Abstract: A currency discriminator for determining the denomination of a bank note or the like is disclosed. It includes a source of light directed at the note to be identified. A 2 mm.times.80 mm stripe is illuminated and the reflected light from the illuminated area is measured by a detector and converted into a digital representation. Synchronizing hardware permits 72 samples, each from a 2 mm.times.80 mm area, to be generated as a bank note is moved past the illuminator. The digital representations are then utilized to develop a four bit correlation number N where each bit is a one if (P.sub.n >P.sub.n-2), (P.sub.n >P.sub.n-4), (p.sub.n >P.sub.n-6), and (P.sub.n >P.sub.n-8) where P.sub.n is the present sample and P.sub.n-2, for example, is the second previous sample. The correlation number N is then compared with the corresponding number in a master list for notes of different denomination.

Abstract: Circuitry for controlling the power output of an R.F. generator for regulating the forward power transmitted into a load of varying impedance, such as an R.F. sputtering target, and for limiting reflected power to a safe predetermined level. Forward power is controlled by circuitry that compares the voltage across the target with a predetermined reference voltage and the amplified output is applied to the signal generator control circuitry. Reflected power is measured by a sensor that outputs a proportional D.C. signal that is compared with a predetermined threshold voltage. Whenever the reflected power signal exceeds this threshold, it removes the effect of the target voltage input signal so that the amplified control signal to the R.F. generator is a function only of the reflected power.

Abstract: A structural element and method of fabricating a structural element having a zero expansion in a given direction. A bar member having left and right hand sections of positive and negative coefficients of thermal expansion is tuned so that expansion of one section is exactly offset by contraction of the other section in a varying temperature environments.

Abstract: A very low absorption beamsampler for diffracting a very small fraction of a laser beam while specularly reflecting substantially all of the main beam with minimal absorption. The beamsampler comprises a plane mirror surface coated with a high-reflectivity multilayer dielectric coating, the topmost dielectric of which is grooved into a grating and coated with a transparent dielectric having a refractive index very similar, but not the same, as the grooved layer to form a weak phase grating for diffracting a weak first order sampling beam.

Abstract: A high power D.C. supply regulated for constant output power to be dissipated in varying loads such as encountered in cathode sputtering systems. A.C. input power is rectified to produce the desired D.C. The output D.C. voltage and load current are measured and a voltage signal proportional to their product is compared with a D.C. input control signal. The comparator "error" output signal controls a pass element that varies a D.C. current through saturable reactors in the A.C. input power lines to regulate the D.C. power into the load. The supply includes a limiting feature that is adjustable to a desired threshold level for limiting D.C. output power, voltage, and/or current so that the limiter will take control from the comparator to hold the supply output at a safe level.

Abstract: The radii of two concave and two convex mirrors have the same absolute value. The two concave mirrors are placed back to back and have a central aperture. The two convex mirrors face the concave mirrors and also have a central aperture. An image at the apex of one of the convex mirrors will be imaged at unit magnification at the vertex of the other convex mirror if the spacing between the concave and convex mirrors is 0.866 times the absolute value of their radius. This system is corrected for all aberrations except astigmatism. Astigmatism is corrected by a double convex thin lens at the intermediate image at the vertices of the concave mirrors. Petzval curvature introduced by the field lens may be corrected by plano-concave lenses near the object and image planes. Alternatively identical shell lenses may be placed on either side of the intermediate image to correct for both astigmatism and Petzval curvature. The lenses may be achromatic doublets to correct for chromatic variation of field aberrations.