The Powell prism bends the roof line like a circular prism. The lens is a laser line generator that stretches a narrow laser beam into a uniformly illuminated straight line.
Powell prisms are quantum leap line generators with better performance than simple cylindrical lenses. The cylindrical lens produces poorly lit lines, a limited non-uniform, Gaussian laser beam. The Powell lens' rounded roof is actually producing spherical aberration redistribution along a large number of complex two-dimensional aspheric curves of light; Reduce the light in the center area and increase the light level at the end of the line. The result is a very uniform lighting line used in all the ways machine vision is applied; From biomedical and automotive assembly to the production of chocolate chip cookies.
The fan Angle
The width of the fan Angle of the Powell prism is a function of the refractive index of the glass and roof angles. The roof is steeper and the refractive index is higher, the wider the fan Angle and the longer the line is for a given projected distance. Small fan angles usually use mild optical glass, N = 1.5, refractive index. Large fan angles, preferably made of high refractive index glass, N = 1.8, or higher, to minimize the steeper Angle of the roof
Laser beam size
The incident laser beam size determines the laser line thickness at a given projection distance. The collimating laser diode has an elliptical beam profile that allows for thin or thick line capability with a single diode module.
An example of a narrow incident beam
An example of a wide-incidence beam
It has a narrow incident beam direction, the long axis of the beam is parallel to the Powell lens roof and produces a thin laser line with a small focusing depth. With a wide incidence beam direction, the long axis of the beam is perpendicular to the Powell prism roof and the band produces thick laser lines with a large focal depth. The diverging fan in the above figure is truncated near the lens. In each case, the beam is focused to the CCD array at a working distance of 500 mm. The clear image below shows the effect of line width on beam shape/direction.
Narrow incident beam - thin line focus narrow depth
Wide incident beam - thick line focal depth
Narrow incident beam Powell lens optical path
Wide incident beam Powell lens optical path
The performance and physical properties of the Powell prism are driven by the beam width. The most significant difference is the print on the foot of the divergent fan on the flat exit surface as the mounting surface. Care must be taken to ensure that the installed hardware does not trap divergent light.
The performance of Powell prism is very sensitive to the characteristics of the incident laser beam and the quality of the aspherical surface of the lens. For demanding applications, uniform irradiation of the laser line is best achieved by matching the specific beam characteristics of the Powell lens to the laser module.
The uniformity of Powell prisms is not an absolute characteristic, it is dependent on the test technique. For example, the uniformity measure will depend on whether an evaluation of the projection line of a Powell prism in machine vision applications sees a surface swept by a camera or a fan detector with a diffused light for laser safety evaluation. Differences in uniformity characteristics increase the fan Angle, and divergence differences over 20 degrees of Powell lens become significant.
An optical prism is used to redirect light at a specified Angle. Optical prisms are ideal for light deflection or image orientation adjustment. The design of an optical prism determines how light interacts with light. When light enters an optical prism, it reflects off a single surface or surfaces before leaving, or refracts as it passes through the substrate. Prism is widely used in laser research, laser optical system, optical imaging, machine vision, life science, biomedical and other fields or products.
MAP optics offers a wide range of optical prisms with substrate or coating. Including rectangular prism, pentagonal prism, Daway prism, roof prism, Angle reflector, wedge prism, Powell prism. Anti-reflective coatings include MgF 2, UV-VIS, UV-AR, VIS 0°, VIS-NIR or multiple laser line options.