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Optics Express Apr 2024Laser-induced filaments have been shown to reduce the voltage necessary to initiate electrical discharges in atmospheric air and guide their propagation over long...
Laser-induced filaments have been shown to reduce the voltage necessary to initiate electrical discharges in atmospheric air and guide their propagation over long distances. Here we demonstrate the stable generation of laser filament-guided electrical discharge columns in air initiated by high energy (up to 250 mJ) 1030 nm wavelength laser pulses of 7 ps duration at repetition rates up to 1 kHz and we discuss the processes leading to breakdown. A current proportional to the laser pulse energy is observed to arise as soon as the laser pulse arrives, initiating a high impedance phase of the discharge. Full breakdown, characterized by impedance collapse, occurs 100 ns to several µs later. A record 4.7-fold reduction in breakdown voltage for dc-biased discharges, which remains practically independent of the repetition rate up to 1 kHz, is observed to be primarily caused by a single laser pulse that produces a large (∼80%) density depression. The radial gaps between the filamentary plasma channel and the hollowed electrodes employed are shown to play a significant role in the breakdown dynamics. A rapid increase of 3-4 orders of magnitude in current is observed to follow the formation of localized radial current channels linking the filament to the electrodes. The increased understanding and control of kHz repetition rate filament-guided discharges can aid their use in applications.
PubMed: 38859252
DOI: 10.1364/OE.506547 -
Optics Express Apr 2024A chip-scale chaotic laser system with optoelectronic delayed feedback is proposed and analyzed by numerical simulation. This chip eliminates the need for bulky delay...
A chip-scale chaotic laser system with optoelectronic delayed feedback is proposed and analyzed by numerical simulation. This chip eliminates the need for bulky delay components such as long optical fibers, free propagation and external cavities, relying solely on internal devices and waveguides to achieve feedback delay. This approach simplifies integration, maintaining a compact chip size. According to the results, the chip-scale system exhibits rich dynamics, including periodicity, quasi-periodicity, and chaotic states. Chaos resembling Gaussian white noise is achieved with picosecond-level delay time, highlighting the complexity of chip-scale signals. Furthermore, time delay signature (TDS) concealment is enhanced with a short delay comparable to the inverse bandwidth τ, albeit at a cost of sacrificing chaotic signal complexity. Applying the photonic integrated circuits to practical applications, 1 Gbps back-to-back communication transmission is feasible. Results demonstrate low bit error rates (BERs) for authorizers (<10) and high BERs for eavesdroppers (>10), ensuring communication confidentiality and chaotic synchronization. Lastly, preliminary experiments validate the feasibility. Our theoretical work has demonstrated the feasibility of hybrid integrated optical chaos circuits with optoelectronic feedback based on photonic wire bonding, which can provide a stable and flexible integrated chaos source.
PubMed: 38859231
DOI: 10.1364/OE.515058 -
Optics Express Apr 2024In this study we demonstrated a compact and cost-effective high energy and average power picosecond laser developed for OPCPA system pumping applications. The system...
In this study we demonstrated a compact and cost-effective high energy and average power picosecond laser developed for OPCPA system pumping applications. The system delivered record high pulse energy at 100 W average power level in a hybrid laser architecture based on a fiber seed laser and free-space end-pumped Yb:YAG amplifiers. The output pulses were compressed to 1 ps pulse duration and the output beam featured M = 1.3, which was further improved to 1.07 by spatial filtering. A silica glass spatially variable wave plate manufactured by direct laser writing was used to reduce depolarization losses from 12% to 5%.
PubMed: 38859186
DOI: 10.1364/OE.520847 -
Optics Express Apr 2024A GaSb-based SEmiconductor Saturable Absorber Mirror (SESAM) enables continuous-wave picosecond mode-locked operation with excellent stability of a...
A GaSb-based SEmiconductor Saturable Absorber Mirror (SESAM) enables continuous-wave picosecond mode-locked operation with excellent stability of a polarization-maintaining mid-infrared Er:ZBLAN fiber laser. The GaSb-based SESAM mode-locked fiber laser delivers an average output power of 190 mW at 2.76 µm at a repetition rate of 32.07 MHz (corresponding to a pulse energy of ∼6 nJ) and exhibits a high signal-to-noise ratio of ∼80 dB. The polarization extinction ratio is more than 23 dB. By employing an intracavity diffraction grating, the laser wavelength is continuously tunable across 2.706-2.816 µm. Passively Q-switched operation of this laser is also demonstrated.
PubMed: 38859169
DOI: 10.1364/OE.517526 -
Optics Express May 2024Foturan glass is a photosensitive transparent material which has attracted much interest for microfluidic applications due to possibility of volume processing by...
Foturan glass is a photosensitive transparent material which has attracted much interest for microfluidic applications due to possibility of volume processing by ultrafast lasers. In this work, we have investigated the effect of picosecond laser on volume processing in Foturan glass when varying the beam diameter incident on a lens. To this end, specific laser focusing configurations have been designed using raytracing models and an analysis protocol has been developed in the lens focusing region in order to describe the focal point displacement occurring at the variation of the incident laser beam diameter. The numerically simulated results were explained in association with Rayleigh length and found to be in good agreement with the experimental data obtained at well-defined conditions. Specifically, it was found that the hollow microstructures developed by thermal treatment and chemical etching after laser irradiation were significantly displaced along the propagation direction when the incident beam diameter varied in the range of 1-3.5 times. This approach aims to bring an essential contribution to the field of ultrashort pulse lasers micro- and nanoprocessing in transparent materials proving that the laser beam focus position and its size can be precisely controlled with high precision by automated optics for the variation of incident laser beam diameter in predefined conditions. This approach has the potential for laser multi-beam processing at various volume depths using the same optics setup and may even be applicable to two-photon excitation microscopy. On the other hand, the processing protocol in Foturan glass may allow understanding transparent material modification by tailoring laser beam characteristics.
PubMed: 38859127
DOI: 10.1364/OE.524602 -
Optics Express May 2024We present a source of indistinguishable photons at telecom wavelength, synchronized to an external clock, for the use in distributed quantum networks. We characterize...
We present a source of indistinguishable photons at telecom wavelength, synchronized to an external clock, for the use in distributed quantum networks. We characterize the indistinguishability of photons generated in independent parametric down-conversion events using a Hong-Ou-Mandel interferometer, and show non-classical interference with coalescence, C = 0.83(5). We also demonstrate the synchronization to an external clock within sub-picosecond timing jitter, which is significantly shorter than the single-photon wavepacket duration of ≈ 35 ps. Our source enables scalable quantum protocols over multi-node, long-distance optical networks using network-based clock recovery systems.
PubMed: 38858987
DOI: 10.1364/OE.521083 -
Optics Express May 2024Temporal cleaning of high-power infrared (IR) pulses generated by a Ti:Sapphire system is demonstrated by the use of the Nonlinear Fourier Filtering (NFF) method. In a...
Temporal cleaning of high-power infrared (IR) pulses generated by a Ti:Sapphire system is demonstrated by the use of the Nonlinear Fourier Filtering (NFF) method. In a proof-of-principle experiment suppression of up to 1000 is achieved for the temporal pedestal prior to the main pulse, with a moderate (20-25%) overall throughput. This includes the same suppression ratio for the picosecond coherent pedestal in the direct vicinity of the main pulse. Based on the instantaneous, intensity-dependent and high-order switching characteristics of NFF, excellent pulse cleaning performance is observed. The efficient, high-contrast removal of the coherent pedestal from the foot of the main pulse even if its duration is shorter than 100 fs is compared with the capability of the plasma mirror technique. Calculations are also performed, supporting the experimentally observed sharp intensity dependence of the switching process, pointing out the dominant role of the ionization-based refractive index change.
PubMed: 38858896
DOI: 10.1364/OE.521567 -
Optics Express May 2024The X-ray sources for Compton radiography of ICF experiments are generated by using intense picosecond lasers to irradiate wire targets. The wire diameter must be...
The X-ray sources for Compton radiography of ICF experiments are generated by using intense picosecond lasers to irradiate wire targets. The wire diameter must be designed thin enough, for example ∼ 10 µm in many published works, to comply a high spatial resolution. This results in a low laser-target interception, which limits the photon yield. We investigated a technique of coded-source radiography based on laser-driven annular sources via Monte Carlo and PIC simulations. The annular X-ray source is formed by laser irradiating tube target in which the effect of electron recirculation plays an important role. We proved that this technique has an increased spatial resolution and contrast than that using the Gaussian source produced by wire targets. Therefore, the diameter of the backlighter target can be significantly increased to uplift laser-target interception without compromising on spatial resolution. This contributes towards a reconciliation between the spatial resolution and photon yield for Compton radiography. The results predict the possibility of improving source photon yield by several times in future experiments.
PubMed: 38858878
DOI: 10.1364/OE.512301 -
The Journal of Physical Chemistry. C,... May 2024Methylammonium lead tribromide perovskite (MAPbBr) is an important material, for example, for light-emitting applications and tandem solar cells. The relevant...
Methylammonium lead tribromide perovskite (MAPbBr) is an important material, for example, for light-emitting applications and tandem solar cells. The relevant photophysical properties are governed by a plethora of phenomena resulting from the complex and relatively poorly understood interplay of excitons and free charge carriers in the excited state. In this study, we combine transient spectroscopies in the visible and terahertz range to investigate the presence and evolution of excitons and free charge carriers at ultrafast times upon excitation at various photon energies and densities. For above- and resonant band-gap excitation, we find that free charges and excitons coexist and that both are mainly promptly generated within our 50-100 fs experimental time resolution. However, the exciton-to-free charge ratio increases upon decreasing the phonon energy toward resonant band gap excitation. The free charge signatures dominate the transient absorption response for above-band-gap excitation and low excitation densities, masking the excitonic features. With resonant band gap excitation and low excitation densities, we find that although the exciton density increases, free charges remain. We show evidence that the excitons localize into shallow trap and/or Urbach tail states to form localized excitons (within tens of picoseconds) that subsequently get detrapped. Using high excitation densities, we demonstrate that many-body interactions become pronounced and effects such as the Moss-Burstein shift, band gap renormalization, excitonic repulsion, and the formation of Mahan excitons are evident. The coexistence of excitons and free charges that we demonstrate here for photoexcited MAPbBr at ultrafast time scales confirms the high potential of the material for both light-emitting diode and tandem solar cell applications.
PubMed: 38835933
DOI: 10.1021/acs.jpcc.3c08509 -
Nature Communications Jun 2024Classical photochemistry requires nanosecond excited-state lifetimes for diffusion-controlled reactions. Excited radicals with picosecond lifetimes have been implied by...
Classical photochemistry requires nanosecond excited-state lifetimes for diffusion-controlled reactions. Excited radicals with picosecond lifetimes have been implied by numerous photoredox studies, and controversy has arisen as to whether they can actually be catalytically active. We provide direct evidence for the elusive pre-association between radical ions and substrate molecules, enabling photoinduced electron transfer beyond the diffusion limit. A strategy based on two distinct light absorbers, mimicking the natural photosystems I and II, is used to generate excited radicals, unleashing extreme reduction power and activating C(sp)-Cl and C(sp)-F bonds. Our findings provide a long-sought mechanistic understanding for many previous synthetically-oriented works and permit more rational future photoredox reaction development. The newly developed excitation strategy pushes the current limits of reactions based on multi-photon excitation and very short-lived but highly redox active species.
PubMed: 38834625
DOI: 10.1038/s41467-024-49006-5