Surface plasmon resonant nanoantennas can confine incident energy onto two-dimensional (2D) transition metal dichalcogenides (TMD) to enhance efficiency of harmonic conversion to higher energies, which is otherwise limited by the intrinsic Å-scale interaction length. Second harmonic generation (SHG) from nanoantenna-decorated 2D TMD was heuristically examined with hyper Rayleigh scattering (HRS), multi-photon microscopy, electron energy loss spectroscopy (EELS), and discrete dipole computation. HRS experimentally quantified the frequency dependence of the second-order nonlinear susceptibility, χ <sup>(2)</sup> , for liquid-exfoliated WS<sub>2</sub>. Measured χ<sup>(2)</sup> fell within 21% of independent density functional theory (DFT) calculations, overcoming the known 100-1000x overestimation of microscopy approaches. EELS supported design of nanoantennas for integration with TMD. Overall SHG conversion efficiencies from chemical vapor-deposited (CVD) 4×10<sup>5</sup> nm<sup>2</sup> MoS<sub>2</sub> crystals on silicon dioxide were enhanced up to 0.025 % W<sup>-1</sup> in the presence of by single 150 nm Au nanoshell monomers and dimers, ostensibly due to augmented local plasmonic fields.
SiC nanoparticles by carbothermal reduction show promising properties in terms of second harmonic and multiphoton excited luminescence. In particular, we estimate a nonlinear efficiency < d < = 17 pm/V, as obtained by Hyper Rayleigh Scattering. We also present results of cell labelling to demonstrate the potential use of SiC nanoparticles for nonlinear bioimaging by simultaneous detection of second harmonic and luminescence.
Bismuth Ferrite nanoparticles have been recently used to selectively interact with malignant cell DNA via in situ
generated second harmonic in a novel theranostics protocol [Nanoscale 6(5), pp. 2929, 2014]. In this report, we
extend the screening of biocompatibility of BFO uncoated uncoated nanoparticles and assess the nanoparticle-
mediated production of reactive oxygen species as a function of excitation wavelength.
The fast development of laser techniques, in particular, the generation of ultrashort femtosecond and even attosecond
pulses opens new frontiers and various experimental tools for biomedical applications. The combination of pulse
shaping and optimal control is a very promising tool based on coherent manipulation of wavepackets on an ultrafast time scale. It already has successfully been applied for optimal dynamic discrimination (ODD) experiments of biomolecules like free amino acids and flavins which are indistinguishable by spectroscopic means. This approach can be extended toward to label free cellular imaging and detection of chemical or biological substances.
In this contribution we present the motivations underlying the introduction of harmonic nanoparticles, i.e. second harmonic contrast agents for nonlinear microscopy. Their properties will be discussed in the light of various biological applications including imaging of stem cells and rare event detection in physiological media.
Shaping light with microtechnology components has been possible for many years. The Texas Instruments digital
micromirror device (DMD) and all types of adaptive optics systems are very sophisticated tools, well established and
widely used. Here we present, however, two very dedicated systems, where one is an extremely simple MEMS-based
tunable diffuser, while the second device is complex micromirror array with new capabilities for femtosecond laser pulse
shaping. Showing the two systems right next to each other demonstrates the vast options and versatility of MOEMS for
shaping light in the space and time domain.
We show the first results of a linear 100-micromirror array capable of modulating the phase and amplitude of the spectral
components of femtosecond lasers. Using MEMS-based reflective systems has the advantage of utilizing coatings tailored
to the laser wavelength range. The innovative features of our device include a novel rotational, vertical comb-drive actuator
and an X-shaped, laterally reinforced spring that prevents lateral snap-in while providing flexibility in the two degrees of
freedom of each mirror, namely piston and tilt. The packaging utilizes high-density fine-pitch wire-bonding for on-chip
and chip-to-PCB connectivity. For the first deployment, UV-shaped pulses will be produced to coherently control the
dynamics of biomolecules.
There are many potential applications for MEMS micromirror devices for femtosecond pulse shaping applications. Their
broadband reflectivity gives them an advantage in comparison to devices such as liquid crystal- and acousto-optical modulators
because of the possibility to directly shape UV pulses in the range 250 - 400 nm, and thus address UV-absorbing
molecules. The identification and discrimination of biomolecules which exhibit almost the same spectra has sparked
some interest in the last years as it allows real-time, environmental and optical monitoring. Here, we present the last
developments using the Fraunhofer IPMS MEMS phase former capable of accomplishing such goals.
We are developing a linear array of micromirrors designed for optical, femtosecond laser pulse shaping. It is a bulkmicromachined
device, capable of retarding or diminishing certain laser frequencies in order to perform phase and amplitude modulation within a frequency band spanning the UV to the near-infrared. The design consists of a linear array of mirrors fixed on either side by springs. They feature two degrees of freedom: Out-of-plane motion for phase shifting and
rotational motion for binary amplitude modulation, both realized using vertical comb drives. The first applications will include femtosecond discrimination experiments on biomolecules.
Proc. SPIE. 6733, International Conference on Lasers, Applications, and Technologies 2007: Environmental Monitoring and Ecological Applications; Optical Sensors in Biological, Chemical, and Engineering Technologies; and Femtosecond Laser Pulse Filamentation
Filamentation, which arises in the propagation of ultrashort laser pulses when the defocusing on the generated
plasma dynamically balances the Kerr self-focusing, is now well described on both the laboratory scale (millijoules
to tens of millijoules, meters to tens of meters) and the atmospheric scale (hundreds of millijoules, hundreds of
meters to kilometers). The scalability of this propagation regime to higher energies and powers is not a priori
assured, as high-order nonlinear effects may prevent long distance propagation leading, for instance, to full beam
collapse. We thus investigated the atmospheric propagation of the 26 J, 32 TW laser pulses delivered by the Alisé beamline, which exceed respectively by one and two orders of magnitude the characteristic power and energy of
ultrashort pulses studied so far. We show that filamentation still occurs at these extreme levels. More than 400
filaments simultaneously generate a supercontinuum propagating up to the stratosphere, beyond 20 km. This
constitutes the highest power "white-light laser" to date.
We also discuss the results of another experiment realized with the Teramobile laser facility: we demonstrated
optimal control on the propagation of ultrashort 5 TW laser pulses in air over distances up to 36 m in a closed-loop
scheme. We optimized three spectral ranges within the white-light continuum, as well as the ionization
efficiency. Optimization results in signal enhancements by typical factors of 2 and 1.4 for the target parameters.
In the case of white-light continuum generation, the feedback-driven procedure leads to shorter pulses by reducing
their chirp, while, as far as air ionization is concerned, the optimization consists in correcting the pulse from its
defects and setting the filamentation onset near the detector.