A Potassium Atom Four-Level Active Optical Clock Scheme

We present an active optical clock scheme with a four-level quantum potassium system.We calculate the population probabilities of each state using the density matrix.At the steady state,ρ33 andρ55 are equal to 8.3%and 3.5%,respectively,and the population inversion between the 5S1/2 and 4P3/2 states is built up in the thermal potassium cell with a 404.7 nm pumping laser.According to the mechanism of the active optical clock,under the action of the 404.7 nm pumping laser,the scheme can output a 1252.2 nm quantum-limited-linewidth laser,which can be directly used as an active optical frequency standard.

Magic Wavelengths for a Lattice Trapped Rubidium Four-Level Active Optical Clock

After being pumped from the 5s_(1/2) ground state to the 6p_(1/2) state,the population inversion between 6s_(1/2) and 5p_(1/2,3/2) can be established for a rubidium four-level active optical clock.We calculate the ac Stark shift due to lattice trapping laser which dominates the frequency shift of clock transition in a lattice trapped rubidium four-level active optical clock.Several magic wavelengths are found,which can form desired optical lattice trapping potential.By choosing a proper intensity and linewidth of the trapping laser,the fractional frequency uncertainty of clock transition due to the ac Stark shift of the trapping laser,is estimated to be below 10^(−18).

A New Pumping-Probing Scheme for the Optically Pumped Cesium Beam Frequency Standard

A new pumping-probing scheme for the optically pumped cesium beam frequency standard has been experimentally tested in our laboratory.The stability of the optically pumped cesium beam frequency standard was measured by comparing its 10 MHz output with an HP5071A commercial cesium atomic clock.The result shows that the frequency stability for the 1 s and 30000s sample times are 1.2×10^(-11) and 3.7×10^(-13),respectively.It was proved that the new pumping scheme works well.

Cs 455nm Nonlinear Spectroscopy with Ultra-narrow Linewidth

Nonlinear spectroscopy has become a useful tool in laser cooling,frequency stabilization and so on.We use the 455.5 nm light beam output of an external cavity diode laser to perform the saturation spectroscopy signal and polarization spectroscopy signal on the 6S_(1/2)→7P3/2 transition in cesium.The measured linewidth of the F4→4,5 transition is as narrow as 1.40 MHz and that of the F3→2,3 transition is 1.67 MHz.Both of them are very close to the natural linewidth of about 1.2 MHz.Our result is the narrowest measured linewidth of Cs 455 nm saturation spectroscopy signal to our knowledge.

Superradiant Laser with Ultra-Narrow Linewidth Based on 40Ca

An experiment setup for narrow linewidth superradiant laser based on the mechanism of an active optical clock is proposed with optical lattice trapped 40 Ca.We obtain the threshold pumping rate analytically and deduce the linewidth of the superradiant laser in a bad cavity regime.The proposed laser has an extremely narrow linewidth at millihertz level and a power level of order 10^(-9) W.

Feasibility of Extreme Ultraviolet Active Optical Clock

We propose an experimental scheme of vacuum ultraviolet(VUV)and extreme ultraviolet(XUV)optical frequency standards with noble gas atoms.Considering metastable state 3𝑃2 noble atoms pumped by a conventional discharging method,the atomic beam is collimated with transverse laser cooling at the metastable state and enters into the laser cavity in the proposed setup.Due to stimulated emission from the metasable state to the ground state inside the laser cavity consisting of VUV reflection coating mirrors,our calculations show that with enough population inversion to compensate for the cavity loss,an active optical frequency standard at VUV and XUV is feasible.

Alternating Current Zeeman and Stark Interference Effect in Ramsey Separated Oscillating Fields

Analytic expressions have been derived of the alternating current(ac)Zeeman and ac Stark effect in an atomic beam magnetic resonance method using Ramsey separated oscillating fields.An interesting feature which will affect the normal Ramsey pattern is that an interference fringe is superimposed on the dispersion lineshapes of the normal ac Zeeman or ac Stark effect.We point out that this new character of ac Zeeman(ac Stark)effect generally exists in all kinds of Ramsey method,for example,in the optical Ramsey atomic interferometer and atomic beam frequency standard.An important implication is that,particularly in an atomic beam frequency standard using Ramsey method,this effect has an influence on the evaluation of the second-order Doppler frequency shift.

世界社会主义发展的基本历程与经验启示

自诞生以来五百余年间,世界社会主义发展先后经历了六个时间段,实现了从空想到科学、从理论到实践、从一国实践到多国发展,从改革到创新的飞跃,形成了诸多重要原则和经验。回顾和总结世界社会主义发展的基本历程与经验启示,展望21世纪世界社会主义发展趋势,对于进一步认识和把握人类社会发展的历史规律、中国特色社会主义的社会主义本质属性,不断谱写中国特色社会主义新篇章有着重要的启迪作用。