Einstein suggested atoms could release excess energy as light in 1916. Ladenburg first observed stimulated emission in 1928. Townes developed maser in 1953, winning 1964 Nobel Prize. Townes and Schawlow proposed optical maser in 1958
Projectors project images onto surfaces using lenses or lasers. Chinese magic mirrors are oldest known image projectors from Han dynasty. Shadow play evolved into shadow puppetry in Asia since 840 CE. Camera obscura principle described by Mozi in 470-391 BC
Uses helium-neon gas mixture (5:1 to 20:1 ratio) at 1 Torr pressure. Operates at 632.8 nm wavelength in air, 632.9 nm in vacuum. Output can shift up to 500 MHz in either direction. Typical cavity length 15-50 cm, power 0.5-50 mW
Laser safety minimizes risks of accidents, especially eye injuries. Government regulations govern laser sales and usage. Thermal effects are primary cause of laser radiation injury. Laser beams can concentrate up to 200,000 times on retina
YAG is a cubic crystalline material with broad optical transparency. Has high hardness, chemical and heat resistance. Critical angle is 33 degrees. Cuts like natural garnet with polishing using alumina or diamond
First practical laser built in 1960 by Theodore Maiman. Lasers concentrate light through stimulated emission of radiation. Laser light is monochromatic, coherent, and produced in precise wavelengths