Glossary
Absorption
Interaction of radiant energy with matter. The higher the absorption capacity of a material, the greater the effect of the material change. The absorption behaviour is determined by the laser wavelength, intensity, angle of incidence and surface roughness. Reflection can be seen as the opposite of absorption.
Axis, optical axis
The optical centre line of the lens system. The line that runs through the centres of curvature of the optical surfaces of a lens.
AR coatings
Anti-reflective coating used on the back of laser output mirrors to suppress unwanted multiple reflections that reduce performance.
Axial flow laser
A gas laser in which the laser gas mixture is channelled through the laser tube in an axial direction. Depending on the design, this can be either the popular fast axial flow or the less popular slow axial flow.beam bender
Beam bender
Hardware assembly or optical device, such as a mirror, that can change the laser beam direction; used to redirect the beam and in a "folded" compact delivery system.
Continuous wave laser (CW)
A laser beam that radiates constantly from the laser source. The term continuous wave is more commonly used and refers to an uninterrupted wave. CW lasers are often used in material processing for welding or cutting. These lasers can also be referred to as continuous wave lasers.
Diffusion-cooled laser
Typically a CO2 laser design that uses diffusion gas cooling to cool surfaces instead of flowing through a heat exchanger. This design is simpler and more compact than axial or cross-flow lasers.
Diode laser
Sometimes referred to as a semiconductor laser, the active element is a p-ri semiconductor junction. When current flows across the junction, intense light is emitted from the edge of the chip in the plane of this junction. The majority of diode lasers have a power in the range of 630 to 1550 nanometres of the spectrum. If individual diodes are used, this is referred to as a single emitter. To increase the power, several laser diodes can be mounted on a so-called bar. These can then be stacked on top of each other to form stacks and optically combined to create high-power systems.
Average output power
The total energy per pulse multiplied by the number of pulses per second. (Joules per second = W). This power is usually also used to specify the power of a laser beam source.
Gaussian beams (TEM00)
The Gaussian beam (TEM00) is ideally suited for numerous applications in laser technology due to its minimal divergence. In practice, however, many lasers deviate from this optimum case. This can be caused by the oscillation of higher transverse modes or by amplitude or phase disturbances due to inhomogeneous amplification of the laser medium.
Cavity (laser resonator)
The laser resonator or the tube in which the laser process takes place. Resonators can have different designs. An optical resonator is a basic component of every laser system. Optical resonator in the form of a fully reflective and a partially reflective mirror, which enables feedback of the radiation emitted in the active medium. The laser resonator, the laser medium and the pump mechanism are the three basic components of a laser.
Rayleigh length
The Rayleigh length is the distance along the optical axis that a laser beam requires until its cross-sectional area doubles, starting from the beam waist; this is important for material fine machining as it results in the energy input per unit area.
In marking applications, no part of the Rayleigh length can be used to compensate for a height deviation (focus distance) and to achieve good results on curved or round surfaces without focus tracking via an optical or mechanical axis.
Beam delivery system
Use of optics such as mirrors, lenses and optical fibres that are arranged in such a way that a laser beam can be directed precisely to a specific location. In addition to beam guidance, optical components that change the properties can also be used. These include, for example, beam expansion and focussing optics to achieve a sharp laser spot.
Beam expander
Optical device that increases or decreases the input beam diameter of the laser. Beam expanders are generally used to increase the diameter of laser beams. The divergence decreases by the same factor, as the product of beam diameter and divergence is constant. In material processing, for example, beam expansion is used to achieve a smaller laser spot. With larger expansion, a reduction in size is achieved by subsequent focussing.
Beam divergence
The tendency of a laser beam to expand in diameter as it moves away from the source. It is measured at certain points in milliradians (mrad). Beam divergence is used to characterise the beam. Normally, beam divergence refers to a circular beam diameter, but it can also be used for elliptical beam cross-sections, taking into account the diameter of the ellipse.
Beam diameter
The diameter of the part of the laser beam that contains at least 86% of the total energy of the beam. In practice, the beam diameter is usually defined as the output diameter of the laser source. In addition to the basic parameters such as wavelength and power, all components of the beam delivery system are also based on the beam diameter.
Beam quality
Ratio between a real beam focal spot diameter and the focal spot diameter that would be generated by a theoretically perfect beam. Accordingly, it is the ratio of the divergence angles of the real beam and an ideal beam with the same waste diameter. The beam quality is often expressed by M2 or K. (1 / m2)
Beam splitting
the use of an optical device to split the laser beam into several beams so that more than one spot on a workpiece can be processed simultaneously, albeit at lower power.
Brightness
The visual perception of the light power of a laser beam in the visible spectrum from approximately 400nm to 780nm, as opposed to the scientifically measured power of the beam.
Carbon dioxide (CO²) - Laser
A gas laser that uses a mixture of carbon dioxide, nitrogen (N2) and helium (He) as the laser-active medium to produce a continuous output of laser light with a wavelength of 10.6 micrometres.
Cathode
The element that provides the electrons for the electrical discharge serves to excite the laser medium.
Coherent radiation
Radiation consisting of wave trains that have a fixed phase relationship in spatial and temporal propagation.
Collimated light
Diverging light beams which are guided in parallel by means of a lens or other device. Collimation makes it possible to guide the laser beam over a greater distance without changing the cross-section. The optical device is called a collimator.
Collimation
The process by which divergent rays (white or natural light) are converted into parallel rays (coherent light).
Convergence
The focussing of light rays through a converging lens.
Short pulse laser
Pulsed lasers with pulse durations in the nanosecond range.
Laser
Acronym for Light Amplification by Stimulated Emission of Radiation = light amplification through the stimulated emission of radiation.
Laser crystal
A solid material in which the atoms are arranged in an orderly fashion. YAG crystals are used as laser sources, for example.
Micron
A unit of measurement, for example for the core in an optical fibre. 10-6 or one thousandth of a millimetre.
Molecular beam epitaxy
Process for the production of laser diodes in a reactor.
Depth of field
The working range of the beam, a function of the wavelength, the diameter of the unfocussed beam and the focal length of the lens. In order to achieve a spot size with a small diameter and therefore a high power density, a short depth of field must be accepted.
Ultra-short pulse laser
Mostly mode-locked, pulsed lasers with pulse durations in the pico to femtosecond range. Due to the extremely short pulse duration, a targeted effect of the laser beam can be achieved with little or no heating of the edge zone. This is also referred to as cold laser processing.
Reinforcement
The growth of the radiation field in the space of the laser resonator when the light wave shoots back and forth between the cavity mirrors. It is an amp-stimulated emission at each pass.
Circular polarisation
Optimal polarisation for CO² laser cutting. The two perpendicular components of the laser beam are out of phase, but have the same amplitude and provide an optimum cut for CO² lasers.