Abstract
For strong field enhancement of ultrashort light pulses, a 3-D metallic funnel-waveguide is analyzed using the finite-difference time-domain (FDTD) method. Then the maximum intensity enhancement actually developed by the funnel-waveguide upon the injection of femtosecond laser pulses is observed using two-photon luminescence (TPL) microscopy. In addition, the ultrafast dephasing profile of the localized field at the hot spot of the funnel-waveguide is verified through the interferometric autocorrelation of the TPL signal. Finally it is concluded the funnel-waveguide is an effective 3-D nanostructure that is capable of boosting the peak pulse intensity of stronger than 80 TWcm(-2) by an enhancement factor of 20 dB without significant degradation of the ultrafast spatiotemporal characteristics of the original pulses.
Highlights
Local field enhancement occurring in nanometer-scale structures [1] has widely been investigated for diverse applications such as surface-enhanced Raman scattering [2], multiphoton interaction for harmonic generation [3,4] and photoemission or photoluminescence [5,6,7,8,9]
Bulk-type nanostructures such as nano-tips [24,25] are capable of providing more robustness to thermal damage, but the resulting hot spot volume tends to reduce due to lower power coupling efficiency to the incident laser field
The two-photon luminescence (TPL) signal generated from the large z partition (z > 0.55 μm) within the hot spot volume contributes more than that of the small z partition (z < 0.55 μm), thereby broadening the pulse duration observed at the inlet aperture even though the actual pulse duration within the hot spot may be shorter than the measured value
Summary
Local field enhancement occurring in nanometer-scale structures [1] has widely been investigated for diverse applications such as surface-enhanced Raman scattering [2], multiphoton interaction for harmonic generation [3,4] and photoemission or photoluminescence [5,6,7,8,9]. Attention is being paid to strong field enhancement of ultrashort light pulses for generation of extreme ultraviolet light in interaction with noble gases [10,11,12,13,14,15,16] This highly nonlinear optical frequency upconversion requires achieving high peak pulse intensities of stronger than 10 TWcm−2 from moderate pulses of ~0.1 TWcm−2 intensity. Bulk-type nanostructures such as nano-tips [24,25] are capable of providing more robustness to thermal damage, but the resulting hot spot volume tends to reduce due to lower power coupling efficiency to the incident laser field In this investigation, we conduct an elaborate evaluation on a 3-D waveguide that was previously designed by the authors for strong field enhancement of femtosecond laser pulses for generation of extreme ultraviolet light [12,13]. This investigation validates that the funnel-waveguide is an effective 3-D nanostructure capable of boosting the peak pulse intensity of stronger than 80 TWcm−2 by an enhancement factor of 20 dB without significant degradation of the ultrafast temporal characteristics of the original pulses
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