Introduction to optics:
The main subfields of optics are geometric optics and wave optics.
Light is the physical agent that impresses the eye, and through this it can be seen.
The nature of light and its structure have been a concern of man since ancient times. Due to the almost non-existent means of light research, the various hypotheses regarding light have long been speculative. More precise were the laws of light propagation, according to which, for example, it propagates in a straight line. This led Rudolph Snellius and Descartes to enunciate the laws of refraction between 1626 and 1637.
The laws of reflection were known since antiquity, it is not known when and by whom they were discovered and enunciated, but it is known that Euclid and Aristotle used them. In his book Kitab al-manazir (The Book on Optics, known in Latin as De Optica), the medieval Arab scholar Ali bin al-Haytham (Latin: Alhazen, 965-1039) talks about the refraction of light in air and water, the properties of camera obscura, and lenses.
The development of the means of research and experimentation has led to the certainty that light phenomena are produced by the alternating electric field of electromagnetic waves, so a ray of light is actually an electromagnetic wave.
General:
Optics is grouped into three major important sections:
Geometric optics, in which the laws of light propagation and the formation of optical images are studied abstracting from the nature of light. Specific phenomena are the reflection of light, the refraction of light.
Wave optics, in which phenomena such as diffraction, interference and polarization of light are explained by the consideration that light is a phenomenon of a wave nature, more specifically an electromagnetic wave.
Photonic optics, in which the photoelectric effect and other effects that highlight the corpuscular, photonic aspect of electromagnetic waves are studied.
Established optical phenomena are: light scattering, rainbow (occurs due to refractive phenomena, light reflection and light scattering), light absorption, light polarization.
Young Device
The Young device uses a monochrome light source S (laser), a screen with two rectangular slits (less than 1 mm wide) and parallel with a distance between them of maximum 1 mm, a screen (white sheet). For observing the interference figure there is no preferential position of the screen, it can be placed at a distance D between 1 m and 5 m from the slits and for this reason it is called non-localized interference.
Both interference and diffraction are based on the Hyugens-Fresnel principle which says that each point on a wavefront behaves as a secondary wave source with the same frequency and phase as the initial wave. The new wavefront is created by summing the amplitudes of the secondary waves.
Diffraction is the phenomenon of light bypassing obstacles that have dimensions comparable to the wavelength of light. The diffracted waves will interfere, resulting in more complicated light fringes, consisting of maximum and minimum intensity.
The diffraction grating is an optical device that consists of a system of narrow, rectilinear, parallel, equal, equidistant and very close slits.
It is done by drawing on a transparent plexiglass plate a number N of rectilinear scratches over a distance L.
The transparent intervals between scratches represent the lattice slots.
We note with
r1,r2 – the distances traveled by the two waves from the slits to the point P, where we analyze the interference
l – Slit Spacing
D - Slit-to-screen distance
x – the distance from the center of the screen (O) to the point P
Δr = r2 – r1 = geometric road difference
δ = n ∙ Δr = Optical roadc
A beam of monochromatic light, coming from the source S, is converted into a parallel beam by the lens L1 and falling under an angle of incidence, i, on the diffraction grating, R.
The diffraction figure can be seen on screen E. The diffraction image shows a central maximum, followed by a succession of higher-order maximums and minimums with intensities decreasing and decreasing.
According to the Huygens-Fresnel principle, each slit of the lattice becomes the seat of coherent secondary waves that form the angle α with the optical axis AO.
Between these where there will always be the same difference in optical path:
δ = δ1 – δ2.
The optical path difference between the incident waves on the network is:
δ1 = l ∙ without i.
The optical path difference between lattice diffracted waves is:
δ2 = l ∙ without α.
δ = δ1 – δ2 = l ( sin i – sin α)
In the case of the diffraction grating, the phenomenon is more complicated because both the diffraction of the secondary waves (from the slits) and the interference of all the secondary waves occur. As there are N traits on the lattice, N beams will interfere with each other.
By interfering with the waves coming from two slits at the distance l on the lattice, we will obtain at point P a maximum if δ = k ∙ λ and a minimum when δ = (2k + 1) ∙ λ
Considering the phenomenon of interference of the N beams, we can say that in all directions for which:
δ = l ( sin i ± sin α) ∙ λ, we have diffraction maxima.