2015/08/05 by Dinesh Kumar Basker, Michael A. Brook, Kalaichelvi Saravanamuttu · 3 citations
Physics and Astronomy · Materials Science · #Nonlinear Photonic Systems #Advanced Fiber Laser Technologies #Liquid Crystal Research Advancements
paper · doi:10.1021/acs.jpcc.5b07117
openalex publication_date 2015/08/05 · openalex created_date 2025/10/10 · openalex updated_date 2026/06/15
We report spontaneous pattern formation due to modulation instability (MI) of a broad, uniform, incandescent beam as it propagates through a fluid medium undergoing cationic ring-opening polymerization of epoxide moieties and show that the dynamics of the process can be controlled through polymerization kinetics. By strong contrast, MI in the half century-old field of nonlinear light propagation has until now been described predominantly in terms of optical parameters such as coherence, intensity and wavelength. The increase in refractive index (Δ n ) originating from the cross-linking polymerization of biscycloaliphatic epoxy monomers pushes the system into a nonlinear regime, where normally negligible spatial noise becomes greatly amplified. The perturbed optical field stabilizes by spontaneously dividing into thousands of self-trapped filaments of light. Because each filament inscribes a permanent microscopic channel along its propagation path, the initially isotropic fluid medium solidifies into a densely packed array of self-induced waveguides. These experiments demonstrated the strong correlation between the kinetics of cationic polymerization and dynamics of MI; the beam becomes unstable only within a narrow parameter range where a critical balance is struck between the photoresponse speed (determined by polymerization rate) and the magnitude of Δ n (determined by extent of cross-linking). The former needs to be sufficiently fast to respond to noise while the latter must be large enough to generate high-refractive index seeds that trigger MI. Outside of this range, MI is entirely suppressed. This study reveals that nonlinear waveforms emerge in a familiar, widely employed epoxide photopolymer system, which for the first time highlights the possibility of tuning MI through the kinetics of a photochemical reaction.