Pulsed recording of anisotropy and holographic polarization gratings in azo-polymethacrylates with different molecular architectures

Abstract

Recording of anisotropy and holographic polarization gratings using 532 nm, 4 ns light pulses has been carried out in thin films of polymers with the same azobenzene content ͑20 wt % ͒ and different molecular architectures. Random and block copolymers comprising azobenzene and methylmethacrylate ͑MMA͒ moieties as well as statistical terpolymers with azobenzene, biphenyl, and MMA units have been compared in terms of recording sensitivity and stability upon pulsed excitation. Photoinduced anisotropy just after the pulse was significantly higher in the case of the block copolymers than in the two statistical copolymers. The stability of the recorded anisotropy has also been studied. While a stationary value of the photoinduced anisotropy ͑approximately 50% of the initial photoinduced value͒ is reached for the block copolymer, photoinduced anisotropy almost vanished after a few hours in the statistical copolymers. Polarization holographic gratings have been registered using two orthogonally circularly polarized light beams. The results are qualitatively similar to those of photoinduced anisotropy, that is, stability of the registered grating and larger values of diffraction efficiency for the block copolymer as compared with the random copolymers. The recording of holographic gratings with submicron period in films several microns thick, showing both polarization and angular selectivity, has also been demonstrated. Block copolymers showed a lamellar block nanosegregated morphology. The interaction among azo chromophores within the nanosegregated azo blocks seems to be the reason for the stability and the photoresponse enhancement in the block copolymer as compared with the statistical ones.

Nanostructuring of Azomolecules in Silica Artificial Opals for Enhanced Photoalignment

“…The large response is due to cooperative rearrangements of microdomains, at the expense, however, of difficult erasure (unwanted for many applications) and slower rates (of several hundreds of milliseconds in the best cases15, 16 but, in general, of many seconds). Sub‐millisecond response is only achieved in pulse laser experiments using very high light doses 17, 18. Further, these systems are costly and require important synthetic efforts associated with covalent reactions, purification difficulties, and poor solubilities 2, 4.…”

Optical and Physical Applications of Photocontrollable Materials: Azobenzene-Containing and Liquid Crystalline Polymers

“…These lasers can be also employed for holographic recording using photocontrollable materials. Grating formation in azobenzene-containing polymers could be observed even in short times, as required for recording [69][70][71]. The short-time photoexcitation also provides benefits for investigating dynamic physical properties via time-resolved investigations [72,73].…”

Holographic storage and multiplexing in azopolyester blends using low energy pulses down to 2 ms

“…In this context, several groups have investigated holographic storage in films of block copolymers (BCs) as well as in blends of BCs and a homopolymer that does not absorb light at the recording wavelength. [16][17][18][19][20][21][22][23][24][25] Thus, H€ ackel et al 22 have been able to store a stable holographic grating in 10 lm thick films of a diBC containing azobenzene in one of the blocks. Due to microphase separation of the blocks, no surface relief gratings, that are deleterious for volume holographic storage, were created.…”