optics-detailed optics-laws of optics-optical instruments


optics, light, optical laws
Light: lifeline of the human race
          Optics generally can be referred to as the study of light. Actually, optics is a branch of Science (Physics) in which we study the behavior and properties of light. It also includes the construction of instruments that use or detect light and more specifically how does it interact with the matter.
          In optics, we usually study the behavior of the visible, ultraviolet, and infrared spectrum of electromagnetic radiation. Because light is an electromagnetic wave of very small wavelength (400Nm-750Nm), the other forms of electromagnetic waves such as radio waves, X-rays and microwaves would also exhibit similar properties.

          But light is different from other electromagnetic radiations in some aspects, such as it's dual characteristics ( that is a particle as well as a wave ). Most of the optical phenomena can be explained using the classical electromagnetic description of light (it's particle nature). The complete electromagnetic description of light is, however, difficult to apply in actual practice. Because in the complete electromagnetic description, we talk about its wave nature. but due to its very small wavelength (400Nm - 750Nm)  compared to other physical objects, it seems to be traveling along a straight line.
          Practical optics is usually done using the simplified models of wave characteristics of light. A common example of these simplifications is geometrical optics. in which we treat light as a bunch of rays that travel in a straight line and bends when they are reflected or refracted. But when we talk about physical optics it is a more comprehensive model of light which includes wave effects such as interference and diffraction.
          Historically the ray-based model of optics was developed first followed by its wave aspect. And later in the 19th century, the light waves were considered to be electromagnetic radiation. Some phenomena of optics also consider light has both waves as well as particle-like properties. Explanations of these dual effects require quantum mechanics. When we consider light's particle-like behavior, it is represented as a collection of photons.
          Optical science is very useful in our daily lives. some common examples are like; spectacles, mirrors, lenses, cameras, telescope, microscope, lasers, optical fibers, LEDs, LCDs, Solar energy and most importantly what we see is optics (light).

Evolution of optics:

1.Early human race:           

The Nimrud lens. Image source: Wikimedia
     Optics is assumed to be started with the development of lenses by early Egyptians and Mesopotamians. The earliest known lenses were made from polished crystals mainly Quartz as early as about 700BC for Assyrian lenses such as Layard / Nimrud lenses.

      Then, the ancient Romans and Greeks are known to make lenses by filling water into glass spheres. These practical developments led the foundation of the theoretical development of light and vision by ancient Indian and Greek philosophers. The word optics is derived from the Greek word ὀπτική (optikē) meaning "appearance, look". In India optics is known as "prakashiki" (प्रकाशिकी): the study of light "Prakash" (प्रकाश ).
          The Greek philosophy developed further, But due to the contradiction between the thoughts of philosophers, it was broken down into two opposing theories. Both of them provided their own vision on the theoretical aspect of optics. One is known as "intromission theory" and the second one is "emission theory".

Intromission theory: 

          The Intromission theory explained vision as coming from objects casting off copies of themselves, that was considered to be captured by our eyes. This theory seems to be appropriate but it remained only like a thought/belief lacking any experimental proof.

Emission theory:

          The emission theory was first explained by Plato. The main idea behind this theory was some imaginary rays emitted by our eyes. Isn't this seems to be shit? But you know at that time this theory was supported by most of the philosophers and physicists. Huh, it sounds crazy.
          The idea was that the virtual approach is accomplished by rays emitted by our eyes. Some hundred years later, Euclid wrote a pamphlet entitled "Optics" where he linked vision to geometry, creating geometrical optics. His work was based on Plato's emission theory.

2.Middle age:

          During this time, the greek ideas about optics were renovated and extended by some Muslim philosophers. One of the earliest of these was Al-Kindi. who wrote on the merits of Aristotelian and Euclidean optics aspects since it could quantify the optical phenomena accurately. In 984 the Persian mathematician "Ibn shal" wrote the pamphlet entitled "On burning mirrors and lenses". Correctly explaining the law of reflection equivalent to Snell's law. He used this law to calculate ideal sizes and shapes of curved mirrors and lenses.

optics, vision, eye
Human eye: optics
          And now there was a great change in the world of optics when Alhazen (Ibn Al-Haytham) wrote the book of optics (Kitab Al-Manazir) and challenged most of the previous optical theories. In this book, he explained the terms reflection and refraction and proposed a new system for the explanation of vision and light that was based on the observations and experiments. He rejected the emission theory and put forward a new idea that light is reflected in all directions in straight lines from all points of the object that is seen/viewed, and then entered the eye. We all know that he was the most accurate person about optics/vision until that time. But that time he was unable to explain how eye captured the rays. His work was largely neglected/avoided by the physicians of that time. Nowadays we know him as the "Father of Optics".

           The practical use of optics in daily life was first started as spectacles (wearable eyeglasses) in Italy around 1286. This was the start of the spectacle industry. The spectacle makers used to use their experimental knowledge gained by observing the effects of lenses rather than using any type of optical theory. Progress in this industry led the foundation of the compound microscope in around 1595 followed by the refracting telescope in 1608.

optics, compound microscope
Compound microscope
optics, refraction telescope
Refraction telescope

3.Modern age:

          In the early 17th century "Johannes Kepler" expanded the geometrical optics and explained reflection by plane and curved mirrors, lenses, pinhole cameras, the intensity of light and most importantly the optical explanations of astronomical events such as astronomical parallax as we solar and lunar eclipses. He also explained the role of the retina as the organ that records images. After the invention of the telescope, Kepler rolled out the theoretical basis on how they worked and how they can be improved. He designed a new and improved version of the telescope using two convex lenses to produce higher magnification which is known as Keplerian telescope.
          In the time period of 1660-1670, "Isaac Newton" developed the Descarte's ideas into a new theory of light, most importantly determining that the white light is actually a mixture of colors, which can be separated into its constituents by passing through a prism. Then in 1690, Christian Huygens proposed a wave theory of light.
optics, evolution of optics, double slit experiment
Double Slit Experiment. image source: Wikimedia Commons
          In 1704 Sir Isaac Newton published a new pamphlet entitled "Opticks". Newtonian optics was generally accepted until the early 19th century. Then in 1801 Thomas Young and Augustin-Jean Fresnel conducted experiments for the interference of light, which established the wave characteristics of light. Young's double slit experiment showed that light follows the superposition phenomenon, which is followed by waves only. This work by Thomas Young led the foundation stone of wave optics and opened up an entirely new era of optics. Wave optics was further developed and successfully explained by the electromagnetic theory by James Clerck Maxwell in 1860 decade.

           The wave aspect of light grew further when in 1899 Max Plank correctly demonstrated black body radiation assuming that the exchange of energy between matter and light occurs only in a discrete amount which he named "Quanta". In 1905 "Albert Einstein" published the theory of the photoelectric effect that confirmed the quantization of Light. Quantum Optics gained Practical importance with the inventions of the MASER in 1953 and LASER in 1960.
optics, laser
Star Wars LASER Blade
          And now we are going to discuss the nature of light, laws of optics, and optical instruments in our next posts. Earlier the nature of light was also a point of contradiction. Some believed it to be a wave and some claim it to be a particle. And actually light acts as both wave as well as a particle. Light has a lot of properties which are mainly classified into three parts, that are:-
          1. Geometrical optics:-                                                                                Read more:-
                                            (a) Rectilinear propagation of light
                                            (b) Speed is finite
                                            (c) Reflection
                                            (d) Refraction
                                            (e) Dispersion

          2. Wave optics:-
                                            (a) Interference
                                            (b) Diffraction
                                            (c) electromagnetic behavior
                                            (d) Polarization
                                            (e) Double refraction

          3. Quantum optics:-
                                            (a) Atomic orbits
                                            (b) Energy levels inside an atom
                                            (c) Quanta
                                            (d) LASER

             Comment down any queries. Share with your friends and loved one, I always appreciate Sharing Knowledge, because it is the only thing that increases more and more when we share it.

Image source:  pixabay.com


optics-detailed optics-laws of optics-optical instruments optics-detailed optics-laws of optics-optical instruments Reviewed by Sourav Mishra on December 20, 2018 Rating: 5


  1. That was quite helpful specially the ancient theories, those were interesting.


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