If you were to section one of these laser pointers, you would see the basic arrangement in the drawing adjacent.

The laser unit is powered by three small cells connected in series to give a maximum voltage of about 4V.

There is a simple push button switch that must be held in to turn the laser on. The source that generates the light is a very small Red LED Laser Diode.

This produces a spherical Wavefront that is collimated to a parallel "Laser" beam by a small lens.

The position of the lens is adjusted by a screw thread and spring to set the exiting beam completely parallel. (In some pointers, the threads are subsequently locked with superglue before despatch.)

Once you have found one of these in the shops or on the internet, it can be converted to a light source simply by removing or unscrewing the front lens. This gives access to the expanding spherical Wavefront from the tiny Laser diode. This leaves you with a nearly perfect light source for optical testing of astronomical mirrors.

If the laser is a type supplied with the lens screw threads locked with superglue, then saw off 4-6mm from the front of the unit with a small hacksaw. This is usually sufficient to release the front lens. The picture adjacent is an example of one of these types with 6mm removed from the front.

To operate the push button needs to be held in. Probably the simplest way to do this is with something like a clothes peg. There is no reason the peg cannot also perhaps double up as part of the arrangement for holding the light source?

The internal batteries have sufficient life for occasional use. They are a common type so are easy to find in the shops and cheap to buy.

Be aware when changing batteries that inside the tube there is a thin cellophane sleeve that stops the metal cases of the batteries shorting out on the inside of the metal tube. If this sleeve gets displaced or slips out, the pointer will not work and the cells will soon run flat. This sleeve slipping out seems to be the major cause of failure of these cheap units.

If the cellophane sleeve does get damaged, - then all is not lost! - Try one turn of sello-tape round a pack of three batteries together, and push the pack carefully back into the tube.

Oldham Optical uses red light sources similar to these Red LED laser Diode modules to test mirrors.

In our case we require regular and continuous use so using the internal batteries would not be very sensible, We would have to change them too often. We have specially made mains power supplies in the workshop to power the lasers. These supplies give a variable DC Voltage adjustable between 2-3.5 Volts to give variable light levels.

So if a considerable amount of testing is being considered then the laser pointer needs to be taken apart to allow wires to be inserted into the pointer to allow external batteries or a mains power supply to be used. This also allows a potentiometer to vary the light level.

Being able to vary the light level is a good bonus. While a bright light is useful for setting up, a very dim light can be better for accurate testing.)

Once the first 4-6mm is cut off to release the lens, the module can be taken apart as follows:-

The LED module is a push fit into the front of the tube. Pressure on the collar can be released with a short longitudinal saw-cut from the front of the tube back about 8mm maximum, as seen in the upper part of the photo adjacent. This will usually allow the module to fall out, - or if not it can be gently pushed out from the back using a screwdriver or similar tool. The module removed is in the lower part of the photo adjacent.

Although Oldham Optical uses mains power supplies in the workshop, we often give demonstrations of astronomical mirror testing at various gatherings away from the workshop. For these rather than take a mains supply that needs somewhere to plug it in, we take a simple external battery unit as depicted adjacent.

This one contains a battery holder for three AA cells together with a 500 Ohm potentiometer to vary the light intensity and a pair of terminals. The circuit of the unit is adjacent.

We suggest a power supply of this type will have more than sufficient capacity for any amount of testing contemplated by an amateur mirror maker and it saves the expense of a mains powered unit. 

A small flexible 2 core cable like "Bell-Wire" is used to wire the module. The negative wire is soldered to one of the switch contacts, - but beyond the switch mechanism itself, - so it no longer needs to be pressed to operate the LED. The laser does not like a lot of heat, - so its a quick dab on with the soldering iron. Preferably use the switch terminal away from the one with the printed circuit board track leading to the laser diode.

In the picture above, the spring that connects the front battery to the module can be seen poking out of the tube. This can be cut off if it gets in the way.

Do not attempt to solder the positive contact. Depending on what type of module you have got, the collar of the module is made either from low melting point metal or is just plastic covered with conductive metallic paint. Instead arrange the positive wire length so when the module is pressed back into the tube, the wire is trapped between the module collar and the tube. The right length can be seen in the photograph above.

The module will easily press back into the tube using a vice. The positive wire should first have the individual cores spread out slightly so they are not bunched up so will make good contact with the tube and collar.

The tube can be shortened as required with a hack saw to clear the longitudinal saw-cut that was originally made to release the module.