Scanning near‐field optical microscope based on a double resonant fibre probe montage and equipped with time‐gated photon detection

Abstract

SummaryWe discuss scanning near-field optical microscope based on original double resonant montage of a fibre probe onto the tuning fork and proprietary electronics capable of fast and precise measurements of the resonant frequency and the quality factor of sensor dithering. Special emphasis is given on the pulsed excitation/gated detection of optical signal. This option as well as the possibility of fast scanning facilitates a lot the problem of single fluorescence centres detection. To illustrate the performance of this microscope, we present first true single-molecule fluorescence resonance energy transfer scanning near-field optical microscope images of single CdSe nanocrystals on glass slide surface and observation of an optical 'pseudoresolution' of densely packed 100-nm-diameter transfluorescent spheres in noisy conditions.

Near-field scanning optical microscopy using polymethylmethacrylate optical fiber probes

“…Beforehand these glass slides were pretreated with 0.1% poly-L-lysine solution (P8920, Sigma-Aldrich) by submerging them into this solution for 30 min and then drying in air for 5-6 h. As follows from experimental results, such a deposition procedure enables the preparation of the samples where isolated fluorescent beads are present. No displacement of the beads during scanning was observed, which is due to both the reasonably strong adhesion of the beads to the poly-lysinetreated glass surface and small forces characteristic for this SNOM, see [10].…”

“…Image sizes: 6 mm  6 mm and 300 nm  700 nm, respectively. Constant quality factor mode of the SNOM controller electronics [9,10] was used as a feedback source.…”

“…Sharpened POF probes were glued onto the tuning fork using the ''double resonance'' principle of operation first introduced in [9] and then successfully used for Scanning Near-field Optical Microscopy of different samples [10,11]. This mode of operation relies specifically on the arrangement of the fiber probe onto the tuning fork (see inset in Fig.…”

“…Attainment of such large quality factors enables us to use the specialized low noise, precise and fast electronics to measure the resonant frequency f res and Q-factor of a tuning fork to control the SNOM operation. Both the proprietary electronics earlier designed essentially for the sensors made by a tuning fork and an AFM cantilever glued on it [10,13], and a commercially available electronics equipment from Nanonis SA, Switzerland, specially adapted to work with this particular SNOM, were exploited.…”

“…In PSTM, the sample is illuminated by an evanescent wave produced by total internal reflection, and the optical field of the sample is probed by locally frustrating the evanescent field with an uncoated tapered optical fiber probe. Essentially, the same SNOM as reported by us in [10] was adapted to operate in this PSTM regime. We do not specially study the efficiency of the light collection by our plastic probes but qualitatively it does not differ much from that of standard fiber probes exploited in the same conditions [14].…”