Visible Light Flashes Research Articles

The collapse of a sonoluminescent cavitation bubble imaged with X-ray free-electron laser pulses

Single bubble sonoluminescence (SBSL) is the phenomenon of synchronous light emission due to the violent collapse of a single spherical bubble in a liquid, driven by an ultrasonic field. During the bubble collapse, matter inside the bubble reaches extreme conditions of several gigapascals and temperatures on the order of 10000 K, leading to picosecond flashes of visible light. To this day, details regarding the energy focusing mechanism rely on simulations due to the fast dynamics of the bubble collapse and spatial scales below the optical resolution limit. In this work we present phase-contrast holographic imaging with single x-ray free-electron laser (XFEL) pulses of a SBSL cavitation bubble in water. X-rays probe the electron density structure and by that provide a uniquely new view on the bubble interior and its collapse dynamics. The involved fast time-scales are accessed by sub-100 fs XFEL pulses and a custom synchronization scheme for the bubble oscillator. We find that during the whole oscillation cycle the bubble’s density profile can be well described by a simple step-like structure, with the radius R following the dynamics of the Gilmore model. The quantitatively measured internal density and width of the boundary layer exhibit a large variance. Smallest reconstructed bubble sizes reach down to R≃0.8μm , and are consistent with spherical symmetry. While we here achieved a spatial resolution of a few 100 nm, the visibility of the bubble and its internal structure is limited by the total x-ray phase shift which can be scaled with experimental parameters.

MP35-10 MECHANISMS OF FIBER-TIP DEGRADATION DURING LASER LITHOTRIPSY

You have accessJournal of UrologyCME1 Apr 2023MP35-10 MECHANISMS OF FIBER-TIP DEGRADATION DURING LASER LITHOTRIPSY Yuri Pishchalnikov, William Behnke-Parks, and Marshall Stoller Yuri PishchalnikovYuri Pishchalnikov More articles by this author , William Behnke-ParksWilliam Behnke-Parks More articles by this author , and Marshall StollerMarshall Stoller More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003269.10AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Ureteroscopic lithotripsy breaks urinary stones using laser pulses delivered to the stone via optical fibers. Degradation of fibers reduces the efficacy of lithotripsy and varies with fiber diameter, stone composition, laser pulse energy and duration. The goal of this work was to reveal the physical mechanisms of fiber-tip damage (burnback) in water and air. METHODS: The dynamics of fiber-tip damage was studied using a high-speed camera Shimadzu HPV-X2 at a frame rate up to two million frames per second. The camera was mounted to a microscope focused on the 242-µm glass-core-diameter fiber positioned in direct contact with a target—typically, a glass slide coated with a 25±5 µm layer of hydroxyapatite (Himed, NY). Selected experiments were conducted with BegoStones and whole surgically retrieved urinary stones. Damaged fibers were cleaved to start each series of 20 pulses with flat fiber tips. Laser pulses were produced using a Lumenis VersaPulse holmium:YAG laser. Temporal profiles of infrared laser pulses and flashes of visible light were resolved using photodetectors. Cross-sectional profiles of laser-beam energy were assessed using Zap-It paper. Microscope images were used to measure the burnback length of the fiber. RESULTS: Burnback of optical fibers was associated with flashes of light (sparks) observed both in water and in air. Sparks in air could crack and fragment the fiber during single laser pulse. Twenty pulses in air produced the burnback length of 0.37 mm at 1.0 J (95% CI: 0.11–0.64 mm) and 0.14 mm at 0.6 J (95% CI: 0.10–0.18 mm), smaller than that at 1.0 J (p=0.010). In water, the fibers were damaged by sparks during the laser pulse and after the pulse during the collapse of laser-induced cavitation bubbles. Contribution of cavitation varied from insignificant to most dramatic, breaking a 1.1-mm length of the fiber in a single laser pulse. Cavitation without sparks showed no burnback with only minor damage of cladding (500 pulses, 1.0 J). Sparks were associated with an increased absorption of laser energy and were observed at laser energies typically >0.5 J and only with certain target materials near the fiber tip. Cross-sections of laser beams were larger with fibers damaged in air than that in water (p=0.007) and both were larger than that with undamaged fibers (p<0.005). CONCLUSIONS: These results suggest that the burnback degradation of optical fibers is associated mainly with laser-induced heating, ionization, and optical breakdown of target material. A better understanding of the mechanisms of fiber-tip damage will aid in development of future improvements to minimize degradation of optical fibers. Source of Funding: Research reported in this publication was supported by the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health under Award Number R43DK129104. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health © 2023 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 209Issue Supplement 4April 2023Page: e473 Advertisement Copyright & Permissions© 2023 by American Urological Association Education and Research, Inc.MetricsAuthor Information Yuri Pishchalnikov More articles by this author William Behnke-Parks More articles by this author Marshall Stoller More articles by this author Expand All Advertisement PDF downloadLoading ...

Visible light flashes induced by pulsed stimulated Brillouin scattering in narrow-linewidth, high-power, near-IR fiber lasers

We report an interesting observation of visible light flashes indicating pulsing events in Near Infrared fiber laser systems. Using a narrow-linewidth, continuous-wave (CW) fiber laser operating at 1064 nm, we observed visible flashes composed of faint, red, orange, yellow and green colors. Concurrently with the visible flashes, the spectra in the backward direction showed different Raman Stokes orders of 1064 nm for a silica medium. We attribute this form of visible light generation to Cherenkov-type phase-matched harmonic generation in optical fibers enabled by high-peak-power parasitic pulses. These pulses are attributed to the onset of stimulated Brillouin scattering. The harmonics of different Raman Stokes orders of the pulses are responsible for the different visible colors observed. This effect is potentially observable in any laser system with a high optical power with a CW, quasi-CW or pulsed form.

Location, orbit, and energy of a meteoroid impacting the Moon during the lunar eclipse of 2019 January 21

ABSTRACT During lunar eclipse of 2019 January 21, a meteoroid impacted the Moon producing a visible light flash. The impact was witnessed by casual observers offering an opportunity to study the phenomenon from multiple geographical locations. We use images and videos collected by observers in seven countries to estimate the location, impact parameters (speed and incoming direction), and energy of the meteoroid. Using parallax, we achieve determining the impact location at lat.$-29.43^{+0.30}_{-0.21}$, lon.$-67.89^{+0.07}_{-0.09}$, and geocentric distance as 356 553 km. After devising and applying a photometric procedure for measuring flash standard magnitudes in multiple RGB images having different exposure times, we found that the flash, had an average G-magnitude 〈G〉 = 6.7 ± 0.3. We use gravitational ray tracing (GRT) to estimate the orbital properties and likely radiant of the impactor. We find that the meteoroid impacted the moon with a speed of $14^{+7}_{-6}$ km s−1 (70 per cent C.L.) and at a shallow angle, θ &amp;lt; 38.2 deg. Assuming a normal error for our estimated flash brightness, educated priors for the luminous efficiency and object density, and using the GRT-computed probability distributions of impact speed and incoming directions, we calculate posterior probability distributions for the kinetic energy (median Kmed = 0.8 kton), body mass (Mmed = 27 kg) and diameter (dmed = 29 cm), and crater size (Dmed = 9 m). If our assumptions are correct, the crater left by the impact could be detectable by prospecting lunar probes. These results arose from a timely collaboration between professional and amateur astronomers that highlight the potential importance of citizen science in astronomy.

Lifetime Enhancement of Visible Light Induced Photocharges in Tungsten and Nitrogenin situCodoped TiO2:WN Thin Films

We report on one-step in situ codoped TiO2 thin films synthesized by cosputtering. The purpose of this acceptor–donor passivated codoping approach is to overcome the optoelectronic limitations that arise for monodoped TiO2 in photocatalytic applications. To evaluate these added benefits, the TiO2:WN thin films were characterized by different techniques. X-ray diffraction patterns and X-ray photoelectron spectral analysis revealed that both N and W dopants are mostly present in the desired substitutional locations. Additionally, the codoping approach was found to reduce the internal strain and defect density of the TiO2:WN films as compared to their monodoped TiO2:N counterparts. This defect reduction is confirmed via photocharge lifetime variation obtained using visible light flash photolysis time-resolved microwave conductivity measurements (FP-TRMC). Photocharge lifetime analysis indicated the presence of three distinct decay processes: charge trapping, recombination, and surface reactions. These charac...

Formation of tyrosine radicals in photosystem II under far-red illumination

Photosystem II (PS II) contains two redox-active tyrosine residues on the donor side at symmetrical positions to the primary donor, P680. TyrZ, part of the water-oxidizing complex, is a preferential fast electron donor while TyrD is a slow auxiliary donor to P680+. We used PS II membranes from spinach which were depleted of the water oxidation complex (Mn-depleted PS II) to study electron donation from both tyrosines by time-resolved EPR spectroscopy under visible and far-red continuous light and laser flash illumination. Our results show that under both illumination regimes, oxidation of TyrD occurs via equilibrium with TyrZ• at pH 4.7 and 6.3. At pH 8.5 direct TyrD oxidation by P680+ occurs in the majority of the PS II centers. Under continuous far-red light illumination these reactions were less effective but still possible. Different photochemical steps were considered to explain the far-red light-induced electron donation from tyrosines and localization of the primary electron hole (P680+) on the ChlD1 in Mn-depleted PS II after the far-red light-induced charge separation at room temperature is suggested.

Comparative investigation of stimulus-evoked rod outer segment movement and retinal electrophysiological activity.

Transient retinal phototropism (TRP) has been observed in rod photoreceptors activated by oblique visible light flashes. Time-lapse confocal microscopy and optical coherence tomography (OCT) revealed rod outer segment (ROS) movements as the physical source of TRP. However, the physiological source of TRP is still not well understood. In this study, concurrent TRP and electroretinogram (ERG) measurements disclosed a remarkably earlier onset time of the ROS movements (≤10 ms) than that (∼38 ms) of the ERG a-wave. Furthermore, low sodium treatment reversibly blocked the photoreceptor ERG a-wave, which is known to reflect hyperpolarization of retinal photoreceptors, but preserved the TRP associated rod OS movements well. Our experimental results and theoretical analysis suggested that the physiological source of TRP might be attributed to early stages of phototransduction, before the hyperpolarization of retinal photoreceptors.

Bioinspired Molecular Lantern: Tuning the Firefly Oxyluciferin Emission with Host-Guest Chemistry.

Fireflies generate flashes of visible light via luciferase-catalyzed chemiexcitation of the substrate (luciferin) to the first excited state of the emitter (oxyluciferin). Microenvironment effects are often invoked to explain the effects of the luciferase active pocket on the emission; however, the exceedingly complex spectrochemistry and synthetic burdens have precluded elucidation of the nature of these interactions. To decipher the effects of microenvironment on the light emission, here the hydrophobic interior of cucurbit[7]uril (CB7) is used to mimic the nonpolar active pocket of luciferase. The hydrophobic interior of CB7 induces shifts of the ground-state pKas by 1.9-2.5 units to higher values. Upon sequestration, the emission maxima of neutral firefly oxyluciferin and its conjugate monodeprotonated base are blue-shifted by 40 and 39 nm, respectively, resulting in visual color changes of the emitted light.

Biophysical mechanism of transient retinal phototropism in rod photoreceptors.

Oblique light stimulation evoked transient retinal phototropism (TRP) has been recently detected in frog and mouse retinas. High resolution microscopy of freshly isolated retinas indicated that the TRP is predominated by rod photoreceptors. Comparative confocal microscopy and optical coherence tomography (OCT) revealed that the TRP predominantly occurred from the photoreceptor outer segment (OS). However, biophysical mechanism of rod OS change is still unknown. In this study, frog retinal slices, which open a cross section of retinal photoreceptor and other functional layers, were used to test the effect of light stimulation on rod OS. Near infrared light microscopy was employed to monitor photoreceptor changes in retinal slices stimulated by a rectangular-shaped visible light flash. Rapid rod OS length change was observed after the stimulation delivery. The magnitude and direction of the rod OS change varied with the position of the rods within the stimulated area. In the center of stimulated region the length of the rod OS shrunk, while in the peripheral region the rod OS tip swung towards center region in the plane perpendicular to the incident stimulus light. Our experimental result and theoretical analysis suggest that the observed TRP may reflect unbalanced disc-shape change due to localized pigment bleaching. Further investigation is required to understand biochemical mechanism of the observed rod OS kinetics. Better study of the TRP may provide a noninvasive biomarker to enable early detection of age-related macular degeneration (AMD) and other diseases that are known to produce retinal photoreceptor dysfunctions.

Interactions of Prosthetic and Natural Vision in Animals With Local Retinal Degeneration.

Prosthetic restoration of partial sensory loss leads to interactions between artificial and natural inputs. Ideally, the rehabilitation should allow perceptual fusion of the two modalities. Here we studied the interactions between normal and prosthetic vision in a rodent model of local retinal degeneration. Implantation of a photovoltaic array in the subretinal space of normally sighted rats induced local degeneration of the photoreceptors above the chip, and the inner retinal neurons in this area were electrically stimulated by the photovoltaic implant powered by near-infrared (NIR) light. We studied prosthetic and natural visually evoked potentials (VEP) in response to simultaneous stimulation by NIR and visible light patterns. We demonstrate that electrical and natural VEPs summed linearly in the visual cortex, and both responses decreased under brighter ambient light. Responses to visible light flashes increased over 3 orders of magnitude of contrast (flash/background), while for electrical stimulation the contrast range was limited to 1 order of magnitude. The maximum amplitude of the prosthetic VEP was three times lower than the maximum response to a visible flash over the same area on the retina. Ambient light affects prosthetic responses, albeit much less than responses to visible stimuli. Prosthetic representation of contrast in the visual scene can be encoded, to a limited extent, by the appropriately calibrated stimulus intensity, which also depends on the ambient light conditions. Such calibration will be important for patients combining central prosthetic vision with natural peripheral sight, such as in age-related macular degeneration.

Single-Cell Analysis of [18F]Fluorodeoxyglucose Uptake by Droplet Radiofluidics.

Radiolabels can be used to detect small biomolecules with high sensitivity and specificity without interfering with the biochemical activity of the labeled molecule. For instance, the radiolabeled glucose analogue, [18F]fluorodeoxyglucose (FDG), is routinely used in positron emission tomography (PET) scans for cancer diagnosis, staging, and monitoring. However, despite their widespread usage, conventional radionuclide techniques are unable to measure the variability and modulation of FDG uptake in single cells. We present here a novel microfluidic technique, dubbed droplet radiofluidics, that can measure radiotracer uptake for single cells encapsulated into an array of microdroplets. The advantages of this approach are multiple. First, droplets can be quickly and easily positioned in a predetermined pattern for optimal imaging throughput. Second, droplet encapsulation reduces cell efflux as a confounding factor, because any effluxed radionuclide is trapped in the droplet. Last, multiplexed measurements can be performed using fluorescent labels. In this new approach, intracellular radiotracers are imaged on a conventional fluorescence microscope by capturing individual flashes of visible light that are produced as individual positrons, emitted during radioactive decay, traverse a scintillator plate placed below the cells. This method is used to measure the cell-to-cell heterogeneity in the uptake of tracers such as FDG in cell lines and cultured primary cells. The capacity of the platform to perform multiplexed measurements was demonstrated by measuring differential FDG uptake in single cells subjected to different incubation conditions and expressing different types of glucose transporters. This method opens many new avenues of research in basic cell biology and human disease by capturing the full range of stochastic variations in highly heterogeneous cell populations in a repeatable and high-throughput manner.

The First Pulse of the Extremely Bright GRB 130427A: A Test Lab for Synchrotron Shocks

Gamma-ray burst (GRB) 130427A is one of the most energetic GRBs ever observed. The initial pulse up to 2.5 seconds is possibly the brightest well-isolated pulse observed to date. A fine time resolution spectral analysis shows power-law decays of the peak energy from the onset of the pulse, consistent with models of internal synchrotron shock pulses. However, a strongly correlated power-law behavior is observed between the luminosity and the spectral peak energy that is inconsistent with curvature effects arising in the relativistic outflow. It is difficult for any of the existing models to account for all of the observed spectral and temporal behaviors simultaneously.

The Bright Optical Flash and Afterglow from the Gamma-Ray Burst GRB 130427A

The optical light generated simultaneously with x-rays and gamma rays during a gamma-ray burst (GRB) provides clues about the nature of the explosions that occur as massive stars collapse. We report on the bright optical flash and fading afterglow from powerful burst GRB 130427A. The optical and >100-megaelectron volt (MeV) gamma-ray flux show a close correlation during the first 7000 seconds, which is best explained by reverse shock emission cogenerated in the relativistic burst ejecta as it collides with surrounding material. At later times, optical observations show the emergence of emission generated by a forward shock traversing the circumburst environment. The link between optical afterglow and >100-MeV emission suggests that nearby early peaked afterglows will be the best candidates for studying gamma-ray emission at energies ranging from gigaelectron volts to teraelectron volts.

Fermi-LAT Observations of the Gamma-Ray Burst GRB 130427A

The observations of the exceptionally bright gamma-ray burst (GRB) 130427A by the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope provide constraints on the nature of these unique astrophysical sources. GRB 130427A had the largest fluence, highest-energy photon (95 GeV), longest γ-ray duration (20 hours), and one of the largest isotropic energy releases ever observed from a GRB. Temporal and spectral analyses of GRB 130427A challenge the widely accepted model that the nonthermal high-energy emission in the afterglow phase of GRBs is synchrotron emission radiated by electrons accelerated at an external shock.

GRB 130427A: A Nearby Ordinary Monster

Long-duration gamma-ray bursts (GRBs) are an extremely rare outcome of the collapse of massive stars and are typically found in the distant universe. Because of its intrinsic luminosity (L ~ 3 × 10(53) ergs per second) and its relative proximity (z = 0.34), GRB 130427A reached the highest fluence observed in the γ-ray band. Here, we present a comprehensive multiwavelength view of GRB 130427A with Swift, the 2-meter Liverpool and Faulkes telescopes, and by other ground-based facilities, highlighting the evolution of the burst emission from the prompt to the afterglow phase. The properties of GRB 130427A are similar to those of the most luminous, high-redshift GRBs, suggesting that a common central engine is responsible for producing GRBs in both the contemporary and the early universe and over the full range of GRB isotropic energies.

En face optical coherence tomography of transient light response at photoreceptor outer segments in living frog eyecup.

This study was designed to test the feasibility of en face mapping of the transient intrinsic optical signal (IOS) response at photoreceptor outer segments and to assess the effect of spatial resolution on functional IOS imaging of retinal photoreceptors. A line-scan optical coherence tomography (LS-OCT) was constructed to achieve depth-resolved functional IOS imaging of living frog eyecups. Rapid en face OCT revealed transient IOS almost immediately (<3 ms) after the onset of visible light flashes at photoreceptor outer segments. Quantitative analysis indicated that the IOS kinetics may reflect dynamics of G-protein binding and releasing in early phases of visual transduction, and high resolution is essential to differentiate positive and negative IOS changes in adjacent locations.

Dynamic near-infrared imaging reveals transient phototropic change in retinal rod photoreceptors

Stiles-Crawford effect (SCE) is exclusively observed in cone photoreceptors, but why the SCE is absent in rod photoreceptors is still a mystery. In this study, we employed dynamic near infrared light imaging to monitor photoreceptor kinetics in freshly isolated frog and mouse retinas stimulated by oblique visible light flashes. It was observed that retinal rods could rapidly (onset: ∼10 ms for frog and 5 ms for mouse; time-to-peak: ∼200 ms for frog and 30 ms for mouse) shift toward the direction of the visible light, which might quickly compensate for the loss of luminous efficiency due to oblique illumination. In contrast, such directional movement was negligible in retinal cones. Moreover, transient rod phototropism could contribute to characteristic intrinsic optical signal (IOS). We anticipate that further study of the transient rod phototropism may not only provide insight into better understanding of the nature of vision but also promise an IOS biomarker for functional mapping of rod physiology at high resolution.

Fast and effective: intense pulse light photodynamic inactivation of bacteria

The goal of this study was to investigate the photodynamic toxicity of TMPyP (5, 10, 15, 20-Tetrakis (1-methylpyridinium-4-yl)-porphyrin tetra p-toluenesulfonate) in combination with short pulses (ms) of an intense pulse light source within 10 s against Bacillus atrophaeus, Staphylococcus aureus, Methicillin-resistant S. aureus and Escherichia coli, major pathogens in food industry and in health care, respectively. Bacteria were incubated with a photoactive dye (TMPyP) that is subsequently irradiated with visible light flashes of 100 ms to induce oxidative damage immediately by generation of reactive oxygen species like singlet oxygen. A photodynamic killing efficacy of up to 6 log(10) (>99.9999%) was achieved within a total treatment time of 10 s using a concentration range of 1-100 μmol TMPyP and multiple light flashes of 100 ms (from 20 J cm(-2) up to 80 J cm(-2)). Both incubation of bacteria with TMPyP alone or application of light flashes only did not have any negative effect on bacteria survival. Here we could demonstrate for the first time that the combination of TMPyP as the respective photosensitizer and a light flash of 100 ms of an intense pulsed light source is enough to generate sufficient amounts of reactive oxygen species to kill these pathogens within a few seconds. Increasing antibiotic resistance requires fast and efficient new approaches to kill bacteria, therefore the photodynamic process seems to be a promising tool for disinfection of horizontal surfaces in industry and clinical purposes where savings in time is a critical point to achieve efficient inactivation of microorganisms.

A Multi-Frame, Megahertz CCD Imager

The Los Alamos National Laboratory's Dual Axis Radiographic Hydrodynamic Test Facility (DARHT) generates flash radiographs of explosive experiments using two linear induction electron accelerators situated at right angles. The DARHT second axis accelerator generates an 18-MeV, 2 kA, 2 musec electron beam which is converted or ldquochoppedrdquo into four individual pulses ranging from 20 to 100 nsec in length at 2 MHz frequency. The individual electron beam pulses are down-converted by a segmented lutetium oxyorthosilicate scintillator, creating four visible light flashes, to image explosively driven events. To record these events, a high efficiency, high speed, imager has been fabricated which is capable of framing rates of 2 MHz. This device utilizes a 512 times 512 pixel charge coupled device (CCD) with a 25 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> active area, and incorporates an electronic shutter technology designed for back-illuminated CCD's, making this the largest and fastest back-illuminated CCD in the world. Characterizing an imager capable of this frame rate presents unique challenges. High speed LED drivers and intense radioactive sources are needed to perform basic measurements. We investigate properties normally associated with single-frame CCD's such as read noise, gain, full-well capacity, detective quantum efficiency (DQE), sensitivity, and linearity. In addition, we investigate several properties associated with the imager's multi-frame operation such as transient frame response and frame-to-frame isolation while contrasting our measurement techniques and results with more conventional devices.

Effect of Intense Pulsed-Light Exposure on Lipid Peroxides and Thymine Dimers in Human Skin In Vivo

Intense pulsed light (IPL) generates high-intensity short flashes of visible light and has been used for about 10 years to improve dermatological conditions such as telangiectasia, pigmented lesions, and skin aging. Although these systems deliver a moderate dose (10-30 J/cm(2)) of visible light, this dose is delivered during a short pulse (2-5 milliseconds), which implies a very high fluence rate (approximately 4000 W/cm(2)). For this reason, we speculated whether the Bunsen-Roscoe law of reciprocity could still be valid in these conditions. Nine healthy volunteers were exposed to IPL or UV-A or simulated solar UV radiation, and then thymine dimer and lipid peroxide concentrations were determined in skin biopsy specimens of the exposed sites. Only exposure to solar UV radiation (7-J/cm(2) UV-A + 80-mJ/cm(2) UV-B) produced measurable amounts of thymine dimers in DNA from skin biopsy specimens, whereas UV-A radiation (40 J/cm(2)) and IPL (9 J/cm(2)) induced 3-fold and 6-fold increases of cutaneous lipid peroxides, respectively. These preliminary results indicate that IPL, although filtered for wavelengths shorter than 500 nm, can generate oxidative stress, a typical hallmark of UV-A, but does not induce thymine dimers. This emphasizes the need for long-term studies involving IPL before using this technique in a recurrent manner.