Injection seeding of a Ti:sapphire laser using a ramp-hold-fire technique

Abstract

The capability of neodymium doped glass to store a high level of energy depends on the concentration of ions, which can be as high as 4-8 10,' ions/cm3. However it is known that dipole-dipole interaction between neighbors ions Nd3+ rise with population, implying a decrease of the lifetime emission of the lasing excited state 4F,iz.1 This increased spontaneous emission becomes an important mechanism loss when using a pumping with duration comparable to the lifetime. Furthermore high densities of inversion are associated to an additional loss mechanism that corresponds to the interaction between two neighboring excited 4F,i, ions. In this process, one ion is further excited to a higher level, while the other returns to the ground ~ t a t e . ~ , ~ Although the highly excited state can relax to 4F3,2 via nonradiative process, this Auger upconversion mechanism limits the energy storage capability of the media and should be taken into account when using laser or diode pumping. This is the motivation of this study. Basically, this loss depends quadratically on the population N,(4F3,,) and appears in the usual rates equations as a -yNf term. After the initial buildup of the excited state population NI, its relaxation follows the law: