Streak Camera Technique Research Articles

Characterization of single-shot attosecond pulses with angular streaking photoelectron spectra

Most of the traditional attosecond pulse retrieval algorithms are based on a so-called attosecond streak camera technique, in which the momentum of the electron is shifted by an amount depending on the relative time delay between the attosecond pulse and the streaking infrared pulse. Thus, temporal information of the attosecond pulse is encoded in the amount of momentum shift in the streaked photoelectron momentum spectrogram $S(p,\ensuremath{\tau})$, where $p$ is the momentum of the electron along the polarization direction and $\ensuremath{\tau}$ is the time delay. An iterative algorithm is then employed to reconstruct the attosecond pulse from the streaking spectrogram. This method, however, cannot be applied to attosecond pulses generated from free-electron x-ray lasers where each single shot is different and stochastic in time. However, using a circularly polarized infrared laser as the streaking field, a two (or three)-dimensional angular streaking electron spectrum can be used to retrieve attosecond pulses for each shot, as well as the time delay with respect to the circularly polarized IR field. Here we show that a retrieval algorithm previously developed for the traditional streaking spectrogram can be modified to efficiently characterize single-shot attosecond pulses. The methods have been applied to retrieve 188 single shots from recent experiments. We analyze the statistical behavior of these 188 pulses in terms of pulse duration, bandwidth, pulse peak energy, and time delay with respect to the IR field. The retrieval algorithm is efficient and can be easily used to characterize a large number of shots in future experiments for attosecond pulses at free-electron x-ray laser facilities.

Single-shot compressed ultrafast photography: a review

Compressed ultrafast photography (CUP) is a burgeoning single-shot computational imaging technique that provides an imaging speed as high as 10 trillion frames per second and a sequence depth of up to a few hundred frames. This technique synergizes compressed sensing and the streak camera technique to capture nonrepeatable ultrafast transient events with a single shot. With recent unprecedented technical developments and extensions of this methodology, it has been widely used in ultrafast optical imaging and metrology, ultrafast electron diffraction and microscopy, and information security protection. We review the basic principles of CUP, its recent advances in data acquisition and image reconstruction, its fusions with other modalities, and its unique applications in multiple research fields.

DNA-Directed Artificial Light-Harvesting Antenna

Designing and constructing multichromophoric, artificial light-harvesting antennas with controlled interchromophore distances, orientations, and defined donor-acceptor ratios to facilitate efficient unidirectional energy transfer is extremely challenging. Here, we demonstrate the assembly of a series of structurally well-defined artificial light-harvesting triads based on the principles of structural DNA nanotechnology. DNA nanotechnology offers addressable scaffolds for the organization of various functional molecules with nanometer scale spatial resolution. The triads are organized by a self-assembled seven-helix DNA bundle (7HB) into cyclic arrays of three distinct chromophores, reminiscent of natural photosynthetic systems. The scaffold accommodates a primary donor array (Py), secondary donor array (Cy3) and an acceptor (AF) with defined interchromophore distances. Steady-state fluorescence analyses of the triads revealed an efficient, stepwise funneling of the excitation energy from the primary donor array to the acceptor core through the intermediate donor. The efficiency of excitation energy transfer and the light-harvesting ability (antenna effect) of the triads was greatly affected by the relative ratio of the primary to the intermediate donors, as well as on the interchromophore distance. Time-resolved fluorescence analyses by time-correlated single-photon counting (TCSPC) and streak camera techniques further confirmed the cascading energy transfer processes on the picosecond time scale. Our results clearly show that DNA nanoscaffolds are promising templates for the design of artificial photonic antennas with structural characteristics that are ideal for the efficient harvesting and transport of energy.

Higher-Order Photon Bunching in a Semiconductor Microcavity

Quantum mechanically indistinguishable particles such as photons may show collective behavior. Therefore, an appropriate description of a light field must consider the properties of an assembly of photons instead of independent particles. We have studied multiphoton correlations up to fourth order in the single-mode emission of a semiconductor microcavity in the weak and strong coupling regimes. The counting statistics of single photons were recorded with picosecond time resolution, allowing quantitative measurement of the few-photon bunching inside light pulses. Our results show bunching behavior in the strong coupling case, which vanishes in the weak coupling regime as the cavity starts lasing. In particular, we verify the n factorial prediction for the zero-delay correlation function of n thermal light photons.

The Complex Excited-state Behavior of a Polyspirobifluorene Derivative: The Role of Spiroconjugation and Mixed Charge Transfer Character on Excited-state Stabilization and Radiative Lifetime

In this study, we report on the unusual fluorescence decay of an alkoxy-substituted polyspirobifluorene. Excited state behavior has been probed as a function of time, using femtosecond photobleaching, single photon counting, and streak camera techniques. Unusually complex decay kinetics are observed, which strongly depend on solvent viscosity and polarity, featuring decay components in both the tens of picoseconds and in the nanosecond time domain. These findings are explained by the consequences of spiroconjugation in combination with excited-state conformational relaxation. We propose that exciton wave function delocalization into the spiro units effectively traps the exciton, allowing it to relax further into a highly emissive state with a very long lifetime as compared to non-spiroconjugated polymer analogues. Frontier molecular orbitals and exciton orbitals have been calculated using a first principles density functional theory (DFT) approach. These results confirm the importance of spiroconjugation as both the highest occupied molecular orbital (HOMO) and the (lowest) exciton level are not localized on the polymer backbone but strongly extend into the side fluorene groups of the spirobifluorene units. The results of our calculations are very sensitive to the substitution pattern on the spirobifluorene units, in particular when oxygen is included. This finding may lead to new materials of this kind with optimized charge carrier transport properties and high luminescence quantum yields.

Study on time-resolved fluorescence dynamics of cyanine dye sensitizing AgBr

The fluorescence spectra of three different dyes adsorbed on the tabular and cubic AgBr microcrystals are obtained by the picosecond time-resolved streak camera technique. The dependence of the ultrafast electron transferring from dye-aggregates to the conduction band of AgBr and the efficiency of spectral sensitization on different kinds of dyes with different concentrations is analyzed. Further more, the microcosmic mechanism of the sensitization process is discussed. It is found that the fluorescence decay curves are fitted very well by the double exponential function, consisting of a slow component and a fast one with large amplitude. We consider this fast one mainly attributable to the electron transfer from dye J-aggregates to the conduction band of AgBr.

Time- and frequency-domain measurements of carrier lifetimes in GaN epilayers

Abstract Results on time-resolved study of GaN photoluminescence (PL) in a power density range from 0.5 mW/cm2 under CW excitation by ultraviolet light emitting diode (UV LED) to 1 GW/cm2 under pulsed excitation by YAG:Nd laser in the temperature range from 8 to 300 K are presented. Measurements of PL response in the frequency domain by using amplitude-modulated emission of a UV LED as well as time-resolved PL measurements using a streak camera and light-induced transient grating technique have been used in the study. Yellow luminescence (YL) intensity increases with increasing temperature up to ∼120 K and faster components in YL decay switch to slower components with increasing temperature under UV LED excitation. At low carrier densities, the trapping decreases the carrier lifetime below 250 ps, while the carrier lifetime in the same GaN sample under excitation ensuring saturation of the traps equals 2 ns.

Dynamics of conformational relaxation in photoexcited oligofluorenes and polyfluorene

In order to disentangle the relaxation effects of exciton migration and conformational rearrangement, a comparative study of a polyfluorene derivative and short oligofluorenes is carried out. We probe their long-time time-dependent relaxation in dilute solution using picosecond single photon counting and streak camera techniques. Conformational relaxation is found in oligo- and polyfluorenes. Oligofluorene relaxation is purely conformational: time scales vary between 10 and $300\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ becoming faster with decreasing chain length and solvent viscosity or increasing temperature. While a rigid ladder-type polymer in solution does not show any picosecond relaxation, polyfluorene in solution exhibits fluorescence dynamics indicating both, conformational relaxation and exciton migration.

Femtosecond single electron bunch generation by rotating longitudinal bunch phase space in magnetic field

A femtosecond (fs) electron bunching was observed in a photoinjector with a magnetic compressor by rotating the bunch in longitudinal phase space. The bunch length was obtained by measuring Cherenkov radiation of the electron beam with a femtosecond streak camera technique. A single electron bunch with rms bunch length of 98 fs was observed for a 32 MeV electron beam at a charge of 0.17 nC. The relative energy spread and the normalized transverse emittance of the electron beam were 0.2% and 3.8 mm-mrad, respectively. The effect of space charge on the bunch compression was investigated experimentally for charges from 0.17 to 1.25 nC. The dependences of the relative energy spread and the normalized beam transverse emittance on the bunch charge were measured.

Bunch Length Monitor Using Two-Frequency Analysis for RF Gun System

An rms (root mean square) bunch length monitor for a laser-driven photocathode rf gun system based on a two-frequency analysis technique has been developed. Typically, the photoelectron beam generated from the rf gun system has an energy of 3–5 MeV and an rms bunch length smaller than 20 ps down to 3–4 ps. This monitor is suitable for such electron beam measurement. The rms bunch length as a function of rf phase was experimentally measured using both the rms bunch length monitor and streak camera technique using a 50 MeV electron beam at the KEK accelerator test facility (KEK-ATF) injector section which has an rf gun system and a 3-m-long accelerator structure. A numerical simulation study was also performed using the PARMELA code. The availability of this monitor was clearly verified by comparing the results. Consequently, this monitor was installed in the rf gun system at Waseda University and the rms bunch length measurement for a 3.5 MeV electron beam was precisely performed using the monitor.

Development of wide-field, multi-imaging x-ray streak camera technique with increased image-sampling arrays

In order to enlarge the field of view of a multi-imaging x-ray streak (MIXS) camera technique [H. Shiraga et al., Rev. Sci. Instrum. 66, 722 (1995)], which provides two-dimensionally space-resolved x-ray imaging with a high temporal resolution of ∼10 ps, we have proposed and designed a wide-field MIXS (W-MIXS) by increasing the number of image-sampling arrays. In this method, multiple cathode slits were used on the photocathode of an x-ray streak camera. The field of view of the W-MIXS can be enlarged up to 150–200 μm instead of ∼70 μm for a typical MIXS with a spatial resolution of ∼15 μm. A proof-of-principle experiment with the W-MIXS was carried out at the Gekko-XII laser system. A cross-wire target was irradiated by four beams of the Gekko-XII laser. The data streaked with the W-MIXS system were reconstructed as a series of time-resolved, two-dimensional x-ray images. The W-MIXS system has been established as an improved two-dimensionally space-resolved and sequentially time-resolved technique.

Time-resolved, two-dimensional electron-temperature distribution of laser-imploded core plasmas

We have developed a multichannel, multiimaging x-ray streak camera technique to measure two-dimensional electron-temperature distributions with a high temporal resolution by adding a multichannel spectrum selection capability to a multiimaging x-ray streak camera technique, and applied it to direct-drive implosion experiments with partially coherent light at Gekko-XII laser facility. It was found that electron-temperature distributions in the laser-imploded core plasmas of ICF targets had low-mode nonuniform structures changing with a temporal scale of 20 ps, and the abrupt drop of the electron temperature appeared in the deceleration phase. We have compared temporal profiles of the experimentally observed x-ray intensity and electron-temperature with those predicted by a one-dimensional hydrodynamic code “ILESTA” to investigate the hot spark heating in the core plasmas.

Initial time-resolved particle beam profile measurements at the Advanced Photon Source

The commissioning of the 7-GeV Advanced Photon Source (APS) storage ring began in early 1995. Characterization of the stored particle beam properties involved time-resolved transverse and longitudinal profile measurements using optical synchrotron radiation (OSR) monitors. Early results include the observation of the beam on a single turn, measurements of the transverse beam sizes after damping using a 100 μs integration time (σx∼150±25 μm, σy∼65±25 μm, depending on vertical coupling), and measurement of the bunch length (στ ∼25 to 55 ps, depending on the charge per bunch). The results are consistent with specifications and predictions based on the 8.2 nm-rad natural emittance, the calculated lattice parameters, and vertical coupling less than 10%. The novel, single-element focusing mirror for the photon transport line and the dual-sweep streak camera techniques, which allow turn-by-turn measurements, will also be presented. The latter measurements are believed to be the first of their kind on a storage ring in the USA.

Recent developments in LIDAR Thomson scattering measurements on JET (invited)

The LIDAR Thomson scattering technique uses the time of flight of a short laser pulse to spatially resolve measurements of electron temperature (Te) and density (ne) in a plasma. The technique was pioneered at JET and the first profiles were obtained in 1986. The initial system used a 3 J, 0.5 Hz, 300 ps ruby laser and microchannel-plate photomultiplier detectors to make Te and ne profile measurements with ∼10 cm spatial resolution. Since then we have sought to improve both the spatial resolution and frequency of measurement during a JET pulse. It has proved possible to develop a 4 Hz version of the ruby laser and to enhance the rate of cycling of detection and digitizing to match. The main LIDAR system has now been upgraded to 4 Hz and first JET profiles obtained with the new system are presented. For a LIDAR system, the spatial resolution δL along the laser path is given by δL=(c/2)(τ2L+τ2D)1/2, where c is the velocity of light, τL the laser pulse width, and τD the detection system response time. Over a limited spatial extent it is possible to improve spatial resolution by using a streak camera detection system. We have successfully improved the spatial resolution by a factor of 2 by setting up a streak camera detection system in parallel with the main photomultiplier system. The much shorter response time of the streak camera gave ∼5 cm resolution over a 75 cm segment of the ∼2 m plasma diameter. This system was used to examine profile details in the outer part of the JET plasma. Results from this high-resolution LIDAR detection system will be presented. Building on the improved spatial resolution obtained with the streak camera technique, we have now designed and installed a new LIDAR scattering system to diagnose the divertor region of the JET plasma. The laser for the new system is again ruby but uses a different principle to obtain short pulses. We have demonstrated with colleagues from the Troitsk Institute the conversion, using SBS pulse compression, of a standard 25 ns ruby laser into a 300 ps system suitable for LIDAR applications. The main components of the JET Divertor LIDAR system are also described.

Ultrafast Fluorescence Spectroscopy of PPV

Abstract The spectrally resolved decay of photoluminescence in PPV - type conjugated polymers has been measured employing fluorescence-up-conversion and Streak-camera techniques. The results are in account with the concept of stochastic excitation transport amoung an energetically disordered manifold of chromophores, identified as subunits of the polymer chain comprising several repeat units. They demonstrate that the primary excitations are of excitonic origin.

Dynamics of singlet excitations in conjugated polymers: Poly(phenylenevinylene) and poly(phenylphenylenevinylene).

The decay of the photoluminescence of the conjugated polymers, poly(phenylenevinylene), poly(phenylphenylenevinylene) (PPV), and PPPV blended with polycarbonate is measured as a function of the position of the spectral detection window employing frequency-up-conversion and streak-camera techniques. Upon probing at the high-energy side of the inhomogeneously broadened ${\mathit{S}}_{1}$\ensuremath{\leftarrow}${\mathit{S}}_{0}$ 0-0 transition, an initial falloff characterized by a (1/e) decay time of about 300 fs is observed. This decay slows down by three orders of magnitude upon shifting the detection window towards lower energies. We present a quantitative analysis of these experimental data by performing simulations of dipole-dipole excitation transfer on a random lattice chain with energetic site disorder. They give evidence for the notion that photon absorption generates neutral excitation undergoing a random walk among segments of the polymer chain with different excitation energies.

The next generation of rf FEL (free electron laser) diagnostics: synchroscan and dual-sweep streak camera techniques

Time-resolved experiments on rf-linac driven free electron laser (FEL) experiments have recently been extended to displaying both the submicropulse and submacropulse effects. By using a synchroscan sweep on a streak camera, key rf phase effects can be studied, and an additional dual sweep feature can provide this information during the macropulse. Successful measurements to date on the Los Alamos and the Boeing FELs include electron-beam micropulse bunching during a macropulse, phase stability effects, micropulse elongation and transit time in a photo-injector, drive-laser phase stability and FEL output evolution. Several of these measurements are the first of their kind on a FEL system.

Multiphonon dephasing of the 1086-cm-1 mode in calcite.

The dephasing time of the 1086-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ mode in calcite has been measured as a function of temperature using a new, innovative single-shot streak-camera technique that measures the phonon dephasing rate in real time. Phonon-phonon interaction models have been proposed and tested to explain the temperature dependence of the experimentally measured dephasing time. It is found that multiphonon splitting and scattering processes involving at least four phonons substantially contribute to the dephasing of the 1086-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ mode in calcite.

Application of streak camera photography for the study of shock wave reflections over a double wedge

The streak camera technique was employed to investigate the reflection process of a planar shock wave over a double wedge. It is shown that this technique is superior to others in precisely determining whether a Mach reflection is direct, stationary or inverse. Furthermore, it provides an excellent means of exactly determining the location of the regular to Mach reflection transition over a double wedge.

Observation of the diffusion-free intermolecular excimer of 9-methyladenine in aqueous solution by picosecond time-resolved spectroscopy

Diffusion-free intermolecular excimer formation in liquid solution is observed for an aqueous solution of 9-methyladenine using the synchroscan streak camera technique. The excimer fluorescence (330 ps lifetime) appears at 380 nm, at longer wavelength than the monomer fluorescence (5 ps lifetime). The excimer is formed via a weakly coupled stacking dimer composed of ground-state monomers.