Robust adiabatic sum frequency conversion

Abstract

We discuss theoretically and demonstrate experimentally the robustness of the adiabatic sum frequency conversion method. This technique, borrowed from an analogous scheme of robust population transfer in atomic physics and nuclear magnetic resonance, enables the achievement of nearly full frequency conversion in a sum frequency generation process for a bandwidth up to two orders of magnitude wider than in conventional conversion schemes. We show that this scheme is robust to variations in the parameters of both the nonlinear crystal and of the incoming light. These include the crystal temperature, the frequency of the incoming field, the pump intensity, the crystal length and the angle of incidence. Also, we show that this extremely broad bandwidth can be tuned to higher or lower central wavelengths by changing either the pump frequency or the crystal temperature. The detailed study of the properties of this converter is done using the Landau-Zener theory dealing with the adiabatic transitions in two level systems.

Fully efficient adiabatic frequency conversion of broadband Ti:sapphire oscillator pulses

“…conversion even with bell-shaped pump beam and pulse profiles. With jdΔk∕dzj 561 cm −2 for λ 3 1.9 μm in our experiment, the condition for adiabatic transfer [7], jdΔk∕dzj ≪ κ 2 , reduces to I 2 ≫ 580 MW∕cm 2 . This corroborates the apparent requirement for full conversion of I 2 ≥ ∼2GW∕cm 2 that can be inferred from Fig.…”

“…Moreover, it covers a 0.7 octave idler band and is potentially scalable to multiple octaves from a single nonlinear crystal. Here we discuss an implementation ideally suited for the seeding of OPCPAs, but the method could be useful generally for providing nJ energy broadband infrared pulses with up to an MHz repetition rate.Adiabatic frequency conversion applies the principle of rapid adiabatic passage (RAP) for full transfer of population between states of a 2-level atom to optical frequency conversion, a concept explored in several previous works [6][7][8][9]. Notably, in the mixing of frequencies, ω 3 ω 1 − ω 2 , where ω 1 > ω 2 , ω 3 , through a quadratic electric susceptibility, the equations of motion are isomorphic to the driven optical Bloch equations for a 2-level atom (neglecting radiative losses) when the wave of frequency ω 2 is strong and undepleted during propagation [6][7][8].…”

“…Notably, in the mixing of frequencies, ω 3 ω 1 − ω 2 , where ω 1 > ω 2 , ω 3 , through a quadratic electric susceptibility, the equations of motion are isomorphic to the driven optical Bloch equations for a 2-level atom (neglecting radiative losses) when the wave of frequency ω 2 is strong and undepleted during propagation [6][7][8]. In the first examples of the technique, adiabatic SFG was demonstrated with a narrowband tunable source seeded and pumped by an optical parametric oscillator [6,7]. Later, the method was used for broadband conversion of an amplified Ti:S pulse with up to 50% internal conversion efficiency, converting an 80 nm pulse to a 40 nm pulse centered at 450 nm via adiabatic SFG and a 30 nm pulse to a 400 nm pulse centered at 3.15 μm via adiabatic DFG [8].…”

“…Using the quasi-phase matching (QPM) technique, we designed an adiabatic 2 cm APKTP grating that satisfies the constraints imposed by the adiabatic inequality [7] for conversion of a signal range of 600 to 760 nm to an idler range of 1405 to 2800 nm with a 1047 nm pump. In order to induce an adiabatic longitudinal change of the effective total phase mismatch parameter, defined as…”

“…Figure 4 shows the PbSe photodiode response to the incident idler power plotted against peak pump intensity. In the adiabatic limit, the LZ theory for adiabatic passage predicts a conversion efficiency [7],…”