Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviolet, and infrared light. Because light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties.
Optical Science term in physics more broadly refers to the study of the behavior of light and its interactions with matter. The spectrum of Optical Sciences encompasses fundamental studies in the way light interacts with matter, through to the development of technologies for the market, classical and quantum photonics, light-matter interactions, nanotechnology, biomedical and biosciences, quantum gases, and quantum materials.
Optical science is relevant to and studied in many related disciplines including astronomy, various engineering fields, photography, and medicine (particularly ophthalmology and optometry, in which it is called physiological optics). Practical applications of optics are found in a variety of technologies and everyday objects, including mirrors, lenses, telescopes, microscopes, lasers, and fibre optics.
Today, we may roughly group the study of optics into three broad subfields of study:
- Geometrical optics, the study of light as rays: Two laws dictate what happens when light encounters a material surface. The law of reflection, evidently first stated by Euclid around 300 BC, states that when light encounters a flat reflecting surface the angle of incidence of a ray is equal to the angle of reflection. The law of refraction, experimentally determined by Willebrord Snell in 1621, explains the manner in which a light ray changes direction when it passes across a planar boundary from one material to another. A direct consequence of this ‘bending’ of light rays is that an object half submerged in a glass of water will appear to be bent.
- Physical optics, the study of light as waves: Physical optics is the study of the wave properties of light, which may be roughly grouped into three categories: interference, diffraction, and polarization. Interference is the ability of a wave to interfere with itself, creating localized regions where the field is alternately extremely bright and extremely dark. Diffraction is the ability of waves to ‘bend’ around corners and spread after passing through an aperture. Polarization refers to properties of light related to its transverse nature. We will cover all these terms in more detail in subsequent posts.
- Quantum optics, the study of light as particles: The reality is that light has both wavelike and particlelike properties, depending on the circumstances of measurement. This is what is known as wave-particle duality, and is one of the cornerstones of modern physics. It is illustrated by the curious progression of squirts mentioned above: individual particles (photons) eventually build up a wavelike pattern – each particle of light evidently ‘carries’ with it the wave information required to build up the diffraction pattern. The field of quantum optics involves the study of this particle (quantum) nature of light.
Most optical phenomena can be accounted for by using the classical electromagnetic description of light. Complete electromagnetic descriptions of light are, however, often difficult to apply in practice. The most common of these, geometric optics, treats light as a collection of rays that travel in straight lines and bend when they pass through or reflect from surfaces. Physical optics is a more comprehensive model of light, which includes wave effects such as diffraction and interference that cannot be accounted for in geometric optics. Some phenomena depend on light having both wave-like and particle-like properties. Explanation of these effects requires quantum mechanics. When considering light’s particle-like properties, the light is modelled as a collection of particles called “photons”. Quantum optics deals with the application of quantum mechanics to optical systems.
All three branches are still actively being researched. Geometrical optics is commonly used in the design of complicated optical systems, and researchers are studying ways to ‘improve’ the geometric models to provide better overlap with the wave theory of light. Physical optics lies on the boundary of engineering and pure science, as new physical consequences of the wave nature of light are still being uncovered and optical devices are being built which take advantage of this wave nature. Quantum optics is used as a tool to better understand the theory of quantum mechanics, though a number of highly speculative applications, such as quantum computing and quantum cryptography, are being explored.
Optical engineering is the field of science and engineering encompassing the physical phenomena and technologies associated with the generation, transmission, manipulation, detection, and utilization of light. Optical engineers use optics to solve problems and to design and build devices that make light do something useful. They design and operate optical equipment that uses the properties of light using physics and chemistry, such as lenses, microscopes, telescopes, lasers, sensors, fiber optic communication systems and optical disc systems (e.g. CD, DVD).
Optical engineering metrology uses optical methods to measure either micro-vibrations with instruments like the laser speckle interferometer, or properties of masses with instruments that measure refraction. Nano-measuring and nano-positioning machines are devices designed by optical engineers. These machines, for example microphotolithographic steppers, have nanometer precision, and consequently are used in the fabrication of goods at this scale
Naval Research Laboratory’s Optical Sciences Division
Naval Research Laboratory’s Optical Sciences Division carries out theoretical and experimental research in these optical wavelenths, with an eye to understanding physical principles involved in optical devices, materials, and phenomena. DCS engineers will focus on extending this understanding in the direction of device engineering and advanced operational techniques.
The Optical Sciences Division carries out a variety of research, development, and application-oriented activities in the generation, propagation, detection, and use of radiation in the wavelength region between near-ultraviolet and far-infrared wavelengths. The Division serves the Laboratory and the Navy as a consulting body of experts in optical sciences. The research, both theoretical and experimental, is concerned with discovering and understanding the basic physical principles and mechanisms involved in optical devices, materials, and phenomena.
- Fiber and solid-state laser/sources
- High-speed (<100 fs) optical probing
- High-power fiber amplifiers
- High-speed fiber-optic communications
- Antenna remoting
- Free space communications
- Photonic control of phased array
- Optical clocks
- Microwave photonics
- Applied Optics Branch – conducts basic and applied research in the areas of Intelligence, Surveillance, and Reconnaissance (ISR) and Infrared Countermeasures (IRCM). This includes full spectrum active and passive multi-intelligence sensor development, laser techniques and integration, advanced image and signal processing algorithm development, real-time target exploitation and product dissemination, maritime sensing, and rapid prototyping efforts for full-system integration on military airborne, space, ground, surface, and sub-surface platforms.
- Optical Techniques Branch – conducts research in the following areas:
- Fiber Optic Interferometric Sensors:
- Transducer Design and Development
- Fiber Sensor Multiplexing Approaches
- Interrogation and Demodulation Techniques
- Distributed Fiber Optic Sensing:
- Phase coherent OTDR
- Brillouin and Raman
- Laser Sensors
- Fiber Laser Sensors
- Distributed Fiber Sensors
- Fiber Tip Sensors
- Application Areas:
- Sonar: Hull, Towed, and Bottom mounted Acoustic Sensor Systems
- Magnetic field sensing
- Distributed Seismic and Acoustic sensing
- Structural Monitoring
- Sensor Data Fusion
Officials of the U.S. Naval Research Laboratory in Washington announced a $9.6 million contract to DCS in Nov 2022 to investigate the use of radiation in the wavelength region between near-ultraviolet and far-infrared wavelengths. These electro-optical technologies could lead to a variety of advanced sensors for applications like missile defense, counter-terrorism, anti-camouflage, and target acquisition. DCS experts will conduct research and development in the generation, propagation, detection, and use of radiation in wavelenths between near-ultraviolet and far-infrared.