Search by keywords or author

Journals > > Topics > Atomic and Molecular Physics

Atomic and Molecular Physics|4 Article(s)

Manipulating the Evolution of Atomic Transient Coherent Effect

Yi-zhuo LI, Yu-jie SUN, and Zhao-ying WANG

This paper mainly focuses on exploring the influence of the radio frequency field's frequency and the different atomic coherent situation on the transient effect. It is found that the polarized coherent atoms can still experience a strong transient effect whether the radio frequency filed is resonant or detuned with the Larmor precession frequency， and the transient oscillation frequency depends on the power and frequency of radio frequency field in terms of Ω=Ω02+δ2. Furthermore， the amplitude of transient effect depends on the population of the coherent atoms is explored. The more polarized coherent atoms， the stronger the transient effect presents. At last， we analyze these phenomena by calculating the absorption of beam based on the Liouville equation. There is a good agreement between the experiment data and the theoretical results. These results can provide further insight into the relationship between the coherence of atoms and the transient effect. This paper mainly focuses on exploring the influence of the radio frequency field's frequency and the different atomic coherent situation on the transient effect. It is found that the polarized coherent atoms can still experience a strong transient effect whether the radio frequency filed is resonant or detuned with the Larmor precession frequency， and the transient oscillation frequency depends on the power and frequency of radio frequency field in terms of Ω=Ω02+δ2. Furthermore， the amplitude of transient effect depends on the population of the coherent atoms is explored. The more polarized coherent atoms， the stronger the transient effect presents. At last， we analyze these phenomena by calculating the absorption of beam based on the Liouville equation. There is a good agreement between the experiment data and the theoretical results. These results can provide further insight into the relationship between the coherence of atoms and the transient effect.

Acta Photonica Sinica

- Publication Date: Oct. 15, 2020
- Vol. 49, Issue 10, 1002001 (2020)

Power Frequency Electric Field Measurement Based on Electromagnetic Induced Transparent Spectrum under Radio Frequency Field

Chungang ZHANG, Wei LI, Hao ZHANG, Mingyong JING, and Linjie ZHANG

The two-photon （852 nm and 509 nm） excitation was used to achieve the preparation of the 53S1/2 Rydberg state of cesium atoms. The electromagnetically induced transparency spectrum of Rydberg atoms in which the radio frequency electric fields in the AC Stark effect was studied. By changing the amplitude of the radio frequency electric fields， the dependance of the Stark frequency shift of Rydberg atoms on the amplitude of the electric field was investigated. In the experiments， the power frequency electric fields were modulated to the radio frequency electric fields. The traceable measurement of the field strength of the power frequency electric field was realized. The field strength sensitivity can reach 0.37 V/cm， and the amplitude measurement dynamic range can reaches 37.2 dB. Moreover， the frequency measurement of power frequency electric fields is demonstrated， and the uncertainty of frequency measurement is smaller than 0.1%. The two-photon （852 nm and 509 nm） excitation was used to achieve the preparation of the 53S1/2 Rydberg state of cesium atoms. The electromagnetically induced transparency spectrum of Rydberg atoms in which the radio frequency electric fields in the AC Stark effect was studied. By changing the amplitude of the radio frequency electric fields， the dependance of the Stark frequency shift of Rydberg atoms on the amplitude of the electric field was investigated. In the experiments， the power frequency electric fields were modulated to the radio frequency electric fields. The traceable measurement of the field strength of the power frequency electric field was realized. The field strength sensitivity can reach 0.37 V/cm， and the amplitude measurement dynamic range can reaches 37.2 dB. Moreover， the frequency measurement of power frequency electric fields is demonstrated， and the uncertainty of frequency measurement is smaller than 0.1%.

Acta Photonica Sinica

- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 154 (2021)

Internal Relationship between Symmetrical and Asymmetric Molecular Harmonic Radiation and Its Structure

Shujuan YU, Zhuqin LIU, Dongmei CAO, Yanfeng LIU, and Yanpeng LI

For symmetric molecules, only odd harmonics are emitted. In particular, the high-order harmonic spectrum shows a significant minimum which corresponds to the minimum in the dipole moment of the bound-continuous state transition. For asymmetric molecules, both odd and even harmonics are emitted. However, in many cases, the striking minimum disappears in the odd or even harmonic spectrum. Fortunately, when the minimum cannot be read from the harmonic spectra directly, it can be probed through the polarization measurement of the odd-even high-order harmonic generation. Specifically, the position of the minimum in the odd or even dipole corresponds to the harmonic order for the maximal ellipticity of the odd or even harmonics. However, for symmetric molecules H2+, the minimum in the transition dipole is not completely consistent with the minimum of the harmonic spectra. For asymmetric molecules HeH2+, the prediction of the dipole minimum by the polarization measurement does not always agree well with the theoretical evaluation. In some cases, a remarkable difference is also observed. This remarkable difference may arise from other mechanisms beyond the description of the simple model, or the inaccurate calculation of dipole moment may be caused only by some rough approximate in relevant theoretical treatments. In this paper, this question is explored by improving the calculation of the dipole moment. The intrinsic relationship between harmonic radiation and the structure of symmetric and asymmetric molecules is studied by a combination of numerical and analytical methods. First, the numerical expressions of the ground state wave functions of symmetric and asymmetric molecules are obtained using the virtual time evolution method. Starting from the accurate ground state wave functions of symmetric and asymmetric molecules, the bound-continuous state transition dipole moments are calculated. The term proportional to the nuclear separation is further subtracted from the transition dipole moment. For symmetric molecules H2+, the calculated odd dipole moment is compared with the harmonic spectrum and the transition dipole moments obtained by the pure analytical method. For asymmetric molecules HeH2+, the calculated odd dipole moment is compared with the harmonic spectrum, the ellipticity of the harmonics and the transition dipole moments obtained by the pure analytical method. Simulation results show that the minimum in the improved odd dipole moments agree more well with that predicted by odd harmonics compared with the transition dipole moments obtained by the pure analytical method for symmetric moleculesH2+. For asymmetric molecules HeH2+, the calculated dipole moment shows a clear minimum, which arises from the effect of two-center interference. However, there is usually no minimum value appearing in the high-order harmonic spectrum of asymmetric molecules. A further comparison between the ellipticity of the harmonics and the corresponding dipole moments shows that the harmonic order at which the ellipticity is maximal corresponds to the order at which the dipole has a minimum. The polarization measurement of harmonics can be used as a tool to detect the position of the minimum value of dipole moment. The obtained ground state wave function significantly improves the consistency between the minimum odd-even dipole moment and the maximum odd-even harmonic polarization at different molecular parameters. These phenomena reveal that the recombination process plays a key role in the harmonic radiation of symmetric and asymmetric molecules and verifies the one-to-one matching between the high-order harmonic spectra and the corresponding dipoles. And molecular orbitals can be reconstructed by transition dipole elements. The research results provide deep insights into the relation between odd high-order harmonic generation and symmetric molecular orbital and the relation between odd-even high-order harmonic generation and asymmetric molecular orbital. The research results have some significance for the role of odd-even harmonic radiation in the ultrafast detection of asymmetric molecules. For symmetric molecules, only odd harmonics are emitted. In particular, the high-order harmonic spectrum shows a significant minimum which corresponds to the minimum in the dipole moment of the bound-continuous state transition. For asymmetric molecules, both odd and even harmonics are emitted. However, in many cases, the striking minimum disappears in the odd or even harmonic spectrum. Fortunately, when the minimum cannot be read from the harmonic spectra directly, it can be probed through the polarization measurement of the odd-even high-order harmonic generation. Specifically, the position of the minimum in the odd or even dipole corresponds to the harmonic order for the maximal ellipticity of the odd or even harmonics. However, for symmetric molecules H2+, the minimum in the transition dipole is not completely consistent with the minimum of the harmonic spectra. For asymmetric molecules HeH2+, the prediction of the dipole minimum by the polarization measurement does not always agree well with the theoretical evaluation. In some cases, a remarkable difference is also observed. This remarkable difference may arise from other mechanisms beyond the description of the simple model, or the inaccurate calculation of dipole moment may be caused only by some rough approximate in relevant theoretical treatments. In this paper, this question is explored by improving the calculation of the dipole moment. The intrinsic relationship between harmonic radiation and the structure of symmetric and asymmetric molecules is studied by a combination of numerical and analytical methods. First, the numerical expressions of the ground state wave functions of symmetric and asymmetric molecules are obtained using the virtual time evolution method. Starting from the accurate ground state wave functions of symmetric and asymmetric molecules, the bound-continuous state transition dipole moments are calculated. The term proportional to the nuclear separation is further subtracted from the transition dipole moment. For symmetric molecules H2+, the calculated odd dipole moment is compared with the harmonic spectrum and the transition dipole moments obtained by the pure analytical method. For asymmetric molecules HeH2+, the calculated odd dipole moment is compared with the harmonic spectrum, the ellipticity of the harmonics and the transition dipole moments obtained by the pure analytical method. Simulation results show that the minimum in the improved odd dipole moments agree more well with that predicted by odd harmonics compared with the transition dipole moments obtained by the pure analytical method for symmetric moleculesH2+. For asymmetric molecules HeH2+, the calculated dipole moment shows a clear minimum, which arises from the effect of two-center interference. However, there is usually no minimum value appearing in the high-order harmonic spectrum of asymmetric molecules. A further comparison between the ellipticity of the harmonics and the corresponding dipole moments shows that the harmonic order at which the ellipticity is maximal corresponds to the order at which the dipole has a minimum. The polarization measurement of harmonics can be used as a tool to detect the position of the minimum value of dipole moment. The obtained ground state wave function significantly improves the consistency between the minimum odd-even dipole moment and the maximum odd-even harmonic polarization at different molecular parameters. These phenomena reveal that the recombination process plays a key role in the harmonic radiation of symmetric and asymmetric molecules and verifies the one-to-one matching between the high-order harmonic spectra and the corresponding dipoles. And molecular orbitals can be reconstructed by transition dipole elements. The research results provide deep insights into the relation between odd high-order harmonic generation and symmetric molecular orbital and the relation between odd-even high-order harmonic generation and asymmetric molecular orbital. The research results have some significance for the role of odd-even harmonic radiation in the ultrafast detection of asymmetric molecules.

Acta Photonica Sinica

- Publication Date: Mar. 25, 2022
- Vol. 51, Issue 3, 0302001 (2022)

Control of Polarization States of Atomic High-order Harmonic Generation

Zhijiang LI, Guoli WANG, Zhihong JIAO, Xiaoyong LI, and Xiaoxin ZHOU

The polarization of high-order harmonics radiated from He driven by counter-rotating two-color laser field， which consists of a elliptically polarized fundamental field and its counter-rotating circular third harmonic pulse， are investigated by numerically solving the two-dimensional time-dependent Schrödinger equation with split operator method. The simulations show that the polarization state of harmonics can be fully controlled from circular polarization， through elliptically， to linearly polarized harmonics， by adjusting the ellipticity， intensity and phase of the fundamental field. This research is helpful for the generation of extreme utilityvehicle and X-ray sources with controllable polarization states in the experiment. The polarization of high-order harmonics radiated from He driven by counter-rotating two-color laser field， which consists of a elliptically polarized fundamental field and its counter-rotating circular third harmonic pulse， are investigated by numerically solving the two-dimensional time-dependent Schrödinger equation with split operator method. The simulations show that the polarization state of harmonics can be fully controlled from circular polarization， through elliptically， to linearly polarized harmonics， by adjusting the ellipticity， intensity and phase of the fundamental field. This research is helpful for the generation of extreme utilityvehicle and X-ray sources with controllable polarization states in the experiment.

Acta Photonica Sinica

- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 161 (2021)

Topics