Pulse picosecond time resolution

Pulse radiolysis systems capable of picosecond time resolution use the fine structure of the output from the electron linear accelerator. Electrons in the accelerating tube respond to positive or negative electric field of the radiofrequency, and they are eventually bunched at the correct phase of the radiofrequency. Thus the electron pulse contains a train of bunches or fine structures with their repetition rate being dependent on the frequency of the radiofrequency (350 ps for the S-band and 770 ps for the L-band). 

The study of the very fast processes that follow on the absorption of radiation in organic systems is a very active field with pulse radiolysis with picosecond time resolution being one of the major tools. This technique, the latest version of which employs twin linear accelerators(69), has time resolution of about 20 ps. These methods are being used to investigate the fast recombination of charges, the formation of excited states and free radicals, mainly in hydrocarbon media, but have also recently been applied to the study of radiation effects in polymers(70). 

Bronskill MJ, Taylor WB, Wolff RK, Hunt JW. (1970) Design and performance of a pulse radiolysis system capable of picosecond time resolution. Rev Sci Instrum 4 333-340. 

Tabata Y, Kobayashi H, Washio M, Tagawa S, Yoshida Y. (1985) Pulse-radiolysis with picosecond time resolution. Radiat Phys Chem 26 473-479. 

Grigoryants VM, Lozovoy W, Chemousov YuD, Shebolaev IV, Arutyunov AV, Anisimov OA, Molin YuN. (1989) Pulse radiolysis system with picosecond time resolution referred to Cherenkov radiation. Radiat Phys Chem 34 349-352. 

In the near future, the ion-beam radiation-chemist community will probably understand earlier processes in the track of heavy ions. This supposes two things accelerators must deliver shorter pulses than those used currently and the detection must be more sensitive and highly time-resolved. That means a picosecond pulse radiolysis research with heavy ions. That is not a foolish project because new designs of accelerators for proton and heavier ions have already started. Physics of plasma has made recent progress and probably in the next year will appear the first results in radiation chemistry with protons with at least a picosecond time resolution. A few intentions have already been published. ... 

Pulse radiolysis with picosecond time resolution has been developed, or is planned, in only a few laboratories. These rather special facilities are described separately in Section 3.9. 

The first pulse radiolysis system capable of picosecond time resolution (20 ps) was in use by 1968 at the University of Toronto [145] and others were subsequently installed at Notre Dame University, Argonne National Laboratory, Tokyo, Osaka, and Hokkaido Universities, the Hahn-Meitner Institute in Berlin, and the Institute of Chemical Kinetics and Combustion in Novosibirsk. Current developments at Brookhaven [104] and Argonne [146] National Laboratories and Tokyo University [147] are aimed at subpicosecond timescales a new picosecond facility is also being installed at Orsay [148]. 

Figure 12. a) Transient absorption spectra obtained upon nanosecond pulsed laser excitation of 1) cw-[Ru"(dcbpy)2(NCS)2] dye in ethanolic solution, and 2) a sensitized Ti02 transparent film. Spectra were recorded 50 ns (la, 2a) and 0.5 ps (lb, 2b) after the laser excitation pulse (A = 605 nm, 5 ns pulse duration), b) Transient absorption spectra recorded 6 ps after ultrafast laser excitation (A = 605 nm, 150 fs pulse duration) of 1) c -[Ru (dcbpy)2(NCS)2] dye in ethanol, and 2) a fresh sensitized titanium dioxide film. Insert, the temporal behavior of the absorbance of the latter system, measured at A = 750 nm with sub-picosecond time resolution. 

Jonah C.D., A wide-time range pulse radiolysis system of picosecond time resolution. Rev. Sci. Instr., 1975,46,62-66. 

K. Konig, U. Wollina, I. Riemann, C. Peuckert, K-J. Halbhuber, H. Konrad, P. Fischer, V. Fuenfstueck, T.W. Fischer, P. Eisner, Optical tomography of human skin with subcellular resolution and picosecond time resolution using intense near infrared femtosecond laser pulses, Proc. SPIE 4620, 191-202 (2002)... 

The methods really amount to nothing more than obtaining the system properties from real time measurements of transient currents following application of a voltage pulse. Techniques of this kind have been in use for many years when the times of interest are milliseconds, seconds or longer, but the special interest in TDS is due to the use of pulse generation and observation techniques with picosecond time resolution which makes possible the equivalent of steady state a.c. measurements at frequencies from a few MHz to several GHz, a region that has traditionally been difficult and tedious by frequency domain methods. 

Over the past decade, Raman spectroscopy has continued to develop as a prime candidate for the next generation of in situ planetary instruments, as it provides definitive stmctural and compositional information of minerals in their natural geological context. A time resolved Raman spectrometer have been developed that uses a streak camera and pulsed miniature microchip laser to provide picosecond time resolution (Blacksberg et al. 2010). The ability to observe the complete time evolution of Raman and fluorescence spectra in minerals makes this technique ideal for exploration of diverse planetary environments, some of which are expected to contain strong, if not overwhelming, fluorescence signatures. In particular, it was found that conventional Raman spectra from fine grained clays. 

Optical absorption spectrophotometry is probably the most commonly used technique [4,a]. Reaction cells are similar to those used in flash work. Photomultipliers cover the uv-visible range the initial photoelectric signal is amplified internally, by an amoimt controlled by selection of the number of dynodes. Nanosecond equipment is commercially available. Picosecond time-resolution has been achieved [l,h]. For the infrared and Raman region, semiconductor photodiodes cover the range 400-3000 nm the vibrational spectra yield structural information about transient species much more detailed and precise than that from electronic spectra. Resonance enhancement of Raman spectra increases their intensity by a factor of 10, and makes them attractive for detection and monitoring [4,b]. They can be recorded with time-resolution down to sub-nanoseconds. Fluorescence detection is sensitive, and fast with single-photon counting or a streak camera (Section 4.2.4.2), it has been used for times down to 30 ps after an electron pulse. Conductivity also provides a fast and sensitive technique [4,c,d,l,m], especially in hydrocarbon solutions, where... 

The limitations to the time resolution are the length of the excitation pulse, the time resolution of the detection equipment and the speed of the chemistry creating the reactants of interest. With lasers presently available with pulse widths less than a picosecond, the pulse length is not a major limitation. Using a pulse-probe detection technique, the only limitation of Ae time resolution may be the formation of the desired reactant. 

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