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The dependence of the polymerization and optical damage thresholds in multi-photon polymerization (MPP) lithography was studied using a broadly-tunable laser system with group delay dispersion (GDD) control. The order of non-linearity and the light–matter interaction mechanisms were investigated using the resolution bridges method for non-photosensitized SZ2080TM and photosensitized SZ2080TM + IRG369 prepolymers. Energy deposition, voxel dimension growth, and the size of the dynamic fabrication window (DFW) were measured in the 700–1300 nm wavelength range at three different pulse durations measured at the sample – 100, 200 and 300 fs. Polymerization was observed at all wavelengths and pulse durations without significant differences in the achieved minimal spatial dimension (

Over the last five years, inorganic lead halide perovskite nanowires have emerged as prospective candidates to supersede standard semiconductor analogs in advanced photonic designs and optoelectronic devices. In particular, CsPbX3 (X = Cl, Br, I) perovskite materials have great advantages over conventional semiconductors such as defect tolerance, highly efficient luminescence, and the ability to form regularly shaped nano- and microcavities from solution via fast crystallization. However, on the way of electrically pumped lasing, the perovskite nanowires grown on transparent conductive substrates usually suffer from strong undesirable light leakage increasing their threshold of lasing. Here, we report on the integration of CsPbBr3 nanowires with nanostructured indium tin oxide substrates possessing near-unity effective refractive index and high conductivity by using a simple wet chemical approach. Surface passivation of the substrates is found out to govern the regularity of the perovskite resonators’ shape. The nanowires show room-temperature lasing with ultrahigh quality factors (up to 7860) which are up to four times higher than that of similar structures on a flat indium tin oxide layer, resulting in more than twofold reduction of the lasing threshold for the nanostructured substrate. Numerical modeling of eigenmodes of the nanowires confirms the key role of low-refractive-index substrate for improved light confinement in the Fabry–Pérot cavity which results in superior laser performance.

Multiphoton photopolymerisation (MPP), also known as 3D nanoprinting, was studied using a wavelength-tunable femtosecond laser. The possibility of using any colour of the spectrum from 500 to 1200 nm with a fixed pulse width of 100 fs revealed an interplay of photophysical mechanisms more delicate than just two-photon photopolymerisation. An effective order of absorption, i.e. the X-photon absorption, as well as optimal exposure conditions were assessed for photosensitised and pure SZ2080TM pre-polymer. The tunability of wavelength greatly influenced the dynamic fabrication window (DFW), optimised conditions resulting in a 10-fold increase. Furthermore, a non-trivial energy deposition by X-photon absorption was noted with an onset of a strong lateral size increase at longer wavelengths and can be understood as due to reaching epsilon-near-zero conditions. Such a control over the voxel aspect ratio and, consequently, the photopolymerised volume, may boost 3D nanoprinting efficiency. Overall, the results reveal wavelength being an important degree of freedom to tailor the MPP process and, if optimised, benefiting broad applications in areas of micro-optics, nanophotonic devices, metamaterials and tissue engineering. [ABSTRACT FROM AUTHOR]

Dispersed pump-probe and pump-dump-probe spectroscopy was applied in order to disentangle the excited states of peridinin and understand their function in vivo. The findings indicate that the unique intramolecular charge transfer state of peridinin is an efficient energy donor to chlorophyll a in the peridinin-chlorophyll-protein complex and thus plays a significant role in global light harvesting.

Fluorescence quenchers have been generated from the triplet states of chlorophylls in the major light-harvesting complex II of green plants. It appears that there is a protective mechanism, significant at high light intensities, with negative feedback that lowers generation of Ch1 triplets when a Ch1 triplet-mediated fluorescence quencher has been generated in the domain. Disappearance of light-induced quenchers was thermally activated with concomitant large entropy changes

Spatial filtering is an important mechanism to improve the spatial quality of laser beams. Typically, a confocal arrangement of lenses with a diaphragm in the focal plane is used for intracavity spatial filtering. Such conventional filtering requires access to the far‐field domain. In microlasers, however, conventional filtering is impossible due to the lack of space in microresonators to access the far‐field. Therefore, a novel concept for more compact and efficient spatial filtering is necessary. In this study, a conceptually novel mechanism of spatial filtering in the near‐field domain is proposed and demonstrated, by a nanostructured multilayer coating—a 2D photonic crystal structure with a periodic index modulation along the longitudinal and transverse directions to the beam propagation. The structure is built on a nanomodulated substrate, to provide the transverse periodicity. The physical vapor deposition is used to provide self‐repeating modulation in the longitudinal direction. A 5 µm thick photonic multilayer structure composed of nanostructured multiple layers of alternating high‐ and low‐index materials providing spatial filtering in the near‐infrared frequencies with 2° low angle passband is experimentally demonstrated. The proposed photonic structure can be considered as an ideal component for intracavity spatial filtering in microlasers. [ABSTRACT FROM AUTHOR]

We have investigated the photophysics of aggregated lutein/violaxanthin in daffodil chromoplasts. We reveal the presence of three carotenoid aggregate species, the main one composed of a mixture of lutein/violaxanthin absorbing at 481 nm, and two secondary populations of aggregated carotenoids absorbing circa 500 and 402 nm. The major population exhibits an efficient singlet fission process, generating μs-lived triplet states on an ultrafast timescale. The structural organization of aggregated lutein/violaxanthin in daffodil chromoplasts produces well-defined electronic levels that permit the energetic pathways to be disentangled unequivocally, allowing us to propose a consistent mechanism for singlet fission in carotenoid aggregates. Transient absorption measurements on this system reveal for the first time an entangled triplet signature for carotenoid aggregates, and its evolution into dissociated triplet states. A clear picture of the carotenoid singlet fission pathway is obtained, which is usually blurred due to the intrinsic disorder of carotenoid aggregates. [ABSTRACT FROM AUTHOR]

Analysis on a range of artificial light-harvesting dyads built fro zinc phthalocyanine (Pc) covalently attached to carotenoids with 9,10 or 11 conjugated carbon-carbon double bonds is performed to determine the energy transfer and excited-state deactivation pathway following excitation of the strongly allowed carotenoid [S.sub.2] state as a function of the conjugation length. A new unseen energy relaxation pathways and a unique type of collective carotenoid-phthalocyanine excited state in carotenophthaloyanine dyads are observed.

Excitation-intensity-dependent pump-probe (PP) measurements have helped in gaining insight into the light-induced dynamics of the light-harvesting 2 (LH2) complex isolated from Rhodopseudomonas acidophila. The S(super *) state has exhibited a different response to the increase of excitation intensity than S(sub 1) state and hence two new models that can describe both the time-resolved and the intensity-dependent data are proposed.

Dispersed multipump-probe (PPP) spectroscopy is used to investigate the role of saturation, annihilation and structures pulses in coherent control experiments on the light-harvesting 2 complex from Rhodopseudomonas acidophila. The conditions that are required for incoherent effects to control experimental signals are discussed with particular emphasis on pulse intensities and are shown that the optimization of a ratio of conservative signals is needed to exclude saturation effects from coherent control studies.

A study was conducted of the optical pump-induced dynamics of the highly asymmetric carotenoid peridinin in methanol by dispersed pump-probe, pump-dump-probe and pump-repump-probe transient absorption spectroscopy in the visible region. The pump-probe measurements show that the decay of the initially excited S2 state populates two excited states.

The ultrafast dynamics of a number of model photoactive yellow protein chromophores is investigated. The observed transient absorption spectra in terms of the spectral signatures ascribed to solvation, excited-state twisting, and vibrational relaxation are also discussed.

A study was conducted, using wavelength and time-resolved pump-probe and pump-dump-probe spectroscopy, to investigate the excited and ground-state photoinduced dynamics of the green fluorescent protein (GFP) chromophore and 4'-hydroxybenzylidene-2,3-dimethylimidazolinone (HBDI). The result identifies two pathways such as a 1-photon excited-state twisting, and a 2-photon ionized process.

In this study, we present the development and characterization of Cu plasma X-ray source driven by 20 W average power high repetition rate femtosecond laser in ambient atmosphere environment. The peak Cu- Kα photon flux of 2.3 × 10 photons/s into full solid angle is demonstrated (with a process conversion efficiency of ~ 10), using pulses with peak intensity of 4.65 × 10 W/cm. Such Cu- Kα flux is significantly larger than others found in comparable experiments, performed in air environment. The effects of resonance plasma absorption process, when optimized, are shown to increase measured flux by the factor of 2-3. The relationship between X-ray photon flux and plasma-driving pulse repetition rate is quasi-linear, suggesting that fluxes could further be increased to 10 photons/s using even higher average powers of driving radiation. These results suggest that to fully utilize the potential of high repetition rate laser sources, novel target material delivery systems (for example, jet-based ones) are required. On the other hand, this study demonstrates that high energy lasers currently used for plasma X-ray sources can be conveniently and efficiently replaced by high average power and repetition rate laser radiation, as a way to increase the brightness of the generated X-rays. [ABSTRACT FROM AUTHOR]