23 research outputs found
Revised Method for Overcoming Visibility Reduction in Hanbury-Brown Twiss Experiments using Random Phase Modulation
  Â
Random Phase Modulation (RPM) is a method to generate a pseudo-thermal light source (PTLS) for testing setup and fitting routines in HBT experiments. By illuminating a rotating ground glass disc (GGD) with a laser, RPM imprints ”s to ms long coherence times, overcoming the limitations of natural thermal light sources. We rotated the GGD at different frequencies. We found the coherence time shifts following theoretical expectations for high frequencies, and deviating at low frequencies, leading to a revision of the formula for finite line broadening of the laser. We determined the first order coherence time of the laser to 0.3620±0.0063 ÎŒs, which is not accessible by conventional gÂČ methods. The light field was found to thermalize for frequencies >35 Hz with a gÂČ value of 1.42. We found a shift of the peak center of the bunching curves with frequency, leading to a deduced lateral misalignment of 3 ”m. RPM was shown to be highly accurate for checking coherence properties and detecting lateral misalignments in HBT setups.</p
Coherent two-dimensional micro-spectroscopy: An investigation of plasmon propagation
A well-known bottleneck for cutting-edge nano-electronic circuits which enable broadband data-processing, is their miniaturization. In the last decade the opto-electronic approach of using surface plasmon-polaritons [1] became a promising concept to achieve this goal due to the deep subwavelength confinement [2] of electromagnetic fields and their propagation velocity near the speed of light. By combining fs laser pulses with optical or photoemission electron microscopy, several spatio-temporally coupled processes in designed nanostructures could be demonstrated, e.g., coherent control of plasmon propagation in nano-circuits [3] and strong coupling of widely separated nano-antennas [4].
Nano-antennas have the unique ability to channel far-field radiation to sub-wavelength dimensions. The resulting strongly confined and enhanced electromagnetic fields boost nonlinear optical effects at the nanoscale [5]. For this purpose, we introduce coherent two-dimensional (2D) micro-spectroscopy which probes the nonlinear optical response of the nano-antennas with sub-micron spatial resolution [6]. An LCD-based pulse shaper in 4f geometry is used to create collinear trains of 12-fs visible/NIR laser pulses in the focus of a numerical aperture of a 1.4 immersion-oil microscope objective [7]. We motivate this new method for getting nonlinear third-order information of the ultrafast dynamics of plasmon propagation via phase cycling, e.g., for the local spatial investigation of the strong coupling between a transition metal dichalcogen-ide (TMD) monolayers and a nano-antenna on top of it.
References
[1] M. L. Brongersma et al. âThe case for plasmonicsâ. Science, 328 (5977): 440-441, 2010.
[2] J.A. Schuller et al. âPlasmonics for extreme light concentration and manipulationâ. Nat. Mater., 9 (3):1 93-204, 2010.
[3] C. Rewitz et al. âCoherent Control of Plasmon Propagation in a Nanocircuitâ. Phys. Rev. Applied., 1: 014007, 2014.
[4] M. Aeschlimann et al. âCavity-assisted ultrafast long-range periodic energy transfer between plasmonic nanoantennasâ.
Light-Sci. Appl., 6: e17111, 2017.
[5] B. Metzger et al. âUltrafast Nonlinear Plasmonic Spectroscopy: From Dipole Nanoantennas to Complex Hybrid Plasmonic
Structuresâ. ACS Photonics, 3 (8):1336â1350, 2016
[6] S. Goetz et al. âCoherent two-dimensional fluorescence micro-spectroscopyâ. Opt. Express, 26 (4):3915-3925, 2018
[7] M. PawĆowska et al. âShaping and spatiotemporal characterization of sub-10-fs pulses focused by a high-NA objectiveâ. Opt.
Express, (22):31496-31510, 2014</p
Determining Coherence Properties of Quantum Light Sources: A Study on Experimental Jitter and Power Dependency
Timing jitter of a single-photon device is essential for determining the coherence properties of quantum light sources. However, Jitter measurements were often not performed at the ultra-diluted light level present for quantum light sources. We investigate the timing jitter of a single-photon device sing a time-to-digital converter (TDC) and HBT interferometry to measure the distribution of delay between start and stop pulses. We determined the Gaussian jitter of a single single channel of the TDC to 7.12 ps, while HBT interferometry showed an excitation power dependency. The functional form of the pulsed histogram was determined using an exponentially modified Gaussian function. The exponential part showed minor effects for low count rates approaching a Lorentz shape count rate, consistent with photons getting converted deeper in the junction. These findings are crucial for understanding the underlying physics of jitter and accurately performing second-order correlation measurements. </p
Quantum Control Spectroscopy of Competing Reaction Pathways in a Molecular Switch
Excitation with shaped femtosecond
laser pulses is a logical extension
of coherent two-dimensional (2D) spectroscopy. Here we combine quantum
control and information from 2D spectroscopy to analyze the initial
steps in three competing reaction pathways of an isomerizing merocyanine
dye. Besides the achievement of control objectives, we show how excitation
with tailored pulses can be used to retrieve photochemical information
that is inaccessible or experimentally demanding to obtain with other
approaches
Ultrafast nonâlinear 2D microspectroscopy reveals coherent phononâmediated intraâ and intervalley exciton interaction in an individual SWCNT
Further developments in molecular electronics, adressing SWCNTs, would benefit strongly from insights in the spatioâtemporal evolution of molecular processes. Ultrafast nonâlinear techniques provide tracking of energy transfer pathways e.g., mediated via electronâphonon coupling [1]. A comprehensive way to observe these dynamics is coherent 2D fluorescence microspectroscopy [2]. This method is a generalization of transient absorption spectroscopy with frequencyâresolved pump and probe steps, combined with spatiallyâresolved optical microscopy. This provides, e.g., to observe the phononâmediated formation and annihilation dynamics of initially bright and darkâstate excitons due to the strong excitonâphonon coupling on the femtosecond timescale. Here, we utilize the thirdâorder 2D signal for monitoring the trapped intraâ and intervalley exciton interaction in a SWCNT [3,4]. To this end, an transformâlimitted LCDâshaped fourâpulse sequence is focused on an (6,4) SWCNT and the fluorescence is detected as a function of interâpulse time delays and phases.
[1] Graham, M. et al., Nano Lett. 12, 813â819 (2012).
[2] Goetz, S. et al., Opt. Express 26, 3915â3925 (2018).
[3] Secchi, A. et al., Phys. Rev. B 88 (2013).
[4] Kislitsyn, D. et al., J. Phys. Chem. Lett. 5, 3138â3143 (2014).</p
Analytic Optimization of Near-Field Optical Chirality Enhancement
We present an analytic derivation
for the enhancement of local
optical chirality in the near field of plasmonic nanostructures by
tuning the far-field polarization of external light. We illustrate
the results by means of simulations with an achiral and a chiral nanostructure
assembly and demonstrate that local optical chirality is significantly
enhanced with respect to circular polarization in free space. The
optimal external far-field polarizations are different from both circular
and linear. Symmetry properties of the nanostructure can be exploited
to determine whether the optimal far-field polarization is circular.
Furthermore, the optimal far-field polarization depends on the frequency,
which results in complex-shaped laser pulses for broadband optimization
Ultrafast non-linear 2D micro-spectroscopy reveals coherent phonon-mediated intra- and intervalley exciton interaction in an individual SWCNT
Poster presentation from  NT19: International Conference on the Science and Application of Nanotubes and Low-Dimensional Materials
21-26 July 2019, WĂŒrzburg, Germany
We perform nonlinear fluorescence-based two-dimensional spectroscopy(F-2DES) on (6,4) SWCNTs at the single molecule level.
We highllight the possibilities with the single molecule setup for fluorescence based experiments at ultra-diluted light levels.
We provide evidence for single-molecular investigation by various methods.
We identifiy an energetic substructure in the phonon sideband of individual SWCNTs, observed with F-2DES measurements.
We evalaute the significance of the peak structure in F-2DES data, by the application of statistical inference methods.
We relate our findings of the energetic peak positions to polaron formation, induced by phonon-mediated intervalley dynamics.
We explain F-2DES data by Liouville pathways.
We further observe vacancy relaxation of laser induced defects in SWCNTs and verify our findings with help of a temperature model
</p
Analytic Optimization of Near-Field Optical Chirality Enhancement
We present an analytic derivation
for the enhancement of local
optical chirality in the near field of plasmonic nanostructures by
tuning the far-field polarization of external light. We illustrate
the results by means of simulations with an achiral and a chiral nanostructure
assembly and demonstrate that local optical chirality is significantly
enhanced with respect to circular polarization in free space. The
optimal external far-field polarizations are different from both circular
and linear. Symmetry properties of the nanostructure can be exploited
to determine whether the optimal far-field polarization is circular.
Furthermore, the optimal far-field polarization depends on the frequency,
which results in complex-shaped laser pulses for broadband optimization
Analytic Optimization of Near-Field Optical Chirality Enhancement
We present an analytic derivation
for the enhancement of local
optical chirality in the near field of plasmonic nanostructures by
tuning the far-field polarization of external light. We illustrate
the results by means of simulations with an achiral and a chiral nanostructure
assembly and demonstrate that local optical chirality is significantly
enhanced with respect to circular polarization in free space. The
optimal external far-field polarizations are different from both circular
and linear. Symmetry properties of the nanostructure can be exploited
to determine whether the optimal far-field polarization is circular.
Furthermore, the optimal far-field polarization depends on the frequency,
which results in complex-shaped laser pulses for broadband optimization
Analytic Optimization of Near-Field Optical Chirality Enhancement
We present an analytic derivation
for the enhancement of local
optical chirality in the near field of plasmonic nanostructures by
tuning the far-field polarization of external light. We illustrate
the results by means of simulations with an achiral and a chiral nanostructure
assembly and demonstrate that local optical chirality is significantly
enhanced with respect to circular polarization in free space. The
optimal external far-field polarizations are different from both circular
and linear. Symmetry properties of the nanostructure can be exploited
to determine whether the optimal far-field polarization is circular.
Furthermore, the optimal far-field polarization depends on the frequency,
which results in complex-shaped laser pulses for broadband optimization