Studies on an optical memory effect in doped gel matrices

Including polarizable dopants into the pores of a gel matrix can lead to an all-optical memory system.1,2 Powerful, linearly polarized optical pump pulses, provided by a femtosecond laser and focused on a doped gel, tend to align the dopants' dipolar moments in the direction of the pump polarization. This induces a strong anisotropy: inserting the sample between two crossed polarizers, whose polarization axes are at 45° to the pump polarization, allows one to probe the resulting birefringence An. In contrast to the optical Kerr effect in solutions, the anisotropy remains during long periods of time, up to several months, despite the thermal Brownian agitation. It is classically explained that the dopants are attached to the matrix through hydrogen bonds. These are broken by the pump beam and the dopants can be realigned. After each optical pulse, new bonds are formed, stabilizing the new orientations (Fig. 1). Aligning the molecules either on one of the polarizers' axes or at 45° enables switching between two states of probe light transmission—low and high. This system can be described as an erasable, rewritable, all-optical memory, potentially with a molecular resolution, yet limited by the optical diffraction.