Coherent control of vibrational transitions: Discriminating molecules in mixtures

Abstract

Identifying complex molecules often entails detection of multiple vibrational resonances, especially in the case of mixtures. Phase shaping of broadband pump and probe pulses allows for the coherent superposition of several resonances, such that specific molecules can be detected directly and with high selectivity. Our particular implementation of coherent anti-Stokes Raman scattering (CARS) spectroscopy and imaging employs broadband pump and probe fields in combination with a narrowband Stokes field. We describe our approach for combining spectral phase shaping and closed-loop optimization strategies to perform chemically-selective microscopy. To predict the optimal excitation profile we employ evolutionary algorithms that use the vibrational phase responses of five distinct molecules with overlapping resonances and investigate the effect of phase instability on the optimization. We have recently shown that modified polynomials and orthogonal rational functions can give rise to improved contours for CARS fitness landscapes. Now, by considering the landscapes associated with different basis sets, we introduce two figures of merit to quantitatively rank basis functions in terms of their "appropriateness" for modeling nonlinear phase-shaped processes.

Searching for an optimal control in the presence of saddles on the quantum-mechanical observable landscape

“…The last two decades have seen a significant expansion of the boundaries of quantum optimal control experiments (OCEs) due to technological advances in experimental resources, especially femtosecond lasers and pulse-shaping capabilities [1][2][3][4][5][6][7][8][9]. OCEs have been successfully performed for a wide range of goals, including the control of molecular vibrational [10][11][12][13][14][15][16][17] and electronic states [18][19][20][21][22][23][24][25][26], the generation and coherent manipulation of X-rays [27][28][29][30][31], the control of decoherence processes [32,33], the selective cleavage and formation of chemical bonds [34][35][36][37][38][39][40], the manipulation of energy flow in macromolecular complexes [41][42][43][44], and the control of photoisomerization reactions [45]…”

“…OCEs have been successfully performed for a wide range of goals, including the control of molecular vibrational [13][14][15][16][17][18][19][20] and electronic states [21][22][23][24][25][26][27][28][29], the generation and coherent manipulation of X-rays [30][31][32][33][34], the control of decoherence processes [35,36], the selective cleavage and formation of chemical bonds [37][38][39][40][41][42][43], the manipulation of energy flow in macromolecular complexes [44][45][46][47], and the control of photoisomerization reactions [48][49][50][51][52]. Optimal control theory (OCT) [7,9,[53][54][55][56] has provided insights into the coherent control of a variety of quantum phenomena, such as electron transfer …”

Manipulation of matter with shaped-pulse light field and its applications

“…Closed-loop and open-loop methods were used to control the ratio between singlet and triplet states of zinc phthalocyanine, a model photosensitizer [185]. Using the shaped broadband pump and probe pulses in CARS, it was demonstrated that the evolutionary algorithm could find optimal pulse shapes, which will enhance the desired molecule's response and suppress the contribution from the other four molecules with overlapping resonance [186]. The method can be used in chemically-selective microscopy.…”

Discriminability of tryptophan containing dipeptides using quantum control

“…In the quest for label-free bioassays and label-free imaging techniques of biological tissues, coherent control [1,2] and in particular optimal dynamic discrimination (ODD) [3][4][5] recently emerged as an attractive novel method. The most relevant biological targets clearly consist of proteins, in which aromatic amino-acids (tryptophan, tyrosine, phenylalanine) provide sensitive fluorescing probes.…”