Hong-Ping Liu

Bio: Hong-Ping Liu is an academic researcher from Chinese Academy of Sciences. The author has contributed to research in topics: Electromagnetically induced transparency & Magnetic field. The author has an hindex of 3, co-authored 10 publications receiving 43 citations. Previous affiliations of Hong-Ping Liu include Dalian Institute of Chemical Physics.

Electromagnetically induced transparency of 87Rb in a buffer gas cell with magnetic field

Abstract: We have studied the phenomenon of electromagnetically induced transparency (EIT) of 87Rb vapor at room temperature in a magnetic field with an arbitrary angle to the laser propagation direction. Rather than exposing atoms to a parallelled or transverse magnetic field as usual, in our work, we apply a magnetic field (up to 45 Gauss) with an arbitrary angle to the laser propagation direction and the spectra become much more complex. More EIT dips are observed due to the Zeeman splitting on the D 2 line of 87Rb in a -type configuration. With a 5 Torr N2 buffer gas in the thermal 2 cm vapor cell, the state has a very short effective lifetime, corresponding to a large energy broadening, which removes the velocity selective optical pumping effect almost completely and keeps the high resolution EIT spectrum for the energy splitting of 87Rb in magnetic fields. The shifting of the EIT resonances with the strength of the applied magnetic field coincides well with the theory based on a full matrix Hamiltonian combined with a spectral decomposition method. Our work can be extended to measure the magnetic field vector in space. The effects of the detuning of the probe and coupling beams on the spectral lines are also investigated.

Photodissociation dynamics of CF3I investigated by two-color femtosecond laser pulses

Abstract: We report an experimental study of the multiphoton dissociation dynamics of CF3I performed on a home-built femtosecond laser pump-probe system; with time-of-flight mass spectrometer. The first repulsive A band and the 5p pi(3)7s sigma v(2) = 1 Rydberg state of CF3I were accessed by one- and two-photon transitions at 267 nm, respectively; with the latter two-photon absorption followed by a further two-photon probe transition at 401 nm to the (B) over tilde state of the parent ion. The observed signals from the CF3+ and I+ fragments show similar multi-component exponential decay patterns but the former is 4 times stronger than the latter. However; the parent CF3I+ signal was observed to evolve in a very different manner; decreasing sharply when probed in the first 289 fs following excitation and subsequently rising again after 860 fs to a constant level below that measured at negative pump-probe delay times when the pump and probe pulses exchange roles. This dip observed in the parent ion profile; is very different from that previously reported at shorter pump wavelengths of 264 nm or 265 ran, and is interpreted as the competition between two different ionization channels. One from the vibrationally excited v(2) = 1 of the irradiated Rydberg state and the other from the dissociative vibrational origin of the same electronic state which is populated by internal vibrational relaxation.

Laser frequency offset-locking using electromagnetically induced transparency spectroscopy of 85 Rb in magnetic field

Abstract: We have experimentally offset-locked the frequencies of two lasers using electromagnetically induced transparency (EIT) spectroscopy of 85Rb vapor with a buffer gas in a magnetic field at room temperature The magnetic field is generated by a permanent magnet mounted on a translation stage and its field magnitude can be varied by adjusting the distance between the magnet and Rb cell, which maps the laser locking frequency to the space position of the magnet This frequency–space mapping technique provides an unambiguous daily laser frequency detuning operation with high accuracy A repeatability of less than 05 MHz is achieved with the locking frequency detuned up to 184 MHz when the magnetic field varies from 0 up to 80 G

Towards a test of string theory using Rydberg atoms

Abstract: The current controversy over the need for an experimental test of String Theory is considered. We report recent experiments on quasi-bound electrons in crossed electric and magnetic fields, in which states of very large electric dipole moment are excited. The excited electron is confined to one side of the atomic nucleus in the outer well of a controllable double-well potential. These states are discussed in relation to a recent theoretical proposal to test the spatial non-commutativity underpinning String Theory by studying Penning orbits of Rydberg atoms in crossed electric and magnetic fields.

High quality electromagnetically induced transparency spectroscopy of 87 Rb in a buffer gas cell with a magnetic field

Abstract: We have studied the phenomenon of electromagnetically induced transparency (EIT) of 87Rb vapor with a buffer gas in a magnetic field at room temperature. It is found that the spectral lines caused by the velocity selective optical pump effects get much weaker and wider when the sample cell is mixed with a 5-Torr N2 gas while the EIT signal is kept almost unchanged. A weighted least-square fit is also developed to remove the Doppler broadening completely. This spectral method provides a way to measure the Zeeman splitting with high resolution, for example, the Λ-type EIT resonance splits into four peaks on the D2 line of 87Rb in the thermal 2-cm vapor cell with a magnetic field along the electric field of the linearly polarized coupling laser. The high-resolution spectrum can be used to lock the laser to a given frequency by tuning the magnetic field.

Imaging CF3I conical intersection and photodissociation dynamics with ultrafast electron diffraction

Abstract: Conical intersections play a critical role in excited-state dynamics of polyatomic molecules because they govern the reaction pathways of many nonadiabatic processes However, ultrafast probes have lacked sufficient spatial resolution to image wave-packet trajectories through these intersections directly Here, we present the simultaneous experimental characterization of one-photon and two-photon excitation channels in isolated CF3I molecules using ultrafast gas-phase electron diffraction In the two-photon channel, we have mapped out the real-space trajectories of a coherent nuclear wave packet, which bifurcates onto two potential energy surfaces when passing through a conical intersection In the one-photon channel, we have resolved excitation of both the umbrella and the breathing vibrational modes in the CF3 fragment in multiple nuclear dimensions These findings benchmark and validate ab initio nonadiabatic dynamics calculations

Electromagnetically induced absorption in a four-state system

Abstract: Summary form only given. It is well-known that nonlinear interference effects in the resonant atom-light interaction can lead to interesting and important phenomena, such as electromagnetically induced transparency (EIT) of atomic medium, coherent population trapping, lasing without inversion, and others. Common to all these phenomena is the appearance of light-induced coherence between atomic levels, which are not coupled by dipole transitions. Recently Akulshin and co-workers (1998-9) have observed subnatural-width resonances in the absorption on the D/sub 2/ line of rubidium vapor under excitation by two copropagating optical waves with variable frequency offset. It is remarkable that, apart from expected EIT-resonances with negative sign, authors detected positive resonances termed as electromagnetically induced absorption (EIA). More recently, similar effects in a (3+5)-state system have been described as a result of constructive interference of the dipole excitation channels. We propose a simple theoretical model for EIA - a four-state N-atom. Remember that three-state /spl Lambda/- and V-systems give the EIT-resonances only.

Electromagnetically induced transparency of 87Rb in a buffer gas cell with magnetic field

Abstract: We have studied the phenomenon of electromagnetically induced transparency (EIT) of 87Rb vapor at room temperature in a magnetic field with an arbitrary angle to the laser propagation direction. Rather than exposing atoms to a parallelled or transverse magnetic field as usual, in our work, we apply a magnetic field (up to 45 Gauss) with an arbitrary angle to the laser propagation direction and the spectra become much more complex. More EIT dips are observed due to the Zeeman splitting on the D 2 line of 87Rb in a -type configuration. With a 5 Torr N2 buffer gas in the thermal 2 cm vapor cell, the state has a very short effective lifetime, corresponding to a large energy broadening, which removes the velocity selective optical pumping effect almost completely and keeps the high resolution EIT spectrum for the energy splitting of 87Rb in magnetic fields. The shifting of the EIT resonances with the strength of the applied magnetic field coincides well with the theory based on a full matrix Hamiltonian combined with a spectral decomposition method. Our work can be extended to measure the magnetic field vector in space. The effects of the detuning of the probe and coupling beams on the spectral lines are also investigated.

Experimental Demonstration of Laser Oscillation Without Population Inversion

Abstract: Laser oscillation without population inversion is demonstrated experimentally in a V-type atomic configuration within the ${D}_{1}\mathrm{and}{D}_{2}$ lines of Rb vapor. It is shown that the effect is due to the atomic interference. The experimental results, as first predicted by careful theoretical analysis, are in a good agreement with detailed calculations.

Dark resonance formation with magnetically induced transitions: extension of spectral range and giant circular dichroism

Abstract: Dark resonances were formed via electromagnetically induced transparency for the first time, to the best of our knowledge, involving magnetically induced ΔF=±2 atomic transitions of alkali metal atoms, which are forbidden at zero magnetic field. The probability of these transitions undergoes rapid growth when 300–3000 G magnetic field is applied, allowing formation of dark resonances, widely tunable in the GHz range. It is established that for ΔF=+2 (ΔF=−2) transition, the coupling laser tuned to ΔF=+1 (ΔF=−1) transition of the hyperfine Λ-system must be σ+ (σ−) polarized, manifesting anomalous circular dichroism.