Microscopes are instruments that produce a magnified image of a small object. They are used in many scientific and industrial applications. Some common applications for microscopes include manufacturing inspection and high-technology quality control. Specific quality control applications for microscopes include semiconductor processing, medical imaging, cell research, and metallurgical analysis. Microscopes are supplied in one of three common configurations, student, benchtop, and research. There are many types of microscopes available including acoustic or ultrasonic, compound, fluorescent or ultraviolet (UV), inverted, laser or confocal, polarizing, portable field, scanning electron microscope (SEM), scanning force or atomic probe microscope (SFM/AFM), stereoscopes and transmission electron microscopes. Acoustic and ultrasonic microscopes, compound microscopes, and fluorescent and UV microscopes are available.
Acoustic and ultrasonic microscopes use sound waves to create images of the sample. Compound microscopes use a single light path. These types of microscopes can have a single eyepiece (monocular) or a dual eyepiece (binocular). Compound microscopes have low depth perception but high resolution and magnification. Fluorescent microscopes and UV microscopes use high-energy and short-wavelength light to excite electrons, causing them to shift to higher orbits. When the electrons fall back to their original energy levels, they emit lower-energy and longer-wavelength light. Inverted, confocal, and polarized light microscopes are industrial microscopes. An inverted microscope locates the illumination system above the stage and the lens system below the stage. A confocal microscope or laser microscope uses a laser-to-light image one plane of a specimen at a time. Polarized light microscopes use two polarizers.
These polarizers are perpendicular to each other so that only light which passes through the specimen reaches the eyepiece. Light is polarized in one plane as it passes through the first filter and reaches the specimen. Regularly spaced, patterned, or crystalline portions of the specimen rotate the light that passes through. Some of this rotated light passes through the second polarizing filter. These regularly-spaced areas appear bright against a black background of microscopes. Types of microscopes include portable field microscopes, electron microscopes, and scanning probes. Portable field microscopes are designed for use outside of a laboratory setting. They have a portable energy source, or it may use natural light for illumination. In electron microscopes the image is formed by a detector which is synchronized with a focused electron beam that scans the object.
The intensity of the image-forming beam is proportional to the back-scattered or secondary emission of the specimen where the probe strikes it. Magnification of electron microscopes is controlled by the length or area scanned. Scanning probe microscopes (SPM microscopes) and atomic force microscopes (AFM microscopes) are used to study surface features by moving a sharp probe over the object’s surface. Atomic force microscopes, stereomicroscopes and transmission electron microscopes are available. Atomic force microscopes enable the user to image the topography of a sample and monitor ultrasonic surface vibrations in the MHz range.
A part of the position-sensing light beam reflected from the cantilever is directed to an external knife-edge detector to detect the distribution of the ultrasonic vibration amplitude. Stereomicroscopes or stereoscopes are microscopes that have two different paths of light, allowing the user to view a specimen in 3-D. Stereomicroscopes have high depth perception but low resolution and magnification. Transmission electron microscopes or TEM microscopes pass image-forming rays through the specimen being observed.
Contrast or diffracted beam images are used to analyze the sample. Important parameters to consider when specifying microscopes include total magnification and resolution. Microscopes can come in one of many types of eyepiece styles. These include monocular, binocular, trinocular or dual head. Important features in specifying microscopes include a digital display, mechanical stages, oil immersion lenses, fine focus, computer interfaces, and image analysis processing software.