Abstract
Simultaneous control of the spatial and temporal properties of the optical near field in the vicinity of a nanostructure is achieved by illumination with broadband optimally polarization-shaped femtosecond light pulses. Here we demonstrate the spatial control of the local linear and nonlinear fluence, the local spectral distribution, and the local temporal intensity profile on a subdiffraction length scale. The boundary-element method is used for a self-consistent solution of Maxwell's equations in the frequency domain. Particular control objectives for spatial field distribution and temporal evolution are expressed as fitness functions in an evolutionary algorithm that optimizes adaptively the polarization-shaped input light pulses. Substantial control according to different goals is demonstrated and the limits of controllability are investigated. The dominating control mechanism is local interference of near-field modes that are excited with the two independent polarization components of the incident light pulses and hence polarization pulse shaping is essential to achieve substantial control in the optical near field. The influence of other control mechanisms is discussed and a number of applications are presented.
Highlights
The optical response of complex nanostructures exhibits fascinating properties, such as subwavelength variation of the field strength, local field enhancement with respect to the incident wave, and local fields with vector components perpendicular to those of the incident field
The rapidly evolving capabilities of controlled nanostructure fabrication allows extensive tailoring of the optical response, leading to the emergence and rapid growth of nanoplasmonics.3. Phenomena such as enhanced transmission through subwavelength holes,4 or subwavelength-sized wave guides consisting of chains of spherical metal nanoparticles5,6 all rely on the complex optical response of well-defined metal nanostructures
Local field enhancement and the detection of nonlinear optical signals improves the lateral resolution in SNOM,7 and secondharmonic microscopy from nanostructured metal films illustrates the intricate problems of local field enhancement and local nonlinear response
Summary
The optical response of complex nanostructures exhibits fascinating properties, such as subwavelength variation of the field strength, local field enhancement with respect to the incident wave, and local fields with vector components perpendicular to those of the incident field. Local field enhancement and the detection of nonlinear optical signals improves the lateral resolution in SNOM, and secondharmonic microscopy from nanostructured metal films illustrates the intricate problems of local field enhancement and local nonlinear response.8 In these experiments the ultrashort laser pulses primarily serve to obtain a strong nonlinear response, whereas the exact spatial and temporal field distribution is of minor importance. The spectral phase of the illuminating laser pulses influences the resulting momentary field distribution in the vicinity of the nanostructure This opens fascinating possibilities for the control of the optical near field as demonstrated in a theoretical study by Stockman et al.. The possibilities for pulse shaping were extended from phase and amplitude shaping to polarization pulse shaping.22–25 This was shown to extend the possibilities in time-resolved spectroscopies such as coherent anti-Stokes Raman spectrometryCARS, and to allow new quantum control schemes in atoms and molecules..
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