| 摘要 |
<p>An optical scanning device for scanning a first (13) and a second (27) type of record carrier in a first and a second mode, respectively, comprises a radiation-generating device (1, 20) for generating a radiation beam (2, 21) having at least a first wavelength in the first mode and at least a second wavelength in the second mode. The device further comprises an objective system (11) for focusing (16) the radiation beam (2) of the first wavelength in the first mode on the first type of record carrier and for focusing (30) the radiation beam (21) of the second wavelength in the second mode on the second type of record carrier (27). The optical scanning device further comprises an optical element (10) with a structure in the radiation beam (2, 21) for introducing vergence and aberration in the radiation beam (21) of the second wavelength. The aberration can be written as a polynomial with at least two terms a2?2 and a4?4. If a2=0 and a4=0, the corresponding values of a4 and a2 are given by a40 and a20, respectively. a2, a4, a20 and a40 satisfy the relation 0.9<((a2/a20)+(a4/a40))<1.1, as well as either the relation 0.20<(a2/a20)<0.90 (if a4<0) or the relation 1.05<(a2/a20)<2.00 (if a4>0).</p> |
