Optical detection alignment/tracking method and apparatus

#1. Field of the Invention

#The present invention is directed to a method and apparatus for tracking the laser beam of an optical detection apparatus employed by a scanning probe microscope (SPM), and more particularly, to a tracking method and apparatus that enables top-down optical access to a probe of an atomic force microscope (AFM).

#2. Description of Related Art

#A preferred exemplary embodiment of the invention is illustrated in the accompanying drawings in which like reference numerals represent like parts throughout, and in which:

#FIG. 1 is a schematic block diagram of a prior art atomic force microscope (AFM);

#FIG. 2 is a schematic cross-sectional side view of an AFM of the preferred embodiment illustrating top-down optical access;

#The preferred embodiments facilitate the construction of AFMs having top-down optical access to the probe and sample, for biological applications, for example, by accommodating movement of all optical detection and tracking components away from the region above the probe. Moreover, the mechanism used to track the laser operates to translate the beam of the deflection system independent of operation of the AFM scanner. Therefore, the preferred embodiments avoid compromising AFM performance contrary to known systems in which, for example, the tracking lens is coupled to the scanner.

#More particularly, the focused laser spot is tracked on the moving probe/tip through an independent and active piezoelectric actuator driven tracking mechanism. The tracking mechanism is active in that, during AFM operation, the mechanism continually determines probe position and, based on calibration data, moves the laser beam into optimum alignment with the probe.

#To do so, the apparatus preferably includes one or more fine piezoelectric actuators (e.g., a piezo stack) in series with a manual laser stage adjustment screw typically used to provide coarse adjustment of the laser beam in a particular direction. Importantly, the fine adjustment laser stage piezo(s) is driven electronically with an independent voltage, the characteristics of which are described further below. For laser tracking applications, as contemplated by the present preferred embodiments, this feature allows for the tracking dynamics to be calibrated for optimal tip tracking performance.