Blue Pulses Research Articles

Two Color Pump-Probe Dichroism and Birefringence Measurements in Atmospheric Molecules

The experimental study of the laser induced alignment of linear atmospheric molecules naturally present into the air using an ultra-short (femtosecond temporal range) and ultra-intense (TW · cm–2 fluence range) linearly polarised laser pulse is described. The measurements are conducted under a two-color pump-probe configuration using an IR pump beam and a blue probe pulse (red-blue configuration), which interacts with the molecules after they have been exposed to the IR alignment pulse. The optical birefringence and dichroism polarimetric signals have been both strictly measured into the same experimental conditions into this two-color configuration. A balanced detection permits the heterodyne signal to be got directly. Under the short and intense laser pulse exposure, the molecules present into the atmospheric air (under standard room temperature conditions) aligne, and periodic transient revivals are observed (field free alignment approach into non-adiabatic conditions). The results obtained are in accordance with those obtained in the red-red configuration and confirm the approach proposed as relevant for atmospheric sensing.

All-Optical Electrophysiology for High-Throughput Functional Characterization of a Human iPSC-Derived Motor Neuron Model of ALS.

SummaryHuman induced pluripotent stem cell (iPSC)-derived neurons are an attractive substrate for modeling disease, yet the heterogeneity of these cultures presents a challenge for functional characterization by manual patch-clamp electrophysiology. Here, we describe an optimized all-optical electrophysiology, “Optopatch,” pipeline for high-throughput functional characterization of human iPSC-derived neuronal cultures. We demonstrate the method in a human iPSC-derived motor neuron (iPSC-MN) model of amyotrophic lateral sclerosis (ALS). In a comparison of iPSC-MNs with an ALS-causing mutation (SOD1 A4V) with their genome-corrected controls, the mutants showed elevated spike rates under weak or no stimulus and greater likelihood of entering depolarization block under strong optogenetic stimulus. We compared these results with numerical simulations of simple conductance-based neuronal models and with literature results in this and other iPSC-based models of ALS. Our data and simulations suggest that deficits in slowly activating potassium channels may underlie the changes in electrophysiology in the SOD1 A4V mutation.

Earth’s Serious Anisotropy, Non-Inertiality, Ether, Gain of Free Energy, Revealed, Part 2

The present paper is of historic importance as well as the second part of [1]. In this second part, we detect important details about the orbit of the Earth and about the velocity (of magnitude 217 km/s) of the solar system around the center of the Milky Way galaxy. Some of these details concern the perihelion and aphelion of the orbit of the Earth. For several years we have observed that the return pulses, on the oscilloscope screen, appear to be more energetic than the initial pulses (See Part 1, Figure 2, for which the blue return pulse crests are much higher than the yellow initial crests). The used oscilloscope is and only must be, a storage oscilloscope, in other words, a computerized oscilloscope with a digital memory. The first oscilloscopes like this, came out, only after 1995, a relatively recent time that all wire velocity experiments and measurements were already completely investigated by science. We do astronomy, without receiving images by an astronomical telescope, but instead by sending signals around a loop and making an analysis using the same oscilloscope as in Part 1. We recommend to the reader to study Part 1 as a prerequisite. The Earth surface is accelerating with a centripetal acceleration, due to its rotation, thus it is not an inertial frame. Also, the Earth is evidently anisotropic, due to the same rotation, a second reason for it being a non-inertial rotating frame.

Highly efficient H-β Fraunhofer line optical parametric oscillator pumped by a single-frequency 355 nm laser

A highly efficient laser system output at the H-β Fraunhofer line of 486.1 nm has been demonstrated. A high pulse energy single-frequency hybrid 1064 nm master oscillator power amplifier was frequency-tripled to achieve 355 nm laser pulses, which acted as the pump source of the beta barium borate nanosecond pulse optical parametric oscillator. With pump energy of 190 mJ, the laser system generated a maximum output of 62 mJ blue laser pulses at 486.1 nm, corresponding to conversion efficiency of 32.6%. The laser spectrum width was measured to be around 0.1 nm, being in conformity with the spectrum width of the solar Fraunhofer line.

Tunable broadband near-infrared absorber based on ultrathin phase-change material

In this work, a tunable broadband near-infrared light absorber was designed and fabricated with a simple and lithography free approach by introducing an ultrathin phase-change material Ge2Sb2Te5 (GST) layer into the metal–dielectric multilayered film structure with the structure parameters as that: SiO2 (72.7 nm)/Ge2Sb2Te5 (6.0 nm)/SiO2 (70.2 nm)/Cu (>100.0 nm). The film structure exhibits a modulation depth of ∼72.6% and an extinction ratio of ∼8.8 dB at the wavelength of 1410 nm. The high light absorption (95%) of the proposed film structure at the wavelength of 450 nm in both of the amorphous and crystalline phase of GST, indicates that the intensity of the reflectance in the infrared region can be rapidly tuned by the blue laser pulses. The proposed planar layered film structure with layer thickness as the only controllable parameter and large reflectivity tuning range shows the potential for practical applications in near-infrared light modulation and absorption.

Picosecond tunable gain-switched blue pulses from GaN laser diodes with nanosecond current injections.

We investigated the gain-switching properties of GaN-based ridge-waveguide lasers on free-standing GaN substrates with low-cost nanosecond current injection. It was observed that the output pulses with intense injection consisted of an isolated short pulse with a duration of around 50 ps at the high-energy side and a long steady-state component at the lower energy side independent of the electric pulse duration. The energy separation between the short pulse and steady-state component can be over 30 meV, favoring short-pulse generation with the spectral filtering technique. The duration of the steady-state component can be tuned freely by controlling the duration and voltage of the electric pulse, which is very useful for generating pulse-width-tunable optical pulses for various applications.

Controlled assembly of high-order nanoarray metal structures on bulk copper surface by femtosecond laser pulses

We report a new one-step maskless method to fabricate high-order nanoarray metal structures comprising periodic grooves and particle chains on a single-crystal Cu surface using femtosecond laser pulses at the central wavelength of 400nm. Remarkably, when a circularly polarized infrared femtosecond laser pulse (spectrally centered at 800nm) pre-irradiates the sample surface, the geometric dimensions of the composite structure can be well controlled. With increasing the energy fluence of the infrared laser pulse, both the groove width and particle diameter are observed to reduce, while the measured spacing-to-diameter ratio of the nanoparticles tends to present an increasing tendency. A physical scenario is proposed to elucidate the underlying mechanisms: as the infrared femtosecond laser pulse pre-irradiates the target, the copper surface is triggered to display anomalous transient physical properties, on which the subsequently incident Gaussian blue laser pulse is spatially modulated into fringe-like energy depositions via the excitation of ultrafast surface plasmon. During the following relaxation processes, the periodically heated thin-layer regions can be transferred into the metastable liquid rivulets and then they break up into nanodroplet arrays owing to the modified Rayleigh-like instability. This investigation indicates a simple integrated approach for active designing and large-scale assembly of complexed functional nanostructures on bulk materials.

Electron emission properties of gated silicon field emitter arrays driven by laser pulses

We report optically modulated electron emission from gated p-type silicon field emitter arrays (Si-FEAs). The device's “volcano” structure is designed to control the photoexcitation of electrons by transmitting light through the small gate aperture, thereby minimizing the photogeneration of slow diffusion carriers outside the depletion region in the tip. Compared to that in the dark, the emission current was enhanced by more than three orders of magnitude in the high field region when irradiated with blue laser pulses. Results from the time-resolved measurements of photoassisted electron emission showed that these possess the same response as the laser pulse with no discernible delay. These results indicate that the volcano device structure is effective at eliminating the generation of diffusion carriers and that a fully optimized FEA is promising as a photocathode for producing high-speed modulated electron beams.

Self-enhancement and suppression of optical pulses by use of photochromism in elastomer.

When violet or green pulses were launched into an elastomer containing photochromic diarylethene, two competitive absorption bands emerged at around 400 and 520 nm. The violet pulses suppressed the former and enhanced the latter, whereas the green pulses induced the opposite reaction. Consequently, these signals self-formed their optical path in the elastomer (self-enhancement). By contrast, blue pulses exhibited either a self-enhancement or suppression characteristic depending on whether the elastomer had been irradiated by the violet or green signal before the blue signal transmission. Measurement of the transient spectra during the irradiation process revealed that the blue photons were absorbed by both 400 and 520 nm bands inducing two competitive photochromic isomerizations simultaneously.

Integrating multimedia and LMS tools to cultivate creative and reflective learners.

The challenge for an instructor, no matter the delivery system, is to inspire students towards creative thinking. Online asynchronous and hybrid courses provide a unique opportunity for instructors to harness mobile multimedia tools such as tablets, and smart phones coupled with Learning Management System (LMS) tools to enhance instructor presence as well as student engagement in the creative process through real-time collaboration and feedback.In this 40-minute “how to” presentation, attendees will be reintroduced to multimedia tools readily available to them like smart phone and tablets along with inexpensive presentation tools such as Camtasia to make engaging presentations. Using Distance Education courses in media criticism and online journalism, the presenter will demonstrate a few tips and tricks to improve image and sound quality. In addition to utilizing lecture presentations, attendees will learn how to integrate multimedia into announcements as well as in “instructional” videos on how to think and write creatively and make presentations using video blogs.Finally, the presentation will explore student-teacher collaboration tools such as Blackboard Collaborate Ultra and Video Blogging via Kaltura CaptureSpace. Furthermore, Blue Pulse – a unique social feedback platform will be discussed as it relates to designing engaging content.

Short Blue Light Pulses (30 Min.) in the Morning are Able to Phase Advance the Rhythm of Melatonin in a Home Setting

It is known that light in the morning is able to induce phase advances of the endogenous clock, however most studies have tested the phase advances in highly controlled laboratory conditions. At home the environmental lighting is more variable. In theory, a high intensity short morning-light pulse in the short-wavelengths-range (blue light) should be capable of inducing phase advances. If this is also true in a home setting, this could be a firm basis supporting light treatment in late chronotypes who suffer from a late sleep phase. In a study carried out in summer, 11 normal to relatively late (habitual midsleep 4:15-6:09 hours) chronotypes (age range 23-27 years, 4f/7m) participated in two conditions: (1) 1 baseline day followed by 3 consecutive days of 30 min. blue morning-light pulses, (2) 1 baseline day followed by 3 consecutive days of 60 min. blue light pulses. Blue light was applied by use of the Philips GoLite BLU (HF3320, blue leds, intensity at the cornea 2306 melanopic-lux, 300 lux, 3.65 W/m2). During all four evenings, subjects were asked to protect themselves from light exposure (<10 lux). The response of the melatonin rhythm, calculated as a shift in dim light melatonin onset (DLMO), to a single 30 min. light pulse varied between subjects and resulted in a non-significant phase advance of 15 (±48) min. (t10 = 1.04; P = 0.33), and a significant advance of 30 (±41) min. to a single 60 min. light pulse. (t10 = 2.40; P < 0.05). After 3 days of light exposure both in the 30- and in the 60 min. light pulses condition significant phase advances of DLMO were observed; 49 (±58) min. (t10 = 2.80; P < 0.05) and 59 (±29) min. (t10 = 6.9; P < 0.001) respectively. No significant differences were found in the DLMO shifts between conditions. In addition there was a trend for a lower sleepiness score directly after waking up after using light for 3 days in both conditions (t10 = 3.38; P = 0.096, 60 min. and (t10 = 4.10; P = 0.070, 30 min.). A prelimin.ary analysis of actimetry data indicated some support for an effect on sleep timin.g. The data support the conclusion that light pulses of 30 min. in the morning on three consecutive days, in a home setting, in combination with dim light during the evenings, can be part of an efficient phase advancing chronotherapy protocol.

Infrared absorption in KTP isomorphs induced with blue picosecond pulses

Picosecond blue-light induced infrared absorption (BLIIRA) was investigated in periodically poled KTiOPO4, Rb:KTiOPO4, RbTiOPO4, KTiOAsO4 and RbTiOAsO4. The dependence of BLIIRA on blue light average power and intensity as well as on crystal temperature was studied. The results show the presence of at least two different types of color centers. A higher level of remnant absorption was observed in the phosphates compared to the arsenates. We attribute the largest portion of the induced absorption to photo-generated electrons and holes self-trapped in the proximity to Ti4+ and O2- ions, respectively, forming polaron color centers. Stabilization of these centers is aided by the presence of mobile alkali metal vacancies in the crystal. The lower level of remnant absorption in arsenates is related to higher population of thermal phonons related to TiO6 group vibrations in arsenates.

Light pulses at night elicit wavelength‐dependent behavioral responses in zebrafish

AbstractZebrafish detect and respond to light by means of visual and non‐visual photopigments that have maximal sensitivity at different wavelengths. This paper describes zebrafish behavior when a 1‐h light pulse of different wavelengths (violet, blue, green, orange and red) was applied at midnight, with light pulse and darkness being used as controls. For each light condition, seven fish were individually tracked 1 h before (P1), during (P2) and after (P3) the light pulse. All the light colors (except orange) led to an increase in the accumulated distance swum during P2 with respect to the baseline (P1) activity, but only the white, violet, blue and green pulses led to higher activity during P3. This activation was partially explained by changes in the maximum swimming speed and/or the freezing behavior time. Thus, the violet and green lights increased the maximum swimming speed during P2, whereas red light produced a decrease in the same in P3. The white and blue pulses elicited longer freezing behavior during P2 than the violet pulse, and only the white and blue lights provoked freezing behavior during P3. Similarly, all colors awakened fish during P2, but only the green, blue, violet and white light affected the sleep rebound during P3. Moreover, zebrafish swam downward only during the white and violet light pulses in P2. Summarizing, shorter wavelengths strongly affected zebrafish behavior, especially after exposure (except for the vertical location). The persistence and magnitude of the effects on zebrafish behavior elicited by different light colors could suggest that dissimilar internal signals of phototransduction are activated by different wavelengths.

Photoreduction of Sm(3+) in Nanocrystalline BaFCl.

We demonstrate that exposure of nanocrystalline BaFCl:Sm(3+) X-ray storage phosphor to blue laser pulses with peak power densities on the order of 10 GW/cm(2) results in conversion of Sm(3+) to Sm(2+). This photoreduction is found to be strongly power-dependent with an initial fast rate, followed by a slower rate. The photoreduction appears to be orders of magnitude more efficient than that for previously reported systems, and it is estimated that up to 50% of the samarium ions can be photoreduced to the divalent state. The main mechanism is most likely based on multiphoton electron-hole creation, followed by subsequent trapping of the electrons in the conduction band at the Sm(3+) centers. Nanocrystalline BaFCl:Sm(3+) is an efficient photoluminescent X-ray storage phosphor with possible applications as dosimetry probes, and the present study shows for the first time that the power levels of the blue light have to be kept relatively low to avoid the generation of Sm(2+) in the readout process. A system comprising the BaFCl:Sm(3+) nanocrystallites embedded into a glass is also envisioned for 3D memory applications.

Speckle-free femtosecond red-green-blue (RGB) source from a fiber laser driven spectrally efficient two zero dispersion wavelength fiber source.

We report a novel ultrafast red-green-blue (RGB) laser source based on second harmonic generation from a two zero dispersion wavelength (TZDW) fiber continuum source. The TZDW fiber source consists of a custom-built Yb:fiber amplifier and a commercially available TZDW photonic crystal fiber (PCF) which enables low noise and efficient frequency conversion from the 1035 nm pump source to two spectrally localized pulses centered at 850 nm and 1260 nm with 39.6% and 33.7% power efficiencies. With angularly multiplexed simultaneous phase matching, we achieve mW average power of red, green and blue pulses at 630 nm, 517 nm and 426 nm from single pass second harmonic generation. With broad RGB bandwidths of 7.4 nm, 3.2 nm and 5.2 nm, the source is inherently speckle-free while maintaining an excellent color rendering capability with higher than 99.7% excitation purity of the RGB color primaries, leading to the coverage of 192% NTSC color gamut (CIE 1976). The reported source features a simple system geometry; its potential in power scaling is discussed with currently available technologies.

Blue Femtosecond Pulse Generated in Periodically Poled Lithium Tantalite

Femtosecond second harmonic generation (SHG) in periodically poled lithium tantalite (PPLT) crystal under conditions of third-order quasi-phase matching is investigated. SHG is easily obtained at average input power of only a few milliwatts. Blue femtosecond pulse is generated by using a PPLT crystal in a simple, single-pass extracavity geometry. The temporal and spectral characteristics of the SHG pulses are presented.

Direct generation of 2-ps blue pulses from gain-switched InGaN VCSEL assessed by up-conversion technique.

Ultra-short pulses in blue region generated from compact and low-cost semiconductor lasers have attracted much attention for a wide variety of applications. Nitride-based vertical-cavity surface-emitting lasers (VCSELs), having intrinsic high material gain and short cavities, favor the generation of ultra-short blue pulses via a simple gain-switching technique. In this study, we fabricated a single-mode InGaN VCSEL consisting of 10-period InGaN/GaN quantum wells (QWs). The output pulses were evaluated accurately with an up-conversion measurement system having time resolution of 0.12 ps. We demonstrated that ultra-short blue pulses, as short as 2.2 ps at 3.4 K and 4.0 ps at room temperature, were generated from the gain-switched InGaN VCSEL via impulsive optical pumping, without any post-processing. The gain-switched pulses we obtained should greatly promote the development of ultra-short blue pulse generation. In addition, this successful assessment demonstrates the up-conversion technique's usefulness for characterizing ultra-short blue pulses from semiconductor lasers.

Characterization of a broadband interferometric autocorrelator for visible light with ultrashort blue laser pulses

We present a compact interferometric autocorrelator that allows the characterization of ultrashort laser pulses in the visible light domain (370–740nm). The presented device uses a GaN photodiode with corresponding two-photon absorption. Different GaN and AlGaN photodiodes were characterized for this purpose. Despite AlGaN diodes have a better matched bandgap for this application, we have found that only the GaN diodes show sufficient nonlinear behavior. Using the autocorrelator we were able to characterize ultrashort frequency doubled Ti:Sapphire laser pulses with a pulse duration down to 18fs in the second harmonic having just a few hundred nanojoules of pulse energy. The broadband behavior and extension towards the UV along with the need for only low energetic pulses are the novelties of this device.

The Use of Solar Radiation by the Photosynthetic Bacterium, Rhodopseudomonas palustris: Model Simulation of Conditions Found in a Shallow Pond or a Flatbed Reactor

Photosynthetic bacteria are attractive for biotechnology because they produce no oxygen and so H2 -production is not inhibited by oxygen as occurs in oxygenic photoorganisms. Rhodopseudomonas palustris and Afifella marina containing BChl a can use irradiances from violet near-UV (VNUV) to orange (350-650 nm) light and near-infrared (NIR) light (762-870 nm). Blue diode-based pulse amplitude modulation technology was used to measure their photosynthetic electron transport rate (ETR). ETR vs Irradiance curves fitted the waiting-in-line model--ETR = (ETRmax × E/Eopt) × exp (1 - E/Eopt). The equation was integrated over pond depth to calculate ETR of Afifella and Rhodopseudomonas in a pond up to 30 cm deep (A376, 1 cm = 0.1). Afifella saturates at low irradiances and so photoinhibition results in very low photosynthesis in a pond. Rhodopseudomonas saturates at ≈15% sunlight and shows photoinhibition in the surface layers of the pond. Total ETR is ≈335 μmol (e(-)) m(-2) s(-1) in NUV + photosynthetically active radiation light (350-700 nm). Daily ETR curves saturate at low irradiances and have a square-wave shape: ≈11-13 mol (e(-)) m(-2) day(-1) (350-700 nm). Up to 20-24% of daily 350-700 nm irradiance can be converted into ETR. NIR is absorbed by water and so competes with the bacterial RC-2 photosystem for photons.

Design Of A Femtosecond Blue Pulse Generation System By Pumping Of Kn Crystal With Cr:LiSAF Lasers

In this paper we described and simulated generation of blue pulse (460nm) by nonlinear KN(KNbO3) crystal ,that pumped by femtosecond diode pumped Cr:LiSAF lasers. Our simulation show that, by focusing of laser oscillator output pulses with characteristics such as 860nm wavelength, 200fs,330MHz repetition rate 14o Pico joule( PJ) energy in KN crystal with 3mm length at 22 0C by 15 mm lens in less than 20 micrometer spot size with single pass produce pulses with 42pJ energy ,425fs , 30% optical efficiency and 1% total efficiency.