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arXiv:1306.0402 · Review of Scientific Instruments

Microwave sidebands for laser cooling by direct modulation of a tapered amplifier

J. Mahnke, Sascha Kulas, I. Geisel, S. Jöllenbeck, W. Ertmer, Carsten Klempt

Published Jun 1, 2013• 1 citation

Abstract

Laser cooling of atoms usually necessitates several laser frequencies. Alkaline atoms, for example, are cooled by two lasers with a frequency difference in the gigahertz range. This gap cannot be closed with simple shifting techniques. Here, we present a method of generating sidebands at 6.6 GHz by modulating the current of a tapered amplifier, which is seeded by an unmodulated master laser. The sidebands enable trapping of 1.1 × 10(9) (87)Rb atoms in a chip-based magneto-optical trap. Compared to the direct modulation of the master laser, this method allows for an easy implementation, a fast adjustment over a wide frequency range, and the simultaneous extraction of unmodulated light for manipulation and detection. The low power consumption, small size, and applicability for multiple frequencies benefit a wide range of applications reaching from atom-based mobile sensors to the laser cooling of molecules.

DOI: 10.1063/1.4811196

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Two methods using a laser-diode tapered amplifier to produce high-power, high-efficiency optical frequency sidebands over a wide tunable frequency range are studied and compared. For a total output of 500 mW at 811 nm, 20% of the power can be placed in each of the first-order sidebands. Functionality and characterization are presented within the sideband frequency region of 0.8-2.3 GHz, and it is shown that both methods can be applied beyond this frequency range. These methods provide a versatile and effective tool for atomic physics experiments.

We have experimentally studied multiple side-band generation for two-frequency components injected into a tapered amplifier (TA) and demonstrated its effects on atomic laser cooling. A heterodyne frequency-beat measurement and a Fabry-Perot interferometer have been applied to analyze the side-band generation with different experimental parameters, such as frequency difference, injection laser power, and TA current. In laser-cooling potassium40 and potassium41 with hyperfine splitting of 1.3 GHz and 254 MHz, respectively, the side-band generation with a small frequency difference has a significant effect on the number of trapped atoms.

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We demonstrate a simple method to obtain accurate optical waveforms with a gigahertz-level programmable modulation bandwidth and a watt-level output power for wideband optical control of free atoms and molecules.Arbitrary amplitude and phase modulations are transferred from microwave to light with a low-power fiber electro-optical modulator.The sub-milliwatt optical sideband is co-amplified with the optical carrier in a power-balanced fashion through a tapered semiconductor amplifier (TSA).By automatically keeping TSA near saturation in a quasi-continuous manner, typical noise channels associated with pulsed high-gain amplifications are efficiently suppressed.As an example application, we demonstrate interleaved cooling and trapping of two rubidium isotopes with coherent nanosecond pulses.

Herein, we report an effective method for the generation of radio-frequency (RF) sidebands in an electro-optic modulator for the simultaneous magneto-optical trapping of two isotopes. This is achieved by switching the RF signals alternately, which suppresses the generation of unwanted frequency signals and improves the laser power per sideband. The generated sidebands are successfully applied to a dual-rubidium-isotope magneto-optical trap (MOT), which results in an increased number of trapped atoms. This simple, flexible, and robust technique can be implemented in experiments that require a large number of atoms in multiple-isotope MOTs and for various applications.