Liquid Crystals

1Singular Optics of Liquid Crystal Defects

Etienne BRASSELET

Laboratoire Ondes et Matière d’Aquitaine (LOMA), Talence, France

1.1. Prelude from carrots

In the late 19th century, a carrot entered into the history of material sciences: as Reinitzer scrutinized the temperature behavior of cholesterol derivatives extracted from a carrot, he noticed “two melting points” (Reinitzer 1989). He thought that his discovery was worthy for consideration by physicists and contacted Lehmann in 1888 for further investigation. These were the early days of thermotropic liquid crystals, for which the temperature is the state parameter. Singularly, defects and light, with all of its colors, are ubiquitous to the observation of liquid crystals (Dierking 2003). This chapter focuses on the singular optical aspects of liquid crystal defects, which are discussed in section 1.6 after having reviewed the regular counterparts in section 1.5. For the sake of consistency, the chapter starts by providing the reader with the necessary, but non-exhaustive, information about liquid crystal structures, optics and behavior under external fields. A jump start is given by Figure 1.1, where the carrot’s orientation rotates by 2π per full-turn around the normal direction to the table, providing an artistic wink at liquid crystals, light and defects.

1.2. Liquid crystals, optics and defects: a long-standing trilogy

The pioneering experimental investigations by Lehmann were made possible by an instrument he developed, ...