Glossary
R
- radiation
- The emission or transmission of energy in the form of waves or particles through space or a material medium. In optics, this term is often used synonymously with electromagnetic radiation.
- See also: infrared radiation, monochromatic radiation, ultraviolet radiation, electromagnetic spectrum
- Raman microscopy
- A family of microscopy techniques based on probing different vibrational states of a molecule via the process of Raman scattering. Raman microscopy relies on the same techniques as Raman spectroscopy, but encompasses imaging-based methods (often performed using a confocal microscope-type design).
- See also: Raman scattering, coherent anti-stokes Raman scattering microscopy, stimulated raman scattering microscopy, inelastic scattering
- Raman scattering
- A type of inelastic scattering where energy from the incident light can either be lost to a system that relaxes to a higher vibrational mode (Stokes) or gained from a system initially at a higher vibrational mode (anti-Stokes).
- See also: inelastic scattering, Raman microscopy, coherent anti-stokes Raman scattering microscopy, stimulated raman scattering microscopy
- Ramsden disc
- see microscope exit pupil
- Ramsden eyepiece
- A microscope eyepiece composed of two plano-convex lenses with their convex faces pointing towards each other.
- Synonyms: external diaphragm eyepiece
- See also: eyepiece
- raster scanning
- A scanning mode used in point-scanning confocal microscopy, where the excitation beam is in a unidirectional pattern across the field of view, sampling the signal at discrete intervals to realize a virtual pixel. Once the signal along a line is acquired, the scanning position is stepped along the opposite lateral axis for acquisition of the next line.
- See also: scanning, point-scanning confocal microscopy
- ratiometric imaging
- Multichannel comparative imaging of ratiometric indicators, a class of fluorophores whose fluorescence spectra depend on their state, to probe their environment. For example, FURA-2 is a ratiometric calcium indicator whose excitation maximum is significantly blue-shifted when bound to calcium.
- ray
- In optics, a ray represents the direction of travel of a wavefront and is perpendicular to the wavefront. It is a useful representation of the direction of energy flow and helps form the basis of ray tracing in geometric optics.
- See also: ray tracing, geometric optics
- ray optics
- see geometric optics
- ray tracing
- An analysis technique by which multiple rays emitting from a point source are drawn through an optical system. Principal and marginal rays are used to simulate how an object on a sample plane is transformed by an imaging system, and projected onto an image plane.
- See also: ray, geometric optics
- Rayleigh scattering
- A type of elastic scattering that occurs upon interaction of light with a particle much smaller than its wavelength and in an amount inversely proportional to the fourth power of the wavelength.
- See also: elastic scattering, scattering, Mie scattering
- real image
- An image of the object formed by an optical system where the collected light is focused into an image in a conjugate field plane. Contrast this with a virtual image, whose location is found by tracing back divergent rays to a focus point that does not actually exist.
- See also: conjugate planes, image, virtual image, ray tracing
- real space
- see image space
- real time imaging
- An imaging technique where captured images can be displayed almost instantly, rather than processed and viewed after the experiment.
- rear focal plane
- see back focal plane
- reciprocal space
- see frequency space
- reference plane
- Either a plane of a locating flange on an optical component or a plane of importance in the optical path (e.g., the intermediate image plane).
- See also: locating flange, aperture plane, field plane
- reference viewing distance
- The distance between the object and the cornea of the human eye. It has been standardized at a value of 250 mm.
- reflected-light based autofocus
- An autofocus technique where an independent light source is used to track an interface (typically the immersion glass interface on a slide or dish bottom) to precisely adjust for changes in focus due to thermal changes or vibrations. This light source is typically near-infrared to prevent interference with imaging channels.
- See also: perfect focus system, autofocus
- reflected-light microscope
- A microscopy technique typically used when the specimen is opaque, not allowing for transmission of light. Differences in detected intensity are largely due to differences in reflectivity and absorption.
- Synonyms: episcopic microscope
- See also: optical train
- reflection
- When the trajectory of a wave incident at the boundary between two media is altered such that the wave continues to propagate back into its original medium. Reflections can be mirror-like (specular) or diffuse.
- See also: mirror, geometric optics, catoptric
- refraction
- The change in direction of propagation of a light wave as a result of its traveling at different speeds at different points along the wavefront, it occurs when a ray is obliquely incident at a refractive index interface with accordance to Snell's law.
- See also: refractive index, Snell's law
- refractive index (RI)
- The ratio of the speed of light in a vacuum to its speed in the medium of interest, often specified as n. The process of refraction occurs when light is obliquely incident at the interface of two media of different refractive index.
- See also: refraction, Snell's law
- regenerative medicine
- A scientific field that uses engineering and life science principles to repair or replace damaged tissues, organs, or cells to restore normal function.
- region of interest (ROI)
- The collection of pixels in an image included in an analytical process - e.g. mean/min/max intensity, signal-to-noise ratio, etc.
- relay lens
- A lens or lens system for forming a new image of an intermediate image. It is useful for correcting image orientation as well as extending the length of the optical train.
- See also: lens, image, intermediate image plane
- relief contrast
- A general term for microscopy techniques that create a relief-type appearance via different methods for creating contrast from proximal optical path length differences, even in mostly transparent specimens. Hoffman modulation contrast is a traditional example in this category.
- See also: modulation contrast, Nikon advanced modulation contrast
- resolution
- A measure of the ability of an imaging system to resolve detail in a specimen. This is typically defined as the minimum distance between two objects that can still be differentiated, typically measured in nanometers or micrometers.
- Synonyms: spatial resolution
- See also: temporal resolution
- resolved distance
- The distance between two distinguishable objects in an image.
- See also: spatial resolution
- resolving power
- see minimum resolvable distance
- resonant scanning
- A high-speed scanning approach that has been applied to point-scanning confocal microscopy where the fast scan (X) is performed using a fast resonant-scanning galvanometric mirror driven by a sinusoidal signal and the slow scan (Y) is performed using a typical linear galvanometer mirror driven by a sawtooth signal.
- See also: point-scanning confocal microscopy, raster scanning
- retardation
- A phase difference introduced between the normal components (eigenpolarizations) of a polarized light wave. It can be purposefully introduced using a fixed-retardation wave plate or a variable-retardation compensator.
- See also: wave plate, compensator, polarized light microscopy
- retardation plate
- see wave plate
- reticle
- see graticule
- revolving nosepiece
- A component of a light microscope which allows a user to switch between different objectives using a rotatable turret assembly. Typically, revolving nosepieces allow for up to 6 different objectives to be chosen from.
- Synonyms: nosepiece turret
- See also: nosepiece, objective lens
- RMS thread
- A thread specification standardized by the Royal Microscopical Society (RMS) which has a diameter of 0.8 inches and 36 threads per inch (TPI).
- rotating stage
- Typically used in a polarizing microscope (POL scope), a rotating stage allows a user to freely rotate a sample 360 degrees relative to the optical axis and precisely measure the degree of rotation.
- See also: stage, polarized light microscopy
