A ruby laser generally includes four parts: a ruby rod, a pulsed xenon lamp, a condenser, and an optical resonator. Its working substance is a ruby rod, which is ground from chromium-doped alumina (Al2O3) artificial crystal (commonly called ruby). The concentration of chromium ions is typically 0.05% based on the weight ratio of chromium oxide to aluminum oxide. Ruby rods have high optical quality requirements. The two ends of the rod are ground and polished into optical parallel planes. The parallelism requirement is better than 10 seconds, the flatness is not less than 1/4 aperture, and the perpendicularity between the end face and the rod axis is not low. At 1 minute, the side is not polished to prevent parasitic laser oscillation. At both ends of the rod (usually outside the condenser), a multi-layered dielectric film reflector is placed, one of which is a total reflection mirror, and the other is a semi-transparent mirror (the reflectance of which can be 70 to 90%) ), These two mirrors constitute the resonant cavity of the laser.
The rubidium ruby laser usually adopts the optical excitation method, that is, the light energy emitted by the pulsed xenon lamp is focused on the ruby rod, and a condenser can be used. The concentrator is an elliptical cylindrical cavity with polished metal plating on the inner wall. The xenon lamp and the ruby rod are placed side by side on the two focal lines of the elliptic cylindrical cavity of the concentrator.
The laser action in erbium rubies is achieved through the stimulated emission process of Cr3 + (chromium ions), so Cr3 + is often called the active ion, which is the "main body" of the laser in ruby. Alumina, the main component of ruby, is only a matrix that contains chromium ions, and only plays an indirect role in the laser. Therefore, in order to understand the working principle of a ruby laser, the energy level structure and optical characteristics of chromium ions in ruby need to be explained.