## 1 Introduction  
The interest in development, characterisation and optimization of novel, functionally-tailored photosensitive materials is omnipresent. This is mainly due to the wide-ranging possibilities for future applications, from volume holographic memory over 3D imaging and waveguides [1; 2; 3; 4], up to optical sensing, photonic circuits and integrated optics [5; 6; 7]. Photosensitive polymers are of particular interest. The underlying mechanism of hologram formation is attributed to a photo-induced change of the refractive index [8; 9].  
Research efforts are concentrated on material composition, processing and sample fabrication on the one hand [7; 8; 9; 10], and on techniques and methods applied for recording and subsequent analysis on the other hand [7; 9; 11; 12; 13; 14; 15; 16]. In each case, there is a particular need to meet the high demands on precision and repetitive accuracy, accompanying volume holographic operations. Beyond mechanical stability of the holographic setup, inherent stability of the photosensitive material constitutes an underestimated influential factor for hologram formation and performance [16; 17]. Long-term stability depends on intrinsic material features, significantly influencing the course of the grating formation, as well as on temperature and thermal history [18]. The UV curing and baking processes are known to significantly affect the film shrinkage and swelling behaviour [13, 19]. The layer thickness represents a crucial factor for the selectivity of optical elements and for storage capacity of memories [18]. However, with thick films, it is more difficult to comply with the stability requirements [7]. As a consequence, viable shrinkage control is needed [16].  
Optical shrinkage, comprising of mechanical deformations of the volume on the one hand and a change of the average refractive index on the other hand [14], proceeds inevitably parallel to the grating formation [13]. Low optical shrinkage during holographic recording is desired, since this is linked to a constant functionality of the final optical element. Optical shrinkage is accompanied by Bragg angle detuning as a result of altered grating constants or modified refractive index. The Bragg selectivity, however, determines the optical functionality [13, 20]. Preliminary results suggest, that a constant functionality beyond high volume stability can be realized by means of an increase of the average refractive index, compensating the impact of mechanical shrinkage associated with photo-induced crosslinking [13].  
In general, there are three different approaches to reduce optical shrinkage. The first deals with advanced material compositions [16, 21, 22, 23], including the incorporation of inorganic substances [10, 24]. The second possibility is to apply special material processing, such as pre-imaging, incoherent-light exposure [25, 26]. The third approach concentrates on the influence of accessible parameters, namely recording intensity, exposure duration and the material's viscosity to control and adjust the optical shrinkage [13].  
The present paper follows such an inherent shrinkage control and contributes by means of spatially resolved analysis of the grating. Specifically, this is accomplished by means of scanning the lateral plane of transmission type gratings to obtain local values of the grating period \(\Lambda\) and the grating slant \(\Phi\). For this purpose, a lateral scan method is introduced, keeping track of the hologram shape, which is determined by the material response to the Gaussian intensity distribution of the recording beams. This is exploited to gain detailed information on the Bragg selectivity.