Light Filaments Research Articles

Spatiotemporal instability and optical filament formation in metamaterials

This study investigates the spatiotemporal instability in artificial metamaterials, with a focus on generating ultrashort pulses or light filaments. We identify the parametric regions where the metamaterial exhibits spatiotemporal instability, enabling the generation of ultrashort pulses. Our approach involves modeling nonlinear pulse propagation in the metamaterial using a (3+1)-dimensional nonlinear Schrödinger equation and performing a standard linear stability analysis to explore the spatiotemporal instability. Leveraging the engineering freedom to tailor the material parameters, we numerically demonstrate the generation of ultrashort pulses through spatiotemporal instability.

Design, implementation, and testing of a system for calibrating solar energy measuring devices

According to ISO 9847, the indoor calibration of pyranometers is based on the use of light filament sources such metal halide and tungsten lamps that are similar to the sun spectrum. The application of LED light sources is currently promoted worldwide in every field. At NIS, a study on the LED pyranometer calibration system was carried out. The results revealed that, in the absence of a diffuser, the uniformity of the FEL lamp and LED source was 0.76 and 0.89, respectively; however, when a diffuser was used, the uniformity increased to 0.92 for the FEL lamp and 0.95 for the LED source. For both systems, the fixed holder’s presence decreased the divergency in repeatability; for the LED source, this was 2%, but for the FEL light, it was 11.5%. In terms of statistical analysis, although the LED calibration system is more stable than the FEL calibration system, none calibration method exhibits any sign of an out-of-control situation, indicating that changes caused by random error are controlled and satisfied. The comparison demonstrated that the filament sources in the pyranometer’s indoor calibration process might be replaced with an LED source.

Intense infrared lasers for strong-field science

The advent of chirped-pulse amplification in the 1980s and femtosecond Ti:sapphire lasers in the 1990s enabled transformative advances in intense laser–matter interaction physics. Whereas most of experiments have been conducted in the limited near-infrared range of 0.8–1 μm, theories predict that many physical phenomena such as high harmonic generation in gases favor long laser wavelengths in terms of extending the high-energy cutoff. Significant progress has been made in developing few-cycle, carrier-envelope phase-stabilized, high-peak-power lasers in the 1.6–2 μm range that has laid the foundation for attosecond X ray sources in the water window. Even longer wavelength lasers are becoming available that are suitable to study light filamentation, high harmonic generation, and laser–plasma interaction in the relativistic regime. Long-wavelength lasers are suitable for sub-bandgap strong-field excitation of a wide range of solid materials, including semiconductors. In the strong-field limit, bulk crystals also produce high-order harmonics. In this review, we first introduce several important wavelength scaling laws in strong-field physics, then describe recent breakthroughs in short- (1.4–3 μm), mid- (3–8 μm), and long-wave (8–15 μm) infrared laser technology, and finally provide examples of strong-field applications of these novel lasers. Some of the broadband ultrafast infrared lasers will have profound effects on medicine, environmental protection, and national defense, because their wavelengths cover the water absorption band, the molecular fingerprint region, as well as the atmospheric infrared transparent window.

Synthesis of solar light driven nanorod-zinc oxide for degradation of rhodamine B, industrial effluent and contaminated river water

Surface water contamination by various dyes and pigments is a global problem caused by rapid industry, particularly textile/dyeing. Bangladesh's export-oriented textile sector has exploded in recent decades, polluting local waterways significantly. In this study, nano-ZnO were prepared using surfactant-assisted sol–gel, hydrothermal and thermal methods. SEM, XRD, reflectance spectrophotometer, EDS and adsorption tests were used to characterize the synthesized nano-ZnO. BET isotherms were used to determine the surface area, pore volume, and pore size of the as-prepared nano-ZnO. The mixed surfactant assisted-sol gel method produced nanorod-ZnO, whereas the hydrothermal and/or thermal methods yielded clusters of needles ZnO, as proven by SEM images. XRD data revealed that the synthesized nanorod-ZnO had a mainly wurtzite crystalline structure and their size was estimated using the Scherrer equation to be about 23.90 nm. EDS spectra confirmed the synthesis of pure nanorod-ZnO. Using a UV–visible reflectance spectrophotometer, the band gap energy of the as-prepared nanorod-ZnO was found to be 3.35 eV. According to BET isotherms, the BET and Langmuir surface areas were 4 and 5.4 m 2 /g, respectively. Prior to analyzing photodegradation, the RB was adsorbing in the presence of various doses of the nanorod-ZnO in the dark, but no adsorption was observed. The photocatalytic activities of the synthesized nano-ZnO were compared to TiO 2 (anatase) for the degradation of RB in an aqueous system under solar light, UV, fluorescence, and tungsten filament light irradiation. Nanorod-ZnO showed exceptional photocatalytic activity in degrading RB in an aqueous solution under solar light irradiation. The results suggest that 0.01 g/50 mL nanorod-ZnO with a solution pH of 7.8 is the best combination for complete degradation of 2.00 × 10 -5 M RB under solar light irradiation. When nano-ZnO was exposed to light, the inhibiting effect of ethanol and/or tert -butanol on the degradation of RB confirmed the formation of mostly hydroxyl free radicals. The synthesized nanorod-ZnO shown substantial photocatalytic activity in the removal of pollutants from industrial effluents and contaminated river water under solar light irradiation. A mechanism of excellent photocatalytic activity of the nanorod-ZnO is discussed.

Spatio-temporal controlled filamentation using higher order Bessel-Gaussian beams integrated in time.

We demonstrate a new method for a systematic, dynamic, high-speed, spatio-temporal control of femtosecond light filamentation in BK7 as a particular example of nonlinear medium. This method is based on using coherent conjugate asymmetric Bessel-Gaussian beams to control the far-field intensity distribution and in turn control the filamentation location. Such spatio-temporal control allows every femtosecond pulse to have a unique intensity distribution that results in the generation of structured filamentation patterns on demand. The switching speed of this technique is dependent on the rise time of the acousto-optic deflector, which can operate in the MHz range while having the ability to handle high peak power pulses that are needed for nonlinear interactions. The proposed and demonstrated spatio-temporal control of structured filaments can enable generation of large filament arrays, opto-mechanical manipulations of water droplets for fog clearing, as well as engineered radiofrequency plasma antennas.

The evolution of headlight devices in the work of otorhinolaryngologists

Invention and improving the methods of ENT examination are closely connected with the technological inventions of the 19th and 20th centuries. The invention of the classical exam head mirror in 1861 and improvement of the manufacturing of compact and powerful sources of light (filament lamps) at the time caused the researchers to create new devices for ENT examination. In particular, a head-mounted electro-mirror was created, the principle of which later became the basis for the development of fiber-optic headlamps. The emergence of powerful halogen and xenon light sources in the mid-20th century and the use of fiber-optics technology led to the development of fundamentally new mirror less headlamps. The traditional head-mounted reflector has gradually disappeared from the practice of an otolaryngologist. For our part, we can see how fiber-optic headlamps have been progressively replaced by heavy-duty LED headlamps over the last nine years. In order to determine the effectiveness of each available headlamp type and to answer the question of whether there is a benefit in using and maintaining a reflector headlamp, and to determine which current head-lamps are effective, we conducted our own research. Summing up the results, we came to the conclusion that despite its historic role in the development of otorhinolaryngology, the headlamp reflector through its low, in comparison with modern illuminators, characteristics have lost its relevance and, apparently, nowadays can serve as a museum exhibit. The head-mounted LED illuminator, a 21st century device, is gaining in popularity and is gradually becoming the standard for use in primary ENT diagnosis and during otorhinolaryngological surgical interventions. Its features such as full autonomy, lightweight, ease of use – especially the alignment of the light beam with the surgeon's eye – long operating time without recharging the battery (7 to 30 days) – depending on the manufacturer and the workload of the device – is beyond competition with any other head-mounted device for ENT organ examination.

Transiently structured head domains control intermediate filament assembly

Low complexity (LC) head domains 92 and 108 residues in length are, respectively, required for assembly of neurofilament light (NFL) and desmin intermediate filaments (IFs). As studied in isolation, these IF head domains interconvert between states of conformational disorder and labile, β-strand-enriched polymers. Solid-state NMR (ss-NMR) spectroscopic studies of NFL and desmin head domain polymers reveal spectral patterns consistent with structural order. A combination of intein chemistry and segmental isotope labeling allowed preparation of fully assembled NFL and desmin IFs that could also be studied by ss-NMR. Assembled IFs revealed spectra overlapping with those observed for β-strand-enriched polymers formed from the isolated NFL and desmin head domains. Phosphorylation and disease-causing mutations reciprocally alter NFL and desmin head domain self-association yet commonly impede IF assembly. These observations show how facultative structural assembly of LC domains via labile, β-strand-enriched self-interactions may broadly influence cell morphology.

Goos–Hänchen shift of a mid-infrared femtosecond filament visualized by the laser coloration method

We present the results of investigation of total internal reflection of a femtosecond light filament in a LiF crystal in the regime of anomalous group velocity dispersion. We measure the Goos–Hänchen shift of the filament in the vicinity of the critical angle for a single femtosecond pulse using the laser coloration method. The obtained experimental values are compared to several existing theoretical models.

Rotating azimuthons in dissipative Kerr media excited by superpositions of Bessel beams

We report the existence of persistently rotating azimuthons in media with self-focusing Kerr and absorption nonlinearities. The nonlinear loss is balanced by power influx from the peripheral reservoir stored in slowly decaying tails of the azimuthons. These modes are excited by a superposition of two Bessel beams with opposite vorticities, $\pm s$, and slightly different conicities. The excited azimuthon exhibits opposite vorticity in its center to that of the input Bessel-beam superposition due to spontaneous inversion of the topological charge in the course of the azimuthon formation. Unlike azimuthons in loss-free media, number $N$ of rotating intensity maxima and $s$ are not mutually independent, being related by $N=2s$. The robustness of the rotating azimuthons is enhanced in comparison to similar static dissipative patterns. They can be excited in almost any transparent material, in the range of intensities for which the nonlinear absorption, induced by multiphoton absorption, is relevant. Close to the ionization threshold, the rotating azimuthons reproduce recently observed helical filaments of light in air and CS$_{2}$.

Two-color, two-dimensional pyrometers based on monochrome and color cameras for high-temperature (>1000 K) planar measurements.

Two high-temperature 2D-pyrometers are described in this work. They are, respectively, based on the comparison of light intensities received by two monochrome cameras with narrow filters and the different color channels in a single color camera. The calibration procedure includes tests with thermocouples in flame flue gases and with a light bulb filament in the range 1050 K-2650 K, although the upper limit may be reliably extrapolated in the two-camera pyrometer. This device shows smaller uncertainties in absolute temperature determination than the other, ∼±15 K in the calibration curve. A combination of the two-color technique with intensity pyrometry is shown to allow the quantification of differences of the order of 1 K for uniform emissivity surfaces. Several examples of application of both pyrometers are presented to assess their spatial resolution and thermal capabilities, including the contact between the hot filament and its support in the light bulb and fine-wire thermocouples with large bead/wire ratios. The optical systems were designed for their use at short working distances and with high spatial resolution (4.7 μm/pixel and 8.7 µm/pixel) but could be adapted to other scenarios.

Femtosecond filament self-reconstruction after an air gap in fused silica

The results of investigation of light filament self-reconstruction after penetration through the air gap in fused silica at anomalous and normal group velocity dispersion are presented. It is revealed that at anomalous dispersion the light bullet formed before the gap was recovered after passing some distance behind the gap up to 1 mm length. This distance increased with the gap length and the bullet pathway before the gap. At normal dispersion filament reconstruction does not occur for a gap larger than 0.1 mm due to dispersive pulse splitting into two subpulses.

Monitoring the Heat of a Material during the Laser Formation of Defects

Results are presented from studying the role of material heating as defects form under conditions of the multiple filamentation of repeated laser pulses in lithium fluoride crystals. A way of monitoring local heating at the sites of light filament transmission is proposed, based on an analysis of the ratio of intensities of absorption bands of simple and aggregate color centers in the spectra of irradiated crystals.

Transiently Structured Head Domains Control Intermediate Filament Assembly

Low complexity (LC) head domains 92 and 108 residues in length are, respectfully, required for assembly of neurofilament light (NFL) and desmin intermediate filaments (IFs). As studied in isolation, these IF head domains interconvert between states of conformational disorder and labile, β-strand-enriched polymers. Solid state nuclear magnetic resonance (ss-NMR) spectroscopic studies of NFL and desmin head domain polymers reveal spectral patterns consistent with structural order. A combination of intein chemistry and segmental isotope labeling allowed preparation of fully assembled NFL and desmin IFs that could also be studied by ss-NMR. Assembled IFs revealed spectra overlapping with those observed for β-strand-enriched polymers formed from the isolated NFL and desmin head domains. Phosphorylation and disease causing mutations reciprocally alter NFL and desmin head domain self-association, yet commonly impede IF assembly. These observations show how facultative structural assembly of LC domains via labile, β-strand-enriched self-interactions may broadly influence cell morphology.

Front Cover: Identification of mNeonGreen as a pH‐Dependent, Turn‐On Fluorescent Protein Sensor for Chloride (ChemBioChem 14/2019)

mNeonGreen: A bright idea for chloride: Chloride-sensitive fluorescent proteins generated from natural and laboratory-guided evolution have a characteristic tyrosine residue that interacts with the anion and π-stacks with the chromophore. Through a structure-guided approach, we have identified that the fluorescent protein mNeonGreen, based on lanYFP from the cephalochordate Branchiostoma lanceolatum, lacks this interaction but still binds chloride. Here, we show mNeonGreen displayed as the light bulb filament, lighting up in the presence of chloride to generate a pH-dependent, turn-on fluorescent response. This discovery sets the stage to further engineer mNeonGreen as a new tool for imaging cellular chloride dynamics. More information can be found in the communication by S. C. Dodani et al. on page 1759 in Issue 14, 2019 (DOI: 10.1002/cbic.201900147).

Transient gain from N2+ in light filaments

We perform high resolution spectroscopy of $N_2^+$ emission in light filaments using a controlled pump at 795 followed by a second harmonic weak probe. Our result suggests that transient gain is achieved by resonant stimulated Raman scattering.

Properties of long light filaments in natural environment**Project supported by the National Natural Science Foundation of China (Grant Nos. 11574387, 11404335, 11474002, and 11535001), the National Basic Research Program of China (Grant Nos. 2013CBA01501 and 2013CB922401), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grants Nos. XDB16010200 and XDB07030300), and the Science Challenge Project, China (Grant No.

The multiple filamentation of terawatt femtosecond (fs) laser pulses is experimentally studied in a natural environment. A more than 30-m long plasma filament with a millimeter diameter is formed by the collimated fs laser pulse freely propagating in an open atmosphere. This study provides the first quantitative experimental data about the electron density of a long range light filament in the atmosphere. The electron density of such a filament is quantitatively detected by using an electric method, showing that it is at the 1011-cm−3 level.

Nanoscale orbital angular momentum beam instabilities in engineered nonlinear colloidal media.

Colloidal media with well-defined optical properties have been widely used as model systems in many fundamental and applied studies of light-matter interactions in complex media. Recent progress in the field of engineered nanoscale optical materials with fundamentally new physical properties opens new opportunities for tailoring the properties of colloids. In this work, we experimentally demonstrate the evolution of the optical vortex beams of different topological charges propagating in engineered nano-colloidal suspension of negative polarizability with saturable nonlinearities. Due to the high power of the incident beam, the modulation instability leads to an exponential growth of weak perturbations and thus splits the original vortex beam into a necklace beam consisting of several bright spots. At a fixed power, the number of observed bright spots is intrinsically determined by the topological charge of the incident beam and agrees well with the predictions of our linear stability analysis and numerical simulations. Besides contributing to the fundamental science of light-matter interactions in engineered soft-matter media, this work opens new opportunities for dynamic optical manipulation and transmission of light through scattering media as well as formation of complex optical patterns and light filamentation in naturally existing colloids such as fog and clouds.

Self-Organized Lattices of Nonlinear Optochemical Waves in Photopolymerizable Fluids: The Spontaneous Emergence of 3-D Order in a Weakly Correlated System.

Many of the extraordinary three-dimensional architectures that pattern our physical world emerge from complex nonlinear systems or dynamic populations whose individual constituents are only weakly correlated to each other. Shoals of fish, murmuration behaviors in birds, congestion patterns in traffic, and even networks of social conventions are examples of spontaneous pattern formation, which cannot be predicted from the properties of individual elements alone. Pattern formation at a different scale has been observed or predicted in weakly correlated systems including superconductors, atomic gases near Bose Einstein condensation, and incoherent optical fields. Understanding pattern formation in nonlinear weakly correlated systems, which are often unified through mathematical expression, could pave intelligent self-organizing pathways to functional materials, architectures, and computing technologies. However, it is experimentally difficult to directly visualize the nonlinear dynamics of pattern formation in most populations-especially in three dimensions. Here, we describe the collective behavior of large populations of nonlinear optochemical waves, which are poorly correlated in both space and time. The optochemical waves-microscopic filaments of white light entrapped within polymer channels-originate from the modulation instability of incandescent light traveling in photopolymerizable fluids. By tracing the three-dimensional distribution of optical intensity in the nascent polymerizing system, we find that populations of randomly distributed, optochemical waves synergistically and collectively shift in space to form highly ordered lattices of specific symmetries. These, to our knowledge, are the first three-dimensionally periodic structures to emerge from a system of weakly correlated waves. Their spontaneous formation in an incoherent and effectively chaotic field is counterintuitive, but the apparent contradiction of known behaviors of light including the laws of optical interference can be explained through the soliton-like interactions of optochemical waves with nearest neighbors. Critically, this work casts fundamentally new insight into the collective behaviors of poorly correlated nonlinear waves in higher dimensions and provides a rare, accessible platform for further experimental studies of these previously unexplored behaviors. Furthermore, it defines a self-organization paradigm that, unlike conventional counterparts, could generate polymer microstructures with symmetries spanning all the Bravais lattices.

Spectrally and angularly resolved measurements of three-halves harmonic emission from laser-produced plasmas

Spectra of three-halves harmonic emissions (3/2) from laser-produced plasmas were measured at different angles, including both forward and backward sides, from the direction of incident laser beams. The /2 emitted from carbon–hydrogen (CH) targets was observed to be larger than that from aluminum (Al) targets with the same incident laser intensity, which supports the argument that the two-plasmon decay (TPD) instability could be inhibited by using medium-Z ablator instead of CH ablator in direct-drive inertial confinement fusion. Besides, the measured /2–incident intensity curves for both materials suggest relatively lower threshold of TPD than the calculated values. In experiments with thin Al targets, the angular distribution of the blue- and red-shifted peaks of /2 spectra were obtained, which shows that the most intense blue- and red-shifted peaks may not be produced in paired plasmons, but the spectra produced by their ‘twin’ plasmons were not observed. Because may have been influenced by other physical processes during their propagation from their birth places to the detectors, the mismatches on emission angle, wavelength shift, and threshold may be qualitatively explained through the assumption that small-scale light filaments widely existed in the corona of laser-produced plasmas.

Nonlinear laser–plasma interactions

Soon after lasers were invented, there was tremendous curiosity on the nonlinear phenomena which would result in their interaction with a fully ionized plasma. Apart from the basic interest, it was realized that it could be used for the achievement of nuclear fusion in the laboratory. This led us to a paper on the propagation of a laser beam into an inhomogeneous fusion plasma, where it was first demonstrated that light would go up to the critical layer (where the frequency matches the plasma frequency) and get reflected from there with a reflection coefficient of order unity. The reflection coefficient was determined by collisional effects. Since the wave was expected to slow down to near zero group speed at the reflection point, the dominant collision frequency determining the reflection coefficient was the collision frequency at the reflection point. It turned out that the absorption of light was rather small for fusion temperatures. This placed a premium on investigation of nonlinear phenomena which might contribute to the absorption and penetration of the light into high-density plasma. An early investigation showed that electron jitter with respect to ions would be responsible for the excitation of decay instabilities which convert light waves into electrostatic plasma waves and ion waves near the critical frequency. These electrostatic waves would then get absorbed into the plasma even in the collisionless case and lead to plasma heating which is nonlinear. Detailed estimates of this heating were made. Similar nonlinear processes which could lead to stimulated scattering of light in the underdense region $$(\omega >\omega _p)$$ were investigated together with a number of other workers. All these nonlinear processes need a critical threshold power for excitation. Another important process which was discovered around the same time had to do with filamentation and trapping of light when certain thresholds were exceeded. All of this work has been extensively verified in laser plasma experiments and have become the backbone of our present understanding of how lasers nonlinearly interact with fully ionized fusion plasmas. A review of this early work will be presented. We shall also present a review of our involvement in the recent work on nonlinear penetration of light into overdense plasmas with gradual and sharp interfaces.