Electric Control of Thermal Contributions to the Nonlinear Optical Properties of Nitrobenzene

Abstract

Thermal effects are inevitable when an absorptive nonlinear optical material interacts with long pulse duration or high repetition rate laser pulses. It results in inaccurate characterization and reduction in efficiency of the nonlinear materials for device applications. In this article, the study investigates the influence of an external electric field on the thermal contribution to the nonlinear optical response of nitrobenzene (NB). Z‐scan measurements are performed on NB using 330 ps laser pulses at a wavelength of 532 nm with variable (10 Hz to 1 kHz) repetition rates. At low repetition rates, NB shows a positive nonlinear refractive index (+ n2), which leads to self‐focusing of the laser beam due to the optical Kerr effect. Cumulative thermal effects occur above a repetition rate of 200 Hz. At high repetition rates (>750 Hz), the sign of n2 becomes negative, implying a self‐defocusing behavior of the sample arising from the thermal‐induced nonlinear refractive index. By applying an external DC field to the NB, a reduction of the thermal contribution can be observed. At a sufficiently high electric field strength, the thermal contribution is suppressed and the inherent Kerr nonlinearity can be observed despite the high repetition rate of the pump laser.

Introducing Optical Nonlinearity in PDMS Using Organic Solvent Swelling

“…Notably, for pure PDMS, we could observe thermal effects only for higher pulse energies above 7.4 µJ. Thermal effects caused by absorption are a well-known phenomenon in NB, with several opportunities for efficient mitigation [42]. Therefore, we have reduced the pulse energies in our measurements on PDMS/NB down to 0.8 µJ and also lowered the repetition rate from 50 Hz to 10 Hz, aiming to mitigate thermal effects.…”