Spatial decoherence of pulsed broad-area vertical-cavity surface-emitting lasers

Area of Science:

• Optics and Photonics
• Semiconductor Lasers
• Laser Coherence

Background:

• Vertical-cavity surface-emitting lasers (VCSELs) are crucial in optical communication and sensing.
• Maintaining spatial coherence in large-aperture VCSELs is essential for applications requiring high beam quality.

Purpose of the Study:

• To investigate the impact of microsecond electrical pulse driving on the spatial coherence of large aperture VCSELs.
• To identify the underlying mechanisms responsible for changes in spatial coherence.

Main Methods:

• Characterization of spatial coherence using far-field intensity distribution measurements.
• Analysis of modal emission properties under pulsed operation.
• Systematic variation of pulse duration and amplitude to study their effects.

Main Results:

• A significant reduction in spatial coherence was observed with microsecond pulse excitation.
• Evidence suggests a breakdown of modal emission is the cause of spatial decoherence.
• A coherence radius of 1.4 micrometers was measured, independent of the VCSEL's Fresnel number.
• Far-field intensity distribution transitioned to a Gaussian profile.

Conclusions:

• Microsecond pulsing disrupts the modal behavior of large aperture VCSELs, leading to reduced spatial coherence.
• Spatial coherence can be actively controlled by adjusting pulse parameters.
• Understanding these dynamics is key for optimizing VCSEL performance in pulsed applications.