Quantum control of femtosecond resonance-enhanced multiphoton-ionization photoelectron spectroscopy

Abstract

We establish a theoretical model based on perturbation theory to show that the resonance-enhanced multiphoton-ionization photoelectron spectroscopy (REMPI-PS) in cesium (Cs) atom can be effectively enhanced and narrowed by appropriately shaping the femtosecond laser pulse, and the corresponding physical control processes can be well illustrated by considering the inter-and intragroup interferences involving on-and near-resonant three-photon excitation pathways. Consequently, a high-resolution REMPI-PS and fine energy-level diagram of the excited states can be obtained in spite of the broad femtosecond laser spectrum. PACS number(s): 32.80. Qk, 32.80.Rm, 42.50.Md Studying the microscopic behaviors of atom and molecule is always an interesting subject of scientists, which is very helpful for understanding and manipulating the macroscopic world. Resonance-enhanced multiphoton-ionization photoelectron spectroscopy (REMPI-PS), involving a resonant single-or multiple-photon absorption to an excited state followed by another photon that ionizes the atom or molecule, has become a powerful technique applied to the atomic and molecular spectroscopy [1][2][3][4][5], and has been widely applied to study the excited or Rydberg state structure and the photoionization and dissociation process [6][7][8][9][10][11][12][13][14]. By observing REMPI-PS, one can determine which excited state is ionized that offers the structure information of the excited states, and also identify the dynamical processes occurring in the excited states that the electrons derive from the ionization of the neutral medium or the dissociation of the parent ion.Nanosecond or picosecond laser pulse was a wellestablished tool to achieve high-resolution REMPI-PS [15-18], but the nanosecond or picosecond REMPI-PS was not suitable to study the dynamical process of the excited state due to the long pulse duration, such as transient population, wavepacket evolution, proton transfer, and so on. The femtosecond laser pulse was considered as an ideal excitation source because of its high laser intensity and short pulse duration [19,20], while an inevitable question for the femtosecond REMPI-PS is poor spectral resolution due to the large laser spectral bandwidth. Recently, the advent of the femtosecond pulse shaping technique by modulating the laser spectral phase and/or amplitude in the frequency domain opened an opportunity to effectively control the femtosecond REMPI-PS. Various phase modulation schemes have been proposed to enhance or narrow the REMPI-PS [21][22][23][24][25][26][27][28][29], and some schemes have been experimentally realized [21][22][23][24][25]. For example, Wollenhaupt et al. experimentally demonstrated the selective excitation of the slow and fast photoelectron components of REMPI-PS by sinusoidal, chirped, or phase-step modulation [21-24]. Krug et al. experimentally achieved the enhancement * sazhang@phy.ecnu.edu.cn † zrsun@phy.ecnu.edu.cnand suppression of REMPI-PS by chirped phase modulation [25]. We theoretically propose a π or cubic p...

Stimulated Emission Enhancement Using Shaped Pulses

“…Here we explore stimulated emission resulting from the third-order polarization of cyanine dye molecules in solution when using a spectral phase step function. Two-photon transition control has been particularly successful when using a phase step because of constructive interference occurring at twice the frequency corresponding to the position of the phase step; this control has been reported for atoms as well as large organic molecules. − The similarity between two-photon excitation and coherent anti-Stokes Raman scattering (CARS) led to a phase step being used to enhance CARS signals. , Under direct resonance with a transition, a phase step has been used on isolated atoms and diatomics, detecting the resonant features as the phase step is scanned within the bandwidth of the excitation pulse. ,− There is only one case when the transmitted laser and resulting third-order polarization has been analyzed theoretically when using a phase step, and that study was inspired by the results being presented here.…”

Effect of laser spectral bandwidth on coherent control of resonance-enhanced multiphoton-ionization photoelectron spectroscopy

“…[15][16][17][18] We showed that the femtosecond-induced REMPI-PS can be greatly narrowed and enhanced by a π or cubic phase modulation. [19][20][21][22][23] In our previous study, 23 we demonstrated that, by measuring the photoelectron intensity at a given kinetic energy and scanning the single π phase step position, a highresolution (2 + 1) REMPI-PS can be obtained. However, in present study we will demonstrate that the high-resolution a) Email: jxding@phy.ecnu.edu.cn b) Email: sazhang@phy.ecnu.edu.cn (2 + 1) REMPI-PS cannot be achieved at any measured position of the kinetic energy by this measurement method, which is dependent of the laser spectral bandwidth.…”

“…Our previous works showed that, by measuring the photoelectron intensity at a given kinetic energy and scanning the single π phase step position, the high-resolution (2 + 1) REMPI-PS can be obtained. 23 In order to show that the highresolution photoelectron spectroscopy will be affected by the laser spectral bandwidth, we measure three different positions of the kinetic energy that are at E meas ν = 1.1022, 1.1084, and 1.1146 eV, as shown with three vertical dashed lines in Fig. 2.…”