2Resolution in microscopy Why is there a barrier in optical microscopy resolution?And how can it be broken?
3Angular spectrum and diffraction limit Describe field as superposition of plane waves (Fourier transform):Field at z=0 (object) propagates in free space asThe propagator H is oscillating forand exponentially decaying forHigh spatial fluctuations do not propagate: diffraction limit
4+ The diffraction limit in conventional microscopy Image of a point source in a microscope, collecting part of the angular spectrum of the source:Rayleigh criterion: two point sources distinguishable if spaced by the distance between the maximum and the first minimum of the Airy patternq+Numerical Aperture determines resolutionAiry pattern (microscope point spread function)
5Breaking the diffraction limit in near-field microscopy A small aperture in the near field of the source can scatter also the evanescent field of the source to a detector in the far field.Image obtained by scanning the apertureAlternatively, the aperture can be used to illuminate only a very small spot.
6Probing beyond the diffraction limit Single emitterMetallic particleAperture probefibre typeAperture probemicrolever type
7self-assembled monolayer, Modified slide from Kobus Kuipers and Niek van Hulst et al.Transmission of light through a near-field tip200 nmExcitation lightAlNSOM probeFIB treated probeAperture ~ nmProtein, dendrimer, DNA, etc.single fluorophoresFluorescenceThin polymer film,self-assembled monolayer,cell membrane, etc.
8Focussed ion beam (FIB) etched NSOM probe lwell defined apertureflat endfaceisotropic polarisationhigh brightness up 1 mW35 nmaperture100 nm100 nmglassWith excitation Ex , kz, :aluminumy500 nmxExEyEzVeerman, Otter, Kuipers, van Hulst, Appl. Phys. Lett. 74, 3115 (1998)
9Shear force feedback: molecular scale topography Steps on graphite (HOPG)Feedback loop:A0Dfpiezo3 x 3 mmw0~ 0.8 nm step~ 3 mono-atomic stepsTuning fork32 kHzQ ~ 500Lateralmovement,A0 ~ 0.1 nm1.7 x 1.7 mmDNA on micasampleDNAwidth 14 nmheight 1.4 nmFeedback on phaseTip -sample < 5 nmRMS ~ 0.1 nmRensen, Ruiter, West, van Hulst, Appl. Phys. Lett (1999)Ruiter, Veerman, v/d Werf, van Hulst, Appl. Phys. Lett (1997)van Hulst, Garcia-Parajo, Moers, Veerman, Ruiter, J. Struct. Biol. 119, 222, (1997)
10Perylene orange in PMMA 100 nm1 mm90o0oRuiter, Veerman, Garcia-Parajo, van Hulst, J. Phys. Chem. 101 A, 7318 (1997)
11Single molecular mapping of the near-field distribution DiIC18 moleculesin 10 nm PMMA layer1.2 x 1.2 mm2;3 nm/pix; 3 ms/pix12045 nmFWHM80counts / pixel404008001200distance (nm)Veerman, Garcia-Parajo, Kuipers, van Hulst, J. Microscopy 194, 477 (1999)
12Mapping the near field of the probe Data from Kobus Kuipers and Niek van Hulst et al.Mapping the near field of the probe
13NFO for Single Molecule Detection : Reduced excitation volume, high resolution,low background0.00.51.01.52.02.53.01020304050kcounts/slateral scan [mm]FWHM = 75 nmS/B 20Single DiD moleculein30 nm polystyrenewith70 nm aperture probevan Hulst, Veerman, Garcia-Parajo, Kuipers. J. Chem. Phys. 112, 7799 (2000)
14Optical discrimination of individual molecules separated by emission45 ± 2 nm0oabc200400 nmOptical discrimination ofindividual moleculesseparated bynm mutual distanceabcdeSample area: 440 x 440 nm2Aperture diameter: 70 nmMutual distance: < 10 nmvan Hulst, Veerman, Garcia-Parajo, Kuipers. J. Chem. Phys. 112, 7799 (2000)
15Time-resolved near-field scanning tunneling microscopy Data from Kobus Kuipers and Niek van Hulst et al.Time-resolved near-field scanning tunneling microscopy120 fs pulsescoupledinto the PhCWTwo arms of the interferometerequal in length givestemporal overlap on the detector
16Pulse caught in 1 position Data from Kobus Kuipers and Niek van Hulst et al.A light pulse caught in time and space40 nm highridge waveguide239.5 x 7.62 mmPulse envelope239.5 x 7.62 mmFixed time delayTE00 pulse, l =1300 nmduration : 120 fsPulse caught in 1 position