Laser control of a dark vibrational state of acetylene in the gas phase—Fourier transform pulse shaping constraints and effects of decoherence

Abstract

We propose a methodology to tackle the laser control of a non-stationary dark ro-vibrational state of acetylene (C2H2), given realistic experimental limitations in the 7.7 μm (1300 cm−1) region. Simulations are performed using the Lindblad master equation, where the so-called Lindblad parameters are used to describe the effect of the environment in the dilute gas phase. A phenomenological representation of the parameters is used, and they are extracted from high-resolution spectroscopy line broadening data. An effective Hamiltonian is used for the description of the system down to the rotational level close to experimental accuracy. The quality of both the Hamiltonian and Lindblad parameters is assessed by a comparison of a calculated infrared spectrum with the available experimental data. A single shaped laser pulse is used to perform the control, where elements of optics and pulse shaping using masks are introduced with emphasis on experimental limitations. The optimization procedure, based on gradients, explicitly takes into account the experimental constraints. Control performances are reported for shaping masks of increasing complexity. Although modest performances are obtained, mainly due to the strong pulse shaping constraints, we gain insights into the control mechanism. This work is the first step toward the conception of a realistic experiment that will allow for population characterization and manipulation of a non-stationary vibrational “dark” state. Effects of the collisions on the laser control in the dilute gas phase, leading to decoherence in the molecular system, are clearly shown.

Modulated super-Gaussian laser pulse to populate a dark rovibrational state of acetylene

“…39 On the dynamical perspective, the couplings lead to the IVR processes. 40 Alike in Aerts et al, 31 we consider here the N s = 0, N r = 2 polyad near 1330 cm -1 , namely the ν 4 + ν 5 band which includes two zero-order states: the bright |0001…”

“…Vibrational eigenstates show complex dynamics that is a combination of the underlying zero-order states motions. The numerical values of the Hamiltonian matrix used in this study can be found in the Supplemental material of Aerts et al 31 and the energetic structure of the rovibrational states involved in the dynamics described below are illustrated in Fig. 1.…”

“…29,30 The effective Hamiltonian together with the effective dipole moment provide the structural parameters (eigenvalues, eigenvectors and transition moments) necessary to optimize laser pulses, as was used in previous studies. [31][32][33][34] These pulses were conceived to control the population of rovibrational dark states, i.e., non-stationary states, of C 2 H 2 . With the structural parameters in this form, we work with the matrix representation formulation of the Schrödinger equation.…”

“…The so-called Lindblad parameters are either calculated from direct measurements of the system-environment kinetics or extracted from measured line broadening coefficients. 32 In a previous study, 31 combination of the most accurate vibration-rotation Hamiltonian available to date, inclusion of the strong experimental shaping limitations in the control pulse optimization procedure and the decoherence due to inelastic collision effects enabled to propose an experimental setup for pulse shaping using masks. Unfortunately, this approach reduced considerably the performance of the control due to the shaping limitations.…”

Generation of 8–20 μm Mid-Infrared Ultrashort Femtosecond Laser Pulses via Difference Frequency Generation

“…The MIR ultrashort pulsed lasers can be widely used in gas detection [7,8], cancer diagnosis [9][10][11], pollutant monitoring [12][13][14][15][16], food quality control [17][18][19][20][21][22][23], and other aspects [24][25][26][27][28], since they own much broader spectral ranges than ultrafast lasers in visible and near-infrared region. In addition, they also play essential roles in strong-field physics [29][30][31][32][33][34], laser surgery [35][36][37][38][39][40][41], attosecond science [42,43], and molecule dynamics [44][45][46] (as shown in Figure 1b), as they feature the ultrashort time domain and have the potential to achieve peak powers. Therefore, there is an essential and broad application value in MIR ultrashort pulse generation research.…”