Femtosecond laser pulse

Assion A, Baumert T, Bergt M, Brixner T, Kiefer B, Seyfried V, Strehle M and Gerber G 1998 Control of chemical reactions by feedback-optimized phase-shaped femtosecond laser pulses Sc/e/ ce 282 919... 

Yan Y X, Gamble E B and Nelson K A 1985 Impulsive stimulated Raman scattering general importance in femtosecond laser pulse interactions with matter, and spectroscopic applications J. Chem. Phys. 83 5391-9... 

Dugan M A, Tull J X and Warren W S 1997 High-resolution acousto-optic shaping of unamplified and amplified femtosecond laser pulses J. Opt. Soc. Am. B 14 2348-58... 

Rulliere C (ed) 998 Femtosecond Laser Pulses (BerWn Springer)... 

Figure 9.41 Potential energy curves for the two lowest electronic states of Nal showing avoided level crossing and the effect of excitation with a femtosecond laser pulse. (Reproduced, with permission, from Rose, T. S., Rosker, M. J. and Zewail, A. H., J. Chem. Phys., 91, 7415, 1989)...

A suitable method for a detailed investigation of stimulated emission and competing excited state absorption processes is the technique of transient absorption spectroscopy. Figure 10-2 shows a scheme of this technique. A strong femtosecond laser pulse (pump) is focused onto the sample. A second ultrashort laser pulse (probe) then interrogates the transmission changes due to the photoexcita-lions created by the pump pulse. The signal is recorded as a function of time delay between the two pulses. Therefore the dynamics of excited state absorption as... 

For studies in molecular physics, several characteristics of ultrafast laser pulses are of crucial importance. A fundamental consequence of the short duration of femtosecond laser pulses is that they are not truly monochromatic. This is usually considered one of the defining characteristics of laser radiation, but it is only true for laser radiation with pulse durations of a nanosecond (0.000 000 001s, or a million femtoseconds) or longer. Because the duration of a femtosecond pulse is so precisely known, the time-energy uncertainty principle of quantum mechanics imposes an inherent imprecision in its frequency, or colour. Femtosecond pulses must also be coherent, that is the peaks of the waves at different frequencies must come into periodic alignment to construct the overall pulse shape and intensity. The result is that femtosecond laser pulses are built from a range of frequencies the shorter the pulse, the greater the number of frequencies that it supports, and vice versa. 

Unfortunately, femtosecond laser pulses are not so readily predisposed to study collisions between atoms and molecules by the pump-probe approach. The reason is that, typically, the time between collisions in the gas phase is on the order of nanoseconds. So, with laser pulses of sub-lOOfs duration, there is only about one chance in ten thousand of an ultrashort laser pulse interacting with the colliding molecules at the instant when the transfer of atoms is taking place in other words, it is not possible to perform an accurate determination of the zero of time. 

Rulliere, C. (ed.) 1998 Femtosecond laser pulses principles and experiments. Berlin Springer. 

Coherent Control with Femtosecond Laser Pulses, Eur. Phys. J. Sci. D, 14(2), (2001). 

L. Sarger and J. Oberle, in Femtosecond Laser Pulses Principles and Experiments,... 

The advent of ultrafast pump-probe laser techniques62 and their marriage with the TOF method also enables study of internal ion-molecule reactions in clus-ters.21,63-69 The apparatus used in our experiments is a reflectron TOF mass spectrometer coupled with a femtosecond laser system. An overview of the laser system is shown in Figure 4. Femtosecond laser pulses are generated by a colliding pulse mode-locked (CPM) ring dye laser. The cavity consists of a gain jet, a... 

Consider the dynamics of ionization of clusters through the C state of an ammonia molecule, where it should be noted that it is also possible that the excitation leads to some population of the B states due to the broad spectral bandwidth of the femtosecond laser pulses. The measurements indicate lifetimes... 

Fig. 3.1. Left visible pump/X-ray probe scheme for femtosecond TRXRD experiments. Hard X-ray pulses are generated by shining intense femtosecond laser pulses on a metal target (laser plasma X-ray source). Right geometrical structure factor of bismuth as a function of inter-atomic distance for diffraction from (111) and (222) lattice planes. From [1] and [2]...

One of the applications of TRXRD is to study complex systems where electric fields couple to multiple degrees of freedom. Though femtosecond laser pulses can generate THz radiation from ferroelectric LiTa03, the corresponding lattice motion remained undetected by optical measurements. Cavalleri and coworkers demonstrated the coherent modulation of the X-ray intensity at 1.5 THz [10], and assigned it as phonon-polariton mode of A symmetry (Fig. 3.3). Nakamura and coworkers detected the coherent LO phonon of CdTe... 

In summary, the main issues were presented here concerning experimental investigation of fast-electron transport in solids irradiated at ultra-high intensity using high-power, femtosecond laser pulses. A discussion was given on... 

Even more elegantly, the local resolution is improved by irradiation with very intense focused femtosecond laser pulses outside the absorption range of the fluoro-phore (e.g., in the near-infrared). The very intense focus of the laser beam—and only this—will excite the fluorophore by nonresonant two-photon absorption. Artifacts by scattered primary radiation are ruled out and the local resolution is comparable to a confocal microscope. In addition, the damage of the sample by laser light absorption is reduced to a minimum. 

S.A. AMimanov, V.A. Vysloukh, A.S. Chirkin, Optics of Femtosecond Laser Pulses (American Institute of Physics, NY 1992). 

W. Rudolph, P. Dom, X. Liu, N. Vretenar, and R. Stock, Microscopy with femtosecond laser pulses applications in engineering, physics and biomedicine. Applied Surface Science 208, 327-332 (2003). 

M. Will, J. Burghoff, S. Nolle and A. Tuennermann, Fabrieation of three-dimensional photonics devices using femtosecond laser pulses, Proc. of SPIE, Vol. 4978, 147-154 (2003). 

In the case of photoexcitation by an intense femtosecond laser pulse the irradiated powder becomes more permanendy colored, gaining an absorption spectrum comparable to a usual merocyanine form. This photo-coloration is threshold dependent and does not occur at fluences below 0.5 mJ/cm. Thermally, this colored form bleaches with complex kinetic components that exist for between minutes and hours. 

Snpatto, W., Debarre, D., Moulia, B., Bronzes, E., Martin, J. L., Farge, E., and Beaurepaire, E. 2005. In vivo modulation of morphogenetic movements in Drosophila embryos with femtosecond laser pulses. Proc. Nat. Acad. Sci. USA 102 1047-52. 

T Advanced Multiphoton and CARS Microspectroscopy with Broadband-Shaped Femtosecond Laser Pulses... 

After having established the basics of femtosecond laser pulses in microspectroscopy, we now turn to more practical aspects of possible experimental implementations laser sources and possibilities for pulse shaping. 

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