A confocal microscope boasts of superior resolution that is much higher compared to a conventional optical microscope. These microscopes are mainly used in measurement applications.
There are two main categories of confocal microscopes. These are categorized as either transmission-type or reflection-type according to the type of illumination being utilized for imaging. Many confocal microscopes that are used in the industrial application are the reflection-type. These microscopes offer a high resolution image in which every area is in focus in the entire field of view including those samples with protrusions or dents on the surface. They allow the non-destructive and non-contact measurement of the three-dimensional shapes.
A microscope that uses a laser as the source of light is called a laser microscope. This is also a confocal microscope. Since it captures a two dimensional image through scanning line-shaped or spot light beams in XY direction, it is also a form of scanning microscope such as the scanning probe microscope and scanning electron microscope.
According to microscopeclub.com – The performance of optical microscopes depends mainly on the wavelength of the used light and the NA or numerical aperture of the objective lens. Even if the wavelength becomes small, unless the numerical aperture is increased, you will not be able to get a higher resolution. For you to observe and see fine patterns, a high magnification and high numerical aperture magnification objective lens is needed.
However, if you will use a high numerical aperture and high magnification lens to observe a rough or sloped surface, it will be impossible to get focus at all points in the entire field of view. It is because higher numerical aperture means a shallower depth of focus. There will be a tradeoff between depth of focus and resolution here. You won’t be able to get both simultaneously.
However, you can resolve this dilemma if a confocal microscope is used. This is made possible because of the confocal optics that the microscope uses.
High Resolution Image
The confocal optics provides a unique characteristic that a conventional microscope lacks. On images captured using confocal options, the areas in focus will be highlighted. It is known as optical sectioning.
The highlighted sections don’t have any interference of unwanted scattered light from areas that are out of focus. Therefore, you can get a high resolution and high contrast image. If you will perform Z-scan*2 then paste high resolution images of every highlighted section, you will be able to produce an image wherein every area is in focus. This means that if you will continuously capture images of areas with the highest brightness while you change focus positions then integrate them into one image, the image you will get focuses at all areas in the field of view. The result is that it seems like there is a deeper depth of focus.
Due to optical sectioning and its effect, confocal optics has Z-direction resolving power. The confocal optics can create three-dimensional structure with the use of Z-position data at every obtained point from Z-scan. It means that a confocal microscope can perform different measurements that cannot be done using traditional optical microscopes like roughness measurement, height gap measurement, and shape measurement.