Femtosecond control

Femtosecond Control of an Elementary Unimolecular Reaction From the Transition-State Region, J. L. Herek, A. Matemy, and A. H. Zewail, Chem. Phys. Lett. 228, 15 (1994). 

The chapter is organized as follows first, the concepts of coherent control in the femtosecond to picosecond domain are outlined together with a short introduction into the theoretical framework of the OCT formalism. Second two different concepts of sub-femtosecond control are discussed and their realization in theory. Examples of controlled molecular quantum dynamics including implicit and explicit control of electron motion are presented. We conclude with an outlook how the control of complex reactions in large molecules could be assisted by steered electronic wavepackets. 

Kling M, von den Hoff P, Znakovskaya I, de Vivie-Riedle R (2013) (Sub-)femtosecond control of molecular reactions via tailoring the electric field of light. Phys Chem Chem Phys 15 9448... 

New concepts of coherent femtosecond control, quantum learning, and feedback control of molecules have been proposed and demonstrated successfully in several laboratories for the past two decades. Moreover, significant advances have been made toward establishing broad foundations and laboratory implementation of control over quantum phenomena in various quantum systems, from atoms to complex molecules. 

Pastirk I, Brown E J, Grimberg B I, Lozovoy V V and Dantus M 1999 Sequences for controlling laser excitation with femtosecond three-pulse four-wave mixing Faraday Discuss. 113 401... 

Tannor D J 1994 Design of femtosecond optical pulses to control photochemical products Molecules in Laser Fields ed A Bandrauk (New York Dekker) p 403... 

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... 

Gaspard P and Burghardt I (ed) 1997 XXth Solvay Conf on Chemistry Chemical Reactions and their Control on the Femtosecond Time Scale (Adv. Chem. Phys. 101) (New York Wiley)... 

Zewail A H 1995 Femtosecond dynamics of reactions elementary processes of controlled solvation Ber. Bunsenges. Phys. Chem. 99 474-7... 

D. J. Tannor, Design of Femtosecond Optical Pdlse Sequences to Control Photochemical Products, in A. D. Bandrark, ed., MoleciM.es in Laser Fields, Dekker, New York, 1994. 

In 1991 a remarkable discovery was made, accidentally, with a Tp -sapphire laser pumped with an Ar+ laser. Whereas we would expect this to result in CW laser action, when a sharp jolt was given to the table supporting the laser, mode locking (Section 9.1.5) occurred. This is known as self-locking of modes, and we shall not discuss further the reasons for this and how it can be controlled. One very important property of the resulting pulses is that they are very short. Pulse widths of a few tens of femtoseconds can be produced routinely and with high pulse-to-pulse stability. Further modification to the laser can... 

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

Agate, B., Brown, C., Sibbett, W. and Dholakia, K. (2004) Femtosecond optical tweezers for in-situ control of two-photon fluorescence. Opt. Express, 12, 3011-3017. 

Figure 12.1 Schematic of the spectroelectrochemistry apparatus at the University of Dlinois. The thin-layer spectroelectrochemical cell (TLE cell) has a 25 p.m thick spacer between the electrode and window to control the electrolyte layer thickness and allow for reproducible refilbng of the gap. The broadband infrared (BBIR) and narrowband visible (NBVIS) pulses used for BB-SFG spectroscopy are generated by a femtosecond laser (see Fig. 12.3). Voltammetric and spectrometric data are acquired simultaneously.

By making use of classical or quantum-mechanical interferences, one can use light to control the temporal evolution of nuclear wavepackets in crystals. An appropriately timed sequence of femtosecond light pulses can selectively excite a vibrational mode. The ultimate goal of such optical control is to prepare an extremely nonequilibrium vibrational state in crystals and to drive it into a novel structural and electromagnetic phase. 

The modest electrical drive requbements of these diodes, and the resulting option to power the laser with standard penlight (AA) batteries, allow these CnLiSAF lasers to boast an impressive electrical-to-optical efficiency of over 4 %, which until recently" was the highest reported overall system efficiency of any femtosecond laser source. The amplitude stability of the laser output was observed to be very stable with a measured fluctuation of less than 1% for periods in excess of 1 h. These measurements were made on a laser that was not enclosed and located in a lab that was not temperature-controlled. In a more enclosed and conbolled local envbonment we would expect the amplitude fluctuations of this laser to be extremely small. While the output powers achievable from these lasers have been limited by the available power from the AlGalnP red laser pump diodes, there are already sbong indications that commercial access to higher-power suitable diode lasers is imminent. 

Let us consider molecular switches based on intramolecular electronic transition. Generally, transfer of energy or an electron within a molecule proceeds in femtoseconds. The aim is to produce molecular electronic devices that respond equally rapidly. Molecular switches that employ optically controlled, reversible electron-transfer reactions sometimes bring both speed and photostability advantages over molecular switches which are usually based on photochemical changes in their molecular structure. Important examples are the molecnlar switches depicted in Scheme 8.3 (Debreczeny et al. 1996). 

This latter application is the key to the broadband femtosecond approach to nonlinear microspectroscopy presented here. From the point of view of coherent control, it becomes clear that high spectral bandwidths are needed providing a hnge nnmber of photon energies and, as such, interfering pathways is necessary to be able to achieve high interference contrast, and thus good controllability of optical processes. 

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