Near-field scanning optical microscope with a high Q-factor piezoelectric sensing element
First Claim
1. A piezoelectric sensing element for use in a near-field scanning optical microscope, comprising:
- a micro tuning fork mounted in a holder, the micro tuning fork including first and second tines and the holder having a piezoelectric element for dithering the micro tuning fork; and
an optical fiber being connectable to a photodetection means and having a thinned end portion having a diameter less than a threshold thickness, the thinned portion of the optical fiber being attached at a first position thereof to the holder and attached at a second position thereof spaced from an end of the optical fiber to said first tine at a position spaced from an end of the first tine, the optical fiber extending transversly across the first and second tines of the micro tuning fork, said first tine being adapted to be adjacent to a surface being scanned.
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Abstract
A perpendicular-mode near-field scanning optical microscope (NSOM) utilizing a piezoelectric micro tuning fork as its height-sensing element is described. The present invention provides a method and apparatus for modifying and attaching an optical fiber to the tuning fork that allows the assembly to retain Q-factors up to 9000, substantially higher than those described so far in the literature for tuning-fork-based instruments. The method involves reducing the diameter of the cladding of the optical fiber down to the 17-25 μm using several chemical etching steps, before the fiber is attached to the tuning fork. A sharp upturn in the Q-factor is observed when the fiber diameter d drops below ˜25 μm. An analysis, which shows that the stretching force constant of a bent fiber is proportional to d4, is used to account for the great sensitivity of the Q-factor to the fiber diameter. The high Q-factors resulted in improved force sensitivity and allowed us to construct a perpendicular mode instrument without the use of additional dithering piezoelements. An improved NSOM operating in the sear force mode is also provided by thinning the optical fiber length running down the length of one of the tines to a thickness in the range from about 50 to 60 μm.
59 Citations
14 Claims
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1. A piezoelectric sensing element for use in a near-field scanning optical microscope, comprising:
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a micro tuning fork mounted in a holder, the micro tuning fork including first and second tines and the holder having a piezoelectric element for dithering the micro tuning fork; and
an optical fiber being connectable to a photodetection means and having a thinned end portion having a diameter less than a threshold thickness, the thinned portion of the optical fiber being attached at a first position thereof to the holder and attached at a second position thereof spaced from an end of the optical fiber to said first tine at a position spaced from an end of the first tine, the optical fiber extending transversly across the first and second tines of the micro tuning fork, said first tine being adapted to be adjacent to a surface being scanned. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A piezoelectric sensing element for use in a near-field scanning optical microscope, comprising:
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a micro tuning fork mounted in a holder, the micro tuning fork including first and second tines and the holder having a piezoelectric element for dithering the micro tuning fork; and
an optical fiber being connectable to a photodetection means and a thinned end portion having a diameter less than a threshold thickness, the thinned portion of the optical fiber being attached at a first position thereof to the holder and being attached at a second position thereof spaced from an end of the optical fiber to a first tine at a position spaced from an end of the first tine, the optical fiber extending transversly across the tines of the micro tuning fork, said first tine being adapted to be adjacent to a surface being scanned in operation. - View Dependent Claims (10, 11, 12, 13, 14)
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Specification