© 2026 Aqora Quantum S.A.S.

Terms Privacy Legal Notice

International Laser Science Conference

Measurement of axial velocity distribution of a laser-cooled atomic beam

J.L. Hall, M. Zhu, Ch Salomon

Published Jan 1, 1986• 0 citations

Abstract

We measured the axial velocity distribution produced by frequency-chirp-cooling a sodium atomic beam, including heating effects produced by an optional frequency-fixed postcooling interaction. Frequency sweeps were produced via a voltage-tuned oscillator feeding a broadband, efficient electrooptic modulator to produce a frequency-agile sideband on the output of a dual-frequency dye laser(Δv = 1.712GHz). After the chirp-cooling, the frequency was held stationary for an adjustable time T before the intensity was reduced 30-fold and the frequency jumped to provide a single readout point on the number of atoms vs frequency curve. All frequency sweeps were derived with rf techniques from a single laser so the velocity scale is absolute and uncontaminated by drifts. The + 880-MHz sweep in 1.6 ms gave an effective absorption rate of 10.7 photons/μs (saturation = 1 gives 31 photons/μs, 1 photon gives 3 cm/s). The swept sideband power was 10 mW in Wo ~ 4 mm, decreasing to ~ 350μW for readout. The measured velocity-offset and –drift rate were 24 MHz and 8 photons/μs at T = 15μs, with the velocity offset increasing to 40 MHz and the rate decreasing to 4 photons/μs at T = 100 μs. Over the same time interval, the velocity width monotonically increased from 12.1 to 17 MHz. The presence of heating—rather than cooling—infixed frequency conditions implies the existence of an optimum chirp rate and is not anticipated by some theories of the laser atom cooling dynamics.

DOI: 10.1364/ils.1986.wc5

Related papers

Laser cooling and trapping of rubidium

Christopher D. Wallace, Timothy T. Grove, T. Dinneen +2 more

We have laser cooled an atomic beam of rubidium with diode lasers and have used these slow atoms to load a magneto-optical trap. The cooling is performed with the frequency-chirp method,1,2 in which the laser's frequency is ramped linearly (by the injection currant) to maintain resonance with the decelerating atoms. Two synchronously chirped lasers are required to prevent optical hyperfine pumping of the ground state. The chirp typically covers 500 MHz in 10 ms. At the end of each ramp, the resulting velocity distribution is measured with a pulsed probe laser. By varying the end point of the chirp, we are able to obtain slow atoms with average velocities ranging from 200 to −50 m/s. The widths of the velocity distributions are measured to be approximately 40 m/s. This relatively large width results from the inherent linewidth (~30 MHz) of the free-running diode lasers used for both cooling and probing.

Quantum Electronics and Laser Science Conference•May 12, 1991•0 citations

Frequency chirped continuous-wave sodium laser guide stars: modeling and optimization

Felipe Pedreros Bustos, Ronald Holzlöhner, Simon Rochester +3 more

We numerically study a method to increase the photon return flux of continuous-wave laser guide stars using one-dimensional atomic cooling principles. The method relies on chirping the laser towards higher frequencies following the change in velocity of sodium atoms due to recoil, which raises atomic populations available for laser excitation within the Doppler distribution. The efficiency of this effect grows with the average number of atomic excitations between two atomic collisions in the mesosphere. We find the parameters for maximizing the return flux and evaluate the performance of chirping for operation at La Palma. According to our simulations, the optimal chirp rate lies between 0.8 − 1.0 M H z / µ s , and an increase in the fluorescence of the sodium guide star up to 60% can be achieved with current 20-W-class guide star lasers.

Journal of the Optical Society of America B•Mar 6, 2020•15 citations

Fokker-Planck analysis of atomic beam cooling by frequency chirp methods

Hartmut Wallis, Wolfgang A. Ertmer

Atomic beam deceleration and cooling by frequency sweep techniques is analysed by means of a Fokker-Planck equation (FPE) with time dependent drift and diffusion coefficients. The effect of compression of the velocity distribution is discussed with respect to theoretical and experimental limitations of atomic beam cooling imposed by the photon recoil. The cooling limit derived from the linear approximation of the FPE fails, if the broadening of the cooled velocity distribution peak by diffusion causes the loss of atoms from the resonant velocity range. This phenomenon is studied by numerical solutions of the FPE. The occurrence of higher final temperatures in previous Monte-Carlo calculations and in experiments is discussed. The anomalous diffusion coefficient caused by the antibunching of the scattered photons is taken into account. The possibility of transverse compression of the atomic beam is investigated by means of a reduced FPE for the transverse degrees of freedom.

Journal of Physics B Atomic Molecular and Optical Physics•Sep 14, 1988•8 citations

Frequency chirped continuous-wave sodium laser guide stars

Felipe Pedreros Bustos, Ronald Holzlöhner, Simon Rochester +3 more

We numerically study a method to increase the photon return flux of continuous-wave laser guide stars using one-dimensional atomic cooling principles. The method relies on chirping the laser towards higher frequencies following the change in velocity of sodium atoms due to recoil, which raises atomic populations available for laser excitation within the Doppler distribution. The efficiency of this effect grows with the average number of atomic excitations between two atomic collisions in the mesosphere. We find the parameters for maximizing the return flux and evaluate the performance of chirping for operation at La Palma. According to our simulations, the optimal chirp rate lies between 0.8-1.0 MHz/$μ$s and an increase in the fluorescence of the sodium guide star up to 60% can be achieved with current 20 W-class guide star lasers.

arXiv:2001.02717•Jan 8, 2020•0 citations

Broadband stimulated laser cooling

Ralph G. DeVoe

A new method is proposed for laser cooling atoms with Doppler shifts an order of magnitude larger than the homogeneous linewidth of the atomic transition. Two traveling waves cross at a small angle and form standing waves whose wavelength is much longer than that of either traveling wave. This allows one to extend the region in which the laser cooling force is proportional to velocity. The resulting broadband stimulated cooling forces are predicted to stop 0.1% of the flux of a 500-K atomic sodium beam in a distance of 300 μm and a time of a few microseconds. This is more than 100 times faster than current methods. Numerical integration and the method of Gordon and Ashkin have been used to calculate the cooling forces which result when two traveling waves cross at an angle 2a. The stimulated cooling forces are reduced in intensity by sin2a but are proportional to velocity over an interval which is larger by 1/sin a. This allows one to stop a substantial fraction of an atomic beam without chirping the laser or Zeeman tuning the atoms.

Annual Meeting Optical Society of America•Jan 1, 1991•0 citations

Formation of a beam of cold atoms by laser frequency tuning

Yu. Rozhdestvensky, Anton K. Vershovskii, E A Ageichik +1 more

We report the possibility of producing a beam of slow atoms with a characteristic velocity of ∼ 1 m s − 1 by the ‘chirp’ method, namely, cooling by variable-frequency radiation. Method modifications are considered, which substantially reduce dimensions of the slower, the width of the longitudinal velocity distribution of the atomic beam, and the area of its cross section. The modified method of laser radiation frequency tuning for cooling rubidium atoms is mathematically simulated.

Quantum Electronics•Oct 11, 2016•0 citations

We measured the axial velocity distribution produced by frequency-chirp-cooling a sodium atomic beam, including heating effects produced by an optional frequency-fixed postcooling interaction. Frequency sweeps were produced via a voltage-tuned oscillator feeding a broadband, efficient electrooptic modulator to produce a frequency-agile sideband on the output of a dual-frequency dye laser(Δv = 1.712GHz). After the chirp-cooling, the frequency was held stationary for an adjustable time T before the intensity was reduced 30-fold and the frequency jumped to provide a single readout point on the number of atoms vs frequency curve. All frequency sweeps were derived with rf techniques from a single laser so the velocity scale is absolute and uncontaminated by drifts. The + 880-MHz sweep in 1.6 ms gave an effective absorption rate of 10.7 photons/μs (saturation = 1 gives 31 photons/μs, 1 photon gives 3 cm/s). The swept sideband power was 10 mW in Wo ~ 4 mm, decreasing to ~ 350μW for readout. The measured velocity-offset and –drift rate were 24 MHz and 8 photons/μs at T = 15μs, with the velocity offset increasing to 40 MHz and the rate decreasing to 4 photons/μs at T = 100 μs. Over the same time interval, the velocity width monotonically increased from 12.1 to 17 MHz. The presence of heating—rather than cooling—infixed frequency conditions implies the existence of an optimum chirp rate and is not anticipated by some theories of the laser atom cooling dynamics.

We have laser cooled an atomic beam of rubidium with diode lasers and have used these slow atoms to load a magneto-optical trap. The cooling is performed with the frequency-chirp method,1,2 in which the laser's frequency is ramped linearly (by the injection currant) to maintain resonance with the decelerating atoms. Two synchronously chirped lasers are required to prevent optical hyperfine pumping of the ground state. The chirp typically covers 500 MHz in 10 ms. At the end of each ramp, the resulting velocity distribution is measured with a pulsed probe laser. By varying the end point of the chirp, we are able to obtain slow atoms with average velocities ranging from 200 to −50 m/s. The widths of the velocity distributions are measured to be approximately 40 m/s. This relatively large width results from the inherent linewidth (~30 MHz) of the free-running diode lasers used for both cooling and probing.

We numerically study a method to increase the photon return flux of continuous-wave laser guide stars using one-dimensional atomic cooling principles. The method relies on chirping the laser towards higher frequencies following the change in velocity of sodium atoms due to recoil, which raises atomic populations available for laser excitation within the Doppler distribution. The efficiency of this effect grows with the average number of atomic excitations between two atomic collisions in the mesosphere. We find the parameters for maximizing the return flux and evaluate the performance of chirping for operation at La Palma. According to our simulations, the optimal chirp rate lies between 0.8 − 1.0 M H z / µ s , and an increase in the fluorescence of the sodium guide star up to 60% can be achieved with current 20-W-class guide star lasers.

Atomic beam deceleration and cooling by frequency sweep techniques is analysed by means of a Fokker-Planck equation (FPE) with time dependent drift and diffusion coefficients. The effect of compression of the velocity distribution is discussed with respect to theoretical and experimental limitations of atomic beam cooling imposed by the photon recoil. The cooling limit derived from the linear approximation of the FPE fails, if the broadening of the cooled velocity distribution peak by diffusion causes the loss of atoms from the resonant velocity range. This phenomenon is studied by numerical solutions of the FPE. The occurrence of higher final temperatures in previous Monte-Carlo calculations and in experiments is discussed. The anomalous diffusion coefficient caused by the antibunching of the scattered photons is taken into account. The possibility of transverse compression of the atomic beam is investigated by means of a reduced FPE for the transverse degrees of freedom.

We numerically study a method to increase the photon return flux of continuous-wave laser guide stars using one-dimensional atomic cooling principles. The method relies on chirping the laser towards higher frequencies following the change in velocity of sodium atoms due to recoil, which raises atomic populations available for laser excitation within the Doppler distribution. The efficiency of this effect grows with the average number of atomic excitations between two atomic collisions in the mesosphere. We find the parameters for maximizing the return flux and evaluate the performance of chirping for operation at La Palma. According to our simulations, the optimal chirp rate lies between 0.8-1.0 MHz/

μ

s and an increase in the fluorescence of the sodium guide star up to 60% can be achieved with current 20 W-class guide star lasers.

A new method is proposed for laser cooling atoms with Doppler shifts an order of magnitude larger than the homogeneous linewidth of the atomic transition. Two traveling waves cross at a small angle and form standing waves whose wavelength is much longer than that of either traveling wave. This allows one to extend the region in which the laser cooling force is proportional to velocity. The resulting broadband stimulated cooling forces are predicted to stop 0.1% of the flux of a 500-K atomic sodium beam in a distance of 300 μm and a time of a few microseconds. This is more than 100 times faster than current methods. Numerical integration and the method of Gordon and Ashkin have been used to calculate the cooling forces which result when two traveling waves cross at an angle 2a. The stimulated cooling forces are reduced in intensity by sin2a but are proportional to velocity over an interval which is larger by 1/sin a. This allows one to stop a substantial fraction of an atomic beam without chirping the laser or Zeeman tuning the atoms.