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. Light is a type of electromagnetic radiation, and other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties.
In optics, chromatic aberration (CA), also called chromatic distortion, color aberration, color fringing, or purple fringing, is a failure of a lens to focus all colors to the same point. It is caused by dispersion: the refractive index of the lens elements varies with the wavelength of light. The refractive index of most transparent materials decreases with increasing wavelength. Since the focal length of a lens depends on the refractive index, this variation in refractive index affects focusing. Since the focal length of the lens varies with the color of the light different colors of light are brought to focus at different distances from the lens or with different levels of magnification. Chromatic aberration manifests itself as "fringes" of color along boundaries that separate dark and bright parts of the image.
Active optics is a technology used with reflecting telescopes developed in the 1980s, which actively shapes a telescope's mirrors to prevent deformation due to external influences such as wind, temperature, and mechanical stress. Without active optics, the construction of 8 metre class telescopes is not possible, nor would telescopes with segmented mirrors be feasible.
Adaptive optics (AO) is a technique of precisely deforming a mirror in order to compensate for light distortion. It is used in astronomical telescopes and laser communication systems to remove the effects of atmospheric distortion, in microscopy, optical fabrication and in retinal imaging systems to reduce optical aberrations. Adaptive optics works by measuring the distortions in a wavefront and compensating for them with a device that corrects those errors such as a deformable mirror or a liquid crystal array.
In astronomy, a guide star is a reference star used to accurately maintain the tracking by a telescope of a celestial body, whose apparent motion through the sky is primarily due to Earth's rotation.
In optics, any optical instrument or system – a microscope, telescope, or camera – has a principal limit to its resolution due to the physics of diffraction. An optical instrument is said to be diffraction-limited if it has reached this limit of resolution performance. Other factors may affect an optical system's performance, such as lens imperfections or aberrations, but these are caused by errors in the manufacture or calculation of a lens, whereas the diffraction limit is the maximum resolution possible for a theoretically perfect, or ideal, optical system.
In optics, the coma, or comatic aberration, in an optical system refers to aberration inherent to certain optical designs or due to imperfection in the lens or other components that results in off-axis point sources such as stars appearing distorted, appearing to have a tail (coma) like a comet. Specifically, coma is defined as a variation in magnification over the entrance pupil. In refractive or diffractive optical systems, especially those imaging a wide spectral range, coma can be a function of wavelength, in which case it is a form of chromatic aberration.
Scanning laser ophthalmoscopy (SLO) is a method of examination of the eye. It uses the technique of confocal laser scanning microscopy for diagnostic imaging of the retina or cornea of the human eye.
A laser guide star is an artificial star image created for use in astronomical adaptive optics systems, which are employed in large telescopes in order to correct atmospheric distortion of light. Adaptive optics (AO) systems require a wavefront reference source of light called a guide star. Natural stars can serve as point sources for this purpose, but sufficiently bright stars are not available in all parts of the sky, which greatly limits the usefulness of natural guide star adaptive optics. Instead, one can create an artificial guide star by shining a laser into the atmosphere. Light from the beam is reflected by components in the upper atmosphere back into the telescope. This star can be positioned anywhere the telescope desires to point, opening up much greater amounts of the sky to adaptive optics.
In physics, the wavefront of a time-varying wave field is the set (locus) of all points having the same phase. The term is generally meaningful only for fields that, at each point, vary sinusoidally in time with a single temporal frequency.
The Extremely Large Telescope (ELT) is an astronomical observatory under construction. When completed, it will be the world's largest optical/near-infrared ELT. Part of the European Southern Observatory (ESO) agency, it is located on top of Cerro Armazones in the Atacama Desert of northern Chile.
David L. Fried was an American scientist, best known for his contributions to optics. Fried described what has come to be known as the Fried Parameter, or r0. The Fried Parameter is a measure of the strength of the turbulence in the atmosphere of Earth. The turbulence causes what is known as seeing in astronomy and usually limits the optical resolution of ground-based telescopes and the detail in their images of astronomical objects. The Fried Parameter describes the smallest diameter of a telescope aperture at which the image fidelity starts to suffer significantly from turbulent airflows in the atmosphere of Earth. The Fried Parameter may change quickly on the time scale of minutes, or less. Typical values for the Fried Parameter in the visible spectrum may range from less than one centimeter to some tens of centimeters at good astronomical sites.
In optics, defocus is the aberration in which an image is simply out of focus. This aberration is familiar to anyone who has used a camera, videocamera, microscope, telescope, or binoculars. Optically, defocus refers to a translation of the focus along the optical axis away from the detection surface. In general, defocus reduces the sharpness and contrast of the image. What should be sharp, high-contrast edges in a scene become gradual transitions. Fine detail in the scene is blurred or even becomes invisible. Nearly all image-forming optical devices incorporate some form of focus adjustment to minimize defocus and maximize image quality.
In optics, tilt is a deviation in the direction a beam of light propagates.
The Strehl ratio is a measure of the quality of optical image formation, originally proposed by Karl Strehl, after whom the term is named. Used variously in situations where optical resolution is compromised due to lens aberrations or due to imaging through the turbulent atmosphere, the Strehl ratio has a value between 0 and 1, with a hypothetical, perfectly unaberrated optical system having a Strehl ratio of 1.
Deformable mirrors (DM) are mirrors whose surface can be deformed, in order to achieve wavefront control and correction of optical aberrations. Deformable mirrors are used in combination with wavefront sensors and real-time control systems in adaptive optics. In 2006 they found a new use in femtosecond pulse shaping.
A Shack–Hartmannwavefront sensor (SHWFS) is an optical instrument used for characterizing an imaging system. It is a wavefront sensor commonly used in adaptive optics systems. It consists of an array of lenses of the same focal length. Each is focused onto a photon sensor. If the sensor is placed at the geometric focal plane of the lenslet, and is uniformly illuminated, then, the integrated gradient of the wavefront across the lenslet is proportional to the displacement of the centroid. Consequently, any phase aberration can be approximated by a set of discrete tilts. By sampling the wavefront with an array of lenslets, all of these local tilts can be measured and the whole wavefront reconstructed. Since only tilts are measured the Shack–Hartmann cannot detect discontinuous steps in the wavefront.
Boston Micromachines Corporation is a US company operating out of Cambridge, Massachusetts. Boston Micromachines manufactures and develops instruments based on MEMS technology to perform open and closed-loop adaptive optics. The technology is applied in astronomy, beam shaping, vision science, retinal imaging, microscopy, laser communications, and national defense. The instruments developed at Boston Micromachines include deformable mirrors, optical modulators, and retinal imaging systems, all of which utilize adaptive optics technology to enable wavefront manipulation capabilities which enhance the quality of the final image.
A ferrofluid mirror is a type of deformable mirror with a reflective liquid surface, commonly used in adaptive optics. It is made of ferrofluid and magnetic iron particles in ethylene glycol, the basis of automotive antifreeze. The ferrofluid mirror changes shape instantly when a magnetic field is applied. As the ferromagnetic particles align with the magnetic field, the liquid becomes magnetized and its surface acquires a shape governed by the equilibrium between the magnetic, gravitational and surface tension forces. Since any shapes can be produced by changing the magnetic field geometries, wavefront control and correction can be achieved.
The Goode Solar Telescope (GST) is a scientific facility for studies of the Sun named after Philip R. Goode. It was the solar telescope with the world's largest aperture in operation for more than a decade. Located in Big Bear Lake; California, the Goode Solar Telescope is the main telescope of the Big Bear Solar Observatory operated by the New Jersey Institute of Technology (NJIT). Initially named New Solar Telescope (NST), first engineering light was obtained in December 2008, and scientific observations of the Sun began in January 2009. On July 17, 2017, the NST was renamed in honor of Goode, a former, and founding director of NJIT's Center for Solar-Terrestrial Research and the principal investigator of the facility. Goode conceived, raised the funds, and assembled the team that built and commissioned the telescope, and it was the highest resolution solar telescope in the world (until the end of 2019) and the first facility class solar telescope built in the U.S. in a generation.
