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Physics of Atomic Frequency Standards Based on Stimulated Resonance Raman Scattering

Richard H. Picard, C. R. Willis

Published Oct 1, 1981• 0 citations
OpenAlex

Abstract

Abstract : This report analyzes a novel technique developed at RADC for high-precision frequency standards operating in the microwave to far infrared regions of the spectrum. The technique is based on stimulated resonance Raman scattering of visible laser light in atomic or molecular beams; it does not require low frequency (microwave to far infrared) radiation to interact with the resonant species, and it is potentially capable of stabilities characteristic of low-frequency atomic standards.

Related papers

Performance of a Microwave Clock Based on a Laser-Induced Stimulated Raman Interactions

Philip Hemmer, Shaoul Ezekiel, C. C. Leiby

Recent experimental work1 has demonstrated that a microwave oscillator can be stabilized using a stimulated-resonance Raman transition in a sodium atomic beam. This Raman technique is of interest because optical lasers rather than microwaves are used in the interaction, and, aside from fundamental interest, the greater flexibility of optical systems may make it possible eventually to develop more-stable and moreportable atomic clocks.

•Jun 18, 1984•2 citations

Precision studies of stimulated-resonance Raman interactions in an atomic beam

Philip Hemmer, G. P. Ontai, Shaoul Ezekiel

Precision studies of stimulated-resonance Raman interactions in a sodium atomic beam were performed with emphasis on Ramsey’s separated-field excitation. Ramsey fringes were obtained for a field separation of up to 30 cm, and the data were consistent with theoretical predictions. Possible applications of this Raman interaction to clock development also were studied by stabilizing a microwave oscillator to a Raman–Ramsey fringe. The resulting oscillator stability of 1.5 × 10−11 for a 1000-sec averaging time compares favorably with commercial cesium clocks when differences in atom transit time and transition frequency are taken into consideration. Finally, potential sources of long-term frequency error, which are important for clock applications, were also partially investigated.

Journal of the Optical Society of America B•Feb 1, 1986•55 citations

Observation of Ramsey Fringes Using a Stimulated, Resonance Raman Transition in a Sodium Atomic Beam

John E. Thomas, Philip Hemmer, Shaoul Ezekiel +3 more

Ramsey fringes have been observed using a stimulated, resonance Raman transition at 1772 MHz excited by two dye lasers in a sodium atomic beam. The width of the central fringe is 650 Hz (half width at half maximum), corresponding to a 30-cm interaction-region separation. The fringes are free from laser jitter because the jitters in both laser beams are correlated. Applications to frequency standards as well as to high-resolution spectroscopy in the microwave to far-ir regions are discussed.

Physical Review Letters•Mar 29, 1982•219 citations

Some investigations into stimulated electronic Raman scattering and related processes in atomic vapours

David Brian Hearn

Stimulated electronic Raman scattering, SERS, is a simple method of efficiently generating widely tunable infrared radiation. This work describes techniques by which the tuning capability of this process may be extended. To this end several schemes in Caesium and Barium vapours have been investigated. In Barium vapour two Raman transitions were studied using fixed frequency lasers. Poor performance of one of these transitions led to the application of biharmonic pumping or 'coherent Raman mixing' to enable generation of infrared light, and was the first observation of this process in an atomic vapour. This technique was subsequently used to generate infrared light from tunable dye laser light, which gave continuous tuning from 1.16µm to 1.5µm. The process was found to be limited by atomic saturation. The effect which saturation has on the generation efficiency is considered theoretically, and predicts quite accurately the observed tuning behaviour. Two methods aimed at reducing molecular absorption effects in SERS in alkali vapours were investigated. The techniques employed either laser excitation and dissociation of the molecules or a reduction in their ground state concentration by superheating of the vapour. Some degree of success was achieved in improving the available tuning from the 6s-7s transition in Caesium. However, the inclusion of the effect of collision broadening of atomic transitions into a calculation of the Raman threshold suggests that little further improvement can be obtained on this transition. A direct measurement of the Raman threshold power on the 6s-5d5/2 transition in Caesium gave excellent agreement with theoretical predictions based on collision broadening of this Raman transition. In addition, this work gave an insight into the role photoionization plays in increasing the threshold under certain circumstances. The analysis suggests that laser pulse duration and vapour column length are important in determining whether Raman threshold can be exceeded.

•Jan 1, 1982•0 citations

Trapped-ion and trapped-atom microwave frequency standards

Peter Fisk

The stability and accuracy of atomic microwave frequency standards (atomic clocks) have been improving at a rate exceeding one order of magnitude per decade for the past 30 years. This sustained improvement has been driven mainly by the many and diverse technological applications requiring highly stable and accurate time and frequency standards. There is no reason to suspect that this rate of progress is slowing. Over the last decade, research and development in atomic frequency standards has tended increasingly towards the use of atom and ion trapping technologies to approach the supposedly ideal unperturbed atomic frequency reference consisting of a single atom or ion either motionless or in free-fall in a perfect, field-free vacuum. This work has been facilitated by the relatively recent development of techniques whereby laser light is used to cool, confine and manipulate atoms or ions. This paper reviews the current status of atomic microwave frequency standards based on trapped atoms and trapped ions, and attempts to explain the motivation for their development and the principles of their operation, with particular emphasis on the physics of factors which limit their performance.

Reports on Progress in Physics•Aug 1, 1997•79 citations

VCSEL-based Raman frequency reference on Rubidium atoms

Laurent P. Balet, Jacques Haesler, Steve Lecomte

As an alternative to coherent population trapping (CPT), stimulated Raman scattering in an atomic vapor and implemented in an optoelectronic microwave oscillator can be designed as a compact microwave frequency reference. Due to its simplified architecture and as an active atomic clock, it has the potential to be less energy demanding than CPT. In this paper, we present experimental results on the behavior and frequency stability of a tabletop Raman oscillator.

European Frequency and Time Forum•Apr 1, 2012•1 citation
Abstract : This report analyzes a novel technique developed at RADC for high-precision frequency standards operating in the microwave to far infrared regions of the spectrum. The technique is based on stimulated resonance Raman scattering of visible laser light in atomic or molecular beams; it does not require low frequency (microwave to far infrared) radiation to interact with the resonant species, and it is potentially capable of stabilities characteristic of low-frequency atomic standards.
Precision studies of stimulated-resonance Raman interactions in a sodium atomic beam were performed with emphasis on Ramsey’s separated-field excitation. Ramsey fringes were obtained for a field separation of up to 30 cm, and the data were consistent with theoretical predictions. Possible applications of this Raman interaction to clock development also were studied by stabilizing a microwave oscillator to a Raman–Ramsey fringe. The resulting oscillator stability of 1.5 × 10−11 for a 1000-sec averaging time compares favorably with commercial cesium clocks when differences in atom transit time and transition frequency are taken into consideration. Finally, potential sources of long-term frequency error, which are important for clock applications, were also partially investigated.
Stimulated electronic Raman scattering, SERS, is a simple method of efficiently generating widely tunable infrared radiation. This work describes techniques by which the tuning capability of this process may be extended. To this end several schemes in Caesium and Barium vapours have been investigated. In Barium vapour two Raman transitions were studied using fixed frequency lasers. Poor performance of one of these transitions led to the application of biharmonic pumping or 'coherent Raman mixing' to enable generation of infrared light, and was the first observation of this process in an atomic vapour. This technique was subsequently used to generate infrared light from tunable dye laser light, which gave continuous tuning from 1.16µm to 1.5µm. The process was found to be limited by atomic saturation. The effect which saturation has on the generation efficiency is considered theoretically, and predicts quite accurately the observed tuning behaviour. Two methods aimed at reducing molecular absorption effects in SERS in alkali vapours were investigated. The techniques employed either laser excitation and dissociation of the molecules or a reduction in their ground state concentration by superheating of the vapour. Some degree of success was achieved in improving the available tuning from the 6s-7s transition in Caesium. However, the inclusion of the effect of collision broadening of atomic transitions into a calculation of the Raman threshold suggests that little further improvement can be obtained on this transition. A direct measurement of the Raman threshold power on the 6s-5d5/2 transition in Caesium gave excellent agreement with theoretical predictions based on collision broadening of this Raman transition. In addition, this work gave an insight into the role photoionization plays in increasing the threshold under certain circumstances. The analysis suggests that laser pulse duration and vapour column length are important in determining whether Raman threshold can be exceeded.
The stability and accuracy of atomic microwave frequency standards (atomic clocks) have been improving at a rate exceeding one order of magnitude per decade for the past 30 years. This sustained improvement has been driven mainly by the many and diverse technological applications requiring highly stable and accurate time and frequency standards. There is no reason to suspect that this rate of progress is slowing. Over the last decade, research and development in atomic frequency standards has tended increasingly towards the use of atom and ion trapping technologies to approach the supposedly ideal unperturbed atomic frequency reference consisting of a single atom or ion either motionless or in free-fall in a perfect, field-free vacuum. This work has been facilitated by the relatively recent development of techniques whereby laser light is used to cool, confine and manipulate atoms or ions. This paper reviews the current status of atomic microwave frequency standards based on trapped atoms and trapped ions, and attempts to explain the motivation for their development and the principles of their operation, with particular emphasis on the physics of factors which limit their performance.