Our front-end software has a trim and effective interface, opening up the full functionality of the PLLPro to the user. The software is also extensible in Tcl, allowing custom user windows and associated functions to be seamlessly integrated into all the program’s pre-built features.

Front-End Main Window (figs. 1a, 1b)
In the main window the user can, firstly, monitor and establish the input gain and the output attenuation. The program’s saved list of known peaks and their settings greatly simplifies resonance selection. Below this in the window is a tabbed section for switching operating modes. Figure 1a shows the PLLPro working in Lock-In Mode, where the user can set the drive frequency and amplitude. The window also displays the amplitude, phase, I, Q, and the two A/D signals—and areas for the user to set a gain or select from four DACs for analog output.

Figure 1b shows drop-down box choices. From left to right they refer to: the analog attenuator for output to the probe drive (with optional auto mode), the digital loop filter, and the amplifier input gains (also with auto mode).

In the Self-Oscillation and PLL Mode tabs, the main window allows the user to toggle between Constant Excitation (CE) and Constant Signal (CS). The user can set the center frequency, frequency offset, phase shifter degree, and the amplitude control setpoint. Data channel status and the configuration of gains and DAC outputs are the same as in Lock-In Mode.

Resonance Peak Search (fig. 2)
The user can perform customized resonance peak searches, both manually and with automatic search criteria. The sweeps are fast and return exact peak location measurements and resonance Q-factor information. In this example, a 40-to-100 kHz search range is entered at the top of the window. Hitting the “Peak Search” button produces the graphs in figure 3a. Our custom search algorithm locates the peaks in this range and indexes them in the “Resonance Peak List” section of the window. Clicking “Measure This Peak” will generate the figure 3b graphs of this chosen peak (index 0).

Graphs of Peak Searches (figs. 3a, 3b)
Both of these pairs of graphs are the results of a peak search sweep. In figure 3a, the top graph gives the detected amplitude versus frequency; the bottom gives the detected phase. In the event of multiple peaks, these graphs allow the user to isolate a desired resonance peak at which to operate the microscope. It will be necessary to zoom into the graph in order to isolate a peak Figure 3b displays the optimal amplitude resonance frequency, Q-factor of the cantilever, and phase shifter setting (bottom half of 3b) of the highest peak in figure 3a.

Gain Adjustment (fig. 4)
Here the user adjusts the amplitude and frequency control gains of the PID controllers.

A/D Channels Setup Window (fig. 5)
This window shows how the user can select input offsets, gains, and filters for the two A/D channels. For each input choice there are options to modify the name, unit, and conversion factor. And when normal and lateral forces are selected as inputs, the user can graphically observe the laser’s position while adjusting the PSD.