Synchroscan Streak Camera Research Articles

Potential diagnostics for the next-generation light sources

There is continued interest in developing a diffraction-limited soft or hard X-ray source. Candidate paths include the storage-ring-based free-electron laser (FEL) and the linac-based self-amplified spontaneous emission (SASE) FEL for the two regimes, respectively. As previously discussed, target beam parameters are σ x,y∼10 μm, σ x′,y′=1 μrad , and σ t ∼1 ps (0.1 ps for the linac case). We report the use of few- to sub-angstrom radiation emitted by a 7-GeV beam transitting a 198-period diagnostics undulator and a bending magnet to characterize the particle beam. A particle beam divergence as low as σ y′=3.3 μrad was measured using an X-ray monochromator. Additionally, a particle beam size of σ y<45 μm and a bunch length of σ t=28 ps with 4-ps resolution were measured using an X-ray pinhole camera with a unique synchroscan and dual-sweep X-ray streak camera as the detector. The adjustable pinhole aperture was varied by more than a factor of 100 to assess spatial resolution and dynamic range issues in the system. These diagnostics demonstrations should scale to next-generation applications.

Use of Few-Angstrom Radiation Imaging to Characterize Ultrabright, Multi-GeV Particle Beams

We have used the 7-GeV stored positron beam at the Advanced Photon Source to approximate relevant particle beam parameters of a diffraction-limited x-ray source and to perform measurements of few- to sub-angstrom radiation. Results are based on the 198-period diagnostics undulator optimized for low-divergence radiation cones ({approximately}{number_sign}{number_sign}2.6 {mu}rad) at {lambda}{approximately}0.5 {Angstrom} on the fundamental and on a unique synchroscan and dual-sweep x-ray streak camera (with a few picosecond resolution) that was phase locked to the accelerator`s master oscillator subharmonic. Scaling of these techniques to future sources is presented. {copyright} {ital 1999} {ital The American Physical Society}

Biomolecular electron transfer under high hydrostatic pressure

The dependence of the photoinduced electron transfer rate on hydrostatic pressure up to 8 kbar was studied at 295 K in a bridged Zn-porphyrin donor and pyromellitimide acceptor supermolecule dissolved in toluene. A picosecond fluorescence emission kinetics of the donor, limited by the electron transfer rate, was detected by using synchroscan streak camera. The experiment was complemented with model calculations based on modified classical and semi-classical nonadiabatic electron transfer theory. A peculiar asymmetric inverted parabola-like dependence of the electron transfer rate on pressure was observed. The dependence was successfully reproduced by nonadiabatic theory in the high-temperature limit assuming that the reorganisation free energy or both the reorganisation free energy and the reaction driving force (linearly) changed with pressure. The reaction driving force dependence on pressure alone failed to explain the asymmetry, suggesting that the electron transfer was accompanied with vibration frequency changes. It was inferred that the effective frequency in the product state should be larger than in the reactant state. The usage of the nonadiabatic theory is well justified due to the fulfilment of the inequalities V《 k B T and V《〈 τ L〉 −1 ( V is the electronic coupling matrix element, 〈 τ L〉 −1 is the solvent relaxation rate). The influence of the donor-acceptor distance reduction under compression on the electron transfer rate was found to be minor.

Synchronisation of subterahertz optical pulse trainfromPLL-controlled colliding pulse modelocked semiconductor laser

The synchronisation of a 192 GHz optical pulse train, generated from a colliding pulse modelocked laser diode, to an electrical signal is successfully demonstrated by a phase-locked loop that uses optical modulation sidebands. The synchronisation is confirmed by a synchro-scan streak camera and the timing jitter is estimated to be 0.6 ps from the RF line spectrum of the beat note between the high-order sidebands generated by 40 GHz electroabsorption modulation.

Multidimensional fluorescence spectroscopy using a streak camera based pulse fluorometer

Modern streak camera based pulse fluorometers readily allow data collection in two-dimensions. We have developed a modular instrument that is easily adapted for recording time-resolved emission spectra, fluorescence depolarization data, and time series of time-resolved fluorescence decays. The instrument is based on a synchroscan streak camera and a passively mode-locked Ti:Sapphire laser using second harmonic generation and third harmonic generation to extend the excitation wavelength range to the visible and ultraviolet. The performance of the instrument was tested using standard biological samples. The dynamic range is typically 600:1, and the detection limit is less than 1 fW. With respect to the fluorescence decay kinetic (first time axis), the temporal resolution is better than 10 ps, and rotational correlation times of 50 ps are measured routinely. For the second time axis, the maximum time resolution is approximately 2 ms.

Synchronised pulse-train generation from passivelymode-locked semiconductor lasers by a phase-locked loop using optical modulationsidebands

The authors present a novel phase-locked loop for synchronising ultra-fast, passively mode-locked semiconductor lasers to an electrical signal. The loop uses beat signals between locked modes and their optical modulation sidebands. A 36.6 GHz rate pulse train is synchronised and measured with a synchro-scan streak camera for the first time.

Test of the deterministic conjecture for the instantaneous time phase fluctuations of an oscillator

The fluctuations observed by recording the picosecond pulses of a mode-locked laser with a synchroscan streak camera are due to the laser jitter and to the variations of the zero crossing of the synchronization. By means of a simple model, it is shown that the dispersions measured when the synchronization is generated from the mode-locker oscillator reflect the instantaneous time phase fluctuations of this oscillator. From the study of the experimental recordings with methods of time series analysis it results that the phase noise of the electronic oscillator is consistent with an underlying low-dimensional strange attractor.

Characterization of female breasts in vivo by time-resolved and spectroscopic measurements in the near infrared spectroscopy

Time-resolved and spectroscopic in vivo measurements were performed to determine the optical properties of the female breast in transmission. The time-resolved measurements were carried out at different positions on the female breast with a Ti:sapphire laser (800 nm) using a synchroscan streak camera. A diffusion model was used to calculate the absorption coefficient mA and the reduced scattering coefficient. In addition, spectroscopic in vivo measurements of more than 100 patients were performed in a wavelength range between 650 and 1000 nm. A variety of pathological alterations could be characterized by measuring patients of different ages, different breast sizes, and at varying locations on the breast. The results indicate that besides the pure detection of the amount of blood in the neovascular network, the volume concentrations of water and fat seem to be of particular importance for discrimination. In order to quantify this observation, an analytical model was developed that takes the volume percentages of fat and water, the concentration and oxygenation of hemoglobin, and the relevant optical parameters into account. Experiments were carried out with volunteers and patients in a clinical environment: Typical observations are presented and analyzed statistically.

Model for the temporal-stability analysis of synchroscan streak camera measurements

In synchroscan streak camera measurements with actively mode-locked lasers, the temporal resolution is considerably better when the synchronization is generated by the laser itself (active configuration) than in the case in which the deflection is obtained from the mode-locker oscillator (passive configuration). These well-known experimental results are interpreted by means of a simple model that includes random fluctuations of the laser and electronic-oscillator periods. Comparison with experimental results clearly indicates that in the active device the timing properties of the camera are limited by the interpulse jitter. Conversely, this suggests that one may take advantage of implementing the passive configuration in order to measure the instantaneous time-phase fluctuations of the mode-locker oscillator directly.

Oscillator phase noise measurements by picosecond synchroscan streak camera

A new method/spl minus/with picosecond resolution/spl minus/allowing the recording of the instantaneous time phase fluctuations of a crystal controlled oscillator is presented. The oscillator under test drives the acoustooptic modelocker of a CW Nd:YAG laser associated with a synchronously pumped dye laser. By means of a streak camera illuminated by the ps dye laser pulses and synchronized by the oscillator signal the statistics of its zero crossings is analyzed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Comments on advanced, time-resolved imaging techniques for free-electron laser experiments

An extensive set of time-resolved imaging experiments has been performed on rf-linac driven free-electron lasers (FELs) over the past few years. These experiments have addressed both micropulse and macropulse timescales on both the charged-particle beam and the wiggler/undulator outputs(spontaneous emission and lasing). A brief review of first measurements on photoinjector micropulse elongation, submacropulse phase slew in drive lasers, submacropulse wavelength shifts in lasers, etc. is presented. This is followed by discussion of new measurements of 35-MeV electron beam micropulse bunch length (≤ 10 ps) using optical transition radiation, some of the first single bend synchrotron radiation beam profile measurements at γ < 80, and comments on the low-jitter synchroscan streak camera tuner. These techniques will be further developed on the 200–650 MeV linac test stand at the Advanced Photon Source (APS) in the next few years. Such techniques should be adaptable to many of the present FEL designs and to some aspects of the next generation of light sources.

Picosecond Decay Dynamics in Porous Silicon

ABSTRACTPicosecond decay dynamics of luminescent porous silicon has been studied using the second harmonics (SH) of a cw modelocked YLF laser and a synchroscan streak camera. Picosecond luminescence decay shows nonexponential behavior that becomes large with decreasing emission energy. When increasing hydrogen termination on the surface of a Si microcrystal occurs, this picosecond luminescence decay becomes faster. Our experimental results indicate that there are two luminescent states in porous Si : a weak luminescent quantum confinement state and a strong luminescent surface localized state.

Reduction of phase noise in passively mode-locked lasers

The phase noise of a colliding-pulse mode-locked ring dye laser and a coupled-cavity mode-locked color-center laser has been reduced by up to two orders of magnitude in the 50-500 Hz range by referencing the cavity frequency of the optical resonators to that of an electronic oscillator. Using this technique a common reference is available to provide a direct electronic signal to the deflection electronics of a synchroscan streak camera so that real-time phase error detection can be achieved. >

Development of a streak-camera-based time-resolved microscope fluorometer and its application to studies of membrane fusion in single cells

A time-resolved microscope fluorimeter based on a synchroscan streak camera and a fast pulsed laser system has been developed to measure the fluorescence lifetime decay under the fluorescence microscope. This system allows one to measure the nanosecond fluorescence lifetimes of fluorophores in a small spot (0.8-6.3 microns diameter) in single cultured cells under a fluorescence microscope, while the cells are being viewed under a high-power objective lens. A signal acquisition time between a second and a minute was usually sufficient to obtain fluorescence decay curves with good quality for 10(3)-10(5) fluorophores localized in 1 microns 2 domain. A signal-to-noise ratio better than 30 was obtained for approximately 30,000 fluorescein-labeled band 3 molecules in a 2 microns 2 region in a single human erythrocyte ghost after signal accumulation for 30 s. The measured lifetimes for a variety of fluorescent probes attached to proteins in solution and lipids in liposomes showed a good agreement with those measured in a cuvette under standard conditions by time-correlated single photon counting. With the development of this instrument, microscope fluorimetry has become a practical, straightforward, quantitative technique for investigation of molecular processes in single cells in culture. Time-resolved microscope fluorimetry has been applied to observe fusion of liposomes in vitro and that of endosomes in single cells by monitoring resonance energy transfer. Inspection of individual liposomes and endosomes revealed the extent of fusion for each vesicle. Since the use of time-resolved microscope fluorimetry eliminates the need for subcellular fractionation or the complex correction procedures in steady-state microfluorimetry, it greatly simplifies the assay for endosome fusion in vivo. The results showed that extensive fusion of sequentially formed endosomes takes place all over the cell matrix in cultured cells. This suggests that extensive fusion with incoming endosomes takes place in many endosomal compartments, possibly sorting organelles, or that the early endosomes fuse with the preexisting network of tubular cisternae of the endosomal compartment at many points in the network. It is concluded that time-resolved microscope fluorimetry is a powerful noninvasive technique for studies of in situ biochemistry and biophysics using cells and tissues.

First measurements of electron-beam transit times and micropulse elongation in a photoelectric injector at the high-brightness accelerator FEL (HIBAF)

Key aspects of the dynamics of a photoelectric injector (PEI) on the Los Alamos high-brightness accelerator FEL (HIBAF) facility have been investigated using a synchroscan streak camera. By phase-locking the streak camera sweep to the reference 108.3 MHz rf signal, the variations of micropulse temporal elongations (30 to 80% over the drive-laser pulse length) and of transit times (25 ps for a 16° phase change) were observed for the first time. These results were in good agreement with PARMELA simulations.

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.

Quenching of the superradiative decay by confined acoustic-phonons in CdS microcrystallites

We report picosecond dynamics of excitons in CdS microcrystallites. We investigated the temperature dependence of the lifetime of the band-edge emission due to the exciton direct recombination using a UV picosecond laser and a synchroscan streak camera. The lifetime was found to be almost constant below a threshold temperature (45 ± 5 K) and to increase proportionally with temperature above this temperature, suggesting the quenching of the superradiance of excitons by the scattering with acoustic-phonons confined in the microcrystallites. The threshold temperature corresponds to the frequency of the radial compression mode (35 cm -1 = 51 K) of the spherical microcrystallites.

Active mode-locking of conventional diode laser by using external cavity

We have actively mode-locked a commercially available conventional diode laser by using an external cavity. A single layer anti-reflection coating was applied to the output end surface of the laser diode. The laser was driven by ultrashort current pulses from a comb generator, and the pulse separation and the round trip time of the cavity were made equal to 10.56 ns. The output was a clean single-peak pulse train without any side peaks. The pulse width measured by a synchroscan streak camera was 20 ps.

Mode-locked, long-cavity, erbium fiber lasers with subsequent soliton-like compression

Erbium fiber lasers are described that have cavity lengths of 20-5000 m and are mode-locked at the fundamental cavity frequency using an integrated-optic intensity modulator driven by a novel pulse generator. Resulting optical pulses at 1536 nm were recorded with a synchroscan streak camera and show durations of 10-80 ps with peak powers over 6 W. The shorter cavities yield nearly transform-limited pulses, which are narrowed by solitonlike compression to approximately 5 ps after propagation through an external 14 km fiber. >

Picosecond spectra of gain-switched AlGaAs/GaAs multiple quantum well lasers

The temporal waveform of the single longitudinal modes emitted by gain-switched AlGaAs/GaAs multiple quantum well lasers is analyzed by means of a synchroscan streak camera system coupled to a spectrograph. It is found that only 50% of the number of the longitudinal modes contributing to the time-averaged spectrum are present during the first relaxation oscillation. The time-dependent shift of the envelope of the mode spectrum is quantitatively explained by a spectral shift of the gain maximum as a function of the time-varying charge carrier density. The results demonstrate that, for the analysis of transient multimode spectra of gain-switched injection lasers, inclusion of the energy dependence of the gain and gain compression is mandatory.