Laser Beam Concentrator/Aiming Device

Photos showing construction of a laser beam concentrator and some shots of it being tested.

Max Carter

Some raw materials:

The pipe is 10" (25cm) o.d. gated PVC irrigation pipe.

Cut to length 37" (92cm):

The length is calculated by adding the focal length of the Fresnel objective lens
to the focal length of the eyepiece lens,
plus a little fudge factor.

cut pipe

The mount:

constructed with 3/4" (19mm) PVC water pipe.

The pipe washed and mounted:

The pipe inside wall painted black:

The view through the pipe without the lens:

The Fresnel lens:

11" x 11" (27.5cm x 27.5cm) (Scientifics 30708-77), focal length about 28.5" (69cm)

The Fresnel lens glued in place and trimmed:

I tried 3 different glues before finding one that would stick to the lens - super glue (cyanoacrylate).

The view through the pipe with the Fresnel lens in place:

Reticle Construction

The reticle is made with 14 AWG copper wire soldered to a small brass washer.
The photo shows the washer and copper wire before soldering:



The reticle installed in the pipe:

The reticle is installed 28.5" from the Fresnel.

The "ground glass" (waxed paper) screen:

I ironed the waxed paper flat before cutting it to size.

The waxed paper screen glued in place on the reticle:

showing the horizon projected onto it (upside down) from the Fresnel lens. (A car is in the foreground.) This completes the short-range version of the concentrator. The photodetector would be mounted in the hole in the washer.

The short-range concentrator in action at night:

The concentrator is viewing an ordinary 3 mW red laser pointer (see Laser Shotgun) 100 yards (91m) away. The first shot was taken with flash. Even with flash, the spot shows up easily on the paper and even appears to be over-exposed. The laser is the little red dot off to the left. This version of the concentrator actually works quite well at longer ranges, especially at night.

The rest of the shots were taken without flash, a little off beam here:



The moon (upper left) got into this shot.

The following photos show the conversion of the short-range version of the Laser Beam Concentrator
to the long-range version.

The first step is to remove the waxed-paper target from the reticle:

The eyepiece components:

The black thing is a 9" x 1.25" aluminum pie pan, painted, with a 1.25" hole punched in the center. The other thing is a 3" (7.5cm) hand magnifier.

The lens is removed from the magnifier and glued to the plate, over the hole.

The glue used is RTV silicone.

The completed eyepiece held in place on the end of the concentrator:

It was decided not to mount the eyepiece permantly at this time in order to allow access to the reticle/photodetector mount.

Photos of the long-range version of the laser beam concentrator in action can be seen here.
More information about this device can be found here.

Warning: This device is meant to be used with a visible class-IIIa (<5 mW) laser at a distance.
Do not look at any higher-powered laser with this device!
Do not view any laser through this device at a distance less than 1/4 mile (400m)!

Related Links

Laser Beam Concentrator Technical Details

Concentrator Built with Glass Lens and Tin Cans

Laser Shotgun

Laser Pointer Audio Modulator

Music on a Light Beam - the System Tested

Sewer-Pipe LED Projector

Range Calculator/Estimator

Related External Link

Using Laser Pointers for Free-Space Optical Communications