Adaptive pulse compression for transform-limited 15-fs high-energy pulse generation

Zeek, E.; Bartels, Randy A.; Murnane, Margaret M.; Kapteyn, Henry C.; Backus, Sterling; Vdovin, Gleb

doi:10.1364/ol.25.000587

Cited by 112 publications

(57 citation statements)

References 21 publications

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“…The laser system generates temporally shaped pulses as short as 15 fs, at a 1 kHz repetition rate, with over 1 mJ of energy [17]. A pulse shaper based on a 19 element deformable mirror is inserted between the oscillator and the ampli®er [18].…”

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confidence: 99%

Coherent learning control of vibrational motion in room temperature molecular gases

Weinacht

Bartels

Backus

et al. 2001

Chemical Physics Letters

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107

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An evolutionary learning algorithm in conjunction with an ultrafast optical pulse shaper was used to control vibrational motion in molecular gases at room temperature and high pressures. We demonstrate mode suppression and enhancement in sulfur hexa¯uoride and mode selective excitation in carbon dioxide. Analysis of optimized pulses discovered by the algorithm has allowed for an understanding of the control mechanism. Ó 2001 Elsevier Science B.V. All rights reserved.Controlling atoms and molecules with coherent optical ®elds has been a longstanding goal in chemical physics [1]. Recently, several experiments in this ®eld have demonstrated successful control of molecular ionization and dissociation [2,3], atomic and molecular¯uorescence [4,5], the shape of electronic and molecular wave packets [6±9], and currents in semiconductors [10,11]. Many of these experiments have employed learning control loops and programmable optical pulse shapers to discover optimal pulse shapes for control [12]. There has been increasing interest in not only achieving control in quantum systems, but also in understanding the control mechanism, which has proven to be a challenging task. Here we demonstrate two experimental advances in coherent control of quantum systems. First, we demonstrate selective control over molecular motion in gases at STP using very short, shaped excitation pulses. Coherent vibrational excitation corresponding to thermal temperatures over 2000 K is achieved. This is important in order to reach the goal of laser selective chemistry [13] on a macroscopic scale, because it extends cryogenic and molecular beam experiments to high temperatures and densities. Second, using a special cost function [14] incorporated into an evolutionary learning algorithm [15], we obtain a clear interpretation of the control mechanism, which is based on impulsive stimulated Raman scattering [16]. This serves as a demonstration of a general technique for systematically gaining insight from solutions found by learning algorithms. Furthermore, as there is no molecular resonance exploited in this excitation scheme, and the

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confidence: 99%

Coherent learning control of vibrational motion in room temperature molecular gases

Weinacht

Bartels

Backus

et al. 2001

Chemical Physics Letters

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107

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“…In our experiment, mJ-energy pulses from a 1-kHz repetition-rate laser system [20] were focused into a 175 -m-diameter argon-filled hollow waveguide. This creates a phase-matched comb of harmonics containing the 23rd-31st orders [21].…”

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confidence: 99%

Learning from learning algorithms: Application to attosecond dynamics of high-harmonic generation

et al. 2004

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Using experiment and modeling, we show that the data set generated when a learning algorithm is used to optimize a quantum system can help to uncover the physics behind the process being optimized. In particular, by optimizing the process of high-harmonic generation using shaped light pulses, we generate a large data set and analyze its statistical behavior. This behavior is then compared with theoretical predictions, verifying our understanding of the attosecond dynamics of high-harmonic generation and uncovering an anomalous region of parameter space. Experiments that study the dynamics of quantum systems, such as optical studies of atomic and molecular dynamics, often employ a "pump-probe" configuration where a pump pulse perturbs a system, and a probe pulse at varying time delay probes its evolution [1]. However, this technique corresponds to a simplified case of the more-general "stimuliresponse" experiment, where by observing the dynamical response of a system to varying stimulus, one can compare experiment with hypothesis. Often, in the case where the physics of a system is relatively simple, a pump-probe experiment can provide the most-readily interpretable data. However, pump-probe experiments can be difficult to interpret in the case of a complex quantum system, where the full dynamics are not already understood. Therefore devising new approaches to uncover and understand the dynamics of quantum systems is very important, in particular in the case of complex chemical and biological systems. Another area that requires a more sophisticated approach is the emerging field of "attosecond science" where subfemtosecond electron dynamics in atoms and molecules are observed. In this area, experimental constraints limit the applicability of a straightforward "pump-probe" experiment, and instead experiments infer various light source properties and electronic dynamics, using various comparisons of experimental observations with theoretical models [2][3][4][5].The more general case of a stimulus-response experiment was discussed by Rabitz [6] for the case of optically probed quantum (i.e., atomic, molecular, or electronic) systems. He suggested that the use of "learning algorithms" could both accomplish coherent control over a quantum system to obtain a desirable outcome [7][8][9][10][11][12], as well as provide information about the quantum system itself. In past work, we demonstrated the power of learning algorithms to selectively optimize the generation of coherent extreme-ultraviolet light using high-harmonic generation (HHG) [2]. By adjusting the phase of the laser field guided by a learning algorithm, we manipulated and optimized the quantum interferences that occur during the HHG process to achieve selective optimization of a single harmonic order. A comparison of theory with experiment was used to identify the mechanism behind the optimization: an optimally shaped light pulse allowed the phase of the radiating electron wave function to be adjusted on 10-20 attosecond time scales to selectively optimize a ...

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“…[Note: to maximize D͑V͒, f͑v͒ 2 f͑V 2 v͒ const.] Later in the text, we compare the excitation of Raman modes with intense transformlimited pulses to that of low-intensity chirped Raman excitation and observe the breakdown of the weak excitation limit described by this analysis.For our experiments, we used 15 fs (ϳ660 cm 21 FWHM bandwidth) laser pulses generated by an amplified Ti:sapphire laser system, at a 1 kHz repetition frequency, and with an energy of ϳ1 mJ [10]. The pulses from our laser 033001-1 0031-9007͞02͞ 88(3)͞033001(4)$20.00…”

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confidence: 99%

“…For our experiments, we used 15 fs (ϳ660 cm 21 FWHM bandwidth) laser pulses generated by an amplified Ti:sapphire laser system, at a 1 kHz repetition frequency, and with an energy of ϳ1 mJ [10]. The pulses from our laser were shaped using two separate techniques.…”

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confidence: 99%

Nonresonant Control of Multimode Molecular Wave Packets at Room Temperature

et al. 2002

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We demonstrate the creation and measurement of shaped multimode vibrational wave packets with overtone and combination mode excitation in CCl 4 . Excitation of wave packets through nonresonant impulsive stimulated Raman scattering allows for coherent control of molecular vibrations without passing through an electronic resonance. This technique is therefore very general and can be implemented in a large class of molecular gases and liquids at STP, which were previously inaccessible because their resonances are in the VUV. DOI: 10.1103/PhysRevLett.88.033001 PACS numbers: 33.80. -b, 42.65.Dr With the advent of ultrafast lasers capable of generating pulses that are short in comparison to molecular time scales, there has been considerable interest in creating and measuring vibrational wave packets. Early experiments generated wave packets in excited electronic states and demonstrated control over the position of these wave packets as a function of time [1]. Recent experiments [2] have included nuclear motion in the ground electronic state, which is directly relevant to controlling and monitoring many chemical reactions. These experiments focused on controlling motion in a single normal mode of the system. Extending control and measurement of vibrational motion to several modes including overtones is an exciting prospect for several types of studies, including mode coupling and bond selective chemistry [3,4]. Furthermore, most past work on ground state vibrations relied on transferring population through an excited electronic state (resonant Raman). In this Letter we demonstrate the creation and measurement of shaped multimode vibrational wave packets in CCl 4 with strong overtone excitation, implying a significant vibrational amplitude. We also control which modes and which mode combinations are excited. A learning algorithm is used to automate the control process. Past work in CCl 4 used sequences of five pulses to excite vibrational modes to investigate intramode coupling and anharmonicity, although no overtone or combination modes were observed [5].The vibrational wave packets in this work are excited with a single pulse far detuned from electronic resonances, achieving nonresonant control of the amplitude of modes in the wave packet, as shown in earlier solid state impulsive stimulated Raman scattering (ISRS) experiments [6,7]. Because it is nonresonant, it can be generalized to any molecular gas or liquid with Raman-active modes that can be excited impulsively, and it is not limited by the need to access resonances in the VUV. This approach works at high pressures and temperatures, and thus may facilitate laser control of chemical reactions with macroscopic product yields. In particular, since changes in chemical bonding will involve a superposition of several modes, control of multimode wave packets may lead to selective control over reactions.Excitation of Raman-active modes involves two photons with a frequency difference equal to the vibrational energy. If the duration of a driving laser pulse t p is sh...

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Adaptive pulse compression for transform-limited 15-fs high-energy pulse generation

Cited by 112 publications

References 21 publications

Coherent learning control of vibrational motion in room temperature molecular gases

Coherent learning control of vibrational motion in room temperature molecular gases

Learning from learning algorithms: Application to attosecond dynamics of high-harmonic generation

Nonresonant Control of Multimode Molecular Wave Packets at Room Temperature

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