Digital photo showing beam from our new diode laser system.
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.
Sam and I are looking at starting a small business hand-making these laser systems and offering them for sale -- and being able to come in at around half the price of units now available (we're looking at $250-$300 or so for the assembled 25mW (27mW Typical) unit including power supply, driver, diode and collimating optics -- all in a self-contained unit with on-off switch, indicator light and AC/DC power). By achieving this level of stability, at this power range and at a reasonable price, holographers (especially hobbyists working with lower-powered lasers) will now have the opportunity to take a giant step forward in their work. Holographers that are already working within the 25-35mW range, will no longer have the high expense of replacing their HeNe systems or recharging their tubes (and why would they even want to anymore?). We are hoping to have a working 50mW system by the end of the calendar year as well.
We're also exploring other options as well, such as offering the complete plans to build your own, as well as a do-it-yourself kit with all the parts (and plans) included.
Please note that the 27mW is the optical output power. The diode is a 35mW diode. The 35mW PowerTechnologies laser diode module (for $500) 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.
If you would like more information on this laser, including information on how to get one of your own, please send an email to: laser@holoworld.com and we will send you the availability and pricing information as soon as we have the first units ready to go.
If you're thinking of moving up in power (or just want to scrap that 25-35mW HeNe after reading the above report) we hope you will consider looking into our new diode system. We've put an awful lot of work into it, and we would like to offer a system that has the feel of a fine hand-crafted instrument, but at the same time rugged enough to withstand the amateur and hobbyist lab environment and provide performace that exceeds what's currently available by a wide margin. And, at a price that's just about "out of pocket". After all, I spent 36 months paying off the loan on my 15mW SpectraPhysics 124B back in the 80's. I don't want anyone to have to do that to enjoy holography. Wish us luck!
This is almost like a revolution, isn't it?
Frank DeFreitas
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