| 摘要 |
Optical system for the automatic alignment of two motifs in which the alignment marks of a first fixed motif forming the reference are constituted by at least one pair of identical periodic optical gratings with a constant spacing P and having a predetermined distance dX from one another such that the equation dX=(n+ epsilon ) P is proved, n being an integer and epsilon a fraction of unity. An optical modulator, for example electro-optical means incorporating a Pockels cell alternately illuminate with the timing of the high frequency control signals, the said gratings in windows, whose position can be regulated in accordance with a given axis. The image of these windows is projected onto gratings carried on a second moving support to be aligned and produces orders of diffraction. An optoelectronic detector detects a predetermined order of diffraction. The high frequency-modulated output signals are transmitted to control circuits for producing the automatic alignment. |
