The Professor's Homebuilt Lasers Site

Over the years I have been asked numerous times about the use of a particular laser for a science fair project. Being an alumni of the International Science and Engineering Fair myself this is a topic I'm more than happy to discuss. If you're interested in what _I_ did, might I first suggest a visit to my Science Page on my personal website which describes my old projects including the one that won first prize in the 1984 ISEF.

Considering the laser for a science fair project, you might be thinking the laser is indeed a solution without a problem ... a kind of cart-before-the-horse. The creators of the device also thought that, and it was over 20 years after it's invention that the true potential of the laser was realized. So, If you're thinking of using a laser for a science fair project (been there, done that) and need ideas, here's a few I've got. If anyone has other ideas, please share them and I'll update this page for the benefit of all ...

Remember, though, that simple construction of a particular laser is not good enough! Being a judge at the regional fair has given me insight as to what constitutes a 'scientific' project. While displays of Tesla coils and lasers are certainly popular exhibits (although many fairs have banned demonstration of these during fairs due to safety concerns), they do not always do well with the judges since often they lack scientific thought. Construction of a laser _could_ be considered an engineering project but one must demonstrate a unique approach towards the problem (e.g. unique tube design, calculation of some parameter and proof of it through experiment). Using a laser as a physics project would require investigation of some scientific phenomenon. And don't forget to state the PROBLEM, HYPOTHESIS, and CONCLUSION ... science fair judges ALWAYS look for that!

Ideas Which Involve Laser Construction

The following ideas involve constructing a laser itself

Using Neon in a nitrogen-type laser. Neon has lower efficiency but has a line in the green at 540.1nm. The pressures are about the same (35 torr) and so a single-stage vacuum pump (or converted compressor) will work fine. Of course there is an added expense of a lecture bottle of Neon gas (I figure about $100). Upper-energy levels for neon _do_ have a shorter lifetime than Nitrogen though so it is even more critical that the laser be designed to discharge as fast as possible: 1.5 nS pulse lengths are reported in the literature. The design might well we similar to a TEA Nitrogen to attain the fast pulses required (There's another idea: a TEA Neon ... haven't seen one of those ever but it should be possible). The project itself could be a study of the quantum-mechanics of the neon atom and lifetime of energy levels therein.
Using Neon in a Marx-bank type laser. If neon is pumped with an ultra-fast electrical discharge in a long ('normal', not transverse) laser tube which consists of a capillary it exhibits many superradiant lines in the green, yellow, and orange. Literature shows such a laser is possible with a laser tube 40cm long made of 1mm i.d. glass capillary. Pressures are low and should be between 0.2 to 0.4 torr for the 594nm orange and 614nm red lines. As well, these lines appear only in a pure discharge so a decent vacuum system is required. Looks relatively easy to make it work otherwise.
Lasing lines of Argon superradiantly. A superradiant laser needs no mirrors: A boon to the amateur on a budget. Several strong Argon lines will laser superradiantly in a long (3m !) laser. With a 1 or 1.5m laser tube likely Aluminum mirrors will work since the gain of such a long tube is extraordinarily high - this has been proven in the literature (Imagine the Scientific American design with a laser tube 1.5m long!). One could go-on to study the gain of the laser and factors affecting it (e.g. magnetic field, discharge current)
Using dyes embedded into plastic resins for a laser. If a laser dye is added to, say, acrylic resin and cast in the form of a rod, a nitrogen-laser pump might be able to make it lase.
Developing an ultra-fast flashlamp for a dye laser. Faster discharges mean lower threshold energies as well. A simple homebuilt capacitor and flashlamp operating at low capacitances but high voltages should discharge in 100nS or less and allow a low-threshold laser to work. One could then do a parametric study of the laser pump and possibly mathematically model the lamp/capacitor circuit developing or proving the model by experiment.
In a similar vein to the above, a superradiant dye laser. This has been demonstrated by using a capillary or a slab and fast flashlamp discharge. If the laser is brought just under the superradiant lasing threshold it may be used as a 'normal' dye laser. This arrangement allows the use of inexpensive optics (since gain is high) and makes alignment easy (drive it superradiantly, align the mirrors to boost output, the 'back off' the power so the laser is operating normally).
Tuning apparatus for dye lasers (This was the topic of my project years ago). I used intra-cavity optical slits, beam expanders, and dielectric filters to reduce linewidth of N2-laser pumped dye lasers.

Ideas Which Use The Laser

The following ideas involve using a laser for the sake of it's coherent light. These are only ideas so I haven't done any real research into the concepts - they may or may not even be possible!

Determining water purity by determining scattering of a laser beam through water. This was outlined in an old Amateur Scientist article years ago.
I.R. Colorimetry using several laser diodes operating at various wavelengths. Laser diodes are now inexpensive (especially IR ones) and available in a variety of wavelengths. One possible project might be determining content of methyl hydrate in ethyl alcohol solutions based on their IR absorption spectra (Great idea for moonshiners but I'm not sure what each spectra looks like :).