Streak Camera Images Research Articles

Chirped fiber Bragg grating detonation velocity sensing

An all optical-fiber-based approach to measuring high explosive detonation front position and velocity is described. By measuring total light return using an incoherent light source reflected from a linearly chirped fiber Bragg grating sensor in contact with the explosive, dynamic mapping of the detonation front position and velocity versus time is obtained. We demonstrate two calibration procedures and provide several examples of detonation front measurements: PBX 9502 cylindrical rate stick, radial detonation front in PBX 9501, and PBX 9501 detonation along curved meridian line. In the cylindrical rate stick measurement, excellent agreement with complementary diagnostics (electrical pins and streak camera imaging) is achieved, demonstrating accuracy in the detonation front velocity to below the 0.3% level when compared to the results from the pin data. Finally, an estimate on the linear spatial and temporal resolution of the system shows that sub-mm and sub-μs levels are attainable with proper consideration of the recording speed, detection sensitivity, spectrum, and chirp properties of the grating.

Nearly Temperature‐Independent Threshold for Amplified Spontaneous Emission in Colloidal CdSe/CdS Quantum Dot‐in‐Rods

Nearly Temperature‐Independent Threshold for Amplified Spontaneous Emission in Colloidal CdSe/CdS Quantum Dot‐in‐Rods

Synchroscan streak camera imaging at a 15-MeV photoinjector with emittance exchange

At the Fermilab A0 photoinjector facility, bunch-length measurements of the laser micropulse and the e-beam micropulse have been done in the past with a fast single-sweep module of the Hamamatsu C5680 streak camera with an intrinsic shot-to-shot trigger jitter of 10–20ps. We have upgraded the camera system with the synchroscan module tuned to 81.25MHz to provide synchronous summing capability with less than 1.5ps FWHM trigger jitter and a phase-locked delay box to provide phase stability of ∼1ps over 10s of minutes. These steps allowed us to measure both the UV laser pulse train at 263nm and the e-beam via optical transition radiation (OTR). Due to the low electron beam energies and OTR signals, we typically summed over 50 micropulses with 0.25–1nC per micropulse. The phase-locked delay box allowed us to assess chromatic temporal effects and instigated another upgrade to an all-mirror input optics barrel. In addition, we added a slow sweep horizontal deflection plug-in unit to provide dual-sweep capability for the streak camera. We report on a series of measurements made during the commissioning of these upgrades including bunch-length and phase effects using the emittance exchange beamline and simultaneous imaging of a UV drive laser component, OTR, and the 800nm diagnostics laser.

Band-Edge Exciton Fine Structure of Small, Nearly Spherical Colloidal CdSe/ZnS Quantum Dots

The exciton fine structure of small (2-3.5 nm) wurtzite (WZ) and zincblende (ZB) CdSe quantum dots (Qdots) has been investigated by means of nanosecond and picosecond time-resolved photoluminescence spectroscopy, at temperatures ranging from 5 K to room temperature. For both crystal structures, we observe a similar dark-bright energy level splitting of 2.4-5 meV, with a larger splitting corresponding to smaller Qdots. In addition, spectrally resolved streak camera images collected at 5 K reveal the presence of a third state, split from the lower dark-bright manifold by 30-70 meV, again independently of the crystal structure of the Qdots. The data thus reveal that small WZ and ZB CdSe Qdots are optically indistinguishable. This contrasts with theoretical calculations within the effective-mass approximation, which, in the limit of spherical Qdots, yield a different fine structure for both. However, experimental and theoretical results converge when taking the Qdot shape into account. With transmission electron microscopy, we determined that our Qdots are prolate, with an aspect ratio of 1.15:1. Incorporating this value into our calculations, we obtain a similar fine structure for both WZ and ZB Qdots. Moreover, the opposite sign of the crystal field and shape anisotropy in CdSe suggests that the lowest energy level in small CdSe Qdots has an angular momentum projection F = 0, in contrast with (perfectly) spherical Qdots, where the lowest level corresponds to the dark ±2 state. From the experimental and theoretical data we conclude that shape anisotropy and exchange interactions dominate over the crystal field anisotropy-induced splitting in this size range.

Preheating of a target by laser radiation through plasma and polymer aerogel

Processing of X-ray and optical streak-camera images after brightness amplification 5 proves unambiguously the existence of a preheating of the foil in two-layer targets (polymer aerogel plus Al foil). We observed this effect earlier at the accuracy limit of the experiment. Preheating may be explained by the initial transmission of laser radiation by an inhomogeneous plasma and aerogel remnants. The fraction of laser energy that passed through a microheterogeneous plasma to the foil or shell is small in comparison with the total energy in the pulse, but it comes to the target (foil or shell) at the initial period of the laser pulse and can be significantly affected by the dynamics of plasma and the efficiency of spherical cryogenic thermonuclear targets.

Development of Vacuum Ultraviolet Streak Camera System for the Evaluation of Vacuum Ultraviolet Emitting Materials

Details of the design and development of a bright vacuum ultraviolet Seya–Namioka type spectrometer and streak camera system with reflection-type input optics is presented. The Seya–Namioka spectrometer has a 40 mm by 45 mm holographic grating with a groove density of 600 grooves/mm, linear dispersion of 8 nm/mm, and effective F-number of 4.2. To eliminate loss of light by absorption, the streak camera imaging unit uses Al and MgF2 coated imaging optics with at least 80% reflection from 125–850 nm and has an effective F-number of 4. It is equipped with a synchronized scan unit that can be tuned to 82 MHz and a slow scan speed unit that can measure up to 2-MHz single event. Temporal response of the system at the 20-ns scanning range is evaluated to be around 260 ps.

Using a Streak Camera to Resolve the Motion of Molecular Excited States with Picosecond Time Resolution and 150 nm Spatial Resolution

A one-dimensional streak camera imaging (1D-SCI) experiment to visualize the spatial motion of luminescent excited-state species in condensed phase systems is presented. A femtosecond pulse is focused through an objective lens to create a localized excited-state population, using either one-photon or two-photon excitation conditions. The time-dependent emission from this spot is then imaged onto the horizontal entrance slit of a streak camera. The resulting one-dimensional projection of the emission spot is detected with picosecond time resolution. Using this setup, the ability to resolve broadening of the excitation spot due to diffusive motion on the order of 150 nm is demonstrated. The 1D-SCI technique is successfully employed to image the translational diffusion of excited-state platinum octaethylporphyrin molecules in a toluene solution at various concentrations. In addition, the absence of long-range (>1 μm) electronic energy transfer in the polymer polyvinylcarbazole is confirmed. In both of these ...

Nanosecond Monitoring of Lateral Crystallization Dynamics Induced by ELA

In this paper we report the direct observations of the lateral crystallizing process induced by single-pulse excimer laser annealing (ELA) for the first time. In order to modulate a beam profile on amorphous-silicon thin films intentionally, a mask projection type ELA system was used. Incorporating an optical microscope, a high speed gated image intensifier and a streak camera imaging system, a novel measuring system successfully revealed the dynamic lateral motion of liquid-solid Si interface with micrometer spatial resolution and nanosecond time domain. Furthermore, it was confirmed that the obtained streak images were well consistent with the simulated beam profiles to induce lateral growth crystallization, and the lateral solidifying velocity of 13m/sec was directly measured when 4μm-long grain had grown by phase-modulated excimer laser annealing (PMELA) method.

Bunch-by-bunch linac beam energy profile diagnostics using storage ring phase rotation and synchrotron radiation

This paper reports a new method of measuring the bunch-by-bunch energy profile of a linear accelerator (linac) electron beam, using a dual-sweep streak camera in the storage ring. This method records the evolution of the time profile in the storage ring following injection. A high-resolution linac beam energy profile is reconstructed from the time profile measured at one-quarter of a synchrotron oscillation period following injection. Conversion between the time profile and energy profile is based on results from a longitudinal phase space tracking simulation. By separating the streak camera images of the different bunches, a bunch-by-bunch energy profile can also be measured.

Analysis of L -shell line spectra with 50-ps time resolution from Mo X -pinch plasmas.

Mo wire X pinches typically emit several x-ray bursts from a bright spot near the crossing of the X -pinch wires. Streak camera images of L -shell line emission from Mo wire X pinches have been analyzed using a non-local thermodynamic equilibrium (NLTE) collisional-radiative atomic kinetics model, providing temperature and density profiles with approximately 50 ps time resolution over the approximately 350 ps x-ray bursts. In conjunction with nonspectroscopic measurements, the analysis is used to propose a picture of the dynamic evolution of the X -pinch plasma. The L -shell spectra from the first x-ray burst indicate an electron density near 10(22) cm(-3) and an electron temperature near 1 keV; subsequent x-ray bursts have L -shell spectra that indicate electron temperatures slightly above 1 keV and electron densities near 10(20) and 10(21) cm(-3). The size of the L -shell line-emitting region is estimated to be near 10 microm for the first x-ray burst and much larger for the later bursts. It is proposed that inner-shell excitation of low ionization stages of Mo in a microm -scale plasma region contributes to the observed radiation from the first micropinch, which typically emits a short burst of >3 keV radiation and has L -shell spectra characterized by broad spectral lines overlaying an intense continuum.

Streamerless guided electric discharges triggered by femtosecond laser filaments

The time evolution of electrical discharges induced and guided between the cathode of a Van de Graf generator and a ground sphere was studied using a 100 fs Ti:Sapphire laser. Nonlinear focusing and ionization effects produce optical and plasma filaments in the discharge region. Streak camera images often exhibit streamers that propagate towards the cathode, but sudden discharge triggering is frequently observed with no streamer precursors. The typical discharge triggering delay time was measured to be 150 ns. Similar time delays were obtained from an air chemistry code used to model the long time behavior of the plasma induced by the short laser pulse. The model shows that ohmic heating of the filament plasma persists over long time scales and inhibits the decay of electron density due to recombination and attachment processes. Eventually the rise in electron temperature causes the avalanche rate to increase to the point where breakdown occurs. The hydrodynamic density reduction process reported by Tzortzakis et al. [Phys. Rev. E 64, 057401 (2001)] is also taken into consideration. Its main effect is found to be a hastening of the breakdown process.

Geometric deformation measurement and correction applied to dynamic streakcamera images

The complete procedure of measuring and correcting geometric deformationsencountered with dynamic streak camera images in the picosecond range ispresented and discussed. First, we describe the experimental setup derived fromthe well known spacing calibration grid method. The implemented measurementbench, adapted to time-resolved 1D imaging, notably exhibits a greataccuracy and repeatability both in space and time thanks to a three-axismotorized translation stage and programmable delay lines. Second, we examineimage restoration by two different analytical transform means (local versusglobal): results and performances of both are compared. Then we dealwith final image reconstruction performed by an original method of localC22spline interpolation.

Study on time of flight property of uniform magnetic sector field analyzers up to the third-order approximation

Time of flight (TOF) is an important concept in many electron optical instruments including TOF analyzers and streak camera image tubes. In this article, successive approximation approach is applied to study the TOF properties of uniform magnetic sector field analyzers. The charged particle trajectories in the magnetic field analyzers are calculated up to the third-order approximation and the corresponding solutions are obtained. Therefore, the TOF properties of the uniform magnetic sector field analyzers are analytically derived up to the third-order approximation.

A Thomson scattering post-processor for the MEDUSA hydrocode

In order to understand the physical processes that occur in laser-produced plasmas it is necessary to diagnose the time-dependent hydrodynamic conditions. Thomson scattering is, in principle, an ideal diagnostic as it provides a non-intrusive method of measuring ion and electron temperature, electron density, plasma velocity, and heat flow. We describe here a post-processor for the MEDUSA hydrocode that simulates streak camera images of the Thomson spectra. The post-processor can be used in three ways: (1) creating simulated streak camera images that can be compared directly with experimental data, (2) evaluating experimental designs to determine the viability of the Thomson scattering diagnostic, and (3) as an automated data analysis routine for extracting hydrodynamic parameters from a calibrated experimental streak camera image.

Investigation of the mechanism for current switching from the outer gas puff to the inner wire array in a structured Z-pinch

Experiments are reported on the implosion of structured loads with outer argon, krypton, and xenon gas puffs and an inner tungsten multiwire array. Experiments were carried out in the GIT-12 generator with a current of 2.6 MA and a current rise time of 270 ns. It is shown that the current successfully switches to the wire array only when the gas puff is sufficiently light. The total implosion time is 300 ns, and the implosion time of a wire array, determined from streak camera images, is 50–70 ns. It is suggested that the switching is efficient only when the active impedance of the gas puff is higher than the transitional resistance of the electrically exploded wires.

Picosecond photoexcitation dynamics in poly(3-butyl-thiophene) films

We have studied photoexcitation dynamics in thin films of poly(3-butyl-thiophene) [P3BT] using ps transient and cw photomodulation techniques, streak camera imaging, electroabsorption and optically detected magnetic resonance spectroscopies. We have determined that intrachain excitons are the primary photoexcitations with a characteristic transient photomodulation spectrum consisting of two photoinduced absorption bands in the near IR spectral range and a broad stimulated emission band in the visible spectral region. The photogenerated excitons are relatively short-lived (150 ps) and can subsequently decay into polaron pairs and triplets, which are longer-lived excitations with lifetimes of order ms. We do not find stimulated emission in very thin P3BT films and this is attributed to high defect concentration close to the film surface.

GAS EMBEDDED COMPRESSIONAL Z-PINCH IN H2 AND D2

Recent experiments in a gas embedded compressional Z-pinch are presented. The experiments have been carried out in H2 and D2, using a pulse power generator capable of delivering a dI/dt ≥ 1012 A/s. The pinch is initiated by a focused laser pulse, which is coaxial with a cylindrical DC microdischarge. This configuration results in double column pinch at early times, which at current rise evolves into a gas embedded compressional Z-pinch. Diagnostics used are Rogowskii coil, single frame holographic interferometry and holographic shadowgraphy, visible streak camera images from which, current, density, line density, pinch radius and plasma motion are obtained. The pinch is characterised by a maximum on axis density which is much higher than the expected value from filling pressure, with a Bennett temperature of 75 eV at 180 kA.

Neutron-induced noise in National Ignition Facility-class diagnostic instruments

Neutron yields from deuterium–tritium-filled inertial-confinement-fusion targets have reached 1014. Above 1013, a significant neutron-induced background appears in images recorded with nearby streak cameras. Since camera components (streak tube, image-intensifier tube, and charge coupled device arrays) are similar to components that will be used in many National Ignition Facility (NIF) instruments, streak camera images provide information about neutron-induced backgrounds that will be encountered in the NIF environment. At a fluence of 107 neutrons/cm2, the background consists of two distinct components: a uniform component equal to nearly 20% of the camera’s linear range and sharp, intense spikes each localized to just a couple of image pixels. About 80% of the uniform background is caused by interactions with the streak tube and image-intensifier tube. Nearly all the sharp spikes are caused by interactions with pixels of the charged-coupled device array. The spikes make the most significant contribution to image noise.

Precise analysis of linear and non-linear chirp parameters of gain-switched distributed feedback laser pulses for the fibre optic compression scheme

Not only linear but also non-linear chirp parameters of a gain-switched distributed feedback (DFB) laser diode (LD) were analysed precisely. For this purpose a method has been developed to determine chirp characteristics from spectrally resolved streak camera images using the short time Fourier transform (STFT) scheme. Using this method a systematic study was carried out also on the dependence of the chirp parameters on the LD driving conditions, through which the importance and preliminary principles of chirp control for the fibre optic compression scheme were clarified.

Dynamics and stability of an expanding laser-induced plasma in a low-density gas

Experimental studies of a laser-produced metal plasma expansion into a gas with a mass density of 0.1--30 \ensuremath{\mu}g/${\mathrm{cm}}^{3}$ have been performed using streak-camera imaging. The results show that plasma expansion dynamics can be described by a snowplow model with a dimension factor dependent on the laser focal spot shape. It has been shown that the plasma boundary becomes unstable at the moment of maximum deceleration (of the order of 10 cm/\ensuremath{\mu}${\mathrm{s}}^{2}$), and the evolution of boundary perturbation has been monitored. An explanation of the observed effect on the basis of Rayleigh-Taylor instability is proposed and confirmed by comparison of simple model predictions with experimental evidence. The evolution of the plasma-front profile has been observed for the times 0t10${\ensuremath{\gamma}}^{\mathrm{\ensuremath{-}}1}$, where \ensuremath{\gamma} is the instability increment. Competition of different unstable modes has been observed.