Abstract
Volume phase gratings, recorded in a photosensitive polymer by two-beam interference exposure, are studied by means of optical microscopy. Transmission gratings and reflection gratings, with periods in the order of 10 μm down to 130 nm, were investigated. Mapping of holograms by means of imaging in sectional view is introduced to study reflection-type gratings, evading the resolution limit of classical optical microscopy. In addition, this technique is applied to examine so-called parasitic gratings, arising from interference from the incident reference beam and the reflected signal beam. The appearance and possible avoidance of such unintentionally recorded secondary structures is discussed.
Highlights
Photosensitive polymers are highly attractive media for photonic applications, such as holographic memory, 3D imaging and waveguides [1,2,3,4,5], as well as for future applications in optical sensing, for photonic circuits and integrated optics [5,6,7,8]
The underlying mechanism of hologram formation in polymers is attributed to a photo-induced change of the refractive index [9,10]
Imaging of volume phase gratings poses a considerable challenge with respect to image contrast and resolution [7]
Summary
Photosensitive polymers are highly attractive media for photonic applications, such as holographic memory, 3D imaging and waveguides [1,2,3,4,5], as well as for future applications in optical sensing, for photonic circuits and integrated optics [5,6,7,8]. Special forms of light microscopy, such as confocal laser scanning, have been applied, in which the signal contrast is assumedly attributed to the remaining fluorescence of the photoinitiation system [15] In this context, it must be stressed that it is usually inappropriate to apply fluorescent or dyes as contrast agents to achieve higher image contrast in low-contrast volume hologram scenes. The imaging task is becoming increasingly complex without conductive species and a fortiori taking account of the three-dimensionality of volume phase gratings It is the third dimension in particular to which the specific applicability of volume holograms can be attributed [19,20]. Techniques are presented on how to analyze respective structures with regard to the spatial characteristics in the sub-micrometer range
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