Streak-camera techniques

Detonation, Lateral Shock Pressure Measurements at an Explosive Column. A high speed streak camera technique used for these measurements is described by L.D. Sadwin ... 

The techniques that have been developed to probe the kinetics of energy transfer processes In materials on a picosecond time scale can be divided into three general categories. They are the optical Kerr gate, the excite and probe technique, and the streak camera technique. 

Miscellaneous Physical Chemistry. The electrochemical oxidation of /3-carotene by a single-step reversible two-electron transfer has been reported.106 The fluorescence lifetimes of a- and j8-carotene have been measured by the streak camera technique to be 5.5 10 ps (6 x 10 2 mol 1 1 in chloroform).107 Ellipsometric measurements of light-absorbing monomolecular layers of several compounds, including 8 -apo-/3-caroten-8 -oic acid (227) have been described.108 The kinetics of autoxidation of amorphous retinyl acetate have been determined.109... 

Fig. 7.12 Schematic representation of the determination of the detonation velocity using the optical fiber/streak camera technique.

The fluorescence lifetimes of both photosynthetic systems and chlorophyll solutions using picosecond excitation and streak camera technique were also reported by Kolman et al. 32) and Shapiro et al. 33s. 

They confirmed that the dwell time of excitations is significantly shortened as the detection window is scanned towards the high-energy tail of the fluorescence spectrum. A more recent example of this phenomenon is the spectrally resolved fluorescence decay from a neat PhPPV film, employing the streak-camera technique [66]. 

A curvature of the same shape, but in a series of discontinuous points representing the shock wave travelling through an explosive, is obtained when the optical fibres/streak camera technique is used. 

The other end of the optical fibre is led to the measuring equipment, which will record detonation wave arrival. The length of the optical fibre may go above 20 m. The experiment configuration when the optical fibre/streak camera technique is applied looks like the one shown in Figure 4.29. The optical fibre ends are fixed using a holder. The moment of the arrival of the detonation wave on the optical fibre is recorded as a light point-trace by a streak camera whose writing speed is 10 mm/ps. 

Figure 4.29. The test arrangem t for the determination of detonation velocity applying the optical fibres/streak camera technique...

Recently Gordon et al. (1976) reexamined the reaction of e , with R (aquo) in a study which included all of the lanthanides. Their rate constant data could be used to divide the series into three groups in terms of reactivity (1) readily reduced ions Sm, Eu, Yb with rate constants in the range of 10 ° M sec (2) an intermediate group, Gd, Ho, Er, and Tm, with rate constants (10 -10 ), and (3) a relatively unreactive group, Pr, Nd, Dy, Tb, and Lu with rate constants 10. Using streak camera techniques they obtained the first spectroscopic evidence for Gd " and Ho, fig. 24.18. 

At still shorter time scales other techniques can be used to detenuiue excited-state lifetimes, but perhaps not as precisely. Streak cameras can be used to measure faster changes in light intensity. Probably the most iisellil teclmiques are pump-probe methods where one intense laser pulse is used to excite a sample and a weaker pulse, delayed by a known amount of time, is used to probe changes in absorption or other properties caused by the excitation. At short time scales the delay is readily adjusted by varying the path length travelled by the beams, letting the speed of light set the delay. 

An optical detector with appropriate electronics and readout. Photomultiplier tubes supply good sensitivity for wavelengths in the visible range, and Ge, Si, or other photodiodes can be used in the near infrared range. Multichannel detectors like CCD or photodiode arrays can reduce measurement times, and a streak camera or nonlinear optical techniques can be used to record ps or sub-ps transients. 

Lifetime instruments using a streak camera as a detector provide a better time resolution than those based on the single-photon timing technique. However, streak cameras are quite expensive. In a streak camera, the photoelectrons emitted... 

Chapter 6 described the current techniques employed in time-resolved fluorescence spectrocopy. The time resolution of these techniques ranges from a few picoseconds (streak cameras) to a few hundreds of picoseconds (single-photon timing with flash lamp excitation). The time resolution can be greatly improved by using the fluorescence up-conversion technique. 

Other near-IR techniques that have been used to measure lifetimes, though not to the same extent as the aforementioned methods, include fluorescence up-conversion,(19 21) parametric amplification, 22 streak camera detection,(23) and two-photon excitation,1(24) The latter technique is particularly useful as it enables the greater penetration depth of near-IR radiation in organic matter to be used to obtain a well-defined region of excitation, e.g., in single cells or mammalian tissue. 

In this section, we will briefly describe the two main techniques devoted to detecting ultrashort pulses the streak camera and the auto correlator. 

The time-resolved techniques that are usually used for FLIM are based on electronic-basis detection methods such as the time-correlated single photon counting or streak camera. Therefore, the time resolution of the FLIM system has been limited by several tens of picoseconds. However, fluorescence microscopy has the potential to provide much more information if we can observe the fluorescence dynamics in a microscopic region with higher time resolution. Given this background, we developed two types of ultrafast time-resolved fluorescence microscopes, i.e., the femtosecond fluorescence up-conversion microscope and the... 

Booster was used to initiate the expl at one end. The radial motion of the cylinder wall was measured in a plane perpendicular to the cylinder axis 7 inches from the booster end, A streak camera recorded the motion, using conventional shadowgraph technique (See under CAMERAS, HIGH-SPEED PHOTOGRAPHIC in Vol 2 of Encycl, p CI3-L). In addn, the deton velocity of the expl was measured by placing pin switches 9-i° apart on the surface of the cylinder, as described, for example, by Cook (Ref 2, p 29). The streak camera record was read on a precision comparator which punched out the data directly on IBM cards. A computer code con-... 

The streak camera viewed the chge upward thru a periscope in which the line of sight was reflected to a horizontal direction by a front surface mirror. Measurements of the peak pressures by the aquarium technique were found to be the C-J or detonation pressures of the thermohydrodynamic theory... 

Detonation Transients and Unstable Detonation Processes. Allen et al (Ref 1) made detonation velocity vs chge length. measurements on RDX (—65+100 mesh), fine grained TNT (—35 —150) coarse, low-density TNT (—8+10) 50/50 fine-coarse TNT, cast TNT, low-density. mixts of 80/20 TNT/AN, and mixts of 90/10 AN/RDX. Deton velocities were measured by a rotating mirror streak camera and by the pin oscillograph technique, in most cases simultaneously Their exptl data showed six different types of velocity transients ... 

Sampling techniques are not as fast as the streak camera because the response time of the detectors is a limiting factor. The interpretation of the data is however much simpler and does not require complex computer programs. 

---