be used to “sift” a document for a key word, and produce bright spots corresponding to each location, a process called “matched filtering.” This project would demonstrate this filtering over pages of text, and photographs containing enemy tanks.
The Demons of Holography
We’ve concentrated on making good holograms in class. Maybe it’s time to learn from some bad ones, where you design the experiment to show a particular holographic problem. So many options exist: fringes on the object, fringes on the plate, scatter in the reference beam, uneven drying, higher order images, lots of halo noise, etc. The bad results have to be planned, though!
Adhesives & Object Holding Technologies
Record holograms (reflection and transmission) made of precarious objects mounted with a variety of adhesives. Is hot-glue adequate? Is Duco epoxy the superior brand? What can you get away with?