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Journal of Applied Physics

Ruby as a Maser Material

Chihiro Kikuchi, John Lambe, George Makhov, R. W. Terhune

Published Jul 1, 1959• 64 citations
Publisher

Abstract

The reasons for the initial choice of ruby as a maser material are outlined and some measurements of the parameters in the spin Hamiltonian and of spin relaxation times are reported. The relative merits of single- and double-pump modes of operation of a four-level maser are discussed and measurements of the oscillator power for the two cases are included.

DOI
10.1063/1.1776979

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Pulsed oscillation of a three-level ruby maser of which pumping microwave was modulated by pulse was investigated. The time lag t d of the oscillation pulse behind the pumping pulse was determined experimentally as a function of the peak level P of the pumping power, and the period T and the width τ of the pumping pulse. A semi-empirical formula t d =t 0(\frac{P_{c}}{P}) k exp [b(\frac{T}{\tau})1-δ\frac{P_{c}}{P}] was obtained. The minimum pulse width τ m required for the oscillation to occur was determined as a function of P and T, which was approximately expressed by τ m =c\frac{T^{m}}{P^{n}}. The above results were qualitatively interpreted in terms of excess population Δ n,

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Cavity Maser Experiments using Ruby at S Band†

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A three-level solid-state maser using ruby has been operated at frequencies near 3000 Mc/s, using a high-efficiency cavity having TEM modes in a rectangular geometry. Two different operating points in the θ = 10° to θ =30 ° region of the ruby spectrum gave maser operation with a pump frequency near 10 500 Mc/s, although the inversion obtained was a. sensitive function of the exact operating point. An operating point at θ = 90°, requiring pumping at 13 500 Mc/s, gave a gain-bandwidth product of better than 50 Mc/s. It was also found possible to pump the 1-4 or ΔM = 3 transition at this same operating point, obtaining 3000 Mc/s amplification with a 23 700 Mc/s pump frequency. Although this mode of operation was not fully explored, it is potentially capable of increasing the gain-bandwidth product by a substantial amount.

Journal of Electronics and Control•Jun 1, 1959•4 citations
The reasons for the initial choice of ruby as a maser material are outlined and some measurements of the parameters in the spin Hamiltonian and of spin relaxation times are reported. The relative merits of single- and double-pump modes of operation of a four-level maser are discussed and measurements of the oscillator power for the two cases are included.
The computational results of a comparison of maser materials for a 32 GHz maser amplifier are presented. The search for a better maser material is prompted by the relatively large amount of pump power required to sustain a population inversion in ruby at frequencies on the order of 30 GHz and above. The general requirements of a maser material and the specific problems with ruby are outlined. The spin Hamiltonian is used to calculate energy levels and transition probabilities for ruby and twelve other materials. A table is compiled of several attractive operating points for each of the materials analyzed. All the materials analyzed possess operating points that could be superior to ruby. To complete the evaluation of the materials, measurements of inversion ratio and pump power requirements must be made in the future.
The use of a quantitative analysis of the dominant source of relaxation in ruby spin systems to make predictions of key maser amplifier parameters is described. The spin-lattice Hamiltonian which describes the interaction of the electron spins with the thermal vibrations of the surrounding lattice is obtained from the literature. Taking into account the vibrational anisotropy of ruby, Fermi's rule is used to calculate the spin transition rates between the maser energy levels. The spin population rate equations are solved for the spin transition relaxation times, and a comparison with previous calculations is made. Predictions of ruby gain, inversion ratio, and noise temperature as a function of physical temperature are made for 8.4-GHz and 32-GHz maser pumping schemes. The theory predicts that ruby oriented at 90 deg will have approximately 50 percent higher gain in dB and slightly lower noise temperature than a 54.7-deg ruby at 32 GHz (assuming pump saturation). A specific calculation relating pump power to inversion ratio is given for a single channel of the 32-GHz reflected wave maser.
Cross relaxation between adjacent intervals may be used to secure an advantage in maser operation comparable to that obtained by ``push-pull'' pumping. Equations for the rate of change of populations in a scheme of four levels (A,B,C,D) when AC is pumped and cross relaxation takes place between BC, CD have been formulated, and the steady-state condition corresponding to various assumptions regarding lattice relaxation times is discussed. In an experimental investigation of maser operation based on this scheme and using ruby as the active material, an inversion of 0.9:1 was obtained at a signal frequency of 14.5 kMc when pumping at 24.5 kMc.
Pulsed oscillation of a three-level ruby maser of which pumping microwave was modulated by pulse was investigated. The time lag t d of the oscillation pulse behind the pumping pulse was determined experimentally as a function of the peak level P of the pumping power, and the period T and the width τ of the pumping pulse. A semi-empirical formula t d =t 0(\frac{P_{c}}{P}) k exp [b(\frac{T}{\tau})1-δ\frac{P_{c}}{P}] was obtained. The minimum pulse width τ m required for the oscillation to occur was determined as a function of P and T, which was approximately expressed by τ m =c\frac{T^{m}}{P^{n}}. The above results were qualitatively interpreted in terms of excess population Δ n,
A three-level solid-state maser using ruby has been operated at frequencies near 3000 Mc/s, using a high-efficiency cavity having TEM modes in a rectangular geometry. Two different operating points in the θ = 10° to θ =30 ° region of the ruby spectrum gave maser operation with a pump frequency near 10 500 Mc/s, although the inversion obtained was a. sensitive function of the exact operating point. An operating point at θ = 90°, requiring pumping at 13 500 Mc/s, gave a gain-bandwidth product of better than 50 Mc/s. It was also found possible to pump the 1-4 or ΔM = 3 transition at this same operating point, obtaining 3000 Mc/s amplification with a 23 700 Mc/s pump frequency. Although this mode of operation was not fully explored, it is potentially capable of increasing the gain-bandwidth product by a substantial amount.