Determining spatial modes of lasers with spatial coherence measurements.

Area of Science:

• Optics and Photonics
• Laser Physics
• Semiconductor Devices

Background:

• Characterizing spatial modes is crucial for understanding laser beam quality and performance.
• Existing methods for measuring arbitrary spatial modes are often complex or indirect.
• Semiconductor lasers, particularly edge-emitting types, are widely used but require precise mode analysis.

Purpose of the Study:

• To introduce a novel experimental technique for extracting both the structure and modal weights of laser spatial modes.
• To demonstrate the capability of measuring arbitrary spatial mode forms.
• To apply and validate the technique on a specific type of semiconductor laser.

Main Methods:

• Analysis of the spatial coherence of the laser beam.
• Development of a technique to extract spatial mode structure and modal weights from coherence data.
• Experimental application to an edge-emitting Fabry-Perot semiconductor laser with a 5 µm stripe width.

Main Results:

• Successfully extracted the fundamental and first-order lateral modes of the semiconductor laser.
• Determined the relative power weights of these modes to be 96.2% and 3.8%, respectively.
• Confirmed the presence of a single transverse mode, indicating high beam quality in that dimension.

Conclusions:

• The developed technique provides a direct and effective method for measuring arbitrary spatial modes and their power distribution.
• This advancement offers a valuable tool for laser characterization, particularly for semiconductor lasers.
• The findings highlight the potential for precise control and optimization of laser modes through advanced diagnostic techniques.