This paper presents the first application of digital speckle pattern interferometry (DSPI) to detect inhomogeneous heat generation on a superconducting ceramic at cryogenic temperatures. The light scattered by the object is recorded with a CCD camera at the same time as a smooth reference beam. Comparison of two non-simultaneous frames provides information about the out-of-plane deformation field. Spatial phase shifting is used in order to get a good quality fringe pattern. The technique has been applied as a non-destructive evaluation of the performance of ceramic high temperature superconducting materials. DSPI allows the determination of the point where a hot spot will be generated with heating levels that do not deteriorate the sample properties. An excellent agreement between DSPI hot spot location and the position of the melting point that appeared in a destructive experiment has been obtained.

Lasers are adequate tools in the processing and characterization of materials. The Applied Superconductivity group at the Aragón Materials Science Institute has been applying different laser techniques in the processing, machining and characterization of bulk high temperature superconductors for high power applications. Textured bulk Bi-2212 superconductors have been obtained using laser melting zone techniques. We have produced thin bars, monoliths and coatings on metallic and ceramic substrates. Ablation techniques have been used to machine the samples with the required shape for technological applications. And finally, optical techniques have been used as non-destructive experiments to detect the location of hot-spots and the positions where environmental degradation starts.

In this paper digital speckle pattern interferometry (DSPI) as a digital image plane holography (DIPH) technique is presented and its potential for fluid velocimetry are discussed. The recording is carried out with a spatial phase shifting (SPS) DSPI set-up, which can also be viewed as an off-axis DIPH set-up. A theoretical study of both SPS-DSPI analysis using a Fourier transform method and DIPH analysis is presented for a set-up with only one illuminated plane. From the DIPH analysis, a way to extend the SPS-DSPI set-up to simultaneously record but independently reconstruct several fluid planes is inferred. Some preliminary results from a convective flow illustrate the feasibility of the quasi 3D recording.

Digital speckle pattern interferometry has been used to detect inhomogeneous heating in YBa 2 Cu 3 O 7−␦ coated conductors. The analysis was performed in a sample with a controlled defect, which causes a significant local reduction in the critical current value, I c . The experiments, which were performed with the sample surrounded by nitrogen vapor, have shown that the location of the initial hot spot leading to the complete transition to the normal state of the conductor ͑quench͒ is strongly dependent on the sample cooling configuration. When the sample is mainly cooled by gas convection, the quench always starts in the low-I c region, while for improved cooling configurations the initial hot spot does not always coincide with this region. The results have been compared with those obtained by direct electric field measurements along the sample in nitrogen vapor and liquid.

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