Na-beam cooling by a mode-locked laser

Strohmeier, P.; Horn, Alexander; Kersebom, T.; Schmand, J.

doi:10.1007/bf01426376

Cited by 22 publications

(16 citation statements)

References 10 publications

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“…As the rate of photons scattered resonantly at the atoms (causing radiation pressure) is proportional to the excited-state population, excitation spectra may be utilized in a very simple way for the determination of the velocity-dependent resonant radiation force acting on two-level atoms in mode-locked laser fields [ 13,14]. The dependence of atomic excitation on the detuning is converted into the dependence on the velocity by the Doppler effect.…”

Section: Discussionmentioning

confidence: 99%

“…(62) of their paper), the correct formula will be derived here, shown to be independent of the pulse profile, and complemented by the off-resonance solution. The results find an interesting application to experiments on atomic-beam deceleration by modelocked laser light [13,14].…”

Section: Introductionmentioning

confidence: 88%

“…The spectral bandwidth of 5 GHz typically results when an intra-cavity etalon is inserted for bandwidth restriction to meet experimental requirements for atomic-beam deceleration [13,14] or deflection [31] with mode-locked laser light.…”

Section: ~ T Lmentioning

confidence: 99%

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Excitation of two-level atoms in mode-locked laser fields

Krüger

1994

Z Phys D - Atoms, Molecules and Clusters

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Abstract. The excitation of two-level atoms in a laser field comprising many equally spaced coupled laser modes corresponding to a coherent pulse train is examined. The atom-field interaction is analysed via the optical Bloch equations for a rotating wave. In the limit of weak excitation they can be solved analytically and the time-averaged atomic excitation turns out to be a linear superposition of the contributions from the individual laser modes. Thus excitation spectra simply reflect the mode structure of the laser spectrum. Excitation spectra for strong fields are obtained by numerical integration of the optical Bloch equations. They exhibit a saturation behaviour differing significantly from the well known single-mode case. The temporal evolution towards the steady state is calculated for several numerical examples to clarify the origin of this behavior. For achieving maximum excitation, the laser pulse area, as in the single-pulse case, should be an odd multiple of zr, and the mode spacing (pulse repetition rate) should exceed the natural linewidth of the atomic transition considerably. Under these conditions the time-averaged excited-state population approaches 1/2 while saturation broadening ensures nearly frequency-independent excitation within an extended fraction of the laser bandwidth.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 88%

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Excitation of two-level atoms in mode-locked laser fields

Krüger

1994

Z Phys D - Atoms, Molecules and Clusters

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“…This technique can be used to cool a certain velocity group of cold atoms, after they have been decelerated in a modelocked laser field [9], then deflected and compressed out of the thermal atomic beam by a magneto-optical modul similar to that of Nellessen et al [10]. Doing so the chance may be enhanced to realize scattering experiments with subthermat polarized atomic beams.…”

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confidence: 98%

Cooling and polarization of a sodium atomic beam by a two mode laser

Nölle

Horn

Hüve

et al. 1994

Z Phys D - Atoms, Molecules and Clusters

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Abstract. Cooling and optical pumping by a circularly polarized two mode laser is applied to a Na atomic beam in transverse geometry. The low velocity components of the beam are transversly cooled to the Doppler limit temperature of 240 btK and are simultaneously spin polarized for more than 90%. PACS: 32.80.P Scattering experiments with subthermal spin polarized atoms in the ground state open a new field of interesting physics [ 1]. From the measured total cross section the long range interatomic potential can be determined. Measuring the differential cross section offers the possibility to investigate hyperfine decoupling processes during the scattering with collision energies about equal to the Na ground state hyperfine splitting (1772 MHz).For information about the scattered particles being distinguishable or undistinguishable we have to manipulate the atomic spin polarization.We have set up an experiment to cool and polarize a Na atomic beam in transverse geometry, i.e., two counterpropagating laser beams of the same circular polarizations illuminate the Na beam at right angle [2] (Fig.

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“…Thus, by the time the next laser pulse arrives, the excited state population is only about 2%. This cooling process is then primarily due to absorbing single photons from individual pulses, and not due to an optical frequency comb effect [9,10,24]. For optimal cooling of a given atomic species, the pulsed laser repetition rate should be of the order of the atom's excited state linewidth, while the energy in each laser pulse should correspond to P exc ≃ 1…”

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confidence: 99%

Broadband laser cooling of trapped atoms with ultrafast pulses

et al. 2006

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We demonstrate broadband laser cooling of atomic ions in an rf trap using ultrafast pulses from a modelocked laser. The temperature of a single ion is measured by observing the size of a timeaveraged image of the ion in the known harmonic trap potential. While the lowest observed temperature was only about 1 K, this method efficiently cools very hot atoms and can sufficiently localize trapped atoms to produce near diffraction-limited atomic images.PACS numbers: 32.80. Pj, 42.50.Vk Laser cooling of atoms [1,2] has become a cornerstone of modern day atomic physics. Doppler cooling and its many extensions usually involve narrow-band, continuous-wave lasers that efficiently cool atoms within a narrow velocity range (∼ 1 m/s) that corresponds to the radiative linewidth of a typical atomic transition. To increase the velocity capture range, several laser cooling methods were investigated that modulate or effectively broaden a narrow-band laser [3,4,5,6,7,8]. Modelocked pulsed lasers have been used to narrow the velocity distribution of atomic beams within several velocity classes given by the bandwidth of each spectral component of the frequency comb [9,10]. In this letter we report the demonstration of Doppler laser cooling of trapped atoms with individual broadband light pulses from a modelocked laser.To efficiently capture and cool high-velocity atoms, it is necessary to achieve a laser bandwidth large enough to cover the large range of atomic Doppler shifts. For example, Cd + ions used in this experiment are initially created with an average kinetic energy of order 1 eV, which corresponds to an average velocity of about 1300 m/s and a Doppler shift of ∆ D ∼ 36 GHz. Power broadening an atomic transition (saturation intensity I s and natural linewidth γ) would require a laser intensity of2 , which can be prohibitively high. For Cd + (γ/2π ≃ 50MHz, I s ≃ 5000W/m 2 ) this requires I ∼ 10 10 W/m 2 . Modulating a narrow-band laser to generate high bandwidths would allow for significantly less laser power, but it is technically difficult to generate a 100 GHz wide modulation spectrum [4]. On the other hand, an ultrafast laser whose pulse is a few picoseconds long will naturally have a bandwidth in the above range, as well as sufficient intensity to excite the transition.The laser cooling rate depends critically on the photon scatter rate, which for a pulsed laser can be no larger than the laser repetition rate R (about 80 MHz for a typical modelocked laser), given that the atom is excited with unit probability by each pulse. We assume that once excited, the atom decays back to the ground state faster than the time period of the modelocked pulse train 1/R. In this case, the atom has little memory between pulses, or equivalently, the absorption spectrum is a single broad line of width ∆ ∼ 1/τ (τ is the pulse duration) and the frequency comb of spacing R has very little contrast.The equilibrium temperature for broadband pulsed laser cooling of trapped atoms is expected to scale approximately with the laser bandwidth ∆, a...

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Na-beam cooling by a mode-locked laser

Cited by 22 publications

References 10 publications

Excitation of two-level atoms in mode-locked laser fields

Excitation of two-level atoms in mode-locked laser fields

Cooling and polarization of a sodium atomic beam by a two mode laser

Broadband laser cooling of trapped atoms with ultrafast pulses

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