GB1420701A - Optical alignment apparatus - Google Patents

Abstract

1420701 Optical alignment IBM UNITED KINGDOM Ltd 23 Nov 1973 54514/73 Heading G2J Alignment apparatus e.g. for an ellipsometer for aligning a light beam with an axis of rotation A comprises a rotary device 1 having two spaced apart discs 2, 3 mounted for rotation in synchronism about the axis A. Each disc 2, 3 is perpendicular to the axis A and has an orifice 4, 5 positioned on the axis, alignment being indicated when the light beam is adjusted in direction to give a steady quantity of light through the orifices while the discs are rotated. In the preferred arrangement, Fig.5, the orifices 4, 5 are identical semicircles with the mid-point of each diameter lying on the axis A. Parallel Alignment. An apparatus similar to that of Fig.5 is used except that one of discs 2, 3 is rotated relative to the other through 180 degrees about axis A. Both discs are rigidly attached to tube 20 which is rotated by motor 24 and transmission 23 while a light beam of preferably circular cross-section is directed through the tube 20. If the beam is not parallel to axis A, a varying amount of light will be detected e.g. by a photomultiplier at the other end of the tube. The beam is thus changed in direction until a steady, low quantity of light is detected. Coaxial alignment. Having achieved parallel alignment, discs 2, 3 are arranged as shown in the Fig. and a parallel beam of light is directed through the tube. If the beam is not coaxial with the tube, a varying light output is detected so the beam is adjusted until a steady, low quantity of light is detected. The cylinder may be 15-20 cm long, the orifices may be 5-10 mm in diameter and the beam may be 2 mm in diameter. The tube may rotate at 100 r.p.m. Circular, square or triangular orifices 4, 5 may be used.