Everything about Microscope totally explained
A
microscope (
Greek:
μικρόν (
micron) = small +
σκοπεῖν (
skopein) = to look at) is an instrument for viewing objects that are too small to be seen by the naked or unaided
eye. The
science of investigating small objects using such an instrument is called
microscopy. The term
microscopic means minute or very small, not visible with the eye unless aided by a microscope. The microscopes used in schools and homes trace their
history back almost 400 years.
The first useful microscope was developed in the Netherlands in the early 1600s. 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. (Galileo had called it the "
occhiolino" or "
little eye".)
The most common type of microscope—and the first to be invented—is the
optical microscope. This is an
optical instrument containing one or more
lenses that produce an enlarged image of an object placed in the focal plane of the lens(es). There are, however, many other microscope designs.
Types
"Microscopes" can largely be separated into three classes,
optical theory microscopes, electron microscopes and scanning probe microscopes.
Optical theory microscopes are microscopes which function through the
optical theory of lenses in order to magnify the image generated by the passage of a
wave through the sample. The waves used are either
electromagnetic in
optical microscopes or
electron beams in
electron microscopes. The types are the Compound Light, Stereo, and the electron microscope.
Optical microscopes
Optical microscopes, through their use of visible wavelengths of light, are the simplest and hence most widely used type of microscope.
Optical microscopes use
refractive lenses, typically of
glass and occasionally of
plastic, to focus light into the eye or another light detector. Typical magnification of a light microscope is up to 1500x with a theoretical
resolution of around 0.2
micrometres or 200
nanometers. Specialised techniques (for example,
scanning confocal microscopy) may exceed this magnification but the resolution is an insurmountable
diffraction limit.
Various
wavelengths of light are sometimes used for special purposes, for example, in the study of biological tissue.
Ultraviolet light is used to illuminate the object being viewed in order to excite a
fluorescent dye which then emits visible light.
Infrared light is used to study thick slices of biological tissue because infrared light's low diffraction coefficient permits viewing deeper into tissue.
Other microscopes which use
electromagnetic wavelengths not visible to the human eye are often called optical microscopes. The most common of these, due to its high resolution yet no requirement for a
vacuum like electron microscopes, is the
x-ray microscope.
Electron microscopes
Electron microscopes, which use beams of
electrons instead of light, are designed for very high magnification usage. Electrons, which can be accelerated to produce a much smaller wavelength than visible light, allow a much higher resolution. The main limitation of the electron beam is that it must pass through a
vacuum as air molecules would otherwise scatter the beam.
Instead of relying on
refraction, lenses for
electron microscopes are specially designed electromagnets which generate magnetic fields that are approximately parallel to the direction that electrons travel. The electrons are typically detected by a
phosphor screen,
photographic film or a charged-coupled device (
CCD).
Two major variants of electron microscopes exist:
Scanning probe microscope
In
scanning probe microscopy (SPM), a physical probe is used either in close contact to the sample or nearly touching it. By rastering the probe across the sample, and by measuring the interactions between the sharp tip of the probe and the sample, a
micrograph is generated. The exact nature of the interactions between the probe and the sample determines exactly what kind of SPM is being used. Because this kind of microscopy relies on the interactions between the tip and the sample, it generally only measures information about the surface of the sample.
A variation of the SPM is the SECM (
Scanning
Electro
Chemical
Microscope). A SECM images a sample in a similar manner as a SPM but the sample is in an electrolyte solution with the SECM using electrochemically active tip.
Other microscopes
Scanning acoustic microscopes use sound waves to measure variations in acoustic impedance. Similar to
Sonar in principle, they're used for such jobs as detecting defects in the subsurfaces of materials including those found in integrated circuits.
Further Information
Get more info on 'Microscope'.
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