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Visible Laser Beam to aim an Infrared CO2 Beam

This study relates to a US patent granted in 1995 on the use of a visible laser beam to aim an infrared CO2 laser beam.

bull.jpg (5174 bytes) Background

Methods of precisely and conveniently delivering laser energy have been of great importance in the development of technologies for laser applications. Many laser applications as welding and surgery require the delivery of a high power infrared laser beam (usually a CO2 laser beam). Because an infrared laser beam is not visible to the naked eye, it is difficult to determine where the beam is being directed. Hence, it is important to employ an additional visible laser whose beam is coaxially superimposed on the infrared beam, to provide a method for aiming. Many delivery systems employ this technique.

bull.jpg (5174 bytes) Prior Art

(1) The conventional method for delivering laser beams employs refractive lenses to focus and guide the laser beams.

(2) Because of the frequency difference between visible and infrared light, chromatic aberration causes the lenses of the delivery system to refract visible and infrared light rays at slightly different angles. This divergence causes the two teams to be focused at different locations, resulting in imprecise aiming.

(3) The earlier systems employed a red aiming beam due to certain limitations in optical materials. Because a single system of lenses, guides both the visible and infrared beams, it is essential that the material from which the lenses are made should transmit the light from both the visible and infrared CO2 laser. Hence, there are few optical materials which meet this requirement. This limitation imposes a restriction on the color of the aiming beam, and hence all aiming beams have been restricted to the red end of the spectrum above 600 nm. The most suitable material for this purpose is zinc selenide which has a transmission range from 600 nm to 18 Ám, which includes the 10.6 Ám light from a CO2 laser.

Red light, however, is an ineffective color for an aiming beam. In surgical applications for example, one usually delivers the laser beam to a red target such as the liver or bloody tissue. In this situation a red aiming beam is difficult to see against the red background. Moreover, the human eye is not as sensitive to red light as compared to other colors.

bull.jpg (5174 bytes) Present Invention

(1) An infrared CO2 laser beam combined with a highly visible, blue-green aiming beam, which can be precisely focused on the same point as the infrared beam. In place of refractive optical guidance, the delivery system of the present invention employs reflective components. These reflective guidance systems do not have chromatic aberration since both visible light and infrared light are reflected in an identical manner. Consequently, the two beams are confocally delivered precisely at the same point on an object, thus, permitting laser operations with unprecedented accuracy.

(2) Reflective delivery systems do not have the material limitations, since there are suitable materials which have high reflective values throughout the whole visible and infrared range.

(3) The blue-green aiming beam provides a ten times better contrast against a red background as compared to a red beam. Moreover, the human eye is seven times more sensitive to blue-green light than to red light.

Figures 1 and 2 are the preferred embodiments of the invention.

Laser
Fig. 1

Laser
Fig. 2

The patent has 10 claims which cover different configurations and designs of an apparatus, for confocally delivering to an object, an infrared beam of light having a wavelength substantially equal to 10 Ám, or an aiming beam of light having a wavelength in the range of 400 nm to 600 nm. The novelty lies in the use of a reflective optical guidance system in place of a refractive system. The utility/usefulness of the invention is quite well established.

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