LASER POINTER / SEMICONDUCTOR LASER HOLOGRAPHY
by Frank DeFreitas Holography Studio
Creative Holography Using
My magical journey of making
Inexpensive Laser Pointers
holograms with a $7.99 laser pointer
and inexpensive laser diodes.
FIRST REPORT (9/13/99)
This is the 15th page of this section on diode laser holography. If this is your first time here, don't forget to click on the laser diode index link at the bottom of this page to see how all this came about.
Digital photo showing beam from our new diode laser system.
Well, after much trial and error over a long, hot summer, Sam and I have successfully built and tested a 25mW laser diode assembly of our own design -- which is designed especially for high-contrast fringe recording and long coherence length in holography.
Actual size of diode compared to US penny.
The laser is designed around the Mitsubishi 35mW laser diode, operating at a wavelength of 658nm. Actual output power after the beam passes through the collimating optics is measured at 27mW continuous wave operation. A slight reduction in operating current and voltage has moved the actual wavelength to 650nm -- which provides a wavelength which gives an increase in the apparent brightness of the laser according to the response curve of the human eye. This results in the creation of a slightly-brighter hologram (to the eye) than would be achieved compared to the same hologram created with 658nm (all things the same).
Top of Prototype power supply/driver circuitry by Sam
We are now operating a prototype unit, which consists of a power supply/driver circuit and laser diode in a brass housing with collimating optics. We will soon develop this into a self-contained unit that you can sit right on your holography table or optical bench.
Sam has done a great job in designing a circuit that provides a high level of fringe contrast and locks those fringes in place. The above shows the prototype driver, which will be made smaller and assembled into the self-contained unit. The driver provides an extreme level of current and voltage stability, even with fluctuations of input power such as in the case of your typical wall outlet. The driver can run from AC or DC power, and has 12-volts in (for DC, of course). It is providing the long-term fringe stability that is normally only achieved with gas lasers by using a fringe-locking device in the holography set-up.
Magnified shot of well-defined, high-contrast fringes -- with a 14-foot(!)
difference in beam paths on the interferometer. Try this with a HeNe!
Coherence length has been measured at a MINIMUM of 14 feet (or 4.5 meters) -- This is as far as I could get on my table without more room. Guess it's time for a bigger table. But, man oh man, did I love just sitting there and looking at those fringes. I just pulled up a chair, got a glass of ice tea, and put my feet up. Life is good.
For split-beam holography, this COMPLETELY REWRITES THE BOOK. No longer do you have to measure your object beam and reference beam and make sure they are the same length. Just place a beamsplitter wherever it is convienent in the set-up, knowing that the fringe integrity will always be intact. This also will allow new table layouts which will lead to more creative uses of multiple object illumination for both mastering and direct recording. In other words, do anything you want with the beam . . . it doesn't matter anymore. Side illumination plus a separate beam going to an overhead mirror? With each beam a different path length? . . . and none of them the same length as the reference beam? No problem any more -- those days are now over.
Not to mention the incredible depth that now becomes obtainable with laser transmission and rainbow work. Might as well go ahead, clean out the basement, and build that 16 foot sandtable. I can't wait to see what images this will lead to from amateurs and hobbyists from around the world! The playing field is getting more and more level each month.
Photo of the collimated laser dot. ("Halo" around dot must have
something to do with the camera lens. It's not there when you look at
it with your eyes.)
The collimating optics are providing a nice spot size, similar to the output of the HeNe. While not easily seen the photo, the dot is slightly oval in shape -- which, actually, is beneficial when working with rectangular recording materials such as found with film and plates. The output is very consistent throughout the entire area of the spread beam, unlike HeNe's where you have that troublesome "hot spot" right in the center that must be spread out evenly -- and results in lost power delivered to the plate from spreading the beam out so much.
Sam working on the electronic circuit.
Please note that the 27mW is the optical output power. The diode is a 35mW diode. The 35mW PowerTechnologies laser diode module on previous pages has an actual optical output power of 27mW.
Sam at "the scope". I have no idea what those straight lines mean,
but Sam was saying "oh man, that's beautiful . . . just beautiful".
So far, the 4 x 5 test results with this laser have been beautiful. I am currently setting up for 8 x 10 shots, and will quickly move onto 30 x 40cm shots soon. I will wait until the 30 x 40cm shots are completed before placing any photos on the web -- so stay tuned. I'd really like to shoot a deep-image laser transmission hologram.
This is almost like a revolution, isn't it?
-- Frank DeFreitas
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