| 摘要 |
PCT No. PCT/FR96/00372 Sec. 371 Date Oct. 30, 1996 Sec. 102(e) Date Oct. 30, 1996 PCT Filed Mar. 8, 1996 PCT Pub. No. WO96/28815 PCT Pub. Date Sep. 19, 1996System for the adjustment of the focusing of a beam on a carrier (5). A first detector (CA) with a wide dynamic range of detection and with limited stability measures the light reflected by the carrier (5). A second detector (CB) with a small dynamic range of detection, high stability and high precision also enables the measurement of the light reflected by the carrier (5). Control circuits are used to control a focusing control device (B). A control logic is used to place the operation of the control device (B) under the control of the first focusing error signal when this signal goes beyond a specified value (a) until the second focusing error signal goes beyond another specified value, the working of the control device (B) being then placed under the control of this second focusing error signal.
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