Optical glass and optical instruments have evolved hand in hand throughout history. Each breakthrough in optical system design often brings new demands on the properties of optical glass, pushing its development forward. In turn, the successful creation of new types of optical glass can revolutionize the performance of optical instruments. The earliest materials used for optical components were natural crystals. Ancient Assyrians are believed to have used crystal lenses, while in ancient China, natural tourmaline (known as "tea mirrors") and citrine were employed. Archaeological findings show that glassmaking was already practiced in Egypt over 3,000 years ago, as well as during China's Warring States period. However, the use of glass for spectacles and mirrors began in Venice during the 13th century. Engels praised this innovation in his work "Dialectics of Nature," calling it one of the great inventions of the time. From then on, with the rise of astronomy and navigation, scientists like Galileo, Newton, and Descartes started using telescopes and microscopes, marking the beginning of glass as the primary material for optical parts. In the 17th century, achromatic correction became a central challenge in optical systems. As glass compositions improved, lead oxide was introduced, leading to the first achromatic lenses by Hull in 1729. This marked the division of optical glass into two major categories: crown and flint glass. In 1768, uniform optical glass was produced in southern France by stirring with a clay rod, laying the foundation for the independent optical glass industry. By the mid-19th century, several industrialized nations had established their own optical glass factories, such as the French Para-Mantu Company (1872), the British Chance Company (1848), and the German Schott Company (1848). During the 19th century, optical instruments saw significant progress. Just before World War I, Germany pushed for rapid development of military optics, requiring more diverse and high-quality optical glass. At this time, a notable physicist, working at the Schott plant, introduced new oxides like BaO, B2O3, ZnO, and P2O3 into the glass, studying their impact on optical properties. This led to the development of new types of glass, including bismuth, boron-bismuth, and zinc-bismuth glasses, as well as special relative partial dispersion glass. These innovations greatly expanded the range of optical glass, improving the quality of camera and microscope objectives. By the 1930s, most research still focused on the Schott plant. In 1934, a series of heavy-duty glasses were developed, such as German SK-16 (620/603) and SK-18 (639/555). This marked a key stage in the development of optical glass. During and after World War II, the demand for advanced optical instruments—such as aerial photography equipment, ultraviolet and infrared spectroscopy devices, and high-performance lenses—led to further developments in optical glass. In 1942, Morey and other scientists from the Soviet Union and Germany introduced rare earth elements and thin oxides into the glass, expanding the variety and producing high-refractive-index, low-dispersion optical glasses like Germany’s LaK and LaF, and the Soviet CTK and ТЬФ series. Research also focused on low refractive index, high dispersion glass, resulting in fluorotitanate-based glasses such as the Soviet ЛФ-9 and ЛФ-12, and the German F-16. Despite these advances, many new optical glass types still faced challenges in processing or application. Therefore, ongoing efforts have been made to improve their physical and chemical properties, optimize production processes, and reduce costs. Looking back at the historical development of optical glass, we can predict future trends: developing ultra-high refractive index glass, creating glass with special relative partial dispersion, advancing infrared and ultraviolet optical glass, replacing harmful components like thorium dioxide, toxic bismuth oxide, and antimony oxide, enhancing chemical stability, improving transparency and reducing radiation, and refining manufacturing techniques to lower costs.
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