Evaporative cooling by pulse width modulation (PWM) of optical dipole traps

TL;DR

This paper presents a novel evaporative cooling method for atoms in optical dipole traps using pulse-width modulation (PWM), which modulates the trap digitally at a fixed frequency to reduce temperature without decreasing laser power.

Contribution

It introduces PWM-based evaporative cooling for optical traps, offering an alternative to traditional methods that maintains constant laser power during cooling.

Findings

Effective reduction in atom temperature and increased phase space density.

Identification of additional atom loss channels during PWM modulation.

Comparison showing PWM as a viable alternative to standard evaporative cooling.

Abstract

We introduce a method for cooling atoms in an optical dipole trap using pulse-width modulation (PWM) technique, without reducing the laser power of the dipole trap. The PWM technique involves digital modulation of the trap at a fixed frequency. The effective time-averaged dipole potential is lowered by adjusting the duty cycle of the modulation, thereby implementing evaporative cooling. We show that, this technique effectively reduces temperature and enhances phase space density. A comparison with the standard method of evaporative cooling has also been made. Apart from the atom loss due to reduction of the effective trapping potential, we observe an additional loss channel originating from the lack of trapping potential during the trap off time. This atom loss is observed at different modulation frequencies which are an order of magnitude higher compared to trapping frequency of dipole trap. The PWM technique provides an alternative to traditional evaporative cooling in scenarios where it is preferred that the laser power of the trap should be constant.