Method of evaluating characteristics of a light beam, apparatus for evaluating the characteristics, and apparatus for adjusting a write unit by employing the evaluation method

An adjustment method comprising the steps of:

• providing a write unit incorporating an optical scanning system to form an electrostatic latent image on a surface of a latent image carrier by a light beam emitted from a laser light source;
• evaluating an offset quantity of said light beam in a horizontal scanning direction by lighting said light beam for a scanning period equivalent to 1 dot and evaluating a beam center of said 1 dot light beam with respect to a reference pixel to determine the offset quantity;
• and
• moving said write unit relatively in said horizontal scanning direction against an image forming unit incorporating at least said latent image carrier in correspondence to the offset quantity of said light beam in said horizontal scanning direction, thereby adjusting said write unit.

An adjustment method wherein at least either an image forming unit or a write unit is moved so that a space therebetween is increased or decreased, in order to adjust an optical path length between a laser light source and a writing object surface of said image forming unit and based on a beam waist position correction quantity obtained by a light beam characteristic evaluation method comprising the steps of:

• (a) lighting said laser light source of a light beam which is employed to scan said writing object surface of said image forming unit linearly during a scanning period equivalent to 1 dot;
• (b) moving an area-type solid-state imaging element which detects said light beam in order along the traveling direction of said light beam with said writing object surface as a reference position, thereby obtaining a beam image at each position by said area-type solid-state imaging element;
• (c) based on each beam image obtained by said area-type solid-state imaging element at each position in a traveling direction of said light beam, computing a beam diameter at said each position of said light beam and thereby computing a beam diameter with respect to a depth direction;
• (d) from said beam diameter and a depth, computing a depth curve representative of a relation of said beam diameter to said depth;
• (e) specifying a beam waist position on the basis of said depth curve;
• and
• (f) from a difference between said beam waist position and said reference position, computing said beam waist position correction quantity.

An adjustment method wherein an optical path length between a laser light source and a surface to be scanned is adjusted based on a beam waist position correction quantity obtained by a light beam characteristic evaluation method comprising the steps of:

• (a) lighting said laser light source of a light beam which is employed to scan said surface linearly during a scanning period equivalent to 1 dot;
• (b) moving an area-type solid-state imaging element which detects said light beam in order along a traveling direction of said light beam with said writing object surface as a reference position, thereby obtaining a beam image at each position by said area-type solid-state imaging element;
• (c) based on each beam image obtained by said area-type solid-state imaging element at each position in the traveling direction of said light beam, computing a beam diameter at said each position of said light beam and thereby computing a beam diameter with respect to a depth direction;
• (d) from said beam diameter and a depth, computing a depth curve representative of a relation of said beam diameter to said depth;
• (e) specifying a beam waist position on the basis of said depth curve;
• and
• (f) from a difference between said beam waist position and said reference position, computing said beam waist position correction quantity.