Y. T. Li

A LabVIEW based measure system for pulse wave transit time

Pulse wave transit time (PWTT) is used as a non-invasive and cuffless method for blood pressure estimation. In this paper, we design a system that can measure PWTT by monitoring ECG and pulse wave continuously. The system includes analog signal sampling in PCB, signal display and data processing in computer. We measure pulse wave by the photo-plethysmograph (PPG) device in finger which includes an infrared LED transmitting light, photodiode in OPT101 as detector, amplifier and filters. We measure ECG by the sensor on limb. We design amplifier, 0.01 Hz high pass filter, 75 Hz low pass filter, and 50 Hz notch filter. After filtering and amplification, ECG and PPG are sampled by MCU and then the data are transmitted to computer. LabVIEW is used to receive, display and process these data, and finally figure out the PWTT. Based on PWTT value, we coarsely calculate the SBP.

Induced magnetic monopole from trapped Λ-type atom

Abstract.We investigate the spatial motion of the trapped atom with thenelectromagnetically induced transparency (EIT) configuration wherenthe two Rabi transitions are coupled to two classical light fieldsnrespectively with the same detuning. When the internal degrees ofnfreedom can be decoupled adiabatically from the spatial motion ofnthe center of mass via the Born-Oppenheimer approximation, it isndemonstrated that the lights of certain profile can provide thenatom with an effective field of magnetic monopole, which is thenso-called induced gauge field relevant to the Berrys phase. Suchnan artificial magnetic monopole structure manifests itself in thencharacterizing energy spectrum. nn

Z-dependence of hot electron generation in femtosecond laser interaction with solid targets

Hot electron emission is studied using 798 nm, 150 fs, p-polarized laser pulses at 1 × 1016 W cm−2, irradiating on plastic (CH), aluminium (Al), titanium (Ti) and copper (Cu) planar targets. The dependence of hot electron generation on atomic number Z is observed experimentally.

Group velocity of a probe light in an ensemble of Lambda atoms under two-photon resonance

We study the propagation of a probe light in an ensemble of Lambda-type atoms, utilizing the dynamic symmetry as recently discovered when the atoms are coupled to a classical control field and a quantum probe field [Sun , Phys. Rev. Lett. 91, 147903 (2003)]. Under two-photon resonance, we calculate the group velocity of the probe light with collective atomic excitations. Our result gives the dependence of the group velocity on the common one-photon detuning, and can be compared with the recent experiment of E. E. Mikhailov, Y. V. Rostovtsev, and G. R. Welch, e-print quant-ph/0309173 .

Non-Abelian geometric quantum memory with an atomic ensemble

We study a quantum information storage scheme based on an atomic ensemble with near (also exact) three-photon resonance electromagnetically induced transparency (EIT). Each 4-level-atom is coupled to two classical control fields and a quantum probe field. Quantum information is adiabatically stored in the associated dark polariton manifold. An intrinsic nontrivial topological structure is discovered in our quantum memory implemented through the symmetric collective atomic excitations with a hidden SU(3) dynamical symmetry. By adiabatically changing the Rabi frequencies of two classical control fields, the quantum state can be retrieved up to a non-Abelian holonomy and thus decoded from the final state in a purely geometric way.

Relativistic electrons produced by reconnecting electric fields in a laser-driven bench-top solar flare

Laboratory experiments have been carried out to model the magnetic reconnection process in a solar flare with powerful lasers. Relativistic electrons with energy up to megaelectronvolts are detected along the magnetic separatrices bounding the reconnection outflow, which exhibit a kappa-like distribution with an effective temperature of ~109 K. The acceleration of non-thermal electrons is found to be more efficient in the case with a guide magnetic field (a component of a magnetic field along the reconnection-induced electric field) than in the case without a guide field. Hardening of the spectrum at energies ≥500 keV is observed in both cases, which remarkably resembles the hardening of hard X-ray and γ-ray spectra observed in many solar flares. This supports a recent proposal that the hardening in the hard X-ray and γ-ray emissions of solar flares is due to a hardening of the source-electron spectrum. We also performed numerical simulations that help examine behaviors of electrons in the reconnection process with the electromagnetic field configurations occurring in the experiments. The trajectories of non-thermal electrons observed in the experiments were well duplicated in the simulations. Our numerical simulations generally reproduce the electron energy spectrum as well, except for the hardening of the electron spectrum. This suggests that other mechanisms such as shock or turbulence may play an important role in the production of the observed energetic electrons.

Effects of counting rate and resolution time on a measurement of the intensity correlation function

Non-photon-number-resolving single-photon-counting modules (SPCMs), also called on-off photon detectors, have been used in quantum optics for investigating the properties of various light fields based on the Hanbury-Brown-Twiss (HBT) experiment. However, for different incident light fields the experimental conditions can affect the measured photon statistics. In this paper, the second-order degree of coherence g{sup (2)}, known as the important factor for quantitying a single-photon source, is experimentally investigated by means of the HBT scheme consisting of two SPCMs. By comparing the results of coherent field with that of the thermal field, we show that the measured g{sup (2)} is affected by the photon-counting rate and the resolution time from pulsed to continuous wave fields. The proper counting rate and resolution time for characterizing the exact photon statistical properties of input fields are determined.

Localization of the relative position of two atoms induced by spontaneous emission

We revisit the back-action of emitted photons on the motion of the relative position of two cold atoms. We show that photon recoil resulting from the spontaneous emission can induce the localization of the relative position of the two atoms through the entanglement between the spatial motion of individual atoms and their emitted photons. The result provides a more realistic model for the analysis of the environment-induced localization of a macroscopic object.

Preplasma effects on the emission directions of energetic electrons in relativistic laser-solid interactions

Motivated by recent experimental observations of fast electron jets emitted along the target surface in intense laser-solid interactions with a large incident angle of the laser pulse, we simulate electron emissions by two-dimensional particle in-cell simulations. When there is no preplasma in advance of the main laser pulse, electrons are emitted dominantly along the target surface. However, when there is preplasma. electron emission changes to the target normal. This difference originates from the different absorption mechanisms and different Coulomb electrostatic fields and self-generated magnetic fields induced in front of the target for the two cases.

Laser opacity in underdense preplasma of solid targets due to quantum electrodynamics effects

We investigate how next-generation laser pulses at 10-200PW interact with a solid target in the presence of a relativistically underdense preplasma produced by amplified spontaneous emission (ASE). Laser hole boring and relativistic transparency are strongly restrained due to the generation of electron-positron pairs and γ-ray photons via quantum electrodynamics (QED) processes. A pair plasma with a density above the initial preplasma density is formed, counteracting the electron-free channel produced by hole boring. This pair-dominated plasma can block laser transport and trigger an avalanchelike QED cascade, efficiently transferring the laser energy to the photons. This renders a 1-μm scale-length, underdense preplasma completely opaque to laser pulses at this power level. The QED-induced opacity therefore sets much higher contrast requirements for such a pulse in solid-target experiments than expected by classical plasma physics. Our simulations show, for example, that proton acceleration from the rear of a solid with a preplasma would be strongly impaired.