Raster and vector are different graphic file types which require different modes of laser processing. The main difference between vector and raster graphics is that raster graphics are composed of pixels, while vector graphics are composed of paths or lines. The main differences between modes required to laser process each type involve the movement of the axles and in the parameters used.
Raster engraving: Raster engraving is the standard process for engraving. This process is the same type of process used by inkjet printers, where a file is printed line by line.
How does this work with a laser? A raster file is a bitmap, which means it is made up of pixels. The image is engraved by the laser machine line by line, point by point, similar to the way in which an inkjet printer applies ink, but instead of ink being applied, material is removed pixel by pixel by the laser. This is a "bi-directional" process in which engraving is done in alternating fashion in both directions.
During the line-by-line raster engraving process, the speeds of the two axles are very different. The speed is high on the x axle (the axle to which the laser head is attached) and lower by comparison on the y axle.
In raster engraving, the ppi parameter (pulses per inch) is important because it controls the density of the laser points.
Vector engraving and cutting: Vector engraving is often referred to as “scoring.” The file to be printed is a graphic file consisting of vectors (lines and curves of a geometry), marked as hairlines in the graphics. When the file is imported from the graphics program, the outline is identified as vector engraving. Vector by vector is traced by the laser and then engraved.
In vector engraving, the axles move simultaneously, and more slowly than in raster engraving. The process itself is the same as in laser cutting; the difference is the selected power setting. If a low power setting is chosen, the line is “scored” as engraving; higher power produces a vector cut.
—Josh Stephens, Trotec Laser