Picoseconds

Tannor D J, Rice S A and Weber P M 1985 Picosecond CARS as a probe of ground electronic state intramolecular vibrational redistribution J. Chem. Phys. 83 6158... 

Such lifetimes vary from less than a picosecond to times greater than the age of the universe [29]. Thus, adsorbed states with short lifetimes can occur during a surface chemical reaction, or long-lived adsorbed states exist in which atoms or molecules remain attached to a surface indefinitely. 

Harris A L, Berg M and Harris C B 1986 Studies of chemical reactivity in the condensed phase. I. The dynamics of iodine photodissociation and recombination on a picosecond time scale and comparison to theories for chemical reactions in solution J. Chem. Phys. 84 788... 

Syage J A, Felker P M and Zewail A H 1984 Picosecond dynamics and photoisomerization of stilbene in supersonic beams. I. Spectra and mode assignments J. Chem. Phys. 81 4685-705... 

Sundstrdm V and Gillbro T 1984 Dynamics of the isomerization of trans-stiibene in n-alcohols studied by ultraviolet picosecond absorption recovery Chem. Phys. Lett. 109 538-43... 

Schroeder J 1997 Picosecond kinetics of trans-cis photoisomerisations from ]et-cooled molecules to compressed solutions Ber. Bunsenges Phys. Chem. 101 643... 

Quack M, Stohner J and Sutcliffe E 1985 Time-dependent quantum dynamics of the picosecond... 

With the advent of short pulsed lasers, investigators were able to perfonn time resolved coherent Raman scattering. In contrast to using femtosecond pulses whose spectral widtii provides the two colours needed to produce Raman coherences, discussed above, here we consider pulses having two distinct centre frequencies whose difference drives the coherence. Since the 1970s, picosecond lasers have been employed for this purpose [113. 114], and since the late 1980s femtosecond pulses have also been used [115]. Flere we shall briefly focus on the two-colour femtosecond pulsed experiments since they and the picosecond experiments are very similar in concept. 

Sakamoto A, Okamoto H and Tasumi M 1998 Observation of picosecond transient Raman spectra by asynchronous Fourier transform Raman spectroscopy 1998 Appl. Spectrosc. 52 76-81... 

Laubereau A and Kaiser W 1978 Vibrational dynamics of liquids and solids investigated by picosecond light pulses Rev. Mod. Phys. 50 607-65... 

Laubereau A and Kaiser W 1978 Coherent picosecond interactions Coherent Nonlinear Optics ed M S Feld and V S Letokov (Berlin Springer) pp 271-92... 

Okamoto H and Yoshihara K 1991 Femtosecond time-resolved coherent Raman scattering from p-carotene in solution. Ultrahigh frequency (11 THz) beating phenomenon and sub-picosecond vibrational relaxation Chem. Phys. Lett. 177 568-71... 

Yu N-T, Nie S and Lipscomb L 1990 Surface-enhanced hyper-Raman spectrosocpy with a picosecond laser. New vibrational information for non-centrosymmetric carbocyanine molecules adsorbed on colloidal silver J. Raman Spectrosc. 21 797-802... 

Free-electron lasers have long enabled the generation of extremely intense, sub-picosecond TFlz pulses that have been used to characterize a wide variety of materials and ultrafast processes [43]. Due to their massive size and great expense, however, only a few research groups have been able to operate them. Other approaches to the generation of sub-picosecond TFlz pulses have therefore been sought, and one of the earliest and most successfid involved semiconducting materials. In a photoconductive semiconductor, carriers (for n-type material, electrons)... 

Especially with LTG GaAs, materials became available that were nearly ideal for time-resolved THz spectroscopy. Due to the low growth temperature and the slight As excess incorporated, clusters are fonned which act as recombination sites for the excited carriers, leading to lifetimes of <250 fs [45], With such recombination lifetunes, THz radiators such as dipole anteimae or log-periodic spirals placed onto optoelectronic substrates and pumped with ultrafast lasers can be used to generate sub-picosecond pulses with optical bandwidths of 2-4 THz. Moreover, coherent sub-picosecond detection is possible, which enables both... 

For a historical review see Lee C H 1984 Picosecond Optoelectronic Devices (New York Academic)... 

In a typical time-resolved SHG (SFG) experiment using femtosecond to picosecond laser systems, two (tlnee) input laser beams are necessary. The pulse from one of the lasers, usually called the pump laser, induces the... 

Sitzmann E V and Eisenthal K B 1988 Picosecond dynamics of a chemical-reaction at the air-water interface studied by surface second-harmonic generation J. Phys. Chem. 92 4579-80... 

Lantz J M and Corn R M 1994 Time-resolved optical second harmonic generation measurements of picosecond band flattening processes at single crystal TiO, electrodes J. Phys. Chem. 98 9387-90... 

Small molecules in low viscosity solutions have, typically, rotational correlation times of a few tens of picoseconds, which means that the extreme narrowing conditions usually prevail. As a consequence, the interpretation of certain relaxation parameters, such as carbon-13 and NOE for proton-bearing carbons, is very simple. Basically, tlie DCC for a directly bonded CH pair can be assumed to be known and the experiments yield a value of the correlation time, t. One interesting application of the measurement of is to follow its variation with the site in the molecule (motional anisotropy), with temperature (the correlation... 

Fleiiweii E J, Casassa M P, Cavanagh R R and Stephenson J C 1989 Picosecond vibrationai energy transfer studies of surface adsorbates Ann. Rev. Rhys. Chem. 40 143-71... 

New metliods appear regularly. The principal challenges to the ingenuity of the spectroscopist are availability of appropriate radiation sources, absorption or distortion of the radiation by the windows and other components of the high-pressure cells, and small samples. Lasers and synchrotron radiation sources are especially valuable, and use of beryllium gaskets for diamond-anvil cells will open new applications. Impulse-stimulated Brillouin [75], coherent anti-Stokes Raman [76, 77], picosecond kinetics of shocked materials [78], visible circular and x-ray magnetic circular dicliroism [79, 80] and x-ray emission [72] are but a few recent spectroscopic developments in static and dynamic high-pressure research. 

Hare D E, Franken J and DIott D D 1995 A new method for studying picosecond dynamics of shocked solids application to crystalline energetic materials Chem. Phys. Lett. 244 224... 

Johnson A M and Shank C V 1989 Pulse compression in single-mode fibres—picoseconds to femtoseconds The Supercontinuum Laser Source ed R R Alfano (New York Springer) pp 399-449... 

Mollenauer L F, Stolen R H and Gordon J P 1980 Experimental observation of picosecond pulse narrowing and solitons in optical fibres Phys. Rev. Lett. 45 1095-7... 

Scherer N F, Khundkar L R, Bernstein R B and Zewail A H 1987 Real-time picosecond clocking of the collision complex in a bimolecular reaction the birth of OH from H + CO2 J. Chem. Phys. 87 1451-3... 

Genberg L, Richard L, McLendon G and Miller R J D 1991 Direct observation of global protein motion in hemoglobin and myoglobin on picosecond time scales Science 251 1051-6... 

Deak J, Richard L, Pereira M, Chui H-L and Miller R J D 1994 Picosecond phase grating spectroscopy applications to bioenergetics and protein dynamics Meth. Enzymol. 232 322-60... 

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