Retrotechtacular: Shedding Light on Holograms

This week’s Retrotechtacular is a 1972 introduction to holography produced by the fine folks at Encyclopædia Britannica. It details quite admirably what holograms are and how they’re made.

Holograms are quite different from photographs, though both are recorded on film. Holography is based on the additive effects of waves: two crests of equal amplitude create a larger crest, while a crest and a trough of equal amplitude cancel each other out, causing an interference effect. The video demonstrates the concept nicely with water ripples and explains that the same effect happens with sound waves and light waves.

Lasers are the key to the intense and spectrally pure light required for holography. Incandescent light consists of too many wavelengths to be effectively split into two identical light wave sources. To create a hologram, a laser is split with an optical device into two beams. One beam is focused directly on the object being recorded and is called the object beam. The second beam is directed away from the scene through a series of mirrors and shone directly onto a film emulsion.

The film records the interference between the waves of the two beams. It appears to be blank after development, but upon close inspection reveals stripes of light and dark. When the exposed film is placed in the path of only the reference beam, the interference patterns recorded on the film split the beam back into two, recreating the scene. With the aid of a screen for projection, the hologram can be seen showing the original object in 2D. Another big difference between photographs and holograms is that even a small portion of a hologram can reproduce the entire scene, but a piece of a photograph is just that.

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Adding a Manual Z-axis To Your Laser

DSC07543 (Custom)

[Martin Raynsford] sells lasers, and laser cuts stuff for a living — we’re kinda jealous. Anyway, laser cutters from China are great, but sometimes lack certain functionality, so he decided to add his own z-axis feature!

The main laser cutter he uses has a very slow z-axis, and it’s also difficult to control — a job can’t be paused to adjust the height offset, the datum must be set every time manually, and you have to be in the very top level of the menu in order to do anything with it! With this in mind, [Martin] decided to add his own z-axis control, completely separate from the laser’s on board control system.

He’s using an Arduino Pro Mini to control the stepper motor with PWM. His new controller has four buttons — fast and slow, in each direction. He’s used the original end stops to protect the axis, and he’s also added a feature to set a datum by holding down both fast and slow buttons at the same time. It ended up being a very cheap upgrade to his system, and he’s also shared the source for anyone looking to recreate it.

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Homebrew Phase Laser Rangefinder


Just when you thought ARM micros couldn’t get any cooler, another project comes along to blow you away. [Ilia] created a phase laser rangefinder (.ru, Google translatitron) using nothing but a laser diode, a pair of magnifying glasses, a few components and an STM32F4 Discovery dev board.

The theory behind this build is using a laser’s phase to determine how far away an object is. By modulating the laser diode’s output at a few hundred Mhz, the reflection from the laser can be compared, giving a fairly reasonable estimate of how far away the target is. This method has a few drawbacks; once the reflection is more than 360 degrees out of phase, the distance ‘loops around’ to being right in front of the detector.

The laser diode used does not have any modulation, of course, but by using an STM32F4 ARM chip, [Ilia]was able to modulate the amplitude of the laser with the help of a driver board hacked out of a 74HC04 chip and a few resistors. Not ideal, but it works.

The receiver for the unit uses a photodiode feeding into the same microcontroller. With an impressive amount of DMA and PLL wizardry (the STM32F4 is really cool, you know), the phase of both the transmission and reflection can be compared, giving a distance measurement.

It’s all an impressive amount of work with a hacked together set of optics, a cheap dev board, and a few components just lying around. For any sort of application in a robot or sensor suite this project would fall apart. As a demonstration of the theory of phase laser rangefinding, though, its top notch.

You can check out a video of [Ilia]‘s rangefinder below. Be sure to full screen it and check out the distance measurement on the LCD. It’s pretty impressive.

Thanks [Володимир] for the link.

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A Cheap Honeycomb Table Replacement for your Laser


CO2 lasers make use of a honeycomb table which allows you to support parts you are cutting — without cutting into the bed too much. Unfortunately they are a consumable part, so they will eventually wear out, and they aren’t that cheap. [Claptrap] came up with an excellent alternative.

A few months ago, his radiator blew in his station wagon, and it had to be replaced. He was about to throw it out when he realized the similarity of the radiators cooling fins, to that of his honeycomb table… He cut it down to size, pressure washed it (though he notes you should probably wash it first before cutting) and put it in place. It works great!

The only caveat we have is that you should probably flush the radiator with a water pump first — you don’t want to be heating up any residual radiator fluid inside the radiator channels!

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Ion Propelled Tie Fighter Now Has a Laser!


[Steven Dufresne] has been playing around with ion propulsion using high voltage lately, and he’s added another spaceship to his experiments — Darth Vader’s TIE Fighter – and as an added bonus, he’s thrown on a laser too!

We originally covered his Ion Wind Propelled Star Trek Enterprise a few months ago, after someone had mentioned that the ion winds he was generating in experiments kind of looked like the warp drives on the Enterprise. Well, someone else pointed out that a TIE Fighter was an even better candidate for this. After all, TIE stands for Twin Ion Engines. So he decided to build one too. The ion winds look even better on this one as he’s turned the entire back of the fighter into the electrode, which creates a wide and very visible arc.

Oh, he also decided to add lasers to it for some extra flare — unfortunately TIE Fighters used green lasers — not red ones. Stick around for the following videos to see the TIE Fighter in all its ionic glory.

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From Schematic to PCB in Four Hours


Last super bowl Sunday, instead of checking the game, [Mattw] decided to extend a design and make a PCB of a trinket clone. [Mattw] altered a trinket clone design by [Morgan Penfield Redfield] to shrink it down, perforated the USB connector to allow for easy removal and put most of the parts on a single layer.

After finalizing the design, [Mattw] put it into the LPKF Protolaser S that Seattle’s Metrix Create Space has. For those of you who don’t know, the LPKF protolaser uses a laser to directly ablate off the copper from the boards.  This makes prototyping much faster without the need for a lot of nasty chemicals.

About six minutes in the Protolaser, some component placement by hand followed by a run through their reflow oven and [Mattw] had three boards ready to be tested. All told, about 4 hours from start to finish.

The end circuit looks great and the LPKF protolaser gives us a case of serious tool envy. If you’re like us and don’t have access to the fancy laser you might try our hand at this high-resolutino photo-etch process.

[via reddit]

Laser-Based PCB Printer


Being able to create PCB’s at home is a milestone in the DIYer’s arsenal. Whether you physically mill or chemically etch boards, it’s a tricky task to perfect. [Charlie & Victor] are working towards a solution to this complicated chore. They call their machine the DiyouPCB. DiyouPCB is an open source PCB etching project consisting of both hardware and software components.

The project is based on using a Blue Ray optical pickup. The pickup was used in its entirety, without any modification, to simplify the build process. In order to use the stock pickup, [Charlie & Victor] had to reverse engineer the communication protocol which also allowed them to take advantage of the auto-focus feature used while reading Blue Ray discs. The frame of the machine is reminiscent of a RepRap, which they used to do preliminary testing and laser tuning. The X and Y axes run on brass bushings and are belt driven by stepper motors which are controlled by an Arduino through a specially designed DiyouPCB Controller Shield.

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