Two Level Metal Vapor Lasers with Thermal Creation of Population Inversion

Abstract

We present a new technique for direct conversion of thermal energy into coherent radiation. The near-surface layer of evaporated excited atoms of rare earth metals is proposed to be used as a converter. There is an inverted population in this layer. Operation principles of two level lasers on the transitions to the ground state using Eu are considered. The fact of detachment of Sm atoms in the excited 4f(N-1)5d6s2 state during the thermal evaporation process has been proved experimentally.

Two-level lasers operating on the transitions to the ground state

“…Their corresponding lifetimes are τ k (λ 1 ) = 0.95⋅10 -6 s and τ k (λ 2 ) = 5.00⋅10 -6 s. Taking into account the average thermal speed ( ) melt v T of the detached Sm atoms (Table 1), we find d s (λ 1 ) = 0.41 mm and d s (λ 2 ) = 2.19 mm. The spontaneous emission on the transition with the wavelength λ 1 was detected experimentally in [9]. For the wavelength λ 1 the partial power P Sm (λ 1 ) = 45.67 W/cm 2 , the power density I Sm (λ 1 ) = 8.10⋅10 7 W/cm 2 , and the efficiency η Sm (λ 1 ) = 0.4701 (47.01%); for the wavelength λ 2 : P Sm (λ 2 ) = 59.17 W/cm 2 , I Sm (λ 2 ) = 1.02⋅10 8 W/cm 2 , and η Sm (λ 2 ) = 0.4606 (46.06%); and for the wavelength λ 3 : P Sm (λ 3 ) = 56.75 W/cm 2 , I Sm (λ 3 ) = 9.41⋅10 7 W/cm 2 , and η Sm (λ 3 ) = 0.4591 (45.91%).…”

“…In order to generate stimulated emission on the 5d → 4f transitions we need totally reflecting and semitransparent resonator mirrors located in front of the output windows. In this case, the two-level system represents a twolevel metal-vapor laser with thermal pumping generating on the transitions to the ground state [9]. Figure 3 shows a schematic drawing of this laser.…”

“…The probability that REM atom would absorb or emit photon before leaving the laser beam equals 1/2. Therefore, one half of REM atoms leaves the laser beam in the excited state [9], the lifetime τ k ∼ 1.31⋅10 -6 s and τ stim ∼ 3.50⋅10 -19 s. On the one hand, the time t λ required for a Eu atom to travel the distance equal to the wavelength λ is about 9.20⋅10 -10 s. On the other hand, the thickness of a planar laser beam known from quantum dynamics cannot be smaller than the radiation wavelength. It is easy to see that τ stim << t λ , i.e.…”

“…According to the model, the intrinsic neutral REM atoms in the excited lowest-lying state of the configuration upper and lower levels of the two-level system, respectively. We proposed a model of two-level REM vapor lasers with thermal production of population inversion (using Eu as an example) and proved experimentally the fact of evaporation of REM atoms in the excited 5d-state (using Sm) in [9]. In this paper, we consider this model in detail and analyze the specific energy parameters to determine the REMs best suited for potential experimental operation of these systems and to estimate their potential.…”

“…For example, population inversion in such systems is formed via collisions of alkali-metal (K, Na, Rb) atoms with buffer gas atoms under non-resonant optical pumping [5][6][7]. In our previous publications [8,9] we showed that it is possible to develop two-level systems with thermal pumping due to the peculiarities of the thermal evaporation process of rare earth metals (REMs). A model of electronic structure of the surface and evaporation process of REMs with an incomplete 4f shell (Ce -Yb) was proposed in [8].…”