Double pass optical system for raster scanners

In a raster scanner the combination of:

• (a) a beam of high intensity light;
• (b) plural mirrors cooperating to form an optical path for routing said light beam back and forth and up and down between at least two operating levels before discharge toward the object to be scanned whereby to provide a relatively compact folded optical path;
• said mirrors including:
• (1) a rotatable polygon for scanning said beam through a preset scan arc;
• (2) a first mirror for directing said beam at an angle from a first operating level to a second operating level;
• (3) a second mirror at said second operating level for intercepting said beam, said second mirror folding said beam and reflecting said beam along said second operating level;
• (4) a third mirror at said second operating level for intercepting said beam, said third mirror folding said beam and reflecting said beam at an angle from said second operating level toward said first operating level;
• said polygon intercepting said beam and reflecting said beam toward said third mirror, said third mirror folding the returned beam from said polygon and reflecting said beam along said second operating level;
• and
• (5) a fourth mirror at said second operating level for intercepting said beam, said fourth mirror reflecting said beam toward the object to be scanned;
• and
• (c) lens means for focusing said beam on the object to be scanned.