Pulse-echo laser ultrasonic propagation imaging is a nondestructive testing technique developed for composite materials and aluminum alloys used in aerospace. Although this method has been in usage for a considerable time, information of the detectable depth and the relationship between ultrasonic frequencies and the acoustic properties of metals is not readily available. Therefore, we investigate the A-scan and C-scan ultrasonic testing data of aluminum alloy, hot rolled steel, stainless steel, and copper alloy, which are used in aircraft bodies, frameworks, and gas pipelines. Experiments are performed with the pulse-width and excitation laser power fixed at 32 ns and approximately 4 W, respectively. The metal specimens include 24 artificial cylindrical defects with a diameter of 5 mm, located at depths of 1–12 mm on the front surface. The A-scan and C-scan data obtained at room temperature indicate the detectable depth for metals via the pulse-echo laser ultrasonic propagation imaging technique.

We have designed, fabricated, and tested a rapid single flux quantum (RSFQ) 1 bit arithmetic logic unit (ALU) block. The circuit consists of three DC current driven SFQ switches and a half-adder. We successfully tested the half-adder cell at clock frequency up to 20 GHz. The switches were commutating output ports of the half-adder to produce AND, OR, XOR, or ADD functions. For a high-speed test, we attached two switches at the input ports of the half-adder to control the high-speed input data by low-frequency pattern generators. The output in this measurement was an eye-diagram. Using this set-up, the circuit was successfully tested up to 20 GHz. The chip was fabricated using a standard HYPRES 1 kA cm −2 Nb Josephson junction fabrication process.

Nb trilayer process has been serving as the most stable fabrication process of the Josephson junction integrated circuits for more than two decades. Fast development of semiconductor fabrication technology has been possible with the recent advancement of the fabrication equipment. In this work, we took an advantage of those advanced fabrication equipments in developing a superconducting arithmetic logic unit (ALU) by using Nb trilayers. We used DC magnetron sputtering technique for metal depositions and RF sputtering technique for SiO 2 depositions. Various dry etching techniques were used to define Josephson junction areas and various patterns of metallic and insulating layers. Our Nb films were stress-free and had the T c 's above 9 K. To enhance the step coverage of Nb films we used reverse bias DC magnetron sputtering technique. The fabricated 1-bit, 2-bit, and 4-bit ALU circuits were tested at a few kilo-hertz clock frequency as well as a few tens gigahertz clock frequency. Our 1-bit ALU operated correctly at up to 40 GHz clock frequency, and the 4-bit ALU operated at 5 GHz clock frequency.

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