Spatial and spectral coherence in propagating high-intensity twin beams

Area of Science:

• Quantum optics
• Photonics
• Coherence theory

Background:

• High-intensity twin-beam states are crucial in quantum optics.
• Understanding their spatial and spectral coherence is key for applications.
• Propagation effects from near-field to far-field alter beam properties.

Purpose of the Study:

• To experimentally investigate the spatial and spectral coherence of high-intensity twin-beam states.
• To analyze the evolution of coherence properties during propagation.
• To establish the relationship between beam coherence and the number of degrees of freedom.

Main Methods:

• Utilized intensity auto- and cross-correlation functions for measurements.
• Employed a setup with a moving crystal and an iCCD camera.
• Analyzed data from an imaging spectrometer at the output plane.

Main Results:

• Observed evolution from near-field spatial position cross-correlations to far-field momentum cross-correlations.
• Noted invariant spectral cross-correlations throughout propagation.
• Quantified the number of degrees of freedom using autocorrelation functions and cross-correlation strength.

Conclusions:

• Beam coherence significantly changes during propagation from near-field to far-field.
• Spectral coherence remains constant, while spatial coherence transforms.
• Intensity cross-correlation strength serves as a viable measure for degrees of freedom.