Book contents
- Frontmatter
- Contents
- Preface to Part 1
- Preface to Part 2
- Preface to the combined volume
- 1 General introduction – author to reader
- PART 1 THE SIMPLE CLASSICAL VIBRATOR
- PART 2 THE SIMPLE VIBRATOR IN QUANTUM MECHANICS
- 13 The quantized harmonic vibrator and its classical features
- 14 Anharmonic vibrators
- 15 Vibrations and cyclotron orbits in two dimensions
- 16 Dissipation, level broadening and radiation
- 17 The equivalent classical oscillator
- 18 The two-level system
- 19 Line broadening
- 20 The ammonia maser
- 21 The family of masers: from laser to travelling-wave oscillator
- Epilogue
- References
- Index
20 - The ammonia maser
Published online by Cambridge University Press: 13 January 2010
- Frontmatter
- Contents
- Preface to Part 1
- Preface to Part 2
- Preface to the combined volume
- 1 General introduction – author to reader
- PART 1 THE SIMPLE CLASSICAL VIBRATOR
- PART 2 THE SIMPLE VIBRATOR IN QUANTUM MECHANICS
- 13 The quantized harmonic vibrator and its classical features
- 14 Anharmonic vibrators
- 15 Vibrations and cyclotron orbits in two dimensions
- 16 Dissipation, level broadening and radiation
- 17 The equivalent classical oscillator
- 18 The two-level system
- 19 Line broadening
- 20 The ammonia maser
- 21 The family of masers: from laser to travelling-wave oscillator
- Epilogue
- References
- Index
Summary
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 2Δ0 less energy than when they entered.
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- Chapter
- Information
- The Physics of Vibration , pp. 571 - 602Publisher: Cambridge University PressPrint publication year: 1989