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(A) Lock-in amplifier signal versus objective axial position. A focus sensitivity of 1.4 mV/nm was measured near the center focus. (B) Example of objective position response following step function change in focus set point. Focus position versus time illustrated for three feedback conditions; strong (fast with some overshoot, less stable), moderate (little overshoot), and weak (slow, more stable) response feedback parameters. To see this figure in color, go online.
