Most commercial AFMs utilize a light-lever force sensor which reflects a focused laser from the back side of a cantilever. The cantilevers can be 20-30 microns wide by 50-300 microns long. The cantilever, cantilever chip, and the probe work together as a coordinated unit, and are micro-machined.  

Some AFMs offer 'pre-aligned' cantilever/cantilever chip/probe units, theoretically eliminating the task of properly landing and reflecting the laser on the back side of the cantilever.  The pre-aligned concept ends up being a challenge to achieve due to the impacts of contamination, the subtle variations in cantilever dimensions, and human error. Thus, even with a 'pre-aligned' design, it becomes necessary to include a mechanical adjustment mechanism on the AFM so that the user can physically move the focused laser beam onto the cantilever. An optical microscope makes a big difference when the AFM user, whether working with a pre-aligned cantilever or a user-aligned cantilever, manually positions the focused laser properly onto the cantilever's back side. 

AFMs typically have scan ranges that are less than 100 microns. This means it's not possible to view large surface areas - or to "get the big picture". That makes sense when you consider you're trying to visualize very small objects, but the problem becomes trying to 'find' the important areas of the sample. For example, the area of interest may be on isolated areas of the sample. A high-quality optical microscope enables the user to rapidly make determinations about the areas of a sample to scan with the AFM. Having a large optical zoom ratio is really helpful: at low magnification the user can find the general area for scanning, and at high magnification the user can find specific areas for AFM scanning.  

In an Atomic Force Microscope (AFM) the probe tip must be moved to a point where it interacts with the various forces associated with a sample's surface. To make the tip's approach to the sample faster, it is helpful to get the probe as close to the surface as possible before utilizing an automated tip approach algorithm. This probe approach is facilitated with an optical microscope in two ways:

• Focusing the optical microscope just above the sample surface, and then using the AFM Z approach mechanism to bring the probe closer until it is focused, i.e. very close to the surface.
   

• In AFMs with a laser beam that is not at a perpendicular angle to the sample's surface, the motion of the laser spot moving across the surface is used to facilitate probe approach. As the tip gets closer to the surface, the two laser spots will coalesce.

The viewing orientations of the optical microscope in relation to the AFM probe, cantilever, and sample are:

• top view
• bottom view
• 45 degree angle view

The top view is the most popular optical microscope orientation with the AFM. The optical microscope is placed directly above the AFM cantilever, yielding an optical view of the top of the AFM cantilever and the top of the surface of the sample to be imaged. Typically, a uniaxial light source is required for a top view microscope.