Development of recording materials for holographic non-destructive testing

This report describes a two year effort on investigating two recording materials for in-situ, real-time holographic nondestructive field testing application, namely, photodielectrics and photoconductor thermoplastic devices (PC-TP). The holographic parameters as well as the recording mechanism of photo-dielectric materials were thoroughly studied. The recording mechanism is attributed to photochemically induced cross links of macromolecules. Resolution on excess of 2500 1/mm and diffraction efficiency approaching 100% were measured. Due to the low exposure sensitivity, about 1 J/sq cm, this recording material could only be incorporated into systems for testing relatively small objects. A number of ways for operating the PC-TP devices more reliably and for improving the spatial bandwidth to over 1800 1/mm were established. Furthermore, the frost formation mechanism was investigated, and means for supressing the frost were determined, thereby leading to improved signal-to-noise ratio. These results together with the high exposure sensitivity (50 erg/sq cm and the improvements in sample fabrication, have led to an operable device which may be incorporated into most holographic non-destructive systems.