CO2 Laser mirror - Beam delivery mirrors

 0ֲ° Phase Shift Mirror

In most laser machines, one or several mirrors are used to forward the laser beam from the cavity to the working head. Usually, each mirror deflects the laser beam at an angle of 90°, corresponding to an angle of incidence of 45°. At these mirrors, reflectance should be as high as possible in order to minimize loss of laser power. In addition, phase shift between the s- and p-polarized components of the reflected beam should be as low as possible in order to avoid disturbing the polarization of the laser beam. Mirrors with such properties are called zero-phase mirrors.

 0ֲ° Phase Shift Mirror

In most laser machines, one or several mirrors are used to forward the laser beam from the cavity to the working head. Usually, each mirror deflects the laser beam at an angle of 90°, corresponding to an angle of incidence of 45°. At these mirrors, reflectance should be as high as possible in order to minimize loss of laser power. In addition, phase shift between the s- and p-polarized components of the reflected beam should be as low as possible in order to avoid disturbing the polarization of the laser beam. Mirrors with such properties are called zero-phase mirrors.

 90ֲ° Phase Shift Mirror

Most CO2 lasers produce a laser beam which has linear polarization. For cutting metal sheets, however, a beam with circular polarization is required if the cutting properties are independent of the cutting direction. To convert a beam from linear to circular polarization, a 90° phase retarder mirror (also called a Lambda/4-mirror) can be used. This mirror has a special coating which produces a phase shift of 90° between the s-and p-polarized components of the reflected beam. If these components have the same intensity and phase (corresponding to linear polarization), the reflected beam undergoes a phase shift of 90° between both components (corresponding to linear polarization).

Windows

Windows for CO2 lasers are used either for protecting sensitive and/or expensive optics, or for separating areas with different gas pressures. In all applications, high transmittance and low absorption are needed in order to minimize distortion of the laser beam. Therefore, such windows usually consist of ZnSe substrates with AR-coatings on both surfaces (the same as focusing lenses).

TelescopicMirror

In many applications, the small diameter of the laser beam produced in the laser cavity is not convenient because the beam has high divergence and high power density. In order to avoid subsequent problems, the beam diameter can be increased by using a telescope consisting of two mirrors – one with a convex surface and the other with a concave surface. Such telescopic mirrors are usually made of copper.

ATFR

In some laser cutting processes, a portion of the beam may reflect off the work piece and into the laser cavity, where it might disturb laser operation. In order to avoid such problems, an ATFR mirror can be inserted into the beam line. An ATFR mirror is characterized by high reflectance (typically 99%) for s-polarized radiation and low reflectance (typically less than 1%) for p-polarized radiation.

 0ֲ° Phase Shift Mirror

In most laser machines, one or several mirrors are used to forward the laser beam from the cavity to the working head. Usually, each mirror deflects the laser beam at an angle of 90°, corresponding to an angle of incidence of 45°. At these mirrors, reflectance should be as high as possible in order to minimize loss of laser power. In addition, phase shift between the s- and p-polarized components of the reflected beam should be as low as possible in order to avoid disturbing the polarization of the laser beam. Mirrors with such properties are called zero-phase mirrors.

In the beam delivery section, of a CO2 laser system, the laser beam is transferred by CO2 laser mirrors from the laser cavity to the cutting head.