The University of Victoria in British Columbia has the world's most powerful microscope. It is a Scanning Transmission Electron Holography Microscope (STEHM) that weighs seven tons and has a height of 4.5 meters. This microscope can magnify up to 30 million times.The history of microscopes can be traced back to the sixteenth century, when its crude form was invented. This instrument got more and more sophisticated with the advent in science and technology; and is now available in various types, which are used for different purposes. The most common among them is the oldest and simplest type, called the optical or light microscope, which comes in different types that include simple, compound, and dissecting microscopes. Electron microscopes are available as transmission electron microscopes (TEM), scanning electron microscopes (SEM), reflection electron microscopes (REM), scanning transmission electron microscopes (STEM), etc. Another type is scanning acoustic microscope, which makes use of sound waves to detect and measure variations in acoustic impedance.
It is an instrument that is used to see those substances and organisms, which cannot be seen with the naked eye. The basic model of a microscope contains one or more lenses that make small objects look bigger, so that the details can be viewed. Nowadays, various advanced models of microscopes are being used for different purposes. Even though there are different types of microscopes, the three basic types are optical (light), electron, and scanning probe microscopes. Though microscopes are classified on the basis of different factors, the main difference between them lies in the mode of illumination or the means of image generation. In optical microscopes, light interacts with the sample and creates the magnified image. In case of electron microscopes, a beam of electrons is used. Given below is a brief overview about optical and electron microscopes.
As mentioned earlier, these are the oldest and simplest types of microscopes, which are otherwise known as light microscopes. They use visible light and a combination of lenses to enlarge the images of the samples.
An electron microscope uses a beam of highly energetic electrons to illuminate the sample. As compared to the optical ones, electron microscopes produce highly magnified images with finer details. Electrostatic and electromagnetic lenses are used in electron microscopes. These lenses control the electron stream and focus it to a specific plane of the sample. This method is similar to that of an optical microscope, which uses light to focus on the specimen.
There are two other types called the reflection electron microscope and the scanning transmission electron microscope. The reflection electron microscope uses the reflected electrons from the specimen to form the image. Usually, techniques like reflection high energy electron diffraction (RHEED) and reflection high-energy loss spectroscopy (RHELS) are used in these microscopes. In case of a scanning transmission electron microscope, a highly focused electron probe raster-scans a thin specimen, and images are formed on the basis of the scattering pattern of electrons.
As the name rightly suggests, a scanning probe microscope has a physical probe that scans the surfaces of the specimen and sends information to a computer that collects the data and generates images on the basis of that data. This microscope is so powerful that it can create images with a resolution of less than one nanometer. Unlike an optical microscope, the surface of the specimen is not seen by the user. The probe moves over the sample several times and collects information. There are different types of scanning probe microscopes. They include atomic force microscopes, magnetic force microscopes, scanning tunneling microscopes, scanning thermal microscopes, scanning voltage microscopes, etc.
This is only a brief overview about the common types of microscopes. Advanced versions like digital microscopes, USB computer microscopes and pocket microscopes are also getting popular. Acoustic microscopes used sound waves for imaging. They are mainly used for finding faults in samples during the manufacturing process. A microscope is deemed fit for a particular task, based on its illumination method, the type of image it produces, magnification, depth of field, and resolution.