The spectral character of the stimulated emission from ruby has been investigated; we found that the zero-field splitting (0.38 cm−1) of the 4A2 ground level and the cavity optical length and its reflectivity determine the spectral character of this emission. At 300°K the system is induced into oscillation in a number of cavity modes separated by Δv = (2le12)−1, where l is the length of the resonator and e12 is the index of refraction for the ordinary ray. At T≅80°K the Ē(2E) → ±32(A2) and the Ē(2E) → ±12(4A2) transitions were identified in the stimulated emission spectrum. Each can oscillate in an axial cavity mode (or modes) plus an off-axis mode at the center of the transition. At 4.2°K the system oscillates in off-axis modes, unless the length of the cavity l is such that it has axial resonances coincident with the transition frequencies. An analysis of the temperature dependence of the oscillation threshold for the separate transitions is presented and is compared with the observed behavior.
The spectral character of the stimulated emission from ruby has been investigated; we found that the zero-field splitting (0.38 cm−1) of the 4A2 ground level and the cavity optical length and its reflectivity determine the spectral character of this emission. At 300°K the system is induced into oscillation in a number of cavity modes separated by Δv = (2le12)−1, where l is the length of the resonator and e12 is the index of refraction for the ordinary ray. At T≅80°K the Ē(2E) → ±32(A2) and the Ē(2E) → ±12(4A2) transitions were identified in the stimulated emission spectrum. Each can oscillate in an axial cavity mode (or modes) plus an off-axis mode at the center of the transition. At 4.2°K the system oscillates in off-axis modes, unless the length of the cavity l is such that it has axial resonances coincident with the transition frequencies. An analysis of the temperature dependence of the oscillation threshold for the separate transitions is presented and is compared with the observed behavior.
The spectral character of the stimulated emission from ruby has been investigated; we found that the zero-field splitting (0.38 cm−1) of the A42 ground level and the cavity optical length and its reflectivity determine the spectral character of this emission. At 300°K the system is induced into oscillation in a number of cavitymodes separated by Δv̄ = (2lε12)−1, where l is the length of the resonator and ε12 is the index of refraction for the ordinary ray. At T≅80°K the Ē(2E) → ±32(A2) and the Ē(2E) → ±12(4A2) transitions were identified in the stimulated emission spectrum. Each can oscillate in an axial cavity mode (or modes) plus an off-axis mode at the center of the transition. At 4.2°K the system oscillates in off-axis modes, unless the length of the cavity l is such that it has axial resonances coincident with the transition frequencies. An analysis of the temperature dependence of the oscillation threshold for the separate transitions is presented and is compared with the observed behavior.
Optical absorption cross sections and the fluorescent quantum efficiency in ruby have been determined. This data has been used to correlate calculations with the analysis of the preceding paper. Stimulated emission from ruby under pulsed excitation has been studied in some detail; the observations are found to depend strongly on the perfection of the particular crystal under study. A peak power output of approximately 5 kw, total output energy of near 1 joule, beam collimation of less than ${10}^{\ensuremath{-}2}$ rad, and a spectral width of individual components in the output radiation of about 6\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$A at 6943 A have been measured. It is suggested that mode instabilities due to temperature shifts and a time-varying magnetic field are contributing to an oscillatory behavior of the output pulse.
We consider ruby as a linear, uniaxial, maxwellian medium, which, in its absorbing state, has axially dependent material constants. It is made active by pumping with electric fields, in the region of shorter-wavelength absorption bands, which, by means of an energy transfer, induce source-type electric fields having constant amplitudes in the R1 and R2 regions, and make possible absorption, spontaneous emission, and stimulated emission. Experiments indicate that the absorption, fluorescence, and laser action are all maximum for electric fields perpendicular to the optic axis, and minimum when the electric field is parallel to the optic axis; the relative irradiances and shapes of the R1 and R2 bands in all cases depend upon the orientation of the plane of polarization of the emerging radiant flux relative to the optic axis. Attempts are made to compute the spectral distributions in the R1 and R2 bands for the ordinary and extraordinary waves, neglecting all boundary-value problems. Agreement was found to be possible only in the region below the threshold of laser action.
Ruby lasers, when operated near threshold at 77°K with a low Q cavity (one end silvered for maximum reflectivity and the other end uncoated) oscillated at two frequencies. The frequency differences near threshold, measured with Fabry-Perot etalons, were in good agreement with the splitting of the R1 doublet, previously measured by microwave methods. As the power of the laser increased, the frequency difference between the oscillating components [2Ē → 4A2(±32, ±½)] decreased. These results are accounted for on the basis of saturation broadening of overlapping Lorentzian lines. The observed variations in the splitting are in good accord with the theory. The rise in temperature of the ruby rods produced a negligible change in the splitting of the R1 doublet. The same mechanism which produces the variation in the splitting should broaden the output spectrum of the laser.
The real and imaginary parts of the complex index of refraction have been measured in the R1 line of optically pumped ruby. The experiments, which employed a temperature-controlled, single-mode ruby laser as a variable-frequency monochromatic source, were performed near liquid-nitrogen temperature, where the R1 doublet structure is well resolved. R1 absorption profiles were measured for several optical-pumping conditions, ranging from zero up to a pump power that excited a population in the 2E state equal to about 60% of the population of the 4A2 ground state. For each pumping condition, the anomalous-dispersion curve was measured interferometrically. The spectral profiles of the absorption coefficient and the anomalous dispersion display a dependence on the optical-pumping conditions that is more complicated than simple saturation of the R1 transitions, but for given pumping conditions the two quantities are correlated as predicted by the Kramers–Kronig relations.
Lasing without population inversion was studied in a three-level solid state medium of ruby. The two closely-spaced lower levels are the Zeeman split sublevels of the ground state 4A2 of ruby, corresponding to M=−3/2 and M=+l/2. The transition between the lower levels is the electric dipole-forbidden. When the angle between the constant magnetic field and C-axis of ruby is 90°, the transition matrix element of the electric dipole-forbidden transition is quite large.1 A strong microwave field which operates at K-band coherently couples the two lower levels.2 Changing the constant magnetic field intensity or adjusting the frequency of the pumping microwave field, the exact resonant excitation can be established. The upper level of the lasing process is the Zeeman split sub-level M=−l/2 of 2E state. The ruby crystal, with about 0.05% chromium concentration, is placed at the center of a cylindrical cavity and cooled by liquid helium. With 500 Gauss magnetic field, the coupling microwave frequency is 13.1 Ghz and the required power is around 100 W/cm2.