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Nature Communications Jun 2024Optical nonreciprocity is manifested as a difference in the transmission of light for the opposite directions of excitation. Nonreciprocal optics is traditionally...
Optical nonreciprocity is manifested as a difference in the transmission of light for the opposite directions of excitation. Nonreciprocal optics is traditionally realized with relatively bulky components such as optical isolators based on the Faraday rotation, hindering the miniaturization and integration of optical systems. Here we demonstrate free-space nonreciprocal transmission through a metasurface comprised of a two-dimensional array of nanoresonators made of silicon hybridized with vanadium dioxide (VO). This effect arises from the magneto-electric coupling between Mie modes supported by the resonator. Nonreciprocal response of the nanoresonators occurs without the need for external bias; instead, reciprocity is broken by the incident light triggering the VO phase transition for only one direction of incidence. Nonreciprocal transmission is broadband covering over 100 nm in the telecommunication range in the vicinity of λ = 1.5 µm. Each nanoresonator unit cell occupies only ~0.1 λ in volume, with the metasurface thickness measuring about half-a-micron. Our self-biased nanoresonators exhibit nonreciprocity down to very low levels of intensity on the order of 150 W/cm or a µW per nanoresonator. We estimate picosecond-scale transmission fall times and sub-microsecond scale transmission rise. Our demonstration brings low-power, broadband and bias-free optical nonreciprocity to the nanoscale.
PubMed: 38871743
DOI: 10.1038/s41467-024-49436-1 -
Biomedical Optics Express Jun 2024The spatial omics information analysis of heterogeneous cells or cell populations is of great importance for biomedical research. Herein, we proposed a picosecond laser...
The spatial omics information analysis of heterogeneous cells or cell populations is of great importance for biomedical research. Herein, we proposed a picosecond laser capture microdissection boosted by edge catapulting combined with dielectrophoretic force (ps-LMED) that enables fast and non-invasive acquisition of uncontaminated cells and cell populations for downstream molecular assays. The target cells were positioned under a microscope and separated by a focused picosecond pulsed laser. The system employed the plasma expansion force during cutting to lift the target and captured it under dielectrophoretic force from the charged collection cap eventually. The principle of our system has been validated by both theoretical analysis and practical experiments. The results indicated that our system can collect samples ranging from a single cell with a diameter of a few microns to large tissues with a volume of 532,500 µm at the moment finishing the cutting, without further operations. The cutting experiments of living cells and ribonucleic acid (RNA) and protein omics analysis results of collected targets demonstrated the advantage of non-destructiveness to the samples and feasibility in omics applications.
PubMed: 38867793
DOI: 10.1364/BOE.525630 -
Nature Communications Jun 2024An antiferromagnet emits spin currents when time-reversal symmetry is broken. This is typically achieved by applying an external magnetic field below and above the...
An antiferromagnet emits spin currents when time-reversal symmetry is broken. This is typically achieved by applying an external magnetic field below and above the spin-flop transition or by optical pumping. In this work we apply optical pump-THz emission spectroscopy to study picosecond spin pumping from metallic FeRh as a function of temperature. Intriguingly we find that in the low-temperature antiferromagnetic phase the laser pulse induces a large and coherent spin pumping, while not crossing into the ferromagnetic phase. With temperature and magnetic field dependent measurements combined with atomistic spin dynamics simulations we show that the antiferromagnetic spin-lattice is destabilised by the combined action of optical pumping and picosecond spin-biasing by the conduction electron population, which results in spin accumulation. We propose that the amplitude of the effect is inherent to the nature of FeRh, particularly the Rh atoms and their high spin susceptibility. We believe that the principles shown here could be used to produce more effective spin current emitters. Our results also corroborate the work of others showing that the magnetic phase transition begins on a very fast picosecond timescale, but this timescale is often hidden by measurements which are confounded by the slower domain dynamics.
PubMed: 38862508
DOI: 10.1038/s41467-024-48795-z -
Lasers in Medical Science Jun 2024Q-switched (QS) Nd: YAG lasers are frequently utilised light sources for tattoo removal due to their precise micro-confined photo-acoustic interaction with exogenous and...
Q-switched (QS) Nd: YAG lasers are frequently utilised light sources for tattoo removal due to their precise micro-confined photo-acoustic interaction with exogenous and endogenous pigments. In order to achieve optimal results, several treatment sessions are usually required. However, the number of sessions depend on tattoo size, design complexity, pigment quantity within dermal layers, and anatomical location. Higher energy settings have often been used to reduce treatment sessions to a minimum however, this approach may lead to possible post-laser skin complications such as pathological wound healing. This case report highlights the importance of recognizing early stages of pathological wound healing encountered after high fluence 1064 nm QS laser tattoo removal. Early implementation of a proportional wound care strategy with anti-neoangiogenic and anti-inflammatory properties through the unconventional use of potent topical steroids applied in a pulsed fashion resulted in positive control of the tissue repair processes. This approach led to effective wound healing re-modulation achieving near normal skin remodelling and optimal tissue healing which in turn, permitted the completion of necessary QS tattoo removal sessions to accomplish successful and safe tattoo fading whilst maintaining overall patient satisfaction.
Topics: Humans; Tattooing; Wound Healing; Lasers, Solid-State; Female; Adult; Low-Level Light Therapy; Tattoo Removal
PubMed: 38861002
DOI: 10.1007/s10103-024-04101-3 -
Optics Express Jun 2024Gallium nitride (GaN) nanowire, as a type of wide bandgap nanomaterial, has attracted considerable interest because of its outstanding physicochemical properties and...
Gallium nitride (GaN) nanowire, as a type of wide bandgap nanomaterial, has attracted considerable interest because of its outstanding physicochemical properties and applications in energy storage and photoelectric devices. In this study, we prepared GaN nanowires via a facile chemical vapor deposition method and investigated their nonlinear absorption responses ranging from ultraviolet to near-infrared in the z-scan technology under irradiation by picosecond laser pulses. The experiment revealed that GaN nanowires exhibit remarkable nonlinear absorption characteristics attributed to their wide bandgap and nanostructure, including saturable absorption and reverse saturable absorption. When compared to bulk GaN crystals, the nanowires provide a richer and more potent set of nonlinear optical effects. Furthermore, we conducted an analysis of the corresponding electronic transition processes associated with photon absorption. Under high peak power density laser excitation, two-photon absorption or three-photon absorption dominate, with maximum modulation depths of 73.6%, 74.9%, 63.1% and 64.3% at 266 nm, 355 nm, 532 nm, and 1064 nm, respectively, corresponding to absorption coefficients of 0.22 cm/GW, 0.28 cm/GW, 0.08 cm/GW, and 2.82 ×10 cm/GW. At lower peak energy densities, GaN nanowires demonstrate rare and excellent saturation absorption characteristics at wavelength of 355 nm due to interband transitions, while saturable absorption is also observed at 532 nm and 1064 nm due to band tail absorption. The modulation depths are 85.2%, 41.9%, and 13.7% for 355 nm, 532 nm, and 1064 nm, corresponding to saturation intensities of 3.39 GW/cm, 5.58 GW/cm and 14.13 GW/cm. This indicates that GaN nanowires can be utilized as broadband optical limiters and high-performance pulse laser modulating devices, particularly for scarce ultraviolet optical limiters, and saturable absorbers for ultraviolet and visible lasers. Furthermore, our study demonstrates the application potential of wide bandgap nanomaterials in nonlinear optical devices.
PubMed: 38859441
DOI: 10.1364/OE.524681 -
Optics Express Apr 2024Compressed ultrafast photography (CUP) is a computational imaging technology capable of capturing transient scenes in picosecond scale with a sequence depth of hundreds...
Compressed ultrafast photography (CUP) is a computational imaging technology capable of capturing transient scenes in picosecond scale with a sequence depth of hundreds of frames. Since the inverse problem of CUP is an ill-posed problem, it is challenging to further improve the reconstruction quality under the condition of high noise level and compression ratio. In addition, there are many articles adding an external charge-coupled device (CCD) camera to the CUP system to form the time-unsheared view because the added constraint can improve the reconstruction quality of images. However, since the images are collected by different cameras, slight affine transformation may have great impacts on the reconstruction quality. Here, we propose an algorithm that combines the time-unsheared image constraint CUP system with unsupervised neural networks. Image registration network is also introduced into the network framework to learn the affine transformation parameters of input images. The proposed algorithm effectively utilizes the implicit image prior in the neural network as well as the extra hardware prior information brought by the time-unsheared view. Combined with image registration network, this joint learning model enables our proposed algorithm to further improve the quality of reconstructed images without training datasets. The simulation and experiment results demonstrate the application prospect of our algorithm in ultrafast event capture.
PubMed: 38859263
DOI: 10.1364/OE.519872 -
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