Frequency up-conversion of intense, ultrashort laser pulses at maximal atomic coherence
| Autor: | Fabian Cipura, Thomas Halfmann, Patric Ackermann |
|---|---|
| Rok vydání: | 2020 |
| Předmět: |
Physics
education.field_of_study Population Physics::Optics Resonance Nonlinear optics Laser pumping Laser 01 natural sciences 010305 fluids & plasmas Atomic coherence law.invention Free induction decay law 0103 physical sciences Physics::Atomic Physics Atomic physics 010306 general physics education Coherence (physics) |
| Zdroj: | Physical Review A. 102 |
| ISSN: | 2469-9934 2469-9926 |
| Popis: | We present experimental data on adiabatically driven frequency conversion with ultrashort (picosecond) laser pulses towards the vacuum-ultraviolet regime, enhanced by coherent population return and preparation of maximal atomic coherences. We generate the sum frequency of an intense pump pulse and a probe pulse via a two-photon resonance in xenon. When we slightly detune the pump laser from two-photon resonance, the atomic populations are adiabatically driven forth and back from the atomic ground state to an excited state. This coherent population return (CPR) prepares the medium in a transient state of maximal atomic coherence, which enhances frequency mixing with a probe laser. We thoroughly study the variation of CPR-enhanced frequency conversion with experimental parameters and compare CPR with conventional, resonantly enhanced frequency conversion. In particular, we investigate the temporal evolution of the atomic coherence and the effect of inevitable ac Stark shifts. We find that ac Stark shifts induce an asymmetry in the spectral characteristics of CPR, which nevertheless permits enhanced frequency conversion. For the case of resonantly enhanced frequency conversion, we show that the atomic coherences are maintained for several tens of picoseconds after the pump pulse, which permits time-delayed frequency conversion. Moreover, we analyze the pressure dependence of the atomic coherence' lifetime and observe a free induction decay at the two-photon coherence with the generation of a second harmonic field. These findings shall push applications of adiabatic light-matter interactions also to the regime of nonlinear optics, driven by intense laser pulses. |
| Databáze: | OpenAIRE |
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