17.06.2010

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Figures at a glance

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Figure 1: Ultrafast coherent excitation of single molecules.

a, Spectra of the fluorophore (DNQDI²⁹; dissolved in toluene) and broad-band excitation laser used (see Methods). b, Single fluorescent molecules were imaged and investigated in an epi-confocal microscope. Each individual molecule was excited with tailored sequences of 15-fs (full-width at half-maximum) pulses defined by the inter-pulse time delay Δt and phase shift φ. Both Δt and φ were controlled with a double-pass 4f pulse shaper based on a spatial light modulator. c, The fluorescence intensity of the single molecules was recorded for different combinations of Δt and φ (for example, (Δt_i, φ_i), (Δt_k, φ_k), and so on), which were applied sequentially, separated by periods of no illumination and repeated until the molecule photobleached.

Figure 2: Single-molecule wave-packet interference.

a, Fluorescence images of single molecules excited with two mutually delayed (Δt), phase-locked laser pulses. b, Integrated intensity as a function of Δt for the fluorescence emission of the three molecules marked in a. A typical background trace is shown for reference. The traces are normalized to their respective average in order to visualize fluctuations in the intensity. Error bars, ±1 s.d. c, Averaged response of 52 molecules compared to the theoretical prediction based on the bulk absorption spectrum. d, Result of the Fourier analysis of 52 single-molecule traces. Distributions and scatter plot of the main frequency component (f) and its corresponding phase (θ). Marker size and bin width include the experimental errors.

Figure 3: Phase control of single-molecule wave packets.

Single-molecule fluorescence intensity as a function of the time delay between two in-phase (φ = 0) and in-antiphase (φ = π) excitation pulses. The excitation intensity was constant for all (Δt, φ) combinations except for the (excluded) points near zero delay with φ = π. a, The fits to the (φ = 0) and (φ = π) traces are based on the bulk absorption spectrum. Fourier analysis of the fits shows that f = 31 THz in both traces and the difference in θ is π. b, Some molecules present fluctuations even for time delays Δt as long as 120 fs and with more than one frequency component. Error bars, ±1 s.d.

Figure 4: Single-molecule time-phase coherent excitation maps.

a–d, Time-phase fluorescence excitation maps of four different molecules excited with a four-pulse sequence. Δt and φ are the time delay and phase shift between each consecutive pulse in the sequence. The fluorescence intensity (colour scale) is normalized to the average. The maximum/minimum ratio, that is, the contrast achievable through control of coherent excitation, is shown in the upper right corner of each plot.