Optics

Refraction of light occurs when light passes from one medium to another, such as air into water, causing it to bend. When you observe a straw in a glass of water, the part of the straw submerged appears shifted or broken at the water's surface due to this bending of light. This optical illusion occurs because the light rays traveling from the submerged part to your eyes change direction as they exit the water, altering your perception of the straw's position.

The fringe width, often denoted as ( \beta ), in a double-slit interference experiment is given by the formula ( \beta = \frac{\lambda D}{d} ), where ( \lambda ) is the wavelength of the light used, ( D ) is the distance from the slits to the screen, and ( d ) is the distance between the two slits. This expression shows that the fringe width is directly proportional to the wavelength and the distance to the screen, and inversely proportional to the slit separation.

Refraction occurs when light travels from one material to another due to a change in its speed as it moves through different media. This change in speed is caused by the varying optical densities of the materials; for example, light slows down when entering a denser medium like water from air. The bending of light at the interface between the two materials is described by Snell's Law, which relates the angles of incidence and refraction to the indices of refraction of the materials involved. This bending effect results in the characteristic change in direction of the light ray.

The relevant properties of a medium for sound transmission include its density, elasticity, and temperature. Density affects the mass of particles that sound waves must move, influencing the speed of sound; higher density typically leads to slower sound transmission. Elasticity, or the ability of a medium to return to its original shape after deformation, directly impacts how efficiently sound waves propagate; more elastic materials transmit sound faster. Additionally, temperature can influence the speed of sound, as warmer temperatures generally increase particle movement, allowing sound waves to travel more quickly.

Fiber optics is important because it enables high-speed data transmission over long distances with minimal signal loss. It supports the backbone of modern telecommunications, including internet, television, and telephone services, allowing for faster and more reliable connections. Additionally, fiber optics is less susceptible to electromagnetic interference compared to traditional copper cables, making it a more secure and efficient choice for data transfer. Its capacity for high bandwidth also facilitates the growing demands of data-heavy applications and technologies.

In the case of linear optical transitions, an electron absorbs a photon from the

incoming light and makes a transition to the next higher unoccupied allowed state. When

this electron relaxes it emits a photon of frequency less than or equal to the frequency of

the incident light (Figure 1.3a). SHG on the other hand is a two-photon process where this

excited electron absorbs another photon of same frequency and makes a transition to

reach another allowed state at higher energy. This electron when falling back to its original

39

state emits a photon of a frequency which is two times that of the incident light (Figure

1.3b). This results in the frequency doubling in the output.

When polarized white light passes through a synthetic fiber, it typically results in the creation of two perpendicular rays. This phenomenon occurs due to the birefringent properties of the fiber, where the light splits into two components with different polarizations. These two rays travel at different velocities and can exhibit varying refractive indices, leading to distinct paths within the fiber.

The angle of refraction is greatest when light travels from a medium with a higher refractive index to a medium with a lower refractive index. According to Snell's Law, as the angle of incidence increases, the angle of refraction also increases, approaching the critical angle. When the angle of incidence is just below the critical angle, the angle of refraction reaches its maximum value just before total internal reflection occurs. Thus, the greatest angle of refraction occurs right before the critical angle is reached.