Re: How does a laser pointer head make shapes and patterns?

Hi Aaron!

The clear window in those little things is... A HOLOGRAM! :)

It's a computer-generated hologram of a simple drawing. It's a special kind of lens which is based on diffraction gratings. It's a lens which bends the laser beam to form a complicated pattern.
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Whenever someone makes a large hologram of a distant object, and then then they illuminate the hologram with a broad cone of laser light, the hologram will re-create the light that came from the original object. Put your eye in the right place, and you'll see the original object That's why holography can record a 3D image: it records the pattern of ray-angles of the original light.

But suppose you shine a very narrow laser beam at the hologram instead. In that case the hologram will split the beam into three beams, and it will divert two of the beams to project two fuzzy images, images of the original object that was holographed. The original laser beam will shine straight through the hologram, and the two images will appear on either side. One of the two images will be upside-down, and the other will not. Holograms just do this naturally. It's part of the physics that makes holography possible.

Here is another product which uses the same effect:

"Holospex"(tm) HOLOGRAM GLASSES
http://www.holospex.com/
http://www.arbors ci.com/Data_Sheets/Files/Holospex.pdf

Holospex glasses are the same as laserpointer image tips. If you shine a laser beam through one lens of Holospex glasses, the image pattern will appear surrounding the spot of laser light upon the wall.

There is one main difference between a standard hologram and the tiny holograms inside the laser-pointer. A standard hologram is designed so that the two images are sent to very large angles away from the original laser beam. That way we can block out one of the pair of images and only observe the other one. (After all, the unwanted image will be upside-down. This unwanted image is called the "pseudo- scopic" image.) We call this process "off-axis holography."

In the holograms used in laser pointers and Holospex glasses, the two images are sent to very shallow angles away from the original laser beam. That way the images will follow the beam, or, in the case of the holo-glasses, the two images will surround any bright point-source of light seen in the environment. These are "on-axis holograms."

There is one case where we can hide the double-image. If you want to project a symmetrical object such as a snowflake or a dollar sign ($), then instead you could make a hologram of HALF of that object. In your holography setup, adjust the object and reference beam angles just right. Then, when you view the completed hologram, you'll find that the two half- images fit together to create a single complete snowflake or dollar sign.
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Can a hobbyist make one of these holograms? Perhaps. I'm not a holography hobbyist myself, but I can see several ways that an advanced hobbyist could create one of these holograms.

It might even be possible to write your own computer program to create the hologram. You'd print out the hologram onto paper in enlarged form, then reduce it about 10,000 times in size by photographing it from a distance. The camera film becomes the hologram.