Patent GB-1247446-A (GB)
Title: Electromagnetic wave apparatus
IPC: G02B27/58
Filed: 1969-07-30
Abstract: 1,247,446. X-ray diffraction apparatus. INTERNATIONAL BUSINESS MACHINES CORP. 30 July, 1969 [14 Aug., 1968], No. 38209/69. Heading H5R. [Also in Division G2] Optical apparatus for determining the intensity distribution of an object being incoherent light waves comprises means for sequentially sampling light from a plurality of separate pairs of different portions of a wave, converging each pair to a common focus, recording and building up an image of the object from the sequentially sampled wave pair portions. In a telescope a pair of mirrors 28, 30 each having an associated hexagonal aperture 38, 39 are mounted on individually movable radial arms 33, 35. The mirrors are movable angularly with respect to each other over a prescribed circumference 26. The hexagonal apertures are also rotatable to maintain an invariant orientation with respect to a single direction. The size and shape of the apertures and the positions to which the mirrors are moved are predetermined to give the desired record of the object intensity distribution. In a given pair of positions each mirror receives a portion 40A, 40B of light information from an object. These beam portions are reflected to a mirror 41, through phase and position compensating means 44, 46 and brought to a common focus on a sensitive plate (e.g. a photographic plate) 48 which records their interaction. The sequence of moves of mirrors 28, 30 and the total number of observations made is fed from, for example, magnetic tape via a digital to analogue converter driving the telescope motors. At each position a small bundle of each of the converging light beams are reflected by a mirror 52 on to a sensing means 54. This sensor 54 detects whether .at each position one of the converging beams is out of phase with the other, and whether one or both mirrors have changed their distance from the focal plane thus giving different optical path lengths from mirror to plate 48. Sensing means 54 includes a " startracker" " device in which the small bundle of beams from mirror 52 are focused on a graticule having an annular transparent area. A photomultiplier having a circular responsive area divided into quadrants is located behind the graticule. The outputs from each quadrant of a pair of adjacent quadrants are compared to determine how a beam is off-centre and thus whether it requires shifting in an X or Y direction at right angles to each other. A shutter enables the device to examine each beam individually. The result is then fed to the appropriate compensator 44 or 46. Such a compensator (Fig. 14) comprises a gimbal mounted optical element 92, in the form of a plane parallel plate. Any positional shift of a beam is effected by a signal from the photomultiplier of sensor 54 operating one or both of gimbal motors (e.g. 102). One of the compensators, e.g. 44, also includes a pair of relatively movable optical wedges 104, 106 forming a phase compensator. Thus, sensor 54 also includes a typical interferometer which has a maximum signal output when the two beams are in phase. If this is not achieved a motor 112 moves wedge 104 until the desired conditions are obtained. When the sequence of records have been made, eg. on strip film, the developed films are sequentially illuminated by coherent light from a laser 130 (Fig. 16) and a record of the Fourier transform of each made as a hologram 140. A mask 144 acts to uniquely locate each record or hologram. When developed and illuminated with a reconstructing reference beam a complete picture of the light intensity of the object is seen. An object 156 is illuminated by X-rays from an aluminium target 152. X-rays are diffracted to a pair of independently rotatable cylinders 160, 162, which contain first and second pairs of sampling mirrors 164A, 164B and 166A, 166B of gold-coated glass. Each of the two pairs of mirrors constitute a grazing incidence X-ray micro-objective, and each pair has a stop 168, 170. A given pair of X-ray beams 172, 174 are brought to a common focus 176 on a photographic emulsion. Mirrors 164A, 164B and stop 168 are fixed to cylinder 160, and the other set to cylinder 162. Thus each mirror pair set can be located at a desired point on a circumference and the intensity of the given pair of X-ray beams recorded at 176. The sequence of movements of the mirror pairs can be digitally recorded and initiated by feeding magnetic tape to a digital/analogue converter which actuates the drives of cylinders 160, 162. After all the recordings have been made the developed film is developed and processed, for example optically. Thus each record is sequentially illuminated by coherent light from a laser 130 (Fig. 16) and a hologram 140 recorded in the Fourier transform plane of a lens 136. A mask 144 uniquely locates each record on the hologram. A complete image of the object is reconstituted by illuminating the hologram with a coherent reference beam.