Build your own laser positioning system

We built the laser alignment systems ourself. These systems have excellent performance at about have the cost of commercial available systems.

We actually use two different designs. One suitable for HeNe tubes and the other for diode lasers.

**Figure:** 1 This is the optical system suited for HeNe tubes. The laser tube is situated at the bottom of the Al. profile. After a collimating system of two lenses the laser beam is splitted by a mirror type beam splitter. The horizontal line is generated by a cylindrical mirror. About one meter higher the vertical line is generated by a similar mirror. This high located mirror ensures a clear laser line at the top of the patient without the need of an extra laser at the ceiling.
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**Figure:** 2 This is the closeup of the optical system. A green HeNe laser tube (Wavelength 543.5nm, Output 0.5mW, Beam Dia. 0.8mm, Beam Div. 1mrad, Beam mode TEM00) is fixed at the bottom of the Al. profile . A collimating system consisting of a 25mm and a 100mm lens is incorporated in the black metal tube with a diameter of 25mm. After the collimator the laser beam is splitted by a glass mirror beam splitter. The cylindrical mirror that produces the laser line is placed at the right of the beam splitter. The advantage of using this cylindrical mirror instead of a cylindrical lens (used in most commercial systems) is that there are no internal reflections, so no ghost lines are produced. This mirror however is the only component of this laser design that is difficult to obtain. Although this design is the most economical (one laser, two lines) it is not really suitable for inexperienced users. Because the two lines are generated by one laser, alignment of the laser and the optical system is critical. In addition, the long Al. profile is sensitive for temperature changes.
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**Figure:** 3 This is the second alignment system. It was original designed to use in combination with fibre optics, connected to HeNe tubes. However this leaded to disappointingq results. Now the fibres are replaced by solid state laser diodes (Edmund optical Ltd, Stock nr. P54-170, Price 867 pond, Wavelength 532nm, Output 2mW, Beam Dia. 1mm, Beam Div. 1.2mrad, Beam mode TEM00). The black square steel plate is bolted to the wall (Drawing fig.4). At the bottom of the Al. U frame (Drawing fig.6) a neodium magnet is glued on. This magnet fixes the laser system onto the steel plate (no mechanical stress!!). With the four bolts the optical (steel) construction can be shifted and tilted for alignment. The two lenses are incorporated in the steel tube. In this design a -40mm and a 150mm lens are used (visit the Linos site). The lenses can be shifted along the slots (Drawing fig.3) to focus the laser at iso-centre. The laser line is generated by a cylindrical mirror.
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**Figure:** 5 Before you start to build this laser alignment system make sure you can obtain this mirror. We had have them tailor-made at our university. The glass used is of a high quality with a smooth surface. In a vacuum the outside of a glass tube is coated with Aluminium and a layer to protect the Al. from oxidation. (With some mechanical modifications it could be possible to use cylindrical mirrors from Edmunds. Stock nr.P46-210 Page 91 of the catalog. I have not tried it but it could work.)
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Optical design software fore free. Unbelievable what you can do with this software. It is professional stuff so you have to invest in learning and understanding it. Then there are no limits.
http://www.sinopt.com
The two files below are the simulations of the optical systems we use.
laser-neg.len
laser-pos.len