Observation of Image Transfer and Phase Conjugation in Stimulated Down-Conversion

Abstract

We observe experimentally the transfer of angular spectrum and image formation in the process of stimulated parametric down-conversion. Images and interference patterns can be transferred from either the pump or the auxiliary laser beams to the stimulated down-converted one. The stimulated field propagates as the complex conjugate of the auxiliary laser. The phase conjugation is observed through intensity pattern measurements. DOI: 10.1103/PhysRevLett.87.133602 PACS numbers: 42.50.Ar, 42.25.Kb The cavity-free stimulated down-conversion is a threewave mixing (TWM) process. TWM has been viewed as a nonlinear optical process, with promising applications for correcting wave front distortions. However, when this process was described by a quantum theory [1], new possibilities were opened. The importance of the quantum approach is closely related to the great success of the spontaneous parametric down-conversion in quantum optics [2] and the connection between the stimulated and the spontaneous processes. The quantum properties of the stimulated down-conversion light has not yet been the subject of intense investigation. It was experimentally observed and studied by Mandel and co-workers [3]. Special attention was given to its coherence properties, presenting characteristics of thermal and coherent states [1,3,4], but its individual quantum state was never put forward.In this Letter, we study experimentally the transfer of angular spectrum and image formation in the stimulated down-conversion, as predicted in Ref. [5]. It was also predicted that the stimulated field propagates as the complex conjugate of one of the input fields. The understanding of the angular spectrum transfer has allowed the observation of the phase conjugation by direct intensity measurements. Our results have a classical counterpart (except for the spontaneous emission part) in the framework of the TWM, but they support the quantum theory of Ref. [5]. The relation between the angular spectrum of the pump, auxiliary (signal), and stimulated (idler) beams has not been demonstrated thus far, to the best of our knowledge. These relations are important because they will help us to separate the spontaneous from the stimulated emission contributions in the total idler field which will help us understand phase conjugation at the quantum level [6].

Control of the shape of the spatial mode function of photons generated in noncollinear spontaneous parametric down-conversion

“…It has been theoretically shown that such noncollinear geometries result in the generation of asymmetrical spatial shapes of the two-photon mode function. The analysis of the ellipticity of the spatial shape is of paramount importance for implementing quantum information protocols based on spatially encoded information [8,9], for the study of entanglement of continuous variables using the momentum and position of two-photon states [16], as well as for those applications addressed to quantum imaging [17,18].…”

Klyshko's advanced-wave picture in stimulated parametric down-conversion with a spatially structured pump beam

“…Experiment. In reference [33], the authors observed effects of phase conjugation by analyzing the symmetry of images transferred from the pump and auxiliary beams to the idler. Here, we illustrate the phase conjugation effects by observing the focusing of the idler beam as we make the auxiliary beam diverge.…”

“…In order to illustrate the concepts above, we use Stimulated PDC (StimPDC), a cavity-free parametric amplifier that has been used to demonstrate image and coherence transfer [30][31][32], phase conjugation [33] and orbital angular momentum conservation [34]. Stimulated emission has also been used for investigating the spectral properties of PDC [35,36].…”

Quantum-optical Description of Phase Conjugation of Vector Vortex Beams in Stimulated Parametric Down Conversion

“…On the other hand, when one of the down-converted modes is seeded with a non-vacuum field such as a laser beam, stimulated parametric down conversion (Stim-PDC) occurs [6]. StimPDC can be used to explore interesting processes such as phase conjugation [7], or produce nonclassical states of light [8][9][10][11].…”