Coherent control holds the promise of becoming a powerful spectroscopic tool for the study of complex molecular systems. Achieving control requires coherence in the quantum system under study. In the condensed phase, coherence is typically lost rapidly because of fluctuating interactions between the solvated molecule and its surrounding environment. We investigate the degree of attainable control on a dye molecule when the fluctuations of its environment are systematically varied. A single successful learning curve for optimizing stimulated emission from the dye in solution is reapplied for a range of solvents with varying viscosity, revealing a striking trend that is correlated directly with the dephasing time. Our results provide clear evidence that the environment limits the leverage of control on the molecular system. This insight can be used to enhance the yield of control experiments greatly.coherent control ͉ quantum-control spectroscopy ͉ solvation dynamics C oherent control has been recognized as a potential spectroscopic tool for the study of complex molecular systems (1). With this technique, a molecular system is selectively guided through a potential energy landscape toward a target quantum state by shaped light fields, often employing a closed-loop learning algorithm (2-9). The central idea is that the pulse shapes corresponding to the highest yield contain spectroscopic information concerning the quantum system, yet often the complexity of these pulses hinders their interpretation. Further, achieving control requires coherence in the quantum system under study. In the condensed phase, coherence is typically lost rapidly because of fluctuating interactions between the solvated molecule and its surrounding environment. In simple molecular systems in the gas phase, coherent control has been used to guide the system into a subspace with enhanced decoherence times (10). For solvated molecules, this approach is infeasible because of the complexity added by the environment. Nonetheless, it has been found surprisingly easy to come up with control fields for a wide range of systems (11), from simple atomic systems to large biomolecules. These control fields exert their influence even when the system is interacting with a fluctuating environment such as a protein or a solvent (8). However, in only a few isolated cases has the goal of deriving fundamental properties of the system and the physical mechanism of control been achieved (3, 4, 7). The complexity of the pulse shape hinders the usefulness of coherent control as a research tool, and more progress needs to be made in understanding the basic mechanisms of control and how these apply to a variety of molecular systems. An important objective is to find ''rules of thumb'' for coherent control, where a given shaped pulse produces a predictable and universal response. A promising route to the realization of this goal is to study a set of systems in which some parameter is systematically varied (12). In this article, we show how the amount of attainable cont...

Abstract. This study describes first steps taken to bring evolutionary optimization technology from computer simulations to real world experimentation in physics laboratories. The approach taken considers a well understood Laser Pulse Compression problem accessible both to simulation and laboratory experimentation as a test function for variants of Evolution Strategies. The main focus lies on coping with the unavoidable noise present in laboratory experimentation. Results from simulations are compared to previous studies and to laboratory experiments.

Pulse shaping techniques are used to improve the selectivity of broadband CARS experiments, and to reject the overwhelming background. Knowledge about the fitness landscape and the capability of tailoring it is crucial for both fundamental insight and performing an efficient optimization of phase shapes. We use an evolutionary algorithm to find the optimal spectral phase of the broadband pump and probe beams in a background-suppressed shaped CARS process. We then investigate the shapes, symmetries, and topologies of the landscape contour lines around the optimal solution and also around the point corresponding to zero phase. We demonstrate the significance of the employed phase bases in achieving convex contour lines, suppressed local optima, and high optimization fitness with a few (and even a single) optimization parameter.

Abstract:Finding an optimal phase pattern in a multidimensional solution landscape becomes easier and faster if local optima are suppressed and contour lines are tailored towards closed convex patterns. Using wideband second harmonic generation as a coherent control test case, we show that a linear combination of spectral phase basis functions can result in such improvements and also in separable phase terms, each of which can be found independently. The improved shapes are attributed to a suppressed nonlinear shear, changing the relative orientation of contour lines. The first order approximation of the process shows a simple relation between input and output phase profiles, useful for pulse shaping at ultraviolet wavelengths.

Many spectroscopic applications of femtosecond laser pulses require properly-shaped spectral phase profiles. The optimal phase profile can be programmed on the pulse by adaptive pulse shaping. A promising optimization algorithm for such adaptive experiments is evolution strategy (ES). Here, we report a four fold increase in the rate of convergence and ten percent increase in the final yield of the optimization, compared to the direct parameterization approach, by using a new version of ES in combination with Legendre polynomials and frequency-resolved detection. Such a fast learning rate is of paramount importance in spectroscopy for reducing the artifacts of laser drift, optical degradation, and precipitation. shaper with common-path spectral interferometry and application to coherent control with a covariance matrix adaptation evolutionary strategy," Rev. Sci. Instrum. 79(3), 033103 (2008).