Streak Camera Recording Research Articles

Simultaneous one-dimensional fluorescence lifetime measurements of OH and CO in premixed flames

A method for simultaneous measurements of fluorescence lifetimes of two species along a line is described. The experimental setup is based on picosecond laser pulses from two tunable optical parametric generator/optical parametric amplifier systems together with a streak camera. With an appropriate optical time delay between the two laser pulses, whose wavelengths are tuned to excite two different species, laser-induced fluorescence can be both detected temporally and spatially resolved by the streak camera. Hence, our method enables one-dimensional imaging of fluorescence lifetimes of two species in the same streak camera recording. The concept is demonstrated for fluorescence lifetime measurements of CO and OH in a laminar methane/air flame on a Bunsen-type burner. Measurements were taken in flames with four different equivalence ratios, namely I center dot = 0.9, 1.0, 1.15, and 1.25. The measured one-dimensional lifetime profiles generally agree well with lifetimes calculated from quenching cross sections found in the literature and quencher concentrations predicted by the GRI 3.0 mechanism. For OH, there is a systematic deviation of approximately 30 % between calculated and measured lifetimes. It is found that this is mainly due to the adiabatic assumption regarding the flame and uncertainty in H2O quenching cross section. This emphasizes the strength of measuring the quenching rates rather than relying on models. The measurement concept might be useful for single-shot measurements of fluorescence lifetimes of several species pairs of vital importance in combustion processes, hence allowing fluorescence signals to be corrected for quenching and ultimately yield quantitative concentration profiles. (Less)

Time-resolved measurement on ablative acceleration of foil plates driven by pulsed laser beam

Coupled with the push-pull type velocity interferometer system for any reflector, an electronic streak camera recording system has been established, which provides subnanosecond time resolution in the detection of interferential fringes. Complete acceleration histories of Al, Au, and Pt foil plates, driven by pulsed laser beam at 30–400 GW/cm2, have been measured by using this system. For the 10-μm-thick Al foil irradiated at 280 GW/cm2, an ablative acceleration up to terminal velocity about 9 km/s within 25 ns has been determined with a velocity uncertainty of ∼1%.

Shock Wave Structure in Polyurethane Foam.

Shock wave propagation in polyurethane (PU(R)) foam was experimentally studied. The experiment was conducted in a shock tube by measuring pressure along the PU(R) foam in a shock tube, by means of holographic interferometry and streak camera recording. It was found that the stress-strain curve of PU(R) has an inflection point. When the pressure behind the incident shock wave was below the inflection-point pressure Pc, the wave impedance ratio of the incident shock wave and transmitted pressure wave Zi/Zt increased sharply. This indicates that only a small amount of energy is transmitted into the foam if the pressure is below Pc. For pressures larger than Pc, Zi/Zt decreases asymptotically to a small finite value.

The cathode spot plasma in low-current air and vacuum break arcs

The radiation from active cathode spots in air and vacuum break arcs was investigated by different experimental techniques: streak camera recording, time-resolved and time-integrated spectroscopy. Spot rotation has been found with two frequencies omega 1=2*105 Hz and omega 2=4-6*107 Hz, and two characteristic radial velocities V1=21 m s-1 and V2=130 m s-1. From spectroscopic measurements, degeneration of the upper excited atom states is deduced, corresponding to a strong non-ideality of the cathode spot plasma with consequences for the particle density (N>1028 m-3).

Shock Wave Structure in Polyurethane Foam.

An experimental study was made of shock wave propagation in polyurethane (PUR) foam. The experiment was conducted in a shock tube by measuring pressure along the PUR foam by means of holographic interferometry and streak camera recording. It was found that the stress-strain curve of PUR have an inflection point. When the pressure behind the incident shock wave was below the inflection point pressure PC, the wave impedance ratio of the incident shock wave and transmitted pressure wave Zi./Zt increased sharply. This indicates that only a small amount of energy is transmitted into the foam if the pressure is below Pc. For pressure larger than Pc, Zi, /Zt decreases asymptotically to a small finite value.

Two-channel, elliptical analyzer spectrograph for absolute, time-resolving time-integrating spectrometry of pulsed x-ray sources in the 100–10 000-eV region

A new spectrographic system has been developed and calibrated in this laboratory for the absolute spectrometry of high-intensity pulsed x-ray sources in the 100–10 000-eV region. This spectral region is analyzed with fixed elliptically curved crystals and molecular or sputtered-or-evaporated multilayers of 2d values in the 3–160-A range. Twin channels are utilized for simultaneous time-integrated photographic recording and for time-resolved x-ray streak camera recording. Absolute calibrations of the elliptical analyzers, of the photographic film, and of the gold and CsI transmission photocathodes have been made using monoenergetic, cw laboratory x-ray sources. The overall transmission characteristics of the spectrograph have also been determined. The instrument has been designed for mounting through a pneumatically controlled high-vacuum valve onto a 4-in. port of a 1-m-diameter source chamber and includes an appendage, high-vacuum, sputter-ion prepumping station. The initial dynamic testing and application of this new spectrographic system has been on the University of Rochester’s LLE 24 laser beam OMEGA source facility.

Streak camera recording of shock wave transit times at large distances using laser illumination

A pulsed laser illumination system for streak camera recording of impact-induced shock wave transit times (∼1 μs) during impact experiments is described. Laser illumination of centimeter-sized subjects offers many advantages over diffuse illumination techniques for streak photography. Source-to-sample and sample-to-camera distances of ∼100 to 102 m can be employed. Light filtering, and simultaneous recording of both the impact event and the camera streak rate calibration, can be carried out easily. For use in such a system we describe a Pockels cell controller in which the reference 10-MHz oscillator signal is synchronously divided down to 38 Hz to provide a trigger signal for laser and streak camera testing.

Time-resolved evolution of laser-produced plasmas in spherical expansion regime

We report experimental results deduced from quantitative Schlieren imaging of plasmas combined with streak camera recording. Flat or spherical targets are illuminated with one laser beam, at different wavelengths (1.06 μm, 0.53 μm, 10.6 μm): We show that time-resolved density profiles are more stationary for shorter wavelength. We measure the rear displacement and front expansion of plasmas created on glass microballoons and solid microspheres. Comparison with hydrocode simulations shows that transport is inhibited for 1.06-μm interaction, and that ablation processes are more efficient for shorter wavelength.

Validity of spherical quantitative refractometry: Application to laser-produced plasmas

We report an experimental laser technique of quantitative Schlieren imaging of spherical plasmas combined with streak camera recording. We show that quantitative refractometry applies for small values of refraction angles, i.e., when the law giving the refraction angle versus the impact parameter of rays passing through the plasma is a linearly decreasing function.

ChemInform Abstract: UV SHORT‐PULSE FRAGMENTATION OF ISOTOPICALLY LABELED ACETYLENE: STUDIES OF EMISSION WITH SUBNANOSECOND RESOLUTION

We have studied fragment emission in the spectral range 200 to 900 nm, following photolysis of acetylene (1–10 Torr) by short ultraviolet pulses (25 ps, 266 nm, 2.5–12 mJ). The dominant component of emission is the C2 d 3Πg→a 3Πu Swan system. Weak singlet C2 emission is observed. CH is also observed, in the A 2Δ→X 2Π and C 2Σ+→X 2Π systems. With isotopic labeling and with streak camera recording, we have demonstrated distinct unimolecular and intermolecular processes yielding C2 d 3Πg. The unimolecular channel proceeds with risetime τ1 = 215±15 ps, while the pressure‐dependent intermolecular component develops over a period of nanoseconds. We discuss the underlying kinetics and the mechanistic implications of the 25 ps excitation.

UV short-pulse fragmentation of isotopically labeled acetylene: Studies of emission with subnanosecond resolution

We have studied fragment emission in the spectral range 200 to 900 nm, following photolysis of acetylene (1–10 Torr) by short ultraviolet pulses (25 ps, 266 nm, 2.5–12 mJ). The dominant component of emission is the C2 d 3Πg→a 3Πu Swan system. Weak singlet C2 emission is observed. CH is also observed, in the A 2Δ→X 2Π and C 2Σ+→X 2Π systems. With isotopic labeling and with streak camera recording, we have demonstrated distinct unimolecular and intermolecular processes yielding C2 d 3Πg. The unimolecular channel proceeds with risetime τ1 = 215±15 ps, while the pressure-dependent intermolecular component develops over a period of nanoseconds. We discuss the underlying kinetics and the mechanistic implications of the 25 ps excitation.