Shaping coherent excitation of atoms and molecules by a train of ultrashort laser pulses

Abstract

We propose a mechanism to produce a superposition of atomic and molecular states by a train of ultrashort laser pulses combined with weak control fields. By adjusting the repetition rate of the pump pulses and the intensity of the coupling laser, one can suppress a transition, while simultaneously enhancing the desired transitions. As an example various superpositions of states of the K2 molecule are shown.

Efficiency of light-frequency conversion in an atomic ensemble

“…By performing a global search we find conditions of pump Rabi frequencies, detunings and signal/idler input frequency to maximize the conversion efficiency as a function of optical depth of the ensemble. Only in the limit of very large optical depth does the maximum efficiency approach the ideal strong coupling result [23]. Under conditions routinely obtained in cold, non-degenerate rubidium gas, with opd ≃ 100−200, optimal conversion efficiencies of the order 80 to 90% are predicted.…”

“…Two strong fields Ωa, Ω b shift the levels with energy ∆E a,b and wavy lines represent the idler field resonances. [22], in the case of resonant pump fields ∆ 1 = ∆ b = 0 [23]. In this ideal limit there is a conservation condition η u + T u = η d + T d = 1.…”

“…For Ω a > Ω b the centers of these windows are at −Ω a , 0, and Ω a , respectively. Choosing the idler detuning ∆ω i = ±Ω a as in [23], the idler interacts with the atomic medium at the center of the left or right window.…”

“…γ 12 + γ 32 , P ≡ e i∆kz−i∆ωt , the four-wave mixing mismatch wavevector ∆k = k a − k s + k b − k i , the frequency mismatch ∆ω = ω a + ω s − ω b − ω i = ∆ 1 − ∆ b + ∆ω s − ∆ω i and various detunings are defined as∆ω i = ω i − ω 3 , ∆ω s = ω s − ω 12 , ∆ 1 = ω a − ω 1 , ∆ 2 = ω a + ω s − ω 2 = ∆ 1 + ∆ω s , ∆ b = ω b − ω23 . The slow-varying atomic operators are definedσ 01 ≡ 1 N zσ l 01 e −ikaz l +iωat ,σ 12 ≡ iksz l +iωst , σ 02 ≡ 1 N zσ l 02 e −ikaz l +iksz l +iωst+iωat ,σ 11 ≡ e −ikiz l +iωit ,σ 22 ≡ e −iω b t e −ik b z l ,σ 33 ≡ −i(ωa−ωi)t+i(ka−iki)z lwhere N z (2M + 1) = N .…”

Controlling molecular orientation by laser pulses with two different envelope shapes

“…Shu et al provided an important insight into the THz-laser-induced molecular orientation and achieved a large orientation degree by the interaction of a SCP with the electric-dipole moment [33]. To further optimize the molecular orientation, researchers proposed many laser field schemes including pulse train [35][36][37][38][39][40][41] and the combination of laser pulses [42][43][44][45]. The combination of two-color femtosecond and delayed terahertz laser pulses has been proven theoretically and experimentally as a versatile method to obtain a high orientation degree.…”