SLU Physics - Determining the Optimal Preamp for Near-Field Scanning Optical Microscopy tuning Fork Based Feedback

Determining the Optimal Preamplifier
for Near-Field Scanning Optical Microscopy
Tuning Fork Based Feedback
Kricket Fellows '03

Abstract:

Tuning fork based lateral force feedback is an effective tip-to-sample distance regulation mechanism in near field scanning optical microscopy. The oscillating piezoelectric potential produced by the tuning fork is proportional to the amplitude of motion of the fiber and is used to keep the probe close to the sample surface. The tuning fork can be vibrated either mechanically or electrically. Additionally, the tuning fork signal can be measured using a voltage preamplifier or a current preamplifier. Thus, there are four possible circuits that can be used to measure the tuning fork signal: a voltage preamp with a mechanical drive (VPMD), a voltage preamp with an electrical drive (VPED), a current preamp with a mechanical drive (CPMD), or a current preamp with an electrical drive (CPED). The experiment presented here examines which circuit yeilds the best signal to noise ratio in the tuning fork signal. The average measured signal to noise ratios for the VPMD, VPED, CPMD and CPED circuits were comparable at 114, 59, 81 and 81, repectively. While the average S/N ration of the VPMD circuit is best, it is not dramatically different from the S/N ration of the current preamp circuits. Therefore, due to the practical advantages of the CPED circuit, it was concluded that the current preamp with an electrical drive is the optimal preamplifier circuit for near-field scanning optical microscopy tuning fork based feedback.

For more information, contact Dr. Catherine Jahncke:

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