OPTICAL PHYSICS: HISTORY, FREQUENT TERMS, LAWS, APPLICATIONS - PHYSICAL - 2025

The physical optics is part of the optical studying the wave nature of light and the physical phenomena that only understood from the wave model. It also studies the phenomena of interference, polarization, diffraction and other phenomena that cannot be explained from geometric optics.

The wave model defines light as an electromagnetic wave whose electric and magnetic fields oscillate perpendicular to each other.

Electromagnetic Wave

The electric field (E) of the light wave behaves in a similar way to its magnetic field (B), but the electric field predominates over the magnetic field due to Maxwell's relationship (1831–1879), which establishes the following:

Where c = Speed ​​of propagation of the wave.

Physical optics does not explain the absorption and emission spectrum of atoms. On the other hand, quantum optics does address the study of these physical phenomena.

History

The history of physical optics begins with the experiments carried out by Grimaldi (1613-1663), who observed that the shadow cast by an illuminated object appeared wider and was surrounded by colored stripes.

He called the observed phenomenon diffraction. His experimental work led him to propose the wave nature of light, as opposed to Isaac Newton's conception that prevailed during the 18th century.

The Newtonian paradigm established that light behaved like a ray of small corpuscles that traveled at high speed in rectilinear paths.

Robert Hooke (1635-1703) defended the wave nature of light, in his studies on color and refraction, stating that light behaved like a sound wave propagating rapidly almost instantaneously through a material medium.

Later Huygens (1629–1695), based on Hooke's ideas, consolidated the wave theory of light in his Traité de la lumière (1690) in which he assumed that the light waves emitted by luminous bodies propagate through of a subtle and elastic medium called ether.

Huygens' wave theory explains the phenomena of reflection, refraction and diffraction much better than Newton's corpuscular theory, and shows that the speed of light decreases when passing from a less dense medium to a denser one.

Huygens' ideas were not accepted by scientists at the time for two reasons. The first was the inability to satisfactorily explain the definition of ether, and the second was Newton's prestige around his theory of mechanics that influenced a vast majority of scientists to decide to support the corpuscular paradigm of light.

Rebirth of wave theory

In the early 19th century, Tomas Young (1773–1829) succeeded in getting the scientific community to accept Huygens' wave model based on the results of his light interference experiment. The experiment made it possible to determine the wavelengths of the different colors.

In 1818 Fresnell (1788–1827) restated Huygens' wave theory in terms of the interference principle. He also explained the phenomenon of birefringence of light, which allowed him to affirm that light is a transverse wave.

In 1808 Arago (1788–1853) and Malus (1775-1812) explained the phenomenon of polarization of light from the wave model.

The experimental results of Fizeau (1819-1896) in 1849 and Foucalt (1819-1868) in 1862 made it possible to verify that light propagates faster in air than in water, contradicting the explanation given by Newton.

In 1872, Maxwell published his Treatise on Electricity and Magnetism, in which he stated the equations that synthesize electromagnetism. From his equations he obtained the wave equation that allowed him to analyze the behavior of an electromagnetic wave.

Maxwell found that the speed of propagation of an electromagnetic wave is related to the propagation medium and coincides with the speed of light, concluding that light is an electromagnetic wave.

Finally, Hertz (1857–1894) in 1888 succeeded in producing and detecting electromagnetic waves and confirming that light is a type of electromagnetic wave.

What does physical optics study?

Physical optics studies the phenomena related to the wave nature of light, such as interference, diffraction and polarization.

Interference

Interference is the phenomenon by which two or more light waves overlap, coexisting in the same region of space, forming bands of bright and dark light.

Bright bands are produced when multiple waves are added together to produce a larger amplitude wave. This type of interference is called constructive interference.

When waves overlap to produce a lower amplitude wave, the interference is called destructive interference, and bands of dark light are produced.

Interference

The way the colored bands are distributed is called the interference pattern. Interference can be seen in soap bubbles or oil layers on a wet road.

Diffraction

The phenomenon of diffraction is the change in the direction of propagation that the light wave experiences when it hits an obstacle or opening, altering its amplitude and phase.

Like the phenomenon of interference, diffraction is the result of the superposition of coherent waves. Two or more light waves are coherent when they oscillate with the same frequency maintaining a constant phase relationship.

As the obstacle gets smaller and smaller compared to the wavelength, the diffraction phenomenon predominates over the reflection and refraction phenomenon in determining the distribution of the light wave rays once it strikes the obstacle..

Polarization

Polarization is the physical phenomenon by which the wave vibrates in a single direction perpendicular to the plane containing the electric field. If the wave does not have a fixed direction of propagation, it is said that the wave is not polarized. There are three types of polarization: linear polarization, circular polarization, and elliptical polarization.

If the wave vibrates parallel to a fixed line describing a straight line in the plane of polarization, it is said to be linearly polarized.

When the electric field vector of the wave describes a circle in the plane perpendicular to the same direction of propagation, keeping its magnitude constant, the wave is said to be circularly polarized.

If the electric field vector of the wave describes an ellipse in the plane perpendicular to the same direction of propagation, the wave is said to be elliptically polarized.

Frequent Terms in Physical Optics

Polarizing

It is a filter that allows only a part of the light that is oriented in a single specific direction to pass through it without letting those waves that are oriented in other directions pass through.

Wave front

It is the geometric surface in which all parts of a wave have the same phase.

Wave amplitude and phase

Amplitude is the maximum elongation of a wave. The phase of a wave is the state of vibration at an instant of time. Two waves are in phase when they have the same state of vibration.

Brewster angle

It is the angle of incidence of light by which the light wave reflected from the source is fully polarized.

Infrared

Light not visible to the human eye in the electromagnetic radiation spectrum from 700 nm to 1000 μm.

Speed ​​of light

It is a speed constant of propagation of the light wave in vacuum whose value is 3 × 10 ⁸ m / s. The value of the speed of light varies when it propagates in a material medium.

Wavelength

A measure of the distance between a crest and another crest or between a valley and another valley of the wave as it propagates.

Ultraviolet

Non-visible electromagnetic radiation with spectrum of wavelengths less than 400 nm.

Laws of Physical Optics

Below are mentioned some laws of physical optics that describe the phenomena of polarization and interference

Fresnell and Arago Laws

1. Two light waves with linear, coherent and orthogonal polarizations do not interfere with each other to form an interference pattern.

2. Two waves of light with linear, coherent and parallel polarizations can interfere in a region of space.

3. Two waves of natural light with linear, non-coherent and orthogonal polarizations do not interfere with each other to form an interference pattern.

Malus Law

Malus' Law states that the intensity of light transmitted by a polarizer is directly proportional to the square of the cosine of the angle that forms the axis of transmission of the polarizer and the axis of polarization of the incident light. In other words:

I = intensity of light transmitted by the polarizer

θ = Angle between the transmission axis and the polarization axis of the incident beam

I ₀ = Incident light intensity

Malus Law

Brewster's Law

The light beam reflected by a surface is fully polarized, in the direction normal to the plane of incidence of the light, when the angle between the reflected beam and the refracted beam is equal to 90 °.

Brewster's Law

Applications

Some of the applications of physical optics are in the study of liquid crystals, in the design of optical systems, and in optical metrology.

Liquid crystals

Liquid crystals are materials that are kept between the solid state and the liquid state, whose molecules have a dipole moment that induces a polarization of the light that falls on them. From this property, screens for calculators, monitors, laptops and cell phones have been developed.

Digital watch with liquid crystal display (LCD)

Optical systems design

Optical systems are often used in everyday life, science, technology, and healthcare. Optical systems allow information to be processed, recorded and transmitted from light sources such as the sun, LED, tungsten lamp or laser. Examples of optical systems are the diffractometer and the interferometer.

Optical metrology

It is responsible for carrying out high resolution measurements of physical parameters based on the light wave. These measurements are made with interferometers and refractive instruments. In the medical area, metrology is used to constantly monitor the vital signs of patients.

Recent Research in Physical Optics

Optomechanical Kerker effect (AV Poshakinskiy1 and AN Poddubny, January 15, 2019)

Poshakinskiy and Poddubny (1) showed that nanometric particles with vibratory motion can manifest an optical-mechanical effect similar to that proposed by Kerker et al (2) in 1983.

The Kerker effect is an optical phenomenon that consists in obtaining a strong directionality of light scattered by spherical magnetic particles. This directionality requires that the particles have magnetic responses of the same intensity as the electrical forces.

The Kerker effect is a theoretical proposal that requires material particles with magnetic and electrical characteristics that currently do not exist in nature. Poshakinskiy and Poddubny achieved the same effect on nanometric particles, without significant magnetic response, that vibrate in space.

The authors showed that particle vibrations can create appropriately interfering magnetic and electrical polarizations, because magnetic and electrical polarity components of the same order of magnitude are induced in the particle when inelastic scattering of light is considered.

The authors propose the application of the optical-mechanical effect in nanometric optical devices by making them vibrate by the application of acoustic waves.

Extracorporeal Optical Communication (DR Dhatchayeny and YH Chung, May 2019)

Dhatchayeny and Chung (3) propose an experimental extracorporeal optical communication (OEBC) system that can transmit vital sign information of people through applications on mobile phones with Android technology. The system consists of a set of sensors and a diode hub (LED array).

Sensors are placed on various parts of the body to detect, process, and communicate vital signs such as pulse, body temperature, and respiratory rate. The data is collected through the LED array and transmitted through the mobile phone camera with the optical app.

The LED array emits light in the Rayleigh Gans Debye (RGB) scattering wavelength range. Each color and color combinations of the emitted light are related to vital signs.

The system proposed by the authors can facilitate the monitoring of vital signs in a reliable way, since the errors in the experimental results were minimal.

References

1. Optomechanical Kerker Effect. Poshakinskiy, AV and Poddubny, A N. 1, 2019, Physical Review X, Vol. 9, pp. 2160-3308.
2. Electromagnetic scattering by magnetic spheres. Kerker, M, Wang, DS and Giles, C L. 6, 1982, Journal of the Optical Society of America, Vol. 73.
3. Optical extra-body communication using smartphone cameras for human vital sign transmission. Dhatchayeny, D and Chung, Y. 15, 2019, Appl. Opt., Vol. 58.
4. Al-Azzawi, A. Physical Optics Principles and Practices. Boca Raton, FL: CRC Press Taylor & Francis Group, 2006.
5. Grattan-Guiness, I. Companion Encyclopedia of the History and Philosophy of the Mathematical Sciences. New York, US: Routledge, 1994, Vol. II.
6. Akhmanov, SA and Nikitin, S Yu. Physical Optics. New York: Oxford University Press, 2002.
7. Lipson, A, Lipson, SG and Lipson, H. Physical Optics. Cambridge, UK: Cambridge University Press, 2011.
8. Mickelson, A R. Physical Optics. New York: Springer Science + Business Media, 1992.
9. Jenkins, FA and White, H E. Fundamentals of Optics. NY: McGraw Hill Higher Education, 2001.