Laser cooling Physical mechanisms and ultimate limits

Yvan Castin, K. Mφlmer, Jean Dalibard +1 more

Desheng Lü, Wei Ren, Yuan Sun +12 more

The invention of laser cooling has fundamentally influenced the research frontier of atomic physics and quantum physics, and recently an intense focus has been on the studies of cold atom physics in microgravity environments. Herein, we report the results of our laser cooling experiment in TianGong-2 space lab, which operated for 34 consecutive months in orbit. Over such an extended operation time, the quality of laser cooling did not experience any significant decline, while the properties of laser cooling in orbital microgravity were systematically studied. In particular, we demonstrate magneto-optical trapping and polarization-gradient cooling in orbit and carefully examine their performances. A comparison of the in-orbit and on-ground results indicates that a higher cooling efficiency exists in microgravity, including a smaller loss rate during the trapping and cooling process and lower ultimate temperature of laser-cooled atoms. Our progress has laid the technical foundations for future applications of cold atoms in space missions with operation times of the order of years.

Stig Stenholm

P. R. Berman

It is shown that the physical mechanisms that give rise to very narrow resonances in nonlinear spectroscopic line shapes and to laser cooling below the so-called Doppler limit are closely related. A general formalism is developed that can be applied to a wide range of problems in nonlinear spectroscopy and laser cooling. To illustrate the formalism, a calculation of the friction force associated with laser cooling is carried out for several cases of current experimental interest.

Yi-Li Xiao, Yan Ma, Wen Wu +2 more

A quantum mechanical Monte Carlo simulation is carried out for one-dimensional laser cooling of Chromium atoms. Chromium atom beam collimation via transverse laser cooling is essential for the fabrication of periodic nanometer scale structures by laser-focused atomic deposition. Such structures can be used as precision pitch standards for nanometer scale measurement and engineering. We explore the roles played by several factors, such as laser intensity and detuning, in the cooling process. Calculation results show different dependencies for cooling rate and ultimate temperature to be reached with given sets of parameters. Also, for atoms with different initial velocities in the transverse direction, the conditions under which optimal collimation effect is achieved can differ. Consequently, the current experimental setup, which utilizes LIF spots from marginal beams to monitor the laser collimation, can produce cooling effects which are not optimal for the end product.

S. V. Petrushkin, Vitali V. Samartsev