Laser induced birefringence in liquids and solutions

Abstract

An apparatus is described with which the electric vector of a suitably defined laser beam has been used to induce optical birefringence in various liquid media. Blue light from a low powered argon laser monitored the birefringence in the sample cell while the infrared (1.06 μm wavelength) radiation of a neodymium doped YAG laser interacted with the sample molecules to give rise to the birefringence effects. The principal object of the study was to manifest effects in dilute solutions of macromolecules. Initial attempts involved mechanically chopping the YAG beam whose power was some 20 W continuous output. Only thermal effects were observed. These experiments are outlined as they give effects which might easily be mistaken for particle orientation effects. By ‘ Q ’ switching the laser, the increased power in the beam was sufficient to induce birefringence in pure liquids and liquid crystals. Finally, when operated in a ‘fixed Q ’ mode, the intermediate power but increased pulse duration (100 μs) enabled the optical Kerr effect to be realized in macromolecular solutions. Typical results are given for suspensions of bentonite clay and potassium hyaluronate in water.