Ultrashort pulsed laser

Kruger, J. and Kautek, W. Ultrashort Pulse Laser Interaction with Dielectrics and Polymers, Vol. 168, pp. 247-290. 

The events taking place in the RCs within the timescale of ps and sub-ps ranges usually involve vibrational relaxation, internal conversion, and photo-induced electron and energy transfers. It is important to note that in order to observe such ultrafast processes, ultrashort pulse laser spectroscopic techniques are often employed. In such cases, from the uncertainty principle AEAt Ti/2, one can see that a number of states can be coherently (or simultaneously) excited. In this case, the observed time-resolved spectra contain the information of the dynamics of both populations and coherences (or phases) of the system. Due to the dynamical contribution of coherences, the quantum beat is often observed in the fs time-resolved experiments. 

With development of ultrashort pulsed lasers, coherently generated lattice dynamics was found, first as the periodic modulation in the transient grating signal from perylene in 1985 by De Silvestri and coworkers [1], Shortly later, similar modulation was observed in the reflectivity of Bi and Sb [2] and of GaAs [3], as well as in the transmissivity of YBCO [4] by different groups. Since then, the coherent optical phonon spectroscopy has been a simple and powerful tool to probe femtosecond lattice dynamics in a wide range of solid... 

Recent rapid developments in ultrashort pulse laser [1-5] make it possible to probe not only the dynamics of population of the system but also the coherence (or phase) of the system. To treat these problems, the density matrix method is an ideal approach. The main purpose of this paper is to briefly describe the application of the density matrix method in molecular terms and show how to apply it to study the photochemistry and photophysics [6-9]. Ultrafast radiationless transactions taking place in bacterial photosynthetic reaction centers (RCs) are very important examples to which the proposed theoretical approach can be applied. 

Abdallah Jr. J, Csanak G, Fukuda Y, Yamakawa K, Akahane Y, Aoyama M, Inoue N, Ueda H, Faenov AYa, Magunov AI, Pikuz TA, Skobelev IYu (2003) Time-dependent Boltzmann kinetic model of X-rays produced by ultrashort-pulse laser irradiation of argon clusters. Phys. Rev. A 68 0632011-0632018... 

B. La Fontaine, D. Comtois, C. Y. Chien, A. Desparois, F. Gerin, G. Jarry, T. W. Johnston, J. C. Kieffer, F. Martin, R. Mawassi, H. Pepin, F. A. M. Rizk, F. Vidal, C. Potvin, P. Couture, H. P. Mercure, Guiding large-scale spark discharges with ultrashort pulse laser filaments, Journal of Applied Physics 88, 610 (2000). 

Most recently, the range of asymmetric photochemistry was extended to shorter wavelengths by the use of synchrotron radiation and two-photon excitation. New developments are visible with high-intensity and ultrashort pulse lasers (see Sec. D of this chapter and Chap. 2 of this book). 

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. 

The conventional narrowband CARS process probes one particular vibrational mode selectively. Conversely, so-called broadband CARS measurements, using ultrashort pulsed laser sources, can probe multiple RS-active vibrational modes simultaneously [19, 29-31]. In the case of two-beam broadband CARS method, one of the two beams has a narrow bandwidth and the other a broad bandwidth. Therefore, the technical issue is how to generate these beams from a single laser source. Typically, subpicosecond pulses from a conventional solid-state femtosecond laser... 

Fushinobu, K., Phinney, L.M., Kurosaki, Y., and Tien, C.L. (1999) Optimization of Laser Parameters for Ultrashort-Pulse Laser Recovery of Stiction-Failed Microstructures, Numerical Heat Transfer, Part A, Vol. 36, pp. 345-357. 

Since single-photon recording does not require ultrashort-pulse lasers, conventional semiconductor lasers can be used in the 3D memories. The optics in CD and DVD devices can be easily applied for a recording system of 3D optical memory. 

The ultrashort-pulse lasers increase the cost of a recording device and make it difficult to produce a compact system, but a compact ultrashoit pulse laser in which Er-doped fiber is used as a resonator has been developed. Semiconductor lasers with mode-locked operations are also under investigation, so the cost and size of ultrashort-pulse lasers will decrease in the future. 

In this chapter, we summarize recent progress in the photochemistry of shortlived species by use of multibeam excitation, including our recent achievements in this field. Our research group has employed various multibeam irradiation methods to reveal reaction processes of various excited intermediates, including basic molecules and biomolecules. We also achieved direct observation of shortlived species utilizing ultrashort pulse lasers. These results are interesting recent examples of reactions induced by multibeam irradiation. Based on the excitation method, this chapter is divided into the following sections Pulse Radiolysis-Laser Flash Photolysis (Section II), Two-Color Two-Laser Flash Photolysis (Section III), and Three-Color Three-Laser Flash Photolysis (Section IV). Each section is further divided into subsections based on the topics. 

In this chapter, several examples of photochemistry of short-lived species by multibeam irradiation are introduced. In many cases, the properties of excited intermediates have been investigated by using nanosecond lasers. Since the lifetime of excited intermediates is usually quite short, investigations employing ultrashort laser pulses are intrinsically important. Various properties estimated by the direct manner will appear in the near future. Recent progress of ultrashort pulse lasers and detection systems will make this possible. On the other hand, utilization of multiple excitations is not limited to the basic study of excited intermediates. These are applicable to biological and environmental fields. Further fruitful results are expected for these explorations. 

Recently, Zewail and co-workers [54] applied the degenerate four-wave mixing (DFWM) technique with an ultrashort pulsed laser to a study of chemical reactions (unimolecular dissociation reaction of Nal, bimolecular reaction Na + H2) in the gas phase. Comparing this technique with other means, they showed that the wave packet motion extracted from the DFWM is in excellent agreement with results obtained from the laser induced fluorescence technique. 

Ultrashort Pulse Laser Interaction with Dielectrics and Polymers... 

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