The Powell Prism scribing is better than the scribing mode of the cylindrical lens, which can eliminate the central hot spot and fading edge distribution of the Gaussian beam.

When a Gaussian laser beam passes through an ordinary cylindrical lens, an unevenly distributed straight line is generated. On the top of a Powell prism is a complex two-dimensional aspherical surface. When the laser passes through, a large amount of spherical aberration occurs, the light path is redistributed, and the central area is reduced. The light, which adds light to the edges, forms a uniform line that is suitable for a variety of machine vision applications such as biomedical, automotive assembly, and food processing.

Fan angle

The fan angle is a function of the refractive index and the top angle of the glass. The higher the slope of the top, the greater the refractive index of the glass, the larger the fan angle at the same projection distance. The small fan angle usually uses an optical glass having a refractive index of n=1.5, and a large fan angle generally uses a high refractive index glass of n=1.8 or increases the top tilt angle.

Laser beam size

In the case of a fixed projection distance, the size of the incident laser beam determines the thickness of the laser line. A parallel beam of elliptical cross-section may produce a wide or narrow two straight lines.

An example of a narrow incident beam

An example of a wide incident beam

In the direction of narrow incident light, the main axis of the laser is parallel to the top of the prism, and narrow laser light is incident to form a small depth of field. In the direction of wide incident light, the axis of the laser is perpendicular to the top of the prism, and a wide depth of laser incidence results in a large depth of field. Under different conditions, the beam is focused on a CCD array with a working distance of 500 mm. The following figure clearly shows the difference between the different incident directions of the laser beam after the beam expansion by the prism, where the spot size on the exit plane is a significant difference.

Narrow incident beam powell lens ray path

Wide incident beam powell lens ray path

Narrow incident beam - thin line narrow depth of focus

Wide incident beam - thin line narrow depth of focus

Line uniformity

The properties of Powell's prism are determined by the characteristics of the incident laser and the quality of the aspherical surface of the lens. A reasonable selection of prisms that match the laser module can produce uniform and consistent laser lines to meet demanding applications.

Light intensity distribution

Uniformly illuminated laser lines, 80% of the length of the center contain more than 80% of the total intensity. If the energy of the middle part is too low, the brightness at both ends will increase. Decreasing the brightness at both ends will help increase the overall utilization efficiency of the laser. The following figure shows the same uniformity of the laser line, when the central region distribution of light intensity is different. difference.

Laser line flatness and accuracy

Straightness and aperture deviation depend on the manufacturing quality of the prism and the precision of the laser module installation. If the laser is not incident at the vertical prism, line curvature will occur, an aperture error will occur between the wedge's wedge top and the bottom exit surface, and eventually an offset will be generated from the target position. If the prisms are installed correctly, the wedge tops of the prisms are only slightly tilted, and the resulting line curvature is also small.

Prism mounting options

The width of the laser beam determines the performance and physical properties of the prism. The most significant difference is the position of the divergence angle on the exit surface. It must be ensured that the divergent beam does not exceed the lens size.

Beams passing through the non-linear sphere of the prism will produce a non-uniform distribution, so choose the right prism based on the diameter of the laser beam. The exit plane of the bottom of the prism is larger than the section of the beam on this surface. The standard 90° prism is only suitable for beam broadening of the incident laser.