Extension of The Laser-Pumped Ruby Maser to Millimeter Wavelengths

A brief description is given on the operation of a microwave ruby maser in which the pump signal is the optical emission of a ruby laser. For operation in the millimeter spectrum the application of a magnetic field of inordinately high intensity can produce Zeeman splitting of the Cr³⁺ levels at millimeter wave energy in the ground state in ruby. To obtain population inversion by optical pumping on the levels requires that the ratio of maser frequency to temperature be v_ij / T <14.4 Gc/sec °K. As the maser temperature is increased the spin lattice relaxation time T₁ decreases in addition to possibly decreasing with increasing magnetic field. Since the power required from the laser is estimated as that required to produce saturation of the optical pump transition in a time less thanT₁, then decreasing T₁ also requires increased laser emission. A broadening of the laser emission has been observed at increased power so that the limit on useful laser power can be given in terms of the absorption line width of the maser optical pumping transition. Treating these various effects conservatively indicates that the laser-pumped ruby maser can be operated over the entire millimeter spectrum, however. The design of an apparatus with a hard superconductor electromagnet producing the field intensity required to accomplish this objective is given.