Liquid-phase adaptive femtosecond quantum control: Removing intrinsic intensity dependencies

Abstract

Adapting optimal control theory and using learning loops to provide experimentally feasible shaping mask patterns Femtosecond adaptive pulse shaping of 800-nm laser pulses is applied to control the multiphoton molecular excitation of the charge-transfer coordination complex ͓Ru(dpb) 3 ͔(PF 6 ) 2 ͑where dpb ϭ4,4Ј-diphenyl-2,2Ј-bipyridine) dissolved in methanol. A phase-only femtosecond pulse shaper provides a mechanism for multiparameter ͑128͒ variation of the incident field, and a closed-loop evolutionary algorithm optimizes pulse shapes within the vast search space. Molecular emission at 620 nm is used as experimental feedback which is proportional to the excited-state population in the long-lived 3 MLCT ͑metal-to-ligand charge-transfer͒ state. The dominant intensity dependence of the multiphoton excitation process is removed by using second-harmonic generation ͑SHG͒ in a thin optical crystal as a general ''reference'' signal. Successful control of the emission/SHG ratio demands that the field adapt to the electronic structure or dynamic needs of the molecule in solution. This suggests that adaptive femtosecond pulse shaping can provide a general means of finding field shapes capable of selectively exciting molecules based on their unique optical properties.

Exploring quantum control landscapes: Topology, features, and optimization scaling

“…OCT simulations have successfully controlled a variety of objectives, including state preparation [2,6,7], molecular isomerization [8][9][10][11][12], dissociation [13][14][15][16], and orientation/alignment [17][18][19]. OCE using ultrafast tailored laser pulses have achieved control over many processes including state preparation [20,21], selective molecular dissociation [22][23][24], generation of high order optical harmonics [25][26][27], and energy transfer and isomerization in large biomolecules [28][29][30]. Simulation models consider from 2 to ∼ 10 2 or more states, and the atoms/molecules used in OCE often have much larger numbers of accessible states.…”

A convenient method to simulate and visually represent two-photon power spectra of arbitrarily and adaptively shaped broadband laser pulses

“…In previous work, several groups have demonstrated that adaptive femtosecond pulse shaping optimizations can improve the measured yield of emission from a molecule (following TPA) relative to SHG (the ratio TPA/SHG) by exploiting a two-photon spectral focusing mechanism [25,27,29]. In these experiments, the adaptive algorithm exerts control by finding pulse shapes that are best able to focus (or shift) the maximum intensity of the SH spectrum into the spectral region where the TPA cross section of the molecule is greatest.…”

“…Two-photon absorption (TPA) and second harmonic generation (SHG) have been investigated in a number of control scenarios [25]- [33]. The development of perturbation theory approaches to this problem builds on the work of the Noordham group [34] and the Silberberg group [35,36].…”

Identification of biological microparticles using ultrafast depletion spectroscopy

“…The method is then extremely sensitive to the details of the potential hypersurfaces, which provides unprecedented selectivity. 23,24 For this, a large number of parameters (corresponding to the amplitude and phase of each spectral component within the exciting laser pulse(s)) has to be controlled. This ''pulse shaping'' technique is usually performed by introducing a liquid crystal array in the Fourier plane between two gratings (4f arrangement).…”

“…Recent experiments using coherent control and multiphoton ultrafast spectroscopy have shown the ability to discriminate between molecular species that have similar one-photon absorption and emission spectra. 23,24 Two-Photon Excited Fluorescence (2PEF) and pulse shaping techniques should allow for selective enhancement of the fluorescence of one molecule versus another that has similar spectra. Optimal Dynamic Discrimination (ODD) 25 of similar molecular agent provides the basis for generating optimal signals for detection.…”