Two-Wave Nonlinear Interaction in Azo-Containing Polymer Films
Supervisor: [ Prof. Victor I. Shmalgausen ]

Figure 1.

Photosensitive polymeric materials are of a great interest now in the fields of holographic recording, dynamic holography and optical data processing. They are considered to be perspective nonlinear media owing to their high sensitivity and complicated dynamical properties that result in variety of multiwave mixing effects observed in experiments. Large nonlinear susceptibilities of azo-containing polymers enable processing of optical signals with the intensities less than 1 mW/cm2. Dynamics of the medium response in these processes strongly depends on the operating conditions. However, some peculiarities of the complex behavior of organic materials in photo-induced processes have not been well studied yet.

Investigations of nonlinear properties of azo dye containing polymers and possibilities of their applications are accomplished actively in our laboratory. One of the main directions is study of holographic characteristics of polymer film samples, optimization of external conditions and recording schedule for more dense holographic recording. The other is concentrated on two-wave mixing phenomena study and their application to dynamic holography and adaptive interferometry.
In our experiments we use rather thick film samples (about 50 mkm) of amorphous and liquid-crysalline azo dye containing polymers having different concentration of azo dye. The polymer films are placed into heat-insulated cells enabling to control temperature of a sample. The recording scheme is classical. Object and reference waves are crossed in the plane of the polymer film and produce an interference pattern (see fig. 1). The excitation light gets into a wing of the azo dye absorption line and provides effective influence on the medium. The wavelength of probe (reading out) light is not absorbed by azo dye and does not affect the polymer. Under acting light the photosensitive molecules forming the polymer undergo isomerization that leads to local change in the refractive index and the absorption coefficient. As a result, a gain-phase relief is formed in the polymer film that represents a gain-phase hologram. Reading out beam diffracts on the lattice restoring the initial image. In the case of dynamic holography the wavelength of reading out light is the same that of recording and the hologram is stored and erased simultaneously. In such situation phase and amplitude modulation of the signal beam is transformed due to the two-wave interaction in nonlinear medium and allows optical signal processing.
Adaptive interferometry is a combination of dynamic holography and adaptive optics. Realization of dynamic holography methods using nonlinear optical media as the beam mixer allow to improve characteristics of interferometric systems as well as essentially simplify their design. Along with some applications, adaptive interferometers can be used for nonlinear materials study.
Experiments show that the system adapts to the external condition variation. This property of adaptive interferometer allows suppress low frequency components while registration of high frequency phase perturbations.

Selected publications:

• Andreeva M.S., Dynamics of two-wave nonlinear interaction in azo-containing photosensitive polymer films with liquid-crystalline propertis. Abstract. 2004. (in Russian)
• A.N. Simonov, M.S. Andreeva, V.I. Shmal'gauzen, V.P. Shibaev, Dynamics of two-wave interaction in azocontaining photosensitive liquid crystalline polymer, Quantum Electronics, 31 (2001) 599.
• M.S. Andreeva, V.I. Shmal'gauzen, Energy coupling of coherent light beams in azocontaining photosensitive polymer, Bulletin of MSU, (2002).
• M.S. Andreeva, V.I. Shmal'gauzen, Energy coupling in azocontaining photosensitive polymer film in two-wave interaction of differently inclined light beams, Izvestia RAN, 8 (2002).
• A.N. Simonov, D.V. Uraev, V.P. Shibaev, S.G. Kostromin, Photoreversible optical data recording in films of amorphous azo dye-containing polymers, Kvantum Elektroniks, 32 (2002) 143. (in Russian)
• A.N. Simonov, D.V. Uraev, S.G. Kostromin, V.P. Shibaev, and A.I. Stakhanov, Polarization-controlled optical recording in azocontaining amorphous polymer films, Laser Physics (in press).