Light pulses, ultrashort

A light pulse of a center frequency Q impinges on an interface. Raman-active modes of nuclear motion are coherently excited via impulsive stimulated Raman scattering, when the time width of the pulse is shorter than the period of the vibration. The ultrashort light pulse has a finite frequency width related to the Fourier transformation of the time width, according to the energy-time uncertainty relation. 

Weber FIP (1967) Method for pulsewidth measurement of ultrashort light pulses generated by phase-locked lasers using nonlinear optics. J Appl Phys 38 2231-2234... 

In contrast, time domain instruments attempt to directly measure the decay characteristics of a fluorophore of interest by excitation with ultrashort light pulses and monitoring the decay using either TCSPC [5] or a time gated image intensifier [8],... 

There is significant debate about the relative merits of frequency and time domain. In principle, they are related via the Fourier transformation and have been experimentally verified to be equivalent [9], For some applications, frequency domain instrumentation is easier to implement since ultrashort light pulses are not required, nor is deconvolution of the instrument response function, however, signal to noise ratio has recently been shown to be theoretically higher for time domain. The key advantage of time domain is that multiple decay components can, at least in principle, be extracted with ease from the decay profile by fitting with a multiexponential function, using relatively simple mathematical methods. 

Eisental, K. B. In Ultrashort Light Pulse, Shapiro, S., ed Spinger-Verlag Berlin, 1977 Chap. 5. 

Akhmanov, S. A., Chirkin, A. S., Drabovich, K. N., Kovrigin, A. I., Khokhlov, R. V., and Sukhorukov, A. P. 1968. Nonstationary nonlinear optical effects and ultrashort light pulse formation. lEEEJ. Quantum Electron. QE-4 598-605. 

The possibility of reflection of electrons by an evanescent wave formed upon the total internal reflection of femtosecond light pulses from a dielectric-vacuum interface is quite realistic. The duration of the reflected electron pulses may be as long as 100 fs. In the case of electrons reflecting from a curved evanescent wave, one can simultaneously control the duration of the reflected electron pulse and affect its focusing (Fig. lc). Of course, one can imagine many other schemes for controlling the motion of electrons, as is now the case with resonant laser radiation of moderate intensity [9, 10]. In other words, one can think of the possibility of developing femtosecond laser-induced electron optics. Such ultrashort electron pulses may possibly find application in studies into the molecular dynamics of chemical reactions [1,2]. 

An ultrashort light pulse is emitted at A and slightly later an ultrafast detection is made at B. The separation in time and space between A and B could be either (1) static because A and B are fixed in space as in most holography (in which case we would refer to the one who makes the experiment the rester (2) dynamic, caused by an ultrahigh velocity (v) of the person... 

Figure 1. An ultrashort light pulse is emitted at A, which is the apex of a Minkowski lightcone. In our coordinate system x-y represent two axes of our ordinary world, while the third axis ct represents time. The widening of the cone upward represents the radius of the sphere of light as it increases with time. An ultrashort observation is later made at B, the apex of an inverted cone. The only way for light to be transmitted from A to B is by scattering objects placed where the two cones intersect. If the observer s velocity (v) is high, this intersection will be an ellipse that is inclined in relation to our stationary world.

Figure 16. The traveler of Fig. 12 emits ultrashort light pulses at Ah A2, A3, A4, A5, and Ag. Finally he makes one ultrashort observation at B. The vertical straight line S-S in the stationary world appears to the traveler to be distorted into the hyperbolic line S1 1.

Fig. 7.2 Two-beam experimental setup for femtosecond transient absorption studies using a white light continuum. A commercially available CPA 2101 laser system delivers the pulses. Ultrashort tunable visible pulses are obtained by the NOPA optical parametric converter. A chopper wheel is used to cut every second pump pulse in order to compare the signal with and without the pump. The white light continuum is generated by a sapphire disc. The time delay between the pump and probe pulses is adjusted by the optical delay rail...

D.J. Bradley, Ultrashort Light Pulses, Springer-Verlag, Berlin, Heidelberg, New York, 1977, p. 17. 

Recent technical developments in ultrashort-pulse lasers enable the CARS spectro-scopist to obtain coherent light pulses shorter than 100 fs. This time scale corresponds to the period of molecular vibrational motions (100 fs ss 100-150 cm depending on the shape of the pulse, for example). One is therefore able to coherently excite many vibrational modes at a time and monitor relaxation processes in real time. 

We have performed optically heterodyne-detected optical Kerr effect measurement for transparent liquids with ultrashort light pulses. In addition, the depolarized low-frequency light scattering measurement has been performed by means of a double monochromator and a high-resolution Sandercock-type tandem Fabry-Perot interferometer. The frequency response functions obtained from the both data have been directly compared. They agree perfectly for a wide frequency range. This result is the first experimental evidence for the equivalence between the time- and frequency-domain measurements. 

Impulsive stimulated Raman scattering (ISRS) Impulsive stimulated Raman scattering (ISRS) is the creation of coherent ground-state nuclear motion through an impulsive force caused by the interaction of a Raman-active medium with an ultrashort light pulse. 

E. P. Ippen and C. V. Shank, Ultrashort Light Pulses, S. L. Shapiro (ed.). New York Springer-Verlag, 1983. 

If an intense ultrashort light pulse at a given wavelength (or frequency) is focused in a liquid or solid medium (water, glass, etc.), its spectrum broadens considerably while propagating in the medium and the output beam appears as a white light beam. This is mainly due to self phase modulation [36], a non linear process that... 

Fig. 7.15. Typical transient absorption set-up using a subpicosecond laser source as the pump and a continuum of white light as the probe. For ultrashort time resolution additional stages for compensating the group velocity dispersion in both light pulses are needed. P pump, F filter.

We assume that our system consists of a Kerr medium of the (s + 1 )th-order nonlinearity and a parametric amplifier driven by a series of ultrashort external classical light pulses. Thus, the Hamiltonian describing our system can be written in the interaction picture as... 

Eberly, J. H., P. Maine, D. Strickland, and G. Mourou, 1987, Laser Focus 23 (10), 84-90. Eisenthal, K. B., 1977, in Ultrashort Light Pulses—Picosecond Techniques and Applications,... 

In early investigations, transfer times of about 100 fs or less were observed for HBT in tetrachloroethylene [16], 2-(2 -hydroxyphenyl)benzoxazole (HBO) in cyclohexane [17], and for methyl salicylate (MS) [18] and OHBA [19] in gas phase. For a number of ESIPT molecules very fast transfer times were found, even at cryogenic temperatures [20]. To resolve the evolution of the transfer and to learn about the mechanism the experimental time resolution had to be improved to better than 50 fs. Such experiments were only possible with the advent of Ti sapphire laser systems and novel nonlinear sources for ultrashort tunable light pulses. Within the last ten years several experiments with extremely high time resolution have been performed. They revealed rich spectroscopic dynamics and resulted in a detailed picture of the ESIPT and the underlying mechanisms. Their comparative discussion is the central issue of this article. 

Ultrashort Light Pulses, Tcpics Appl. Phys., 18, 16 (1977). 

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