Spatio-Temporal Supermodes:Rapid Reduction of Spatial Coherence in Highly Multimode Lasers

Abstract

Spatial coherence quantifies spatial field correlations over time, and is one of the fundamental properties of light. Here we investigate the spatial coherence of highly multimode lasers in the regime of short time scales. Counter intuitively, we show that in this regime, the temporal (longitudinal) modes play a crucial role in spatial coherence reduction. To evaluate the spatial coherence we measured the temporal dynamics of speckle fields generated by a highly multimode laser with over $10^5$ lasing spatial (transverse) modes, and examined the dependence of speckle contrast on the exposure time of the detecting device. We show that in the regime of short time scale, the spatial and temporal modes interact to form spatio-temporal supermodes, such that the spatial degrees of freedom are encoded onto the temporal modes. As a result, the speckle contrast depends on the number of temporal modes, and the degree of spatial coherence is reduced and the speckle contrast is suppressed. In the regime of long times scale, the supermodes are no longer a valid representation of the laser modal structure. Consequently, the spatial coherence is independent of the temporal modes, and the classical result, where the speckle contrast is suppressed as the number of spatial modes, is obtained. Due to this new spatio-temporal mechanism, highly multimode lasers can be used for speckle suppression in high-speed full-field imaging applications, as we demonstrate here for imaging of a fast moving object.

References in corpus (15)

• Direct observation of Anderson localization of matter-waves in a controlled disorder
• Speckle-free laser imaging
• An atom-by-atom assembler of defect-free arbitrary 2d atomic arrays
• Experimental evidence of high-resolution ghost imaging and ghost diffraction with classical thermal light
• Multimode optical fiber based spectrometers
• Low-spatial coherence electrically-pumped semiconductor laser for speckle-free full-field imaging
• Transport through modes in random media
• Efficient method for controlling the spatial coherence of a laser
• Real-time wavefront-shaping through scattering media by all optical feedback
• Generating non-Rayleigh speckles with tailored intensity statistics
• Dissipative Topological Defects in Coupled Laser Networks
• Dynamically manipulating topological physics and edge modes in a single degenerate optical cavity
• Coherence switching of a degenerate VECSEL for multimodality imaging
• Experimental generation of an optical field with arbitrary spatial coherence properties
• A narrow-band speckle-free light source via random Raman lasing

Cited by in corpus (11)

• Complex Lasers with Controllable Coherence
• Rapid Phase Retrieval by Lasing
• Suppressing meta-holographic artifacts by laser coherence tuning
• Rapid fair sampling of XY spin Hamiltonian with a laser simulator
• Accelerating speckle suppression by a degenerate cavity laser with an intracavity phase diffuser
• Electrically pumped semiconductor laser with low spatial coherence and directional emission
• Experimental demonstration of crowd synchrony and first-order transition with lasers
• Synchronization in coupled laser arrays with correlated and uncorrelated disorder
• Real-time full-field imaging through scattering media by all-optical feedback
• Parallel random LiDAR with spatial multiplexing of a many-mode laser
• Degenerate optical resonator for the enhancement of large laser beams