Spatial, spectral, and temporal coherence of ultraintense twin beams

Abstract

Using the model of parametric interaction based on the spatio-spectral Schmidt modes and generalized parametric approximation, we analyze coherence and mode structure of ultra-intense twin beams generated in the regime with pump depletion. We show that the increase of spatial and spectral coherence with the increasing pump power observed for moderate powers is replaced by the decrease for the pump powers at which pump depletion occurs. This behavior of coherence is opposed to that exhibited by the number of spatio-spectral modes effectively constituting the twin beam. The conditions for maximal coherence are analyzed considering pump-beam parameters (spectral width, transverse radius). The existence of additional coherence maxima occurring at even higher pump powers is predicted and explained by the oscillatory evolution of the modes' populations.

Internal dynamics of intense twin beams and their coherence

“…To include the quantum statistical character of the signal and idler fields in multi-thermal PDC, we first propose a model based on the generalized parametric approximation (GPA) 34 . In this approximation, the pump field is taken as a classical field arising from the classical solution written in Eq.…”

“…The curves plotted in Figs 1 , 2 , 3 , 4 have been obtained for a β barium borate (BBO) crystal cut for a nearly collinear spectrally degenerate type-I interaction (cut angle deg), having effective length mm and pumped by a beam 530 μ m-wide with the central wavelength nm and spectrum 1.2-nm wide (see Methods for details about the experiment). The Schmidt modes considered in both models have been determined in 36 (for more detailed analysis of the modes, see 37 ) and applied for un-depleted 17 as well as depleted 34 pump beams. These curves fit the experimental points obtained for an 8-mm long BBO crystal measured under the described conditions.…”