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We theoretically and experimentally investigate the laser-detected magnetic resonance spectra dressed by a radio-frequency magnetic field in F g = 4 of D1 line of cesium atoms. The analytical expression of the transmission spectrum for magnetic resonance dressed by a radio-frequency magnetic field is derived and has substantial agreement with the transmission spectra observed in the experiment. The theoretical prediction of the ratio of the amplitudes of the two sidebands with the detuning is basically consistent with the experimental data, which confirms the validity of the analytical expression. The separation between the two sidebands under resonance shows a highly linear proportion to the amplitude of the dressing field, which may provide a useful scheme for the measurement of radio-frequency magnetic field and magnetic imaging.

We have theoretically and experimentally investigated the laser-detected magnetic resonance induced by radio-frequency two-photon processes in ${F}_{g}=4$ of ${D}_{1}$ line of cesium atoms. The effective Hamiltonian for the interaction between the two radio-frequency magnetic fields and sublevels at the ground state of ${F}_{g}=4$ is derived. By appropriately selecting the frequencies of the two radio-frequency fields, the Raman two-photon process and the cascade two-photon process can occur, which induce the magnetic resonance detected through laser transmission spectra. The theoretical calculation results fit well with the experimental data. Our results maybe apply for measuring the high bandwidth radio-frequency magnetic fields in space and studying the magnetic-induction tomography.

The existing photodetectors at home and abroad are generally lack adjustable gain and bandwidth, which makes it difficult to optimize various parameters. A low noise differential photodetector is designed. Its main gain is adjustable in the range of 10k-l0M, bandwidth is adjustable in the range of DC-3Mhz, and compensation amplification gain is adjustable in the range of 1-10. The equivalent noise model of PIN (positive-intrinsic-negative) photodiode and its amplifier circuit is analyzed. The optimal signal-to-noise ratio is 47dB and the minimum resolvable optical power is 1nW. The output voltage amplitude is linear with the input light intensity. When the signal frequency is within 3MHz, the signal can be detected without distortion. While meeting the performance requirements, the adjustable parameters are easy to explore the influence of gain, bandwidth and other factors on the experimental results, which is flexible and easy to be applied and promoted in precision spectroscopy and quantum optics experiments.

We present a theoretical study of double-resonance alignment magnetometers using linearly polarized light, in which the effect of atomic high-order multipole moments is considered. Starting from the effective master equation of our system obtained by eliminating the excited state adiabatically, we derive the full evolution equations of the atomic multipole moments. The analytic solutions of resonance signals involving the four-order multipole moments effect are obtained by using the perturbation approach. We present that the four-order multipole moments effect is negligible in the weak laser field, and the results reduce to that obtained by a three-step approach. However, the role of four-order multipole moments coupled by two-order tensor moments is more significant with the increasing Rabi frequency of light, which cannot be ignored. Meanwhile, the analytic expressions of relaxation processes are also studied, which are a linear combination of the laser-induced equivalent relaxation rate Γ L and the spin-exchange collision rate Γ g . The expected domain of validity of the three-step approach on light power is roughly given by Γ L < 1 2 Γ g . In addition, the steady-state results of resonance signals are presented in a strong radio-frequency magnetic field; in that case, the physical mechanism of the splitting of resonance signals is discussed. These results are valid for arbitrary light power and for an arbitrarily oriented static magnetic field.

We demonstrate a simple technique to lock the frequency of a laser to an atomic transition with a new technique of subnatural linewidth spectroscopy. The coupled rubidium system exhibits an enhanced absorption spectrum of the probe beam with a subnatural linewidth. Compared with other techniques with an additional laser, our scheme only utilizes a single laser, which will be locked. The observed spectroscopic linewidth is down to about 3.5 MHz. The laser frequency fluctuation is about 226 kHz after locking on. The demonstrated scheme offers a convenient and low-cost technique for laser frequency stabilization and related precision measurements.

A DC current sensor based on an optically pumped atomic magnetometer is proposed. It has a high linearity in a wide operation range, since the magnetometer measures the absolute magnitude of the magnetic field produced by the current to be measured. The current sensor exhibits a high accuracy with a non-moment solenoid and magnetic shielding to suppress the influence from the environment. The absolute error of the measured current is below 0.08 mA when the range is from 7.5 mA to 750 mA. The relative error is 5.54 × 10−5 at 750 mA.

Nanocomposites of silica, single-wall carbon nanotubes, and graphite nanoplatelets in an epoxy matrix were prepared using a novel single-step room temperature ionic liquid (RTIL) preparation strategy. Silica nanocomposites showed improved fracture toughness and modulus, carbon nanotube composites showed electrical network percolation at 8.6 × 10 −5 volume fraction, and graphite nanoplatelets composites showed electrical percolation at 1.7 × 10 −2 volume fraction. These results were compared with literature results for nanocomposites made with volatile solvents, demonstrating the viability of the RTIL nanocomposite preparation strategy.

A special bifilar 40t electroslag remelting(ESR) furnace for slab products has been fabricated to produce heavy plates for special application. The slab ingots were rolled to heavy plates, and then the mechanical properties of which were investigated. The impact toughness of heavy plates with different position, directions and under welding condition were performed at the temperature ranging from -70°C to room temperature. The tensile experiments at room temperature were carried out to check the tensile properties of heavy plates in different position, directions and under welding condition. The secondary cooling technology developed improves greatly the quality of solidification. Adjusting taper of the mold and using CaF2-CaO-Al2O3-SiO2-MgO slag are necessary for improving surface quality of the ESR slab. The ESR slabs with the maximum thickness of the world in size of 980 mm thickness, 2000 mm wideness and 2800 mm length have been produced successfully. The heavy plates with 410 mm in thickness can be obtained after rolling the 40 tons ESR slabs. The results of mechanical properties show that the heavy plates produced by ESR furnace for slab products exhibits excellent ductility, impact and isotropic properties in different position, directions and under welding condition.