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Optics Express

Multistage optical Stark decelerator for a pulsed supersonic beam with a quasi-cw optical lattice

Yaling Yin, Qi Zhou, Lianzhong Deng, Yong Xia, Jianping Yin

Published Jun 11, 2009• 19 citations
Publisher

Abstract

We propose a new scheme to realize a multistage optical Stark deceleration for a supersonic molecular beam using a time-varying red-detuned quasi-cw optical lattice with a length of up to 10 mm. We analyze the motion of the slowed molecules inside the optical decelerator, and study the dependences of the velocity of the slowed molecular packet on the synchronous phase angle and the number of the deceleration stages (i.e., the number of the optical-lattice cells) by using Monte-Carlo method. Our study shows that the proposed optical Stark decelerator cannot only efficiently slow a pulsed supersonic beam from 230 m/s to zero (standstill), but also obtain an ultracold molecular packet with a temperature of sub-mK due to bunching effect in the multistage optical Stark decelerator, which can be trapped in the optical lattice by rapidly turning off the modulation signal of the lattice. Also, we compare the decelerated results of our multistage optical Stark decelerator with a single-stage optical one, and find that our scheme cannot only obtain a colder molecular packet under the same molecular-beam parameters and deceleration conditions, but also be directly used to trap the slowed cold molecules after the deceleration, while don't need to use another molecular trap.

DOI
10.1364/oe.17.010706

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European Quantum Electronics Conference (EQEC)•Jan 1, 2003•0 citations
We propose a new scheme to realize a multistage optical Stark deceleration for a supersonic molecular beam using a time-varying red-detuned quasi-cw optical lattice with a length of up to 10 mm. We analyze the motion of the slowed molecules inside the optical decelerator, and study the dependences of the velocity of the slowed molecular packet on the synchronous phase angle and the number of the deceleration stages (i.e., the number of the optical-lattice cells) by using Monte-Carlo method. Our study shows that the proposed optical Stark decelerator cannot only efficiently slow a pulsed supersonic beam from 230 m/s to zero (standstill), but also obtain an ultracold molecular packet with a temperature of sub-mK due to bunching effect in the multistage optical Stark decelerator, which can be trapped in the optical lattice by rapidly turning off the modulation signal of the lattice. Also, we compare the decelerated results of our multistage optical Stark decelerator with a single-stage optical one, and find that our scheme cannot only obtain a colder molecular packet under the same molecular-beam parameters and deceleration conditions, but also be directly used to trap the slowed cold molecules after the deceleration, while don't need to use another molecular trap.
According to the optical Stark deceleration theory of using a stationary quasi-cw red-detuned optical lattice to slow and trap an arbitrary pulsed molecular beam, we propose a novel idea of using a modulated optical lattice instead of a stationary one to realize a multistage optical Stark deceleration. We analyze the motion of the decelerated molecules inside the optical decelerator, and study the dependence of the velocity of the decelerated molecular packet on the synchronous phase angle and the number of the deceleration stages (i.e. half the number of the optical-lattice cells) by using the Monte-Carlo method. The simulation results show that it takes longer time for the molecules to reach the detector as the number of the deceleration stages increases. The decelerated molecular wave packets are gradually separated from the large wave packets of the original molecular velocity distribution. And the higher the number of the deceleration stages, the lower the decelerated molecular speed is. In addition, we also study the influence of the initial phase angle of synchronous molecules under the same conditions. It is demonstrated that the higher the initial phase angle of synchronous molecules, the lower the decelerated molecular speed is and the smaller the number of molecules in the deceleration wave packet, so the phase space is compressed. The result also shows that the modulated optical Stark decelerator does not have the process of molecular free flight, and thus improving the efficiency of deceleration for molecules. The ultra-cold molecules can be trapped in the optical lattice by rapidly turning off the modulation signal of the lattice. Comparing with the previous scheme, the doubled number of the deceleration stages is reached in the same optical lattice length since a modulated optical lattice is used. For a length of optical lattice of 3.71 mm, theoretical simulation results demonstrate that the speed of methane molecules is decelerated from 280 m/s to 172 m/s. Comparing with the previous results from 280 m/s to 232 m/s, the deceleration effect is improved by 26%. Our scheme can not only obtain an ultra-colder molecular packet under the same molecular-beam parameters and deceleration conditions, but also be directly used to trap the slowed cold molecules after the deceleration without needing to use other techniques for molecular trapping.
We propose a promising scheme to realize the deceleration of a pulsed subsonic molecular beam by using a multistage optical Stark decelerator (i.e., a 1D quasi-cw traveling optical lattice), which is composed of two nearly counter-propagating, time-varying, red-detuned light fields with an intensity of ~10⁷Wcm⁻² and a fixed frequency difference between them. We also study the influence of the velocity reduced amount of the traveling lattice, the lattice power, the synchronous phase angle, the deceleration-stage number and the temporal profile of laser pulses on the molecular slowing results by using 3D Monte-Carlo method. Our study shows that the proposed decelerator cannot only be used to slow a pulsed subsonic beam from 240m/s to standstill, but also to obtain a cold molecular packet with a temperature of a few µK, and the corresponding fraction of cold molecules is 10⁻⁶-10⁻⁷, which strongly depends on the synchronous phase angle. And we also find that a pair of appropriate rising and falling times of laser pulses will lead to a better slowing effect than that produced by the top-hat temporal ones.
We propose a promising scheme to repeatedly decelerate a pulsed molecular beam using a red-detuned quasi-cw semi-Gaussian laser beam (SGB) and an electrostatic storage ring. Using the Monte-Carlo simulation method, we demonstrate that this promising optical Stark decelerator can be used to efficiently slow a pulsed ND 3 molecular beam extracted from a Stark decelerator or a cryogenic reservoir by using a single SGB. The deceleration effect of this scheme on the intensity of the SGB is discussed in detail.
We propose a promising scheme to decelerate a cw filtering out molecular beam using a red-detuned quasi-cw semi-Gaussian laser beam. By using Monte-Carlo simulation method, we demonstrate this optical Stark deceleration scheme, and study its decelerated dynamic process for a cw ND3 molecular beam as well as the dependence of the deceleration effect on the border width of the semi-Gaussian beam. Our study shows that the proposed scheme can be used to efficiently slow a cw ND3 molecular beam, and obtain a relative average kinetic-energy loss of 9.33% by using a single semi-Gaussian beam with a well depth of 7.3 mK.
We propose a novel scheme to decelerate a cw precooled molecular beam by using an optical Stark decelerator, which is composed of a red-detuned cw semi-Gaussian beam. The dynamical process of the optical Stark deceleration for a cw methane molecular beam is studied by Monte Carlo simulations. It is realized that the proposed optical Stark decelerator can be used to continuously slow a cw methane molecular beam with a longitudinal temperature of 30 mK, and a maximum reduction in the most probable speed of 0.388 m/s (corresponding to a relative change of 9.93%) can be obtained by using a single semi-Gaussian beam with a power of 500 W and a maximum central intensity of about 7.96 × 10 7 W/cm 2 .
This work presents the proposed schemes for decelerating cold molecules created in pulsed supersonic expansions using pulsed optical lattices. The first scheme relies on the application of a decelerating optical lattice with a dipole-potential well depth of approximately 1 K, created by rapidly chirping medium-intensity fields in the 10 W/cm/sup 2/ range. This scheme is an optical analog of the Start decelerator that has been successfully used to slow a range of polar molecules. A significant fraction (about 10%) of the very heavy I/sub 2 /molecules in an Ar buffer gas is shown to be slowed by using this method over sub-microsecond time scales. In the second technique, an optical lattice with larger well depth in the 100 K range travelling at half the supersonic beam velocity is used to trap a significant fraction of the cold, high-velocity molecules. This technique is developed based on the property of periodic motion of the trapped molecules in the optical lattice; the molecules reverse their initial (relative) velocities in the lattice reference frame after half a period. Using this method the cold molecules can be transferred from high speed to zero velocity on nanosecond time scales. As an example, 33% of a CO molecule beam (1 K) with a velocity of 230 m/s is slowed utilising optical intensities of less than 10/sup 12/ W/cm/sup 2/.