Sam's Laser FAQ, Copyright © 1994-2001, Samuel M. Goldwasser, All Rights Reserved.
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    Laser Experiments and Projects

    !!!UNDER CONSTRUCTION!!!

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    Laser Experiments and Projects Introduction

    Scope of This Chapter

    This chapter provides a variety of suggestions for experiments and projects using lasers ranging from trivial to quite advanced. Some utilize the optical properties of the laser beam like its ability to be well collimated or highly focused while other depend on the unique coherence and monochromicity of the laser light itself.

    Currently, they are just suggestions. (If you can't wait, there are also some links to Web sites with educational laser projects below.) Eventually, additional details of the setup and required supplies will be added. However, even then, in most cases, most of the details will be left as an exercise for the student. What fun or challenge would it be if we told you everything? After all, besides its educational value, hands-on experience should indeed be both fun and challenging! However, where more information is available in this document, links are provided.

    A 1 to 5 mW internal mirror helium-neon laser will be suitable for most of the experiments (though a somewhat higher power one would be better for those like holography). It should be possible to procure such a laser for under $50, possibly under $25 depending on your resourcefulness and scrounging abilities. See the chapter: Laser and Parts Sources.

    Some experiments may require a polarized laser but for most, any type will do, even a better quality (one with an adjustable focusing lens) laser pointer - and those are practically given away in cereal boxes these days. :) Where access to the laser cavity is required, an external mirror HeNe or Ar/Kr ion laser will be needed. A one-Brewster HeNe laser setup can be put together quite inexpensively (probably under $100) using a surplus one-Brewster HeNe tube and power supply, the OC mirror from a deceased HeNe laser, and some scrap materials available in any well equipped junk box. Of course, if you have access to a nice lab laser, that would be fine as well but probably not nearly as much fun or as rewarding compared building one (at least partially) yourself. :)

    Alternatives like bare laser diodes and appropriate drive circuitry may be more desirable for projects like laser communications where modulation is required. And, other color lasers (than the boring red HeNe or laser pointer) will be desirable for laser display.

    Laser Experiments and Projects Acknowledgements

    The material in this chapter has been derived from various sources including:

    Laser Experiments Safety

    All of these experiments can be performed with a fully enclosed 1 mW HeNe laser (or laser head and power supply) which poses minimal risk to vision and no shock hazard from even gross carelessless (though not totally, perhaps, from deliberate abuse). However, some, like those dealing with holography, could benefit from a 5 mW or larger laser. Higher power lasers, especially those above 5 mW, need to be treated with great respect as even momentary eye exposure can cause permanent damage to vision.

    In addition, those experiments requiring access to the interior of the resonator of an external mirror laser may expose the user to potentially lethal voltages in the vicinity. If possible, any exposed high voltage terminals should be well insulated or blocked from accidental access. And, where all you have is an exposed HeNe laser tube and separate power supply, building all this into a safe enclosure is highly recommended.

    Read the chapter: Laser Safety in its entirety and follow its guidelines - particularly in regards to the safety of others who may not be as aware as you in dealing with your equipment.

    Suggested Lasers and Optics Science Museum Interactive Exhibits

    Here is a subset of the experiments listed later in this chapter that might be appropriate for a hands-on exhibit in a science museum that still does science (as opposed to multimedia marketing!):

    Basic principles:

    Applications:

    Other Laser Experiments and Projects Resources

    Here are some optics sites (not laser specific) oriented towards kids: Also see the chapter: Laser Information Resources.



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    Basic Experiments with Lasers

    Beam Characteristics

    Geometric Optics

    The Series Mirror Paradox

    When neutral density filters are placed one after the other, their ND numbers (-log attenuation) add. So two ND1 filters (T = .1) in series results in a equivalent ND2 filter (T = .01).

    Now, what happens if multiple dichroic mirrors are placed in series? Under certain condition, more light will get through than might be expected. For example, using the same example as above, if T = .1 for both mirrors, the resulting output may actually be as high as for an equivalent mirror with T = .05 (rather than T = .01). Why? Under what conditions will this happen? How does the T factor of each mirror affect this behavior? What other factors are important?



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    Diffraction and Interference

    Single Edge Diffraction

    Interference Involving Multiple Sources

    Foucult Experiment

    Schlieren Optics

    Complex Diffraction and Interference Patterns

    Determining Laser Wavelength Using a Ruler

    Spectral Lines in HeNe Laser Tube Discharge Versus Output Wavelength



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    Experiments Inside the Laser Cavity

    The External Mirror Laser

    These require access to a laser with at least one external mirror. The usual choice would be a modest size lab type HeNe laser. Unfortunately, these aren't the sort of thing one typically has at home. And, even if you find one, it may not be convenient (or permitted if it isn't yours!) to gain access to the cavity. However, it is possible to put together something that is every bit as good for minimal cost using a HeNe laser head with an internal HR mirror and Brewster window at the other end. A HeNe laser power supply and easy to construct mirror mount completes the assembly which provides full access to the inside of the cavity between the Brewster window and external mirror. One-Brewster HeNe tubes and laser heads are available on the surplus market but you may have to ask. As an example of such a laser head, see the section: A One-Brewster HeNe Laser Tube. A complete laser using this laser head is described in the section: Sam's Instant External Mirror Laser Using a One Brewster HeNe Tube.

    Mirrors

    Brewster Windows

    Transverse Modes

    Etalons

    Perpendicular Window Trick

    See: Perpendicular Uncoated Windows in a Low Gain Laser.

    Resonator with Intermediate Mirror

    Scattering

    Particle Counting

    Optical Tweezers

    Single Pass Gain

    Experiments With the Mirror/Optics Test Jig Using One Brewster HeNe Laser Tube

    The setup described in the section: Mirror/Optics Test Jig Using One-Brewster HeNe Laser Tube may be used to perform a variety of experiments requiring access to the inside of an adjustable length resonator using various mirrors or other optics. With the commonly available one-Brewster HeNe laser tubes like the Melles Griot 05-LHB-570, either multimode or single mode operation is possible depending on the external configuration.

    Here are some suggested experiments and questions to ponder using this rig:



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    Fourier Optics

    Fourier Transform

    Spatial Harmonics

    Spatial Filtering



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    Advanced Laser Experiments

    Michelson Interferometer

    High Resolution Interferometer

    Waste Beam Interferometer

    Monitor the leakage (waste beam) from the HR of a common HeNe laser tube to detect sub-wavelength changes in the distance from the OC to an external mirror.

    The Laser Oscillator

    Holography



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    Laser Measurements

    Laser Rangefinder

    Laser Beacon

    Laser Level

    Laser Seismometer



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    Laser Surveillance

    Laser Burglar Alarm

    The simplest type of system would use the beam from low power laser (e.g., red laser pointer, HeNe laser, or IR diode laser module) sent around the perimeter of a building or in criss-cross fashion within an area to be protected. It is best to use front surface mirrors for this but for a reasonable number of bouces (say, less than a couple dozen), ordinary rear surface mirrors will work just fine. However, I can usually scavange front surface mirror bits while taking walks along highways where fender-benders occur frequently. Automotive side-view mirrors are actually quite decent. :)

    Simple Beam Break Detector

    The circuit below will activate a relay (K1) when dark. It will easily detect a laser pointer after many bounces from mediocre mirrors, a flashlight, 100 W bulb at several feet without a lens, etc. All components are probably available from Radio Shack, certainly from DigiKey or Mouser. The only not totally common parts are PD1 and K1. I used a Photonic Devices, Inc. part number PDB-V107 (about $2 from Digikey) for PD1. This has a nice large active area of 17 mm but almost any silicon photodiode will work including those salvaged from computer mice and barcode scanners. K1 is a low current relay from Radio Shack but I don't know if it is still listed in their current catalog. There is nothing critical in this circuit.
                                                          o--- NC (Light)
                                                COM ---o/
                                                          o--- NO (No light)
           +6 V o-------+---------+---------------+----+
       (4 AA Cells)     |         |               |    |
                        |         \              _|_    )|| K1
                        /         / R3    1N4148 /_\    )|| 6V coil
                        \ R1      \ 1.5K          |     )|| 500 ohms
                        / 3.3K    /               |    |
                        \         |               +----+
                        |         |                    |
                      __|__       |      5.6K      B |/ C
         LIGHT ---->  _/_\_ PD1   +------/\/\--------|    Q2 2N3904
              Sensor    |         |                  |\ E
            Photodiode  |     B |/ C                   |
             PDB-V107   +-------|    Q1 2N3904         |
                        |       |\ E                   |
                        \         |                    |
                     +->/ R2      |                    |
                     |  \ 100K    |                    |
                     |  / Sens.   |                    |
                     |  |         |                    |
        Return o-----+--+---------+--------------------+
    



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    Laser Communications

    Modulation

    Detection

    Free Space Link



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    Laser Display

    Simple Deflection

    Laser Oscilloscope

    Laser Digital Clock

    Raster Scan

    Multicolor Merging



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    Laser Games

    Laser Maze

    Build a covered 2-D or 3-D (or higher if your Universe supports it) maze placing a fixed collimated laser (laser pointer, diode laser module, or HeNe laser aimed into the maze and planar mirrors at various locations on swivel mounts. The objective would be to adjust the mirrors so that the beam passed through the maze and exited at some predetermined location without removing the cover. Perhaps, peep holes could be placed at strategic locations to help. The maze need not be Cartesian. :)



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    Sam's Laser FAQ, Copyright © 1994-2001, Samuel M. Goldwasser, All Rights Reserved.
    I may be contacted via the Sci.Electronics.Repair FAQ Email Links Page.