Search

If an elementary hologram with grating vector K is recorded in a photosensitive material, the complex refractive index is modulated with the same spatial frequency K. A beam-coupling measurement is a proper tool for simultaneous investigation of the absorption grating and the refractive-index grating, which correspond to the imaginary and the real parts of the complex refractive-index modulation, respectively. Using beam-coupling analysis makes it possible to determine the magnitude of the refractive index and the absorption grating as well as their phase shift with respect to the writing intensity pattern, with one single-beam-coupling measurement. The theoretical foundation of beam-coupling analysis is given. A few numerical examples point out the main characteristic of beam-coupling analysis.

Holographic recording and erasure experiments in Cd13P4S22I2 crystals are reported. The refractive index change of the volume phase hologram is larger than ?n=1.5×10-4, whereas the static dielectric constant of this reversible storage medium is only about 10. These are rather unusual properties if compared with electrooptic KNbO3.

A new holographic observation technique for 180° domains is demonstrated with a cerium-doped strontium barium niobate sample containing two antiparallel ferroelectric domains. The method relies on the fact that the phase shift of holographically written refractive-index gratings is +π/2 or − π/2 with respect to the initial light interference pattern depending on the orientation of the domains. As a consequence, readout of these gratings creates at the exit face of the sample new interference patterns shifted by 0 or π with respect to the initial one. These patterns, providing an image of the domain structure, are observed by microscope.

Using the new electromagnetic shockwave source of the Modulith SL 20 shockwave-induced renal trauma was evaluated by acute and chronic studies in the the canine kidney model. In a further study the electromagnetic shockwave source of the Lithostar Plus Overhead module was tested. Overall, 92 kidneys were exposed to shock waves coupled either by water bath (Modulith lab type) or by water cushion (Modulith prototype, Lithostar Overhead) under ultrasound localization. The generator voltage ranged between 11 and 21 kV, the number of impulses between 25 and 2500. After application of 1500/2500 shocks the extent of the renal lesion depended strictly on the applied generator voltage and was classified into 4 grades: Grade 0, no macroscopic trauma detectable (at 11–12 kV); grade 1, petechial medullary bleeding (at 13 kV); grade 2, cortical hematoma (at 14–16 kV); and grade 3, perirenal hematoma (17–20 kV). Whereas at low and medium energy levels the number of shocks played only a minor role, at maximal generator voltage (20 kV) even 25 impulses induced a grade 2 and 600 shocks a grade 3 lesion, emphasizing the importance of shockwave limitation in the upper energy range. In shockwave-induced renal trauma a vascular lesion was predominant and cellular necrosis was secondary. Coupling with a water cushion resulted in a 15%–20% decrease in the disintegrative and traumatic effect, which was compensated for by increasing the generator voltage by 2 kV. Long-term studies showed complete restitution following grade 1 and 2 trauma, whereas after a grade 3 lesion a small segmental and capsular fibrosis without hyperplasia of the juxtaglomerular apparatus was observed. Based on the characteristic ultrasound pattern found in the first study, the threshold for induction of grade 1 lesion was investigated. With both lithotripters a wide range for induction of a grade 1 lesion (Modulith 234–411, Lithostar Plus 220–740) and also a significant overlapping with grade 0 and 2 lesions was seen at low energy settings (levels 2–4). In contrast, the range of shocks (Modulith 96–150, Lithostar Plus 90–142) and overlapping was minimal when high energy was used (levels 7–9). Finally, the disintegration-trauma coefficient combining the results obtained in a standard stone model with those of the canine kidney model was introduced.

Beam-coupling topography is a non-destructive holographic technique for spatially resolved recording of hysteresis loops and for imaging of domains. Its basic principle is interference of rays diffracted from a holographic grating with collinear, transmitted ones. Full domain contrast and noise suppression is achieved by appropriate control of intensity and phase of the interfering beams. The method is applied to antiparallel a-domains in (Sr0.61Ba0.39)Nb2O6:Ce.