Holographic surface relief gratings written in azobenzene containing films were studied for the use as masters for
polymeric thin film distributed feedback (DFB) lasers. Light induced mass transport driven by E-Z isomerization in
azobenzene containing materials have shown to be attractive for all optical and one-step fabrication of periodic surface
structures with varying parameters for different optical applications. Based on new azobenzene materials and their
holographic processing deep surface relief gratings were generated with grating pitches in the range of 400 nm as
resonant structures for second order DFB lasers emitting in the VIS range. Nanoimprint techniques enabled multiple
duplications of azobenzene master gratings in UV adhesives. The replicas were coated via spin casting with thin films of
red light emitting polymer layers to form DFB thin film lasers. These active layers are guest-host-systems consisting of
an UV-light absorbing conjugated polymer as host transferring its excitation via Förster resonant energy transfer to a red
emitting conjugated polymer. Simple adjustment of grating depth via controlling of illumination time allowed it to
investigate the influence of the corrugation depth and thereby the coupling of laser light and grating on the lasing
behavior of second order DFB lasers in the red region. For this purpose multiple surface structures with different
corrugation depths of up to 130 nm were generated holographically, duplicated and coated.
The defined preparation of anisotropic films of functionalized polymers is important for different fields of optical applications. A promising way to create such films is based on the interaction of photochromic polymers with linearly polarized light. Different mechanisms are known to generate anisotropy. The best studied process is the photoorientation in the steady state of the E/Z photoisomerization of azobenzene moieties. But azobenzene based systems have some disadvantages. For this reason the light-induced orientation of photochromic liquid crystalline polymers without azobenzene moieties is presented. In the case of the studied photochromic LC polymers the light-induced anisotropy is used as a starting point for the thermal development of the order by a thermal post-orientation step based on the self-organization of LC polymers. This two-step orientation process combining a photoinduced and a subsequent thermal ordering process is a very promising way to orient efficiently LC polymers containing photochromic moieties. The light induced and the thermal developed order of four different polymers containing a mesogenic, a photochromic and a fluorescent stilbene side group were compared with respect to the composition of the polymers. This orientation procedure results in films with anisotropic fluorescence properties in the case of two of the investigated polymers.
Liquid crystalline polymethacrylates with benzanilide and photochromic azobenzene side groups and a related terpolymer containing an additional side group with a phenylethynyl substituted anthracene chromophore were oriented by the irradiation with linearly polarized light. The orientation of both polymers were compared irradiating with polarized visible or, alternatively, UV light. Caused by the co-operativity of the photoorientation process, the light-induced orientation of the azobenzene groups is connected to the alignment of the non-photochromic side groups below the glass transition temperature. The light-induced order generated in the glassy state was significantly amplified by the subsequent annealing of the irradiated films at temperatures in the mesophases. Factors of amplification of about 30 were found in the case of both polymers. The photo-induction process and its amplification by thermotropic self-organization were investigated in dependence on the polymer composition, the irradiation dose and the wavelength of the incident light with respect to the absorption of the dye and its limited photo-stability. The required dose or the irradiation time, respectively, were significantly reduced by the optimization of the light-induced and thermal processing. In this way, dichroic films of co- and terpolymers were created. However, the green fluorescence of the anthracene chromophore is effectively quenched by the azobenzene side group within the film.
The irradiation with linearly polarized light generates optical anisotropy in isotropic films of photochromic amorphous and liquid crystalline polymers due to photoorientation. The photochemically induced orientation of the photochromic side groups causes a co-operative orientation of the non-photochromic parts of the polymers such as the non-photochromic side groups. The orientational order photogenerated in the glassy state acts as an initializing force to align LC polymers by thermotropic self-organization on annealing above Tg. The combination of both ordering principles can result in a significant amplification of the light-induced in-plane anisotropy or, results alternatively in a homeotropic alignment of the side groups. The dependence of the photoorientation process and its thermal amplification on the liquid crystallinity, aggregation and the irradiation conditions is discussed.