History of optics

History of optics

Optics began with the development of lenses by the ancient Egyptians and Mesopotamians, followed by theories on light and vision developed by ancient Greek and Indian philosophers, and the development of geometrical optics in the Greco-Roman world. The word "optics" is derived from the Greek term "τα όπτικά" which referred to matters of vision. ["Oxford English Dictionary", [http://dictionary.oed.com] ] Optics was significantly reformed with the development of physical optics and physiological optics in the medieval Islamic world, and then significantly advanced in early modern Europe, where diffractive optics began. These earlier studies on optics are now known as "classical optics". The term "modern optics" refers to areas of optical research that largely developed in the 20th century, such as quantum optics.

Early history of optics

The earliest known lenses were made from polished crystal, often quartz, and have been dated as early as 700 BC for Assyrian lenses such as the Layard / Nimrud lens. There are many similar lenses from ancient Egypt, Greece and Babylon. The ancient Romans and Greeks filled glass spheres with water to make lenses. However, glass lenses were not thought of until the Middle Ages.

In ancient India, the philosophical schools of Samkhya and Vaisheshika, from around the 6th–5th century BC, developed theories on light. According to the Samkhya school, light is one of the five fundamental "subtle" elements ("tanmatra") out of which emerge the gross elements.

In contrast, the Vaisheshika school gives an atomic theory of the physical world on the non-atomic ground of ether, space and time. (See "Indian atomism".) The basic atoms are those of earth ("prthivı"), water ("apas"), fire ("tejas"), and air ("vayu"), that should not be confused with the ordinary meaning of these terms. These atoms are taken to form binary molecules that combine further to form larger molecules. Motion is defined in terms of the movement of the physical atoms. Light rays are taken to be a stream of high velocity of "tejas" (fire) atoms. The particles of light can exhibit different characteristics depending on the speed and the arrangements of the "tejas" atoms. Around the first century BC, the "Vishnu Purana" refers to sunlight as the "the seven rays of the sun".

In the fifth century BC, Empedocles postulated that everything was composed of four elements; fire, air, earth and water. He believed that Aphrodite made the human eye out of the four elements and that she lit the fire in the eye which shone out from the eye making sight possible. If this were true, then one could see during the night just as well as during the day, so Empedocles postulated an interaction between rays from the eyes and rays from a source such as the sun.

In 55 BC, Lucretius, a Roman who carried on the ideas of earlier Greek atomists, wrote:

"The light and heat of the sun; these are composed of minute atoms which, when they are shoved off, lose no time in shooting right across the interspace of air in the direction imparted by the shove." – "On the nature of the Universe"

Despite being similar to later particle theories, Lucretius's views were not generally accepted and light was still theorized as emanating from the eye.

Later in 499, Aryabhata, who proposed a heliocentric solar system of gravitation in his "Aryabhatiya", wrote that the planets and the Moon do not have their own light but reflect the light of the Sun.

The Indian Buddhists, such as Dignāga in the 5th century and Dharmakirti in the 7th century, developed a type of atomism that is a philosophy about reality being composed of atomic entities that are momentary flashes of light or energy. They viewed light as being an atomic entity equivalent to energy, similar to the modern concept of photons, though they also viewed all matter as being composed of these light/energy particles.

The beginnings of geometrical optics

The early writers discussed here treated vision more as a geometrical than as a physical, physiological, or psychological problem. The first known author of a treatise on geometrical optics was the geometer Euclid (c. 325 BC–265 BC). Euclid began his study of optics as he began his study of geometry, with a set of self-evident axioms.

# Lines (or visual rays) can be drawn in a straight line to the object.
# Those lines falling upon an object form a cone.
# Those things upon which the lines fall are seen.
# Those things seen under a larger angle appear larger.
# Those things seen by a higher ray, appear higher.
# Right and left rays appear right and left.
# Things seen within several angles appear clearer.

Euclid did not define the physical nature of these visual rays but, using the principles of geometry, he discussed the effects of perspective and the rounding of things seen at a distance.

Where Euclid had limited his analysis to simple direct vision, Hero of Alexandria (c. AD 10–70) extended the principles of geometrical optics to consider problems of reflection (catoptrics). Unlike Euclid, Hero occasionally commented on the physical nature of visual rays, indicating that they proceeded at great speed from the eye to the object seen and were reflected from smooth surfaces but could become trapped in the porosities of unpolished surfaces. [D. C. Lindberg, "Theories of Vision from al-Kindi to Kepler", (Chicago: Univ. of Chicago Pr., 1976), pp. 14-15.] This has come to be known as "emission theory".

Hero demonstrated the equality of the angle of incidence and reflection on the grounds that this is the shortest path from the object to the observer. On this basis, he was able to define the fixed relation between an object and its image in a plane mirror. Specifically, the image appears to be as far behind the mirror as the object really is in front of the mirror.

Like Hero, Ptolemy (c. 90–c. 168) considered the visual rays as proceeding from the eye to the object seen, but, unlike Hero, considered that the visual rays were not discrete lines, but formed a continuous cone. Ptolemy extended the study of vision beyond direct and reflected vision; he also studied vision by refracted rays (dioptrics), when we see objects through the interface between two media of different density. He conducted experiments to measure the path of vision when we look from air to water, from air to glass, and from water to glass and tabulated the relationship between the incident and refracted rays. [D. C. Lindberg, "Theories of Vision from al-Kindi to Kepler", (Chicago: Univ. of Chicago Pr., 1976), p. 16; A. M. Smith, Ptolemy's search for a law of refraction: a case-study in the classical methodology of 'saving the appearances' and its limitations, "Arch. Hist. Exact Sci". 26 (1982), 221-240; Ptolemy's procedure is reported in the fifth chapter of his "Optics".]

His tabulated results have been studied for the air water interface, and in general the values he obtained reflect the theoretical refraction given by modern theory, but the outliers are distorted to represent Ptolemy's "a priori" model of the nature of refraction.Fact|date=September 2008

Optical revolution in the Islamic world

Al-Kindi (c. 801–873) was one of the earliest important optical writers in the Islamic world. In a work known in the west as "De radiis stellarum", al-Kindi developed a theory "that everything in the world ... emits rays in every direction, which fill the whole world." [Cited in D. C. Lindberg, "Theories of Vision from al-Kindi to Kepler", (Chicago: Univ. of Chicago Pr., 1976), p. 19.] This theory of the active power of rays had an influence on later Western scholars such as as Robert Grosseteste and Roger Bacon. [citation|first=David C.|last=Lindberg|journal=Isis|volume=62|issue=4|date=Winter 1971|pages=469–489 [471] |doi=10.1086/350790|title=Alkindi's Critique of Euclid's Theory of Vision]

Ibn Sahl (c. 940-1000) was a Persian mathematician associated with the court of Baghdad. About 984 he wrote a treatise "On Burning Mirrors and Lenses" in which he set out his understanding of how curved mirrors and lenses bend and focus light. In his work he discovered a law of refraction mathematically equivalent to Snell's law. [R. Rashed, "A Pioneer in Anaclastics: Ibn Sahl on Burning Mirrors and Lenses", "Isis" 81 (1990): 464–91.] He used his law of refraction to compute the shapes of lenses and mirrors that focus light at a single point on the axis.

The beginnings of physical optics

Ibn al-Haytham (known in as "Alhacen" or "Alhazen" in Western Europe) (9651040), often regarded as the "father of modern optics",R. L. Verma "Al-Hazen: father of modern optics", "Al-Arabi", 8 (1969): 12-13.] formulated "the first comprehensive and systematic alternative to Greek optical theories." [D. C. Lindberg, "Alhazen's Theory of Vision and its Reception in the West", "Isis", 58 (1967), p. 322.] He initiated a revolution in optics and visual perception,citation|last1=Sabra|first1=A. I.|author1-link=A. I. Sabra|last2=Hogendijk|first2=J. P.|year=2003|title=The Enterprise of Science in Islam: New Perspectives|pages=85–118|publisher=MIT Press|isbn=0262194821|oclc=237875424 50252039] Citation |last=Hatfield |first=Gary |contribution=Was the Scientific Revolution Really a Revolution in Science? |editor1-last=Ragep |editor1-first=F. J. |editor2-last=Ragep |editor2-first=Sally P. |editor3-last=Livesey |editor3-first=Steven John |year=1996 |title=Tradition, Transmission, Transformation: Proceedings of Two Conferences on Pre-modern Science held at the University of Oklahoma |page=500 |publisher=Brill Publishers |isbn=9004091262 |oclc=19740432 234073624 234096934] [Citation|journal=The Medieval History Journal|volume=9|issue=1|pages=89–98|year=2006|doi=10.1177/097194580500900105|title=The Gaze in Ibn al-Haytham|first=Gérard|last=Simon] [citation|title=Burning Instruments: From Diocles to Ibn Sahl|first=Hélèna|last=Bellosta|journal=Arabic Sciences and Philosophy|year=2002|volume=12|pages=285–303|publisher=Cambridge University Press|doi=10.1017/S095742390200214X] [citation|title=Portraits of Science: A Polymath in the 10th Century|first=Roshdi|last=Rashed|journal=Science|date=2 August 2002|volume=297|issue=5582|page=773|doi=10.1126/science.1074591|pages=773|pmid=12161634] [Citation |last=Lindberg |first=David C. |year=1967 |title=Alhazen's Theory of Vision and Its Reception in the West |journal=Isis |volume=58 |issue=3 |pages=321–341 [332] |doi=10.1086/350266 ] and laid the foundations for modern physical optics. [Citation |last=Toomer |first=G. J. |year=1964 |date=December 1964 |title=Review: "Ibn al-Haythams Weg zur Physik" by Matthias Schramm |journal=Isis |volume=55 |issue=4 |pages=463–465 |doi=10.1086/349914] Ibn al-Haytham's key achievement was twofold: first, to insist that vision only occurred because of rays entering the eye and that rays postulated to proceed from the eye had nothing to do with it; the second was to define the physical nature of the rays discussed by earlier geometrical optical writers, considering them as the forms of light and color. He developed a camera obscura to demonstrate that light and color from different candles passed through a single aperture in straight lines, without intermingling at the aperture. [David C. Lindberg, "The Theory of Pinhole Images from Antiquity to the Thirteenth Century," "Archive for History of the Exact Sciences", 5(1968):154-176.] He then analyzed these physical rays according to the principles of geometrical optics. Ibn al-Haytham also employed the experimental scientific method as a form of demonstration in optics. He wrote many books on optics, most significantly the "Book of Optics" ("Kitab al Manazir" in Arabic), translated into Latin as the "De aspectibus" or "Perspectiva", which disseminated his ideas to Western Europe and had great influence on the later developments of optics. [D. C. Lindberg, "Theories of Vision from al-Kindi to Kepler", (Chicago: Univ. of Chicago Pr., 1976), pp. 58-86.]

Another aspect associated with Ibn al-Haytham's optical research is related to systemic and methodological reliance on experimentation ("i'tibar") and controlled testing in his scientific inquiries. Moreover, his experimental directives rested on combining classical physics ("'ilm tabi'i") with mathematics ("ta'alim"; geometry in particular) in terms of devising the rudiments of what may be designated as a hypothetico-deductive procedure in scientific research. This mathematical-physical approach to experimental science supported most of his propositions in "Kitab al-Manazir" ("The Optics"; "De aspectibus" or "Perspectivae") and grounded his theories of vision, light and colour, as well as his research in catoptrics and dioptrics. His legacy was further advanced through the 'reforming' of his "Optics" by Kamal al-Din al-Farisi (d. ca. 1320) in the latter's "Kitab Tanqih al-Manazir" ("The Revision of" [Ibn al-Haytham's] "Optics"). [ Nader El-Bizri, "A Philosophical Perspective on Alhazen’s Optics," "Arabic Sciences and Philosophy", Vol. 15, Issue 2 (2005), pp. 189-218 (Cambridge University Press)] [ Nader El-Bizri, "Ibn al-Haytham," in "Medieval Science, Technology, and Medicine: An Encyclopedia", eds. Thomas F. Glick, Steven J. Livesey, and Faith Wallis (New York — London: Routledge, 2005), pp. 237-240. ] The "Book of Optics" established experimentation as the norm of proof in optics,cite journal |last=Gorini |first=Rosanna |title=Al-Haytham the man of experience. First steps in the science of vision |journal=Journal of the International Society for the History of Islamic Medicine |volume=2 |issue=4 |pages=53–55 |date=October 2003 |url=http://www.ishim.net/ishimj/4/10.pdf |format=pdf |accessdate=2008-09-25] and gave optics a physico-mathematical conception at a much earlier date than the other mathematical disciplines of astronomy and mechanics. [Citation | last=Dijksterhuis | first=Fokko Jan | year=2004 | title=Lenses and Waves: Christiaan Huygens and the Mathematical Science of Optics in the Seventeenth Century | publisher=Springer | isbn=1402026978 | pages=113–5 | oclc=228400027 56533625: quote|"Through the influential work of Alhacen the onset of a physico-mathematical conception of optics was established at a much earlier time than would be the case in the other mathematical sciences."] The book was influential in both the Islamic world and in Western Europe.

Avicenna (980-1037) agreed with Alhazen that the speed of light is finite, as he "observed that if the perception of light is due to the emission of some sort of particles by a luminous source, the speed of light must be finite." [George Sarton, "Introduction to the History of Science", Vol. 1, p. 710.] Abū Rayhān al-Bīrūnī (973-1048) also agreed that light has a finite speed, and he was the first to discover that the speed of light is much faster than the speed of sound.MacTutor|id=Al-Biruni|title=Al-Biruni]

Abu 'Abd Allah Muhammad ibn Ma'udh, who lived in Al-Andalus during the second half of the 11th century, wrote a work on optics later translated into Latin as "Liber de crepisculis", which was mistakenly attributed to Alhazen. This was a "short work containing an estimation of the angle of depression of the sun at the beginning of the morning twilight and at the end of the evening twilight, and an attempt to calculate on the basis of this and other data the height of the atmospheric moisture responsible for the refraction of the sun's rays." Through his experiments, he obtained the value of 18°, which comes close to the modern value. [citation|title=The Authorship of the Liber de crepusculis, an Eleventh-Century Work on Atmospheric Refraction|first=A. I.|last=Sabra|author-link=A. I. Sabra|journal=Isis|volume=58|issue=1|date=Spring 1967|pages=77–85 [77] |doi=10.1086/350185]

In the late 13th and early 14th centuries, Qutb al-Din al-Shirazi (1236-1311) and his student Kamāl al-Dīn al-Fārisī (1260-1320) continued the work of Ibn al-Haytham, and they were the first to give the correct explanations for the rainbow phenomenon. Al-Fārisī published his findings in his "Kitab Tanqih al-Manazir" ("The Revision of" [Ibn al-Haytham's] "Optics"). [MacTutor|id=Al-Farisi|title=Al-Farisi]

In 1574, Taqi al-Din (1526–1585) wrote the last major Arabic work on optics, entitled "Kitab Nūr hadaqat al-ibsār wa-nūr haqīqat al-anzār" ("Book of the Light of the Pupil of Vision and the Light of the Truth of the Sights"), which contains experimental investigations in three volumes on vision, the light's reflection, and the light's refraction.cite web|author=Dr. Salim Ayduz|title=Taqi al-Din Ibn Ma’ruf: A Bio-Bibliographical Essay|url=http://muslimheritage.com/topics/default.cfm?ArticleID=949|date=26 June 2008|accessdate=2008-07-04)] The book deals with the structure of light, its diffusion and global refraction, and the relation between light and colour. In the first volume, he discusses "the nature of light, the source of light, the nature of the propagation of light, the formation of sight, and the effect of light on the eye and sight". In the second volume, he provides "experimental proof of the specular reflection of accidental as well as essential light, a complete formulation of the laws of reflection, and a description of the construction and use of a copper instrument for measuring reflections from plane, spherical, cylindrical, and conical mirrors, whether convex or concave." The third volume "analyses the important question of the variations light undergoes while travelling in media having different densities, i.e. the nature of refracted light, the formation of refraction, the nature of images formed by refracted light." He also invented an early rudimentary telescope.citation|first=Hüseyin Gazi|last=Topdemir|title=Takîyüddîn'in Optik Kitabi|publisher=Ministry of Culture Press, Ankara|year=1999 (cf. cite web|author=Dr. Hüseyin Gazi Topdemir|title=Taqi al-Din ibn Ma‘ruf and the Science of Optics: The Nature of Light and the Mechanism of Vision|publisher=FSTC Limited|url=http://muslimheritage.com/topics/default.cfm?ArticleID=951|date=30 June 2008|accessdate=2008-07-04)]

The beginnings of physiological optics

Ibn al-Haytham discussed the topics of medicine and ophthalmology in the anatomical and physiological portions of the "Book of Optics" and in his commentaries on Galenic works. [Steffens (cf. [http://ummahpulse.com/index.php?option=com_content&task=view&id=85&Itemid=54 Review by Sulaiman Awan] )] He accurately described the process of sight, [Bashar Saad, Hassan Azaizeh, Omar Said (October 2005). "Tradition and Perspectives of Arab Herbal Medicine: A Review", "Evidence-based Complementary and Alternative Medicine" 2 (4), p. 475-479 [476] . Oxford University Press] the structure of the eye, image formation in the eye and the visual system. He also discovered the underlying principles of Hering's law of equal innervation, vertical horopters and binocular disparity,cite journal | author=Ian P. Howard | year=1996 | title=Alhazen's neglected discoveries of visual phenomena | journal=Perception | volume=25 | issue=10 | pages=1203 – 1217 | doi=10.1068/p251203] and improved on the theories of binocular vision, motion perception and horopters previously discussed by Aristotle, Euclid and Ptolemy.Harv|Wade|1998] Harv|Howard|Wade|1996]

He discussed ocular anatomy, and was the first author to deal with the "descriptive anatomy" and "functional anatomy" of the eye independently. Much of his decriptive anatomy was faithful to Galen's gross anatomy, but with significant differences in his approach. [Gul A. Russell, "Emergence of Physiological Optics", pp. 689-90, in Harv|Morelon|Rashed|1996] For example, the whole area of the eye behind the iris constitutes what Ibn al-Haytham uniquely called the "uveal sphere", and his description of the eye was devoid of any teleological or humoural theories associated with Galenic anatomy. [Gul A. Russell, "Emergence of Physiological Optics", p. 690, in Harv|Morelon|Rashed|1996] He also described the eye as being made up of two intersecting globes, which was essential to his functional anatomy of the eye. [Gul A. Russell, "Emergence of Physiological Optics", p. 692, in Harv|Morelon|Rashed|1996]

After describing the construction of the eye, Ibn al-Haytham makes his most original anatomical contribution in describing the functional anatomy of the eye as an optical system, [Gul A. Russell, "Emergence of Physiological Optics", p. 691, in Harv|Morelon|Rashed|1996] or optical instrument. His multiple light-source experiment via a reduction slit with the camera obscura, also known as the lamp experiment, provided sufficient empirical grounds for him to develop his theory of corresponding point projection of light from the surface of an object to form an image on a screen. It was his comparison between the eye and the beam-chamber, or "camera obscura", which brought about his synthesis of anatomy and optics, giving rise to a new field of optics now known as "physiological optics". As he conceptualized the essential principles of pinhole projection from his experiments with the pinhole camera, he considered image inversion to also occur in the eye,Gul A. Russell, "Emergence of Physiological Optics", p. 689, in Harv|Morelon|Rashed|1996] and viewed the pupil as being similar to an aperture. [Gul A. Russell, "Emergence of Physiological Optics", p. 695-8, in Harv|Morelon|Rashed|1996] Regarding the process of image formation, however, he incorrectly agreed with Avicenna that the lens was the receptive organ of sight, but correctly hinted at the retina also being involved in the process.cite book | author=N. J. Wade | year=1998 | title=A Natural History of Vision | publisher=Cambridge, MA: MIT Press | isbn=0262231948 | oclc=37246567]

Optics in medieval Europe

The English bishop, Robert Grosseteste (c. 1175–1253), wrote on a wide range of scientific topics at the time of the origin of the medieval university and the recovery of the works of Aristotle. Grosseteste reflected a period of transition between the Platonism of early medieval learning and the new Aristotelianism, hence he tended to apply mathematics and the Platonic metaphor of light in many of his writings. He has been credited with discussing light from four different perspectives: an epistemology of light, a metaphysics or cosmogony of light, an etiology or physics of light, and a theology of light. [D. C. Lindberg, "Theories of Vision from al-Kindi to Kepler", (Chicago: Univ. of Chicago Pr., 1976), pp. 94-99.]

Setting aside the issues of epistemology and theology, Grosseteste's cosmogony of light describes the origin of the universe in what may loosely be described as a medieval "big bang" theory. Both his biblical commentary, the "Hexaemeron" (1230 x 35), and his scientific "On Light" (1235 x 40), took their inspiration from Genesis 1:3, "God said, let there be light", and described the subsequent process of creation as a natural physical process arising from the generative power of an expanding (and contracting) sphere of light. [R. W. Southern, "Robert Grosseteste: The Growth of an English Mind in Medieval Europe", (Oxford: Clarendon Press, 1986), pp. 136-9, 205-6.]

His more general consideration of light as a primary agent of physical causation appears in his "On Lines, Angles, and Figures" where he asserts that "a natural agent propagates its power from itself to the recipient" and in "On the Nature of Places" where he notes that "every natural action is varied in strength and weakness through variation of lines, angles and figures." [A. C. Crombie, "Robert Grosseteste and the Origins of Experimental Science", (Oxford: Clarendon Press, 1971), p. 110]

The English Franciscan, Roger Bacon (c. 1214–1294) was strongly influenced by Grosseteste's writings on the importance of light. In his optical writings (the "Perspectiva", the "De multiplicatione specierum", and the "De speculis comburentibus") he cited a wide range of recently translated optical and philosophical works, including those of Alhacen, Aristotle, Avicenna, Averroes, Euclid, al-Kindi, Ptolemy, Tideus, and Constantine the African. Although he was not a slavish imitator, he drew his mathematical analysis of light and vision from the writings of the Arabic writer, Alhacen. But he added to this the Neoplatonic concept, perhaps drawn from Grosseteste, that every object radiates a power ("species") by which it acts upon nearby objects suited to receive those "species". [D. C. Lindberg, "Roger Bacon on Light, Vision, and the Universal Emanation of Force," pp. 243-275 in Jeremiah Hackett, ed., "Roger Bacon and the Sciences: Commemorative Essays," (Leiden: Brill, 1997), pp. 245-250; "Theories of Vision from al-Kindi to Kepler", (Chicago: Univ. of Chicago Pr., 1976), pp. 107-18; "The Beginnings of Western Science", (Chicago: Univ. of Chicago Pr., 1992, p. 313.] Note that Bacon's optical use of the term "species" differs significantly from the genus / species categories found in Aristotelian philosophy.

Another English Franciscan, John Pecham (died 1292) built on the work of Bacon, Grosseteste, and a diverse range of earlier writers to produce what became the most widely used textbook on Optics of the Middle Ages, the "Perspectiva communis". His book centered on the question of vision, on how we see, rather than on the nature of light and color. Pecham followed the model set forth by Alhacen, but interpreted Alhacen's ideas in the manner of Roger Bacon. [D. C. Lindberg, "John Pecham and the Science of Optics:" Perspectiva communis, (Madison, Univ. of Wisconsin Pr., 1970), pp. 12-32; "Theories of Vision from al-Kindi to Kepler", (Chicago: Univ. of Chicago Pr., 1976), pp. 116-18.]

Like his predecessors, Witelo (c. 1230–1280 x 1314) drew on the extensive body of optical works recently translated from Greek and Arabic to produce a massive presentation of the subject entitled the "Perspectiva". His theory of vision follows Alhacen and he does not consider Bacon's concept of "species", although passages in his work demonstrate that he was influenced by Bacon's ideas. Judging from the number of surviving manuscripts, his work was not as influential as those of Pecham and Bacon, yet his importance, and that of Pecham, grew with the invention of printing. [D. C. Lindberg, "Theories of Vision from al-Kindi to Kepler", (Chicago: Univ. of Chicago Pr., 1976), pp. 118-20.]

*Peter of Limoges (1240–1306)
*Theodoric of Freiburg (ca. 1250–ca. 1310)

Renaissance and early modern optics

Johannes Kepler (1571–1630) picked up the investigation of the laws of optics from his lunar essay of 1600. Both lunar and solar eclipses presented unexplained phenomena, such as unexpected shadow sizes, the red color of a total lunar eclipse, and the reportedly unusual light surrounding a total solar eclipse. Related issues of atmospheric refraction applied to all astronomical observations. Through most of 1603, Kepler paused his other work to focus on optical theory; the resulting manuscript, presented to the emperor on January 1, 1604, was published as "Astronomiae Pars Optica" ("The Optical Part of Astronomy"). In it, Kepler described the inverse-square law governing the intensity of light, reflection by flat and curved mirrors, and principles of pinhole cameras, as well as the astronomical implications of optics such as parallax and the apparent sizes of heavenly bodies. "Astronomiae Pars Optica" is generally recognized as the foundation of modern optics (though the law of refraction is conspicuously absent). [Caspar, "Kepler", pp 142–146]

Willebrord Snellius (1580–1626) was most famous for the law of refraction now known as Snell's law. He mathematically formulated the law of refraction that is named after him in 1621.

René Descartes (1596–1650) made contributions to the field of optics. He showed by using geometric construction and the law of refraction (also known as Descartes' law) that the angular radius of a rainbow is 42 degrees (i.e. the angle subtended at the eye by the edge of the rainbow and the ray passing from the sun through the rainbow's centre is 42°). [cite book|last=Tipler|first=P. A. and G. Mosca|year=2004|title=Physics for Scientists and Engineers|location= |publisher=W. H. Freeman|isbn=0-7167-4389-2|oclc=51095685 52359293 53194746 56567284] He also independently discovered the law of reflection, and his essay on optics was the first published mention of this law. [cite encyclopedia|year=2008|encyclopedia=Encarta|url=http://encarta.msn.com/encyclopedia_761555262/Rene_Descartes.html#s3|title=René Descartes|publisher=Microsoft|accessdate=2007-08-15]

Christiaan Huygens (1629–1695) wrote several works in the area of optics. These included the "Opera reliqua" (also known as "Christiani Hugenii Zuilichemii, dum viveret Zelhemii toparchae, opuscula posthuma") and the "Traitbe de la lumiaere".

Isaac Newton (1643–1727) investigated the refraction of light, demonstrating that a prism could decompose white light into a spectrum of colours, and that a lens and a second prism could recompose the multicoloured spectrum into white light. He also showed that the coloured light does not change its properties by separating out a coloured beam and shining it on various objects. Newton noted that regardless of whether it was reflected or scattered or transmitted, it stayed the same colour. Thus, he observed that colour is the result of objects interacting with already-coloured light rather than objects generating the colour themselves. This is known as Newton's theory of colour. From this work he concluded that any refracting telescope would suffer from the dispersion of light into colours, and invented a reflecting telescope (today known as a Newtonian telescope) to bypass that problem. By grinding his own mirrors, using Newton's rings to judge the quality of the optics for his telescopes, he was able to produce a superior instrument to the refracting telescope, due primarily to the wider diameter of the mirror. In 1671 the Royal Society asked for a demonstration of his reflecting telescope. Their interest encouraged him to publish his notes "On Colour", which he later expanded into his "Opticks". Newton argued that light is composed of particles or "corpuscles" and were refracted by accelerating toward the denser medium, but he had to associate them with waves to explain the diffraction of light ("Opticks" Bk. II, Props. XII-L). Later physicists instead favoured a purely wavelike explanation of light to account for diffraction. Today's quantum mechanics, photons and the idea of wave-particle duality bear only a minor resemblance to Newton's understanding of light.

In his "Hypothesis of Light" of 1675, Newton the existence of the ether to transmit forces between particles. In 1704, Newton published "Opticks", in which he expounded his corpuscular theory of light. He considered light to be made up of extremely subtle corpuscles, that ordinary matter was made of grosser corpuscles and speculated that through a kind of alchemical transmutation "Are not gross Bodies and Light convertible into one another, ...and may not Bodies receive much of their Activity from the Particles of Light which enter their Composition?" [cite journal |last=Dobbs |first=J.T. |year=1982 |month=December |title=Newton's Alchemy and His Theory of Matter |journal=Isis |volume=73 |issue=4 |pages=p. 523 |doi=10.1086/353114 quoting "Opticks"] Newton also constructed a primitive form of a frictional electrostatic generator, using a glass globe.

The beginnings of diffractive optics

The effects of diffraction of light were first carefully observed and characterized by Francesco Maria Grimaldi, who also coined the term "diffraction", from the Latin "diffringere", 'to break into pieces', referring to light breaking up into different directions. The results of Grimaldi's observations were published posthumously in 1665. [cite book | title = Memoires pour l'histoire des sciences et des beaux arts | author = Jean Louis Aubert | publisher = Impr. de S. A. S.; Chez E. Ganeau| location = Paris | year = 1760 | pages = 149 | url = http://books.google.com/books?vid=OCLC58901501&id=3OgDAAAAMAAJ&pg=PP151&lpg=PP151&dq=grimaldi+diffraction+date:0-1800&as_brr=1 ] [cite book | title = A Treatise on Optics | author = Sir David Brewster | year = 1831 | publisher = Longman, Rees, Orme, Brown & Green and John Taylor | location = London | pages = 95 | url = http://books.google.com/books?vid=OCLC03255091&id=opYAAAAAMAAJ&pg=RA1-PA95&lpg=RA1-PA95&dq=grimaldi+diffraction+date:0-1840&as_brr=1 ] Isaac Newton studied these effects and attributed them to "inflexion" of light rays. James Gregory (1638–1675) observed the diffraction patterns caused by a bird feather, which was effectively the first diffraction grating. In 1803 Thomas Young did his famous experiment observing interference from two closely spaced slits. Explaining his results by interference of the waves emanating from the two different slits, he deduced that light must propagate as waves. Augustin-Jean Fresnel did more definitive studies and calculations of diffraction, published in 1815 and 1818, and thereby gave great support to the wave theory of light that had been advanced by Christiaan Huygens and reinvigorated by Young, against Newton's particle theory.

Lenses and lensmaking

The earliest known lenses were made from polished crystal, often quartz, and have been dated as early as 700 BC for Assyrian lenses such as the Layard / Nimrud lens. [http://news.bbc.co.uk/1/hi/sci/tech/380186.stm BBC News, "World's oldest telescope?"] ] There are many similar lenses from ancient Egypt, Greece and Babylon. The ancient Romans and Greeks filled glass spheres with water to make lenses.

Glass lenses were not thought of until the Middle Ages. Ibn al-Haytham (Alhacen) wrote about the effects of pinhole and concave lenses in his "Book of Optics",Harv|Wade|Finger|2001] Harv|Elliott|1966|Chapter 1] which was influential in the development of the modern telescope. [O. S. Marshall (1950). "Alhazen and the Telescope", "Astronomical Society of the Pacific Leaflets" 6, p. 4.] The earliest evidence of "a magnifying device, a convex lens forming a magnified image," also dates back to his "Book of Optics".citation|last1=Kriss|first1=Timothy C.|last2=Kriss|first2=Vesna Martich|title=History of the Operating Microscope: From Magnifying Glass to Microneurosurgery|journal=Neurosurgery|volume=42|issue=4|pages=899–907|date=April 1998|doi=10.1097/00006123-199804000-00116] Roger Bacon used parts of glass spheres as magnifying glasses and recommended them to be used to help people read. Roger Bacon got his inspiration from Alhacen in the 11th century. He discovered that light reflects from objects and does not get released from them. Around 1284 in Italy, Salvino D'Armate is credited with inventing the first wearable eye glasses. [cite web |last=Bellis |first=Mary |title=The History of Eye Glasses or Spectacles |work=About.com:Inventors |url=http://inventors.about.com/od/gstartinventions/a/glass_3.htm |accessdate=2007-09-01]

Between the 11th and 13th century "reading stones" were invented. Often used by monks to assist in illuminating manuscripts, these were primitive plano-convex lenses initially made by cutting a glass sphere in half. As the stones were experimented with, it was slowly understood that shallower lenses magnified more effectively.

There is some documentary evidence, but no surviving designs or physical evidence, that the principles of telescopes were known in the late 16th century. Leonard Digges, [ [http://cnx.org/content/m11932/latest/ Galileo's Telescope - by: Albert Van Helden] ] Taqi al-Dincitation|first=Hüseyin Gazi|last=Topdemir|title=Takîyüddîn'in Optik Kitabi|publisher=Ministry of Culture Press, Ankara|year=1999] and Giambattista della Porta [Giambattista della Porta, (2005), "Natural Magick", page 339. NuVision Publications, LLC.] independently developed rudimentary telescopes in the 1570s and 1580s. However, the earliest known working telescopes were the refracting telescopes that appeared in the Netherlands in 1608. Their development is credited to three individuals: Hans Lippershey and Zacharias Janssen, who were spectacle makers in Middelburg, and Jacob Metius of Alkmaar. Galileo greatly improved upon these designs the following year. Niccolò Zucchi is credited with constructing the first reflecting telescope in 1616. In 1668, Isaac Newton designed an improved reflecting telescope that bears his name, the Newtonian reflector.

The first microscope was made around 1595 in Middleburg, Holland. [ [http://nobelprize.org/educational_games/physics/microscopes/timeline/index.html Microscopes: Time Line ] ] Three different eyeglass makers have been given credit for the invention: Hans Lippershey (who also developed the first real telescope); Hans Janssen; and his son, Zacharias. The coining of the name "microscope" has been credited to Giovanni Faber, who gave that name to Galileo Galilei's compound microscope in 1625. [Stephen Jay Gould(2000). The Lying Stones of Marrakech, ch.2 "The Sharp-Eyed Lynx, Outfoxed by Nature". London: Jonathon Cape. ISBN 0224050443]

Quantum optics

Light is made up of particles called photons and hence inherently is "grainy" (quantized). Quantum optics is the study of the nature and effects of light as quantized photons. The first indication that light might be quantized came from Max Planck in 1899 when he correctly modelled blackbody radiation by assuming that the exchange of energy between light and matter only occurred in discrete amounts he called quanta. It was unknown whether the source of this discreteness was the matter or the light. In 1905, Albert Einstein published the theory of the photoelectric effect. It appeared that the only possible explanation for the effect was the existence of particles of light called photons. Later, Niels Bohr showed that the atoms were also quantized, in the sense that they could only emit discrete amounts of energy. The understanding of the interaction between light and matter following from these developments not only formed the basis of quantum optics but also were crucial for the development of quantum mechanics as a whole. However, the subfields of quantum mechanics dealing with matter-light interaction were principally regarded as research into matter rather than into light and hence, one rather spoke of atom physics and quantum electronics.

This changed with the invention of the maser in 1953 and the laser in 1960. Laser science—i.e., research into principles, design and application of these devices—became an important field, and the quantum mechanics underlying the laser's principles was studied now with more emphasis on the properties of light, and the name "quantum optics" became customary.

As laser science needed good theoretical foundations, and also because research into these soon proved very fruitful, interest in quantum optics rose. Following the work of Dirac in quantum field theory, George Sudarshan, Roy J. Glauber, and Leonard Mandel applied quantum theory to the electromagnetic field in the 1950s and 1960s to gain a more detailed understanding of photodetection and the statistics of light (see degree of coherence). This led to the introduction of the coherent state as a quantum description of laser light and the realization that some states of light could not be described with classical waves. In 1977, Kimble et al. demonstrated the first source of light which required a quantum description: a single atom that emitted one photon at a time. This was the first conclusive evidence that light was made up of photons. Another quantum state of light with certain advantages over any classical state, squeezed light, was soon proposed. At the same time, development of short and ultrashort laser pulses—created by Q switching and modelocking techniques—opened the way to the study of unimaginably fast ("ultrafast") processes. Applications for solid state research (e.g. Raman spectroscopy) were found, and mechanical forces of light on matter were studied. The latter led to levitating and positioning clouds of atoms or even small biological samples in an optical trap or optical tweezers by laser beam. This, along with Doppler cooling was the crucial technology needed to achieve the celebrated Bose-Einstein condensation.

Other remarkable results are the demonstration of quantum entanglement, quantum teleportation, and (recently, in 1995) quantum logic gates. The latter are of much interest in quantum information theory, a subject which partly emerged from quantum optics, partly from theoretical computer science.

Today's fields of interest among quantum optics researchers include parametric down-conversion, parametric oscillation, even shorter (attosecond) light pulses, use of quantum optics for quantum information, manipulation of single atoms, Bose-Einstein condensates, their application, and how to manipulate them (a sub-field often called atom optics), and much more.

Research into quantum optics that aims to bring photons into use for information transfer and computation is now often called photonics to emphasize the claim that photons and photonics will take the role that electrons and electronics now have.

See also

* History of physics
* List of astronomical instrument makers



* Crombie, A. C. "Robert Grosseteste and the Origins of Experimental Science". Oxford: Clarendon Press, 1971.
* Lindberg, D. C. "Alhazen's Theory of Vision and its Reception in the West", "Isis" 58 (1967), 321-341.
* Lindberg, D. C. "Theories of Vision from al-Kindi to Kepler". Chicago: University of Chicago Press, 1976.
* Temple, R. "The Crystal Sun". London: Arrow Books, 2000 ISBN 0-09-925679-7.
* [http://www.bbc.co.uk/radio4/history/inourtime/inourtime.shtml History of Optics (audio mp3)] by Simon Schaffer, Professor in History and Philosophy of Science at the University of Cambridge, Jim Bennett, Director of the Museum of the History of Science at the University of Oxford and Emily Winterburn, Curator of Astronomy at the National Maritime Museum (recorded by the BBC).

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