Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

CRC Press eBooks

AMMONIA BEAM MASER

Murray, Iii Sargent

Published Mar 5, 2018• 0 citations
Publisher

Abstract

To treat the laser in a realistic way, we need the density matrix concepts and formalism given in Chap. 7. This material makes it possible to incorporate dipole phase decays due, for example, to collisions and to treat multimode electric fields in a straightforward way. Nevertheless, it is gratifying to find that we can already determine the field intensity for a simplified model of the ammonia beam maser, the first device of the maser-laser genre. The maser was originally conceived in 1951 by Townes, who noted his thoughts on the back of an envelope during a period of contemplation on a bench in Franklin Park, Washington, DC.T The device was realized experimentally by Gordon, Zeiger, and Townes (1954). In this chapter, we treat the maser along the lines given by Lamb (1960). The analysis is not complicated by atomic (molecular) lifetimes, because they are long compared to the Rabi flopping time, which is the optimal transit time for molecules in the maser cavity. Furthermore, by considering single-mode, steady-state operation, we can assume by energy conservation (1) that the energy given up by the atoms due to stimulated emission is gained by the field, and (2) that this energy flow balances the cavity losses.

DOI
10.1201/9780429493515-12

Related papers

SEMICLASSICAL LASER THEORY

Murray, Iii Sargent

In Chap. 5, the steady-state solution for the intensity in the ammonia beam maser was determined by energy conservation, that is, the energy given up by the molecules (gain) was equated to the losses in the maser cavity. Although attractive in its simplicity, this method provides no clue to the time depend­ ence of the intensity or to mode pulling (index of refraction) and cannot be used for treating multimode operation. These and other limitations can be avoided by describing maser action by a classical electromagnetic field gov­ erned by Maxwell’s equations and by demanding that the field be self-con­ sistent, that is, that the field E inducing polarization of the active medium be equal to the resulting field E ' as depicted in Fig. 8-1.

CRC Press eBooks•Mar 5, 2018•1 citation

The ammonia maser

Alfred Brian Pippard

The original maser of Gordon, Zeiger and Townes, driven by a focussed stream of ammonia molecules in their antisymmetrical state, provides a conveniently explicit example on which to base a discussion of the principles underlying coherent excitation of a vibrator by stimulated emission. It was shown in chapter 18 how a quadrupole electrostatic lens served to separate symmetric from antisymmetric states, and we shall assume that separation is perfect; it is easy to extend the argument to include a proportion of molecules in the symmetric state. In addition we shall ignore any complications arising from the multitude of rotational states leading to the fine structure shown in fig. 18.8, and shall assume that only one line contributes, for example the strong 3,3 line at 23.9 GHz. Since the microwave cavity resonator, if it is to be excited by the molecules, must normally be very closely tuned to their natural frequency this assumption is realistic. The simplest intuitive approach to the maser is by way of Einstein's treatment of radiation in terms of stimulated and spontaneous processes.† Excited molecules passing through the resonator, when it is already in an oscillatory condition, are stimulated by the field; if the resonator frequency is well matched to the molecular levels they may make a transition down to the ground state and on leaving the resonator have 2Δ 0 less energy than when they entered.

Cambridge University Press eBooks•Nov 16, 1989•0 citations

Concept of Laser

Swapan K. Saha

The theory of stimulated emission was put forwarded by A. Einstein (1917), which predicted that as light passed through a substance it could stimulate the emission of more light. In 1954, this phenomenonwas used by Charles Townes andArthur Schawlow in the construction of a microwave amplification by stimulated emission of radiation (maser) using ammonia gas and microwave radiation. Later, this operating principle of maser was put forth to the optical frequencies by them from the Bell Telephone laboratories in 1958, which led to the realization of the device, known as light amplification by stimulated emission of radiation (laser; Townes and Schawlow, 1958). A laser is a quantum optical device that produces a nearly monochromatic (single wavelength), and coherent beam of light by exciting atoms to a higher energy level and causing them to radiate their energy in phase.

•Jan 14, 2015•0 citations

Rate equations

Thomas Erneux, P. Glorieux

Modeling lasers may be realized with different levels of sophistication. Rigorously it requires a full quantum treatment but many laser dynamical properties may be captured by semiclassical or even purely classical approaches. In this book we deliberately chose the simplest point of view, i.e. purely classical equations, and try to extract analytically as much information as possible. The basic framework of our approach is provided by the rate equations . In their simplest version, they apply to an idealized active system consisting of only two energy levels coupled to a reservoir. They were introduced as soon as the laser was discovered to explain (regular or irregular, damped or undamped) intensity spikes commonly seen with solid state lasers (for a historical review, see the introduction in). These rate equations are discussed and sometimes derived from a semiclassical theory in textbooks on lasers. They capture the essential features of the response of a single-mode laser and they may be modified to account for specific effects such as the modulation of a parameter or optical feedback. The most basic processes involved in laser operation are schematically represented in Figure 1.1. N 1 and N 2 denote the number of atoms in the ground and excited levels, respectively. The process of light–matter interaction is restricted to stimulated emission and absorption.

Cambridge University Press eBooks•Apr 29, 2010•0 citations

On flow masers with separated emission fields

Wilfred H. U. Krause

In 1954 the invention of the ammonia molecular beam maser oscillator, through Charles Hard TOWNES and co-workers and Nikolai Gennadievich BASOV and Alexander Mikhailovich PROKHOROV, opened a new area of applied physics, the field of quantum electronics. Ten years later the importance of the invention of the new device which consists essentially of a microwave resonator and excited ammonia molecules which pass through the resonator was acknowledged by the award of the 1964 NOBEL Prize in physics to the above workers. \nSoon after the invention of the maser principle, an ammonia beam maser utilizing separated emission fields was brought into operation, a device which consists of two separated microwave resonators through which the ammonia beam maser passes in succession. It is now well known that this two-cavity variant has great practical advantages over the original one-cavity ammonia beam maser. \nHowever, not all of the macroscopic effects observed using the two-cavity ammonia beam maser could be explained in a straight­forward manner. One of the more obscure effects presents itself as follows: If the frequency of the auto-oscillation in the first resonator is detuned from one side of the possible frequency range in which generation occurs to the other then the intensity of the electromagnetic radiation in the second cavity can go through two maxima, with a gap in the middle. \nThis effect, the "double-hump detuning phenomenon", which was first observed by the Russian research group of BASOV in 1962, has since then been a challenge to several theoretical and experimental workers. BASOV and co-workers themselves made two different attempts in order to explain this phenomenon. At the Third International Conference on Quantum Electronics, held in Paris in 1963, this team reported that the effect might occur because the transition probability of the molecules passing through the second resonator depends on the degree of excitation of the first cavity. However, in 1967 BASOV and co-workers published a paper where it is suggested that the double-hump detuning phenomenon might well arise because of the interference which occurs between the emissions from molecules which move with different velocities and radiate fields with different phases. \nOn the other hand, research activities in fields other than microwave spectroscopy have made it possible to devise masers which are similar to the ammonia beam maser in that excited particles pass through a tuned resonant component, but which emit at quite different frequencies, e.g. in the audio-frequency ranee or in the mm wave range. However, up to now none of these different masers has been furnished with a successive resonator. \nIt is the purpose of this thesis to report for the first time the successful operation of a tandem maser which is not a two-cavity molecular beam maser. The author devised and investigated a maser where excited protons in water pass successively through two tuned solenoids. \nThe system is based on a conventional proton magnetometer maser oscillating in the magnetic field of the earth at a frequency near to 2 kHz. \nThe general result of the investigation is that despite \nthe enormous frequency difference (audio-frequency compared with a microwave frequency) the two coil nuclear maser behaves in much the same way as a two cavity ammonia beam maser. For the two-coil nuclear maser the double-hump detuning phenomenon can be explained \nin terms of the motion of the macroscopic nuclear magnetization, and an analysis by means of BLOCH'S equations is possible. It is shown that the double-hump detuning phenomenon is produced by a fundamental radiation process occurring in the first emission coil and 1 therefore, that it is not a second-order effect such as could occur because of the non-uniform velocity distribution of the excited particles. \nIt is also shown that for the two-resonator ammonia beam maser the detuning phenomenon can be explained in terms of quantum mechanical probabilities, when a uniform velocity distribution of the ammonia molecules is assumed. Those results agree qualitatively with the results which have been obtained using BLOCH's equations and which have been verified experimentally by means of the two-coil nuclear maser. \nA second distinctive feature of the conventional two-cavity ammonia beam maser is that if the first resonator is sufficiently detuned, generation in the second resonator can take place simultaneously at two different frequencies. The analogous effect has been observed using the two-coil nuclear maser. \nThe conventional one-coil nuclear maser which is currently used as a magnetometer has the disadvantage that it does not offer a suitable criterion for tuning the oscillation frequency accurately to the LARMOR frequency. For the two-cavity ammonia beam maser it has previously been proposed to modulate mechanically the inter-cavity distance and to use zero phase modulation as a means of tuning the maser frequency accurately to the centre frequency of the molecular transition. It is shown that by modulating mechanically the inter­coil distance of the two-coil nuclear maser. a suitable tuning criterion can be obtained in an analogous manner. A second tuning criterion is offered by the double-hump detuning phenomenon. \nIn Chapter I the maser principle is discussed using a classical model, and the different maser types which are of interest in the context of this thesis are enumerated. Chapter II contains a review of previous work on two-cavity ammonia beam masers. \nChapter III reviews the conventional theory of nuclear masers. In Chapters IV to IX the two-coil nuclear maser is investigated. Chapter X contains a general discussion of the two-resonator maser problem in terms of quantum-mechanical probabilities. Some general remarks concerning practical applications of two-resonator masers \nare made. The conclusions are summarized in a final section.

•Jan 1, 1969•0 citations

Basic Theory of Lasers and Masers: A Density Matrix Approach

Jacques Vanier

•Oct 1, 1971•8 citations
To treat the laser in a realistic way, we need the density matrix concepts and formalism given in Chap. 7. This material makes it possible to incorporate dipole phase decays due, for example, to collisions and to treat multimode electric fields in a straightforward way. Nevertheless, it is gratifying to find that we can already determine the field intensity for a simplified model of the ammonia beam maser, the first device of the maser-laser genre. The maser was originally conceived in 1951 by Townes, who noted his thoughts on the back of an envelope during a period of contemplation on a bench in Franklin Park, Washington, DC.T The device was realized experimentally by Gordon, Zeiger, and Townes (1954). In this chapter, we treat the maser along the lines given by Lamb (1960). The analysis is not complicated by atomic (molecular) lifetimes, because they are long compared to the Rabi flopping time, which is the optimal transit time for molecules in the maser cavity. Furthermore, by considering single-mode, steady-state operation, we can assume by energy conservation (1) that the energy given up by the atoms due to stimulated emission is gained by the field, and (2) that this energy flow balances the cavity losses.
In Chap. 5, the steady-state solution for the intensity in the ammonia beam maser was determined by energy conservation, that is, the energy given up by the molecules (gain) was equated to the losses in the maser cavity. Although attractive in its simplicity, this method provides no clue to the time depend­ ence of the intensity or to mode pulling (index of refraction) and cannot be used for treating multimode operation. These and other limitations can be avoided by describing maser action by a classical electromagnetic field gov­ erned by Maxwell’s equations and by demanding that the field be self-con­ sistent, that is, that the field E inducing polarization of the active medium be equal to the resulting field E ' as depicted in Fig. 8-1.
The original maser of Gordon, Zeiger and Townes, driven by a focussed stream of ammonia molecules in their antisymmetrical state, provides a conveniently explicit example on which to base a discussion of the principles underlying coherent excitation of a vibrator by stimulated emission. It was shown in chapter 18 how a quadrupole electrostatic lens served to separate symmetric from antisymmetric states, and we shall assume that separation is perfect; it is easy to extend the argument to include a proportion of molecules in the symmetric state. In addition we shall ignore any complications arising from the multitude of rotational states leading to the fine structure shown in fig. 18.8, and shall assume that only one line contributes, for example the strong 3,3 line at 23.9 GHz. Since the microwave cavity resonator, if it is to be excited by the molecules, must normally be very closely tuned to their natural frequency this assumption is realistic. The simplest intuitive approach to the maser is by way of Einstein's treatment of radiation in terms of stimulated and spontaneous processes.† Excited molecules passing through the resonator, when it is already in an oscillatory condition, are stimulated by the field; if the resonator frequency is well matched to the molecular levels they may make a transition down to the ground state and on leaving the resonator have 2Δ 0 less energy than when they entered.
The theory of stimulated emission was put forwarded by A. Einstein (1917), which predicted that as light passed through a substance it could stimulate the emission of more light. In 1954, this phenomenonwas used by Charles Townes andArthur Schawlow in the construction of a microwave amplification by stimulated emission of radiation (maser) using ammonia gas and microwave radiation. Later, this operating principle of maser was put forth to the optical frequencies by them from the Bell Telephone laboratories in 1958, which led to the realization of the device, known as light amplification by stimulated emission of radiation (laser; Townes and Schawlow, 1958). A laser is a quantum optical device that produces a nearly monochromatic (single wavelength), and coherent beam of light by exciting atoms to a higher energy level and causing them to radiate their energy in phase.
Modeling lasers may be realized with different levels of sophistication. Rigorously it requires a full quantum treatment but many laser dynamical properties may be captured by semiclassical or even purely classical approaches. In this book we deliberately chose the simplest point of view, i.e. purely classical equations, and try to extract analytically as much information as possible. The basic framework of our approach is provided by the rate equations . In their simplest version, they apply to an idealized active system consisting of only two energy levels coupled to a reservoir. They were introduced as soon as the laser was discovered to explain (regular or irregular, damped or undamped) intensity spikes commonly seen with solid state lasers (for a historical review, see the introduction in). These rate equations are discussed and sometimes derived from a semiclassical theory in textbooks on lasers. They capture the essential features of the response of a single-mode laser and they may be modified to account for specific effects such as the modulation of a parameter or optical feedback. The most basic processes involved in laser operation are schematically represented in Figure 1.1. N 1 and N 2 denote the number of atoms in the ground and excited levels, respectively. The process of light–matter interaction is restricted to stimulated emission and absorption.
In 1954 the invention of the ammonia molecular beam maser oscillator, through Charles Hard TOWNES and co-workers and Nikolai Gennadievich BASOV and Alexander Mikhailovich PROKHOROV, opened a new area of applied physics, the field of quantum electronics. Ten years later the importance of the invention of the new device which consists essentially of a microwave resonator and excited ammonia molecules which pass through the resonator was acknowledged by the award of the 1964 NOBEL Prize in physics to the above workers. \nSoon after the invention of the maser principle, an ammonia beam maser utilizing separated emission fields was brought into operation, a device which consists of two separated microwave resonators through which the ammonia beam maser passes in succession. It is now well known that this two-cavity variant has great practical advantages over the original one-cavity ammonia beam maser. \nHowever, not all of the macroscopic effects observed using the two-cavity ammonia beam maser could be explained in a straight­forward manner. One of the more obscure effects presents itself as follows: If the frequency of the auto-oscillation in the first resonator is detuned from one side of the possible frequency range in which generation occurs to the other then the intensity of the electromagnetic radiation in the second cavity can go through two maxima, with a gap in the middle. \nThis effect, the "double-hump detuning phenomenon", which was first observed by the Russian research group of BASOV in 1962, has since then been a challenge to several theoretical and experimental workers. BASOV and co-workers themselves made two different attempts in order to explain this phenomenon. At the Third International Conference on Quantum Electronics, held in Paris in 1963, this team reported that the effect might occur because the transition probability of the molecules passing through the second resonator depends on the degree of excitation of the first cavity. However, in 1967 BASOV and co-workers published a paper where it is suggested that the double-hump detuning phenomenon might well arise because of the interference which occurs between the emissions from molecules which move with different velocities and radiate fields with different phases. \nOn the other hand, research activities in fields other than microwave spectroscopy have made it possible to devise masers which are similar to the ammonia beam maser in that excited particles pass through a tuned resonant component, but which emit at quite different frequencies, e.g. in the audio-frequency ranee or in the mm wave range. However, up to now none of these different masers has been furnished with a successive resonator. \nIt is the purpose of this thesis to report for the first time the successful operation of a tandem maser which is not a two-cavity molecular beam maser. The author devised and investigated a maser where excited protons in water pass successively through two tuned solenoids. \nThe system is based on a conventional proton magnetometer maser oscillating in the magnetic field of the earth at a frequency near to 2 kHz. \nThe general result of the investigation is that despite \nthe enormous frequency difference (audio-frequency compared with a microwave frequency) the two coil nuclear maser behaves in much the same way as a two cavity ammonia beam maser. For the two-coil nuclear maser the double-hump detuning phenomenon can be explained \nin terms of the motion of the macroscopic nuclear magnetization, and an analysis by means of BLOCH'S equations is possible. It is shown that the double-hump detuning phenomenon is produced by a fundamental radiation process occurring in the first emission coil and 1 therefore, that it is not a second-order effect such as could occur because of the non-uniform velocity distribution of the excited particles. \nIt is also shown that for the two-resonator ammonia beam maser the detuning phenomenon can be explained in terms of quantum mechanical probabilities, when a uniform velocity distribution of the ammonia molecules is assumed. Those results agree qualitatively with the results which have been obtained using BLOCH's equations and which have been verified experimentally by means of the two-coil nuclear maser. \nA second distinctive feature of the conventional two-cavity ammonia beam maser is that if the first resonator is sufficiently detuned, generation in the second resonator can take place simultaneously at two different frequencies. The analogous effect has been observed using the two-coil nuclear maser. \nThe conventional one-coil nuclear maser which is currently used as a magnetometer has the disadvantage that it does not offer a suitable criterion for tuning the oscillation frequency accurately to the LARMOR frequency. For the two-cavity ammonia beam maser it has previously been proposed to modulate mechanically the inter-cavity distance and to use zero phase modulation as a means of tuning the maser frequency accurately to the centre frequency of the molecular transition. It is shown that by modulating mechanically the inter­coil distance of the two-coil nuclear maser. a suitable tuning criterion can be obtained in an analogous manner. A second tuning criterion is offered by the double-hump detuning phenomenon. \nIn Chapter I the maser principle is discussed using a classical model, and the different maser types which are of interest in the context of this thesis are enumerated. Chapter II contains a review of previous work on two-cavity ammonia beam masers. \nChapter III reviews the conventional theory of nuclear masers. In Chapters IV to IX the two-coil nuclear maser is investigated. Chapter X contains a general discussion of the two-resonator maser problem in terms of quantum-mechanical probabilities. Some general remarks concerning practical applications of two-resonator masers \nare made. The conclusions are summarized in a final section.